As a former math teacher, I'm embarrassed to admit that there is an error in my formula for the calculation of RMS power. The peak voltage should be corrected to RMS (i.e. multiplied by .707) prior to being squared and divided by the speaker impedance......not after :(
Thats fine.....it makes some of us feel smarter lol.....another worthwhile video uncle Doug......I get all the young trainee's to watch these, its very helpful :)
Knowledgeable men such as yourself who are willing to take the time to share are rare, and absolutely beyond value to the rest of us . Thanks again sir. You will always have a willing and eager audience.
Re: AC and DC co-existing within the same conductor. I tied my brain into knots trying to follow and interpret tube amp schematics before I caught onto this principle. Finding that simple key removed the "magic" and suddenly there was light. :)) Years later, I think I still have marks from all the head scratching.
CraftAero Same here. I was reading the tube amp books I have, but nobody came out and said it; it was assumed you knew it. Then one day a few years back I was watching Uncle Doug being coached by Rusty (RIP Rusty, we miss you) on this, and BAM! , there it was! The mystery was solved. Thank you Uncle Doug for your great videos. Love the pet cameos too!
Well Doug , I’m a 53 year old electrician who never got into electronics until watching your videos. When this covid thing broke out, I decided it was time for a new hobby. So I bought a bench scope, bench meter, a new solder station, a couple of power supplies, variac and a sig-gen. I’ve been watching your vids pretty religiously and you have taught me so much already. I really have to thank you sir. I doubt you’d ever need it but if you ever have mains or premise wiring issues, I’m all ears!
It's quite gratifying to hear that you have put the videos to good, practical use, Mike. Congratulations on your new hobby and best of luck with all your projects.
"It's not easy for a black cat to hide in a white sink." Sounds like some ancient piece of wisdom. On an unrelated note: I really appreciate your videos. I have learned a great deal. I am developing my own audio electronics bench for working on tube amplifiers and later I will work on ham radio rigs. I have a nice oscilloscope but I do not have a signal generator. I see them varying in price from $15 to $5000. Do you have any advice as to what features I should be looking for? Thank you. John
Uncle Doug+ Very professional. I love the fact you go into detail for the beginners. Most would overlook most of what you do, thank you! This is a real seminar, not the average UA-cam video.
Doug. I wish you had been my electronics lecturer! There were so many things that I didn't understand that It took me years to realise. This is probably, no definitely, the best simple introduction to a scope. Again it took me years to work most of this out.
I appreciate your methodical approach to introducing us to a CRO. I particularly appreciated you saying things like BNC Connector, in a manner which could be understood. I am working with model trains and considering purchasing an Oscilloscope. I am hoping that such a device could record a sequence of events, and allow me to play them back. For example, a Capacitor Discharge Unit (CDU) charges a large value Capacitor (I'm using 10,000uF, 63Volts), by directing a supply voltage of 16VAC through a Non-polar 220uF 50Volt Capacitor, thence splitting the flow to two diodes pointing in opposite polarity, which charge the big capacitor. I wish that I could include the schematic, but you can probably get the idea. After a couple of seconds, the big capacitor is changed to about 44VDC, and is ready to supply that jolt of power to a Solenoid, to change points. I would like to be able to record that couple of seconds, and play it back in slow motion. I am hoping that an Oscilloscope could do that for me. Thank you for an interesting presentation. I hope that you, or one of your subscribers might respond to this entry, Arthur
I don't own a digital oscilloscope, Arthur, but some models may be able to record and playback. You'll have to check on Ebay or the internet in general. Good luck. Thanks !!
I like old style cro. I have also the same tech.I also love the frequency generator.You made a perfect combination of the limiter and the isolation transformer.I have enjoyed it and learned something usefull.
Another excellent video, you said nothing wrong but I think there may be some confusion regarding DC and AC signals on the scope and the use of the AC DC coupling switch. When the scope channel is set to AC it is capacitively coupled and blocks any DC on the signal, when the switch is set to DC in passes everything DC and AC and will display the AC signal riding on the DC level. Lastly the Add function is purely a mathematical function used to give the addition of the two channels, if is often use to provide a pseudo differential measurements between 2 points in a circuit as apposed to some point and ground. For example to measure the voltage drop across an resistor that is not tied to ground clip channel one probe to one side of the resistor and the channel 2 probe to the other side of the resistor (do not clip the probe's ground clips to anything, actually it is best to remove them from the probes) then set the scope to add channel one and channel 2 and set invert to invert channel 2
Great video but I don't recommend leaving a light bulb current limiter hooked up to an amp when signal tracing or measuring output. The limiter will feed the amp a low voltage and all amp voltages and measured gain will be lower than normal. Once you verify an amp is powering up normally go ahead and disconnect the current limiter.
Uncle Doug,how did I ended up here? I was trying to understand how AC is measured by 10x probes. Usually I'm here for amps, this is a bonus info video.
Uncle Doug, quick question. I just acquired my first oscilloscope, a Hitachi V-509. I wanted to check the phase of a sine wave at the speaker terminal. In other words, does the amp circuit produce a sine wave exactly like the input at the output or is it reversed. I wanted to use that info to determine if I should hook my speakers up in reverse. As far I know, a vintage Tweed Bassman 5F6-A circuit inverts the signal at the output. But, I want to check a 1959 Bandmaster. I don't know anything about scopes. I bought it to determine outer foils on capacitors. Not that reversing the speaker leads makes a huge difference in sound, I just wanted to see if it was a doable test. I don't want to use a dummy load, just keep the speakers hooked up. Also, other UA-camrs have me concerned about grounding and damaging the scope. One suggested using a ground lift adapter on the scope plug itself. Thanks for your advice.
You're welcome, MS. From my experience, the phase of the output sine wave is not a concern. Recall that even at moderate frequencies, i.e. 2000Hz, the phase is reversing 2000 times per second......far faster than your ear can detect.
Excellent video.....I bought a Sencore SC61 Oscilloscope and a Tenma 72-455A Signal generator like yours and followed everything you said on this video...I'm soon going to be one of your patrons cause I love your videos and the way you teach....I also like Mr Carlson's Lab videos but there soooo long and a lot of stuff he says goes over my head.
Moving along on my AC568 Bassman head, so many refrained questions but stumped: regarding both my speaker jacks I find all contact points have continuity to ground and to each other. Shouldn't "something" be isolated such as the Tip from the Ring? Whether plug is inserted or not everything connects.
The speaker receptacle has continuity through the secondary winding of the output transformer. The speaker plug has continuity through the speaker's voice coil.
Awesome stuff as always! Yes please more videos about uses and trouble shooting on amps like this! I just scored a similar analog oscilloscope to my tool kit, yay!
My Oscilloscope only has one channel and is about as old as the amp in this video (not really... the scope is probably somewhere from the late 70's to early 80's)...... can i just switch between ac and dc instead of having separate channels for each signal? I understand i wouldn't be able to mix the two signals and i'd have to take into account the different division settings but it should all be possible with a single channel scope right? It's an old Sovjet made C1-94 analog tube driven Oscilloscope my dad gave me who got it from my grandfather so i'd really like to use it in my amp adventures.
THX uncle doug n jack;-) now to find scope . thats all i lack. ANY 1 wanting 2 DONATE 1 out there? I see the fresh kitty water in the sink. mine wants fresh water in the sink also. ;-)
Cats are shy they like To hide +if that faucet Leeks any he will drink From it. What a beautiful funny black Cat. Thanks for the vid On the oscilloscope. Dwight JT.
In the old Pink Panther movies Inspector Clouseau had manservant, Kato who would hide out and attack when the Inspector was most vulnerable. Well, I just realized that Jack is your Kato. In this video he almost eviscerated your hand! Once a ninja is given a mission, it is very difficult to get them to backdown.
Dear Uncle Doug, another excellent video, when these signals are mixed, is this the same concept of an AC signal riding on top of a DC signal. In other words, an AC signal being input to an amplifier where there is a bias placed on the amplifier. Thank you kindly...
Thanks, Mark. Yes, the AC waves ride atop the smooth DC, but never mix......just, as you said, like the AC music signal coexisting with the -DC bias voltage on the grid.
I wish I knew how you connected the 8 ohm load. Did you disconnect the the speaker wires and clip them to the load or maybe you used a 1/4 inch plug in a headphone jack that disconnects the speaker? Don't know what model amp this is so I don't know the available options...
You either connect the speaker wires to the load, or you disconnect the cabinet speaker and plug the load into the speaker output jack on the amp, if it has one.
Hi Uncle Doug! Your oscilloscope is plugged in your Isolation Transformer? Or in your wall receptacle grounded to earth? If it is plug in your wall receptacle, then are you connecting the chassis with the earth ground? thanks
Thanks every so much for this - I've heard people say you can blow yourself up with oscilloscpes on amps but the same people will tell all sorts of old wives tales about valve amps! Thanks for explaining the sea of controls, fairly simple really. Much obliged Doug!
It's our pleasure, Prince. Don't let the lunatic fringe (we all know you're out there) interfere with your appreciation of vintage amps and oscilloscopes ;)
Got a Randall RG-100HG amp head for guitar. I get no sound at all. Got the schematic but sice they are a bit rare no troubleshooting available. Not a tube amp. Got any suggestions where to look? Powers up and transformer puts out power to the Bridge.
There are all sorts of reasons for it to be silent, David, and no one on Earth can guess the right one(s) without testing and examining it. You need to find someone locally to take a look at it.
O.K. then the calculation looks like this? RMS Output=(Peak V x .707)squared ? 6squared/8 x .707=3.18? I hope this is correct.It would be the first time for me.
Hi - I understand the isolation transformer bit and the lifting of the ground to the amplifier but I would have thought that as soon as you attach the Sig Gen which is itself grounded to the input that it becomes grounded that way and defeats the object. Of is the Sig Gen output floating?
If you want to isolate the circuit being tested from earth ground, you would have to ensure that no device, including the signal generator, provides an inadvertent earth ground.
My cats hoped this would be a how to hide tutorial from Jack, the plus side is they are both now oscilloscope experts. They still want to know when you will post Jack's tutorial though?
It's no coincidence, Simon. In an isosceles rt. triangle (with 45 degree angles) the sin is the side opposite (1) divided by the hypotenuse (square root of 2). Thus the sin is the reciprocal of the square root of two......which is the same factor for RMS determination.
Uncle Doug-A friend has asked me to look at his DOD Digital Delay R-908. I'm a hobbyist level guy. The sound goes in and the sound comes out, but the sound is not affected by the flange, delay, echo, switches etc. It just remains clean sound. I replaced all the electrolytic caps on both boards, and the op-amp IC's. I thought maybe I could see where the failure is by tracing the signal through the 2 PCB boards and maybe find the problem. I don't have an ocilloscope, so I thought I would ask you if there's another way to diagnose the problem. I've seen people use audio signal trace probes, some are home-built, and thought maybe that would work. What are your thoughts, and do you have a schematic, video, etc. that shows how to build and use one? Thanks.
Hey Uncle Doug! Love all that you do and can’t stop watching video after video! I’m trying to follow this video to hunt down some noise and calculate my 1965 bassman’s output. I’m having success but one thing I noticed while putting test tone through my amp connected to the dummy load is that I can still hear quite a bit of test tone coming from what appears to be either the power tubes or output transformer! Is this normal or possibly related to one of the many issues that plague this amp currently? Thanks in advance! I always wish I had someone like you looking over my shoulder giving me pointers!
Thanks, Cody. It's uncommon, but occasionally components in the amp circuit will vibrate sympathetically with a signal input. Tighten the transformer screws and wiggle the 6L6's to see if you can identify the "canary" and maybe stop its duet with the output signal.
Hello again, Doug. Something's that confusing me is: Is the RMS output for an amp the same at all times or is it dependent on the input signal? The same can be asked regarding what you said about putting a mark on the volume knob to mark the position where distortion occurs - is that irrespective of the signal strength? I suspect it is but for a hifi amp different sources produce different signal strengths, right, or do they all max out at +1/-1 volts? Please don't throw me a charged cap!
Uncle Doug, Love all of your work, I'm slightly confused on the final Peak volt output of 6V DC. Shouldn't that be AC? I thought all current in a sign wave was AC. Thanks
Hi, I too miss your puppy. Question: I am learning to use my OScope and want to use it to diagnose a problematic SS preamp - a Solo 110. What I am confused about (among many other things) is whether I need to put a load on the preamp (output). If so, do I connect it to an amplifier? Then, the amplifier to a dummy load which I have?
So do I, James. I am no expert with SS gear, but to me, if you want to observe the performance of a preamp, it should be connected to a power amp and functioning as it does normally, which would also require a dummy load for the power amp.
Thanks for the reply. I learned from a SS electronics expert friend that a dummy load was not necessary - which does not make much sense to me. But, who am I to question right? Thanks for this video and all the others.
Outstanding video finally starting to absorb enough of your lessons. If we don't have a scope how else can we measure the amplitude of the signal from tube to tube. My little 5F1 amp is now stable in heater and HV but no signal at all?? Great stuff Doug, Thank You, Dennis in Virginia
Thanks, Dennis. Since amplitude is a measure of voltage, you can try to use a voltmeter.....but since the signal amplitude varies constantly, you will never get an accurate reading. The oscilloscope freezes the wave so you can measure its amplitude.
That's a good point, MP. If the frequency generator is not isolated, it will provide an earth ground to the DUT through the cable that connects the two devices. If you want complete, pre-first-ground-clip isolation of the DUT, then, yes, the FG should be isolated.
Hi Uncle Doug, i am following your video for a long time and i am learning a lot of things, thank you a lot. But after watching this one there is a thing i did not understand and it is about isolation transformer: i am operating on my 100 watts marshall 2203, testing with multimeter and oscilloscope and i would like to understand if, when, how and beacuse an isolation transformer is useful to me. Can you help me please ?
I have posted several videos on isolation transformers, Matteo. I'm sure they will answer all your questions. I prefer to keep all correspondence in this format or on my FB page: Uncle Doug's Vintage Amps.
The clipping point is also dependent on the strength of the input signal. Electric guitars don't output anything near +/- 2V, so that's why it went into clipping at such a low volume as the signal generator is overdriving the input compared to what it was designed for. Another great video, Doug, thanks again!
I've always operated under the impression that typical guitar signals are 300mV pk-pk and line-level signals are 1V pk-pk. This is something that I think I picked up from Craig Anderton's book.
I tested a pair of humbucker pickups several years ago (both activated) and got a 0.7V output. To me, 1V is a close approximation that allows for easy numerical comparison.
Is it true that if youre connecting your oscilloscope (3 prong, grounded ac cord) probes to a solid state amp (2 prong ac cord) that you do not require an isolation transformer for safety? I.e. isolation transformer is only needed when the device under test has a 3 prong ac cord?
LestonDr; Yes, could very well and I have done just that as do many, many repair techs. Of course, when you get to the converter and IF stages you will be on a different frequency than the incoming signal, like 455KHz for AM or 10.7MHz FM. Most scopes can "see" those frequencies if they have the bandwidth like Uncle Doug's is 40MHz. 10 to 20MHz will probably work OK too but more bandwidth is usually always better and more expensive, new or used, but just for broadcast bands not that necessary. Also, the very low signal level of regular radio programing may be a little low for some scopes. Of course, if tuned to a station, the signal may be out of the bandwidth of the scope. If you're going to use a radio station broadcast try using a station at the lower end of the band to start with. You'll want to use your 10x probe so it won't load the circuit especially if the radio is solid state, but you may be tempted to your a 1x probe on the first RF amp or at the converter due to low signal level or pushing the bandwidth limits of your scope. That may load the circuit and cause a little confusion about the signal strength. You may not want to connect the RF generator directly to the radio. You can couple it to the radio by using a simple coil of wire to induce the signal to the antenna input, or use a capacitor. By varying the output level of an RF generator connected to your antenna input, The signal level can adjusted so you can get a decent waveform on the scope. And, of course, you can modulate the RF from the generator with an audio generator (many RFGs have a 400 or 1,000 Hz audio oscillator built in for that purpose) so you can see a modulated envelope in the RF and IF stages. So yes, you can use the same technique as Uncle Doug shows here, comparing input and output to look for distortion or loss of amplification, any differences, etc. Just one more thing, since I have time to type. If you inject a known signal into the front end, and have a dummy load connected instead of a speaker (Always a good thing! Don't drive yourself and anyone else in the house nuts.) start with the scope probe in the middle of the signal path. If you see distortion, low or no signal, go half way towards the RF input from where you started probing, maybe output of the converter. ~OR~ if you see good, clean signal, head towards the dummy load, perhaps halving the distance again, like the output of the detector or middle of the audio amp. This will help to quickly isolate where the trouble is, considering the power supply is fine. Check the PS first! Always! Just like Uncle Doug shows. Don't listen to Jack. There are other You Tube videos on this somewhere, maybe not quite like Uncle Doug's, though. Mr. Carlson's Lab, Radio Mechanic, the Radio Shop may be places to try if you're not already scribed up with them. They're very good, too. Hope that helps a little.
LestonDr as Cavemannspace said, you can, but don't expect to see a whole lot right off the antenna because the RF signals will be very small (most will be too small to see on an oscilloscope) and all them will be present at the same time so it will look like noise. If you pass the antenna through a narrow band pass filter you might be able to see the stronger signals but you will start seeing things after your first IF stage, just be sure to keep your probe on 10x because you don't want to load down the signal path.
looks like I have to hunt down the elusive ocilloscope/ signal generator.. this looks pretty straight-forward , just have to have plenty of original Taco Doritos and some light beer and a nose for smoke :^)
Excellent video. Great information here. Explained better than what I have found elsewhere. Just curious did this include before and after of all tubes? I am unsure of how many times were in this amp. Schematic may have helped. Thanks again.
@@UncleDoug From my notes, :) it stated +/- 1 volt for the frequency generator. +/- 8 volts for the first stage of amplification and +/- 50 volts for the second stage of amplification. When I looked at the back of the amplifier it appeared to be more than just 2 tubes. One could be a rectifier tube. Also what is the range of amplification for vacuum tubes? Haven't found any info this. Also is there a limit on the number of stages? Is a preamp actually required? These questions also not found anywhere. Ever think of making a video on the different types of amplifiers? It took a lot of studying to find out there are three types(I could be wrong here, just started studying) 1 tubes 2. PNP or NPN and 3 Op Amps. Thanks again.
Yes, the extra tube was a rectifier. The highest amplification factor I have seen is 100, found in the 12AX7. No limit on the number of stages, but diminishing returns sets in rather quickly. Yes, the pre-amp is required to step the voltage up high enough to drive the output tubes. There are more types of amp, LF. Look up Types A, AB, C, etc.
Doug, I don't see how you can keep track of Jack. Maybe you should have named him Houdini. Yeah, thanks for the reminder, U.D. Learn the functions and take advantage of the options(8-). About everything resembling a signal is riding on some dc level in a tube amp...including that pesky ac hum you may have to track down.
I've got two dual-channel Oscilloscopes in my collection of test equipment, one is a solid-state 20Mhz DSE Q-1804 I bought back in the late 90's, the other is an old Telequipment D33R 15Mhz Tube Oscilloscope that needs a new CRT and some restoration work done on it, they really are useful pieces of test equipment to have, once you know how to use them properly, having the ability to see how a circuit is actually behaving is like the difference between working blind and working with 20/20 vision.
Once again, thank you for the clear/informative video's. For Christmas i'm getting a Siglent 4 channel 100 Mhz scope and I just won bids at work (Zoll Medical - Leader sig gen, Fluke DMM and a 10A/20V power supply) so, I'll have a fairly well rounded home lab bench in a few weeks. Having successfully build and gig with 2 tube amps, it will be nice to finally "see" more deeply into what is going on in each gain/transformer stage of subsequent builds, mods, and some day designs. Thank you!
Great video again,thanks!!!! Because of youre videos ive been able to fix many amps and build bassmans and tweed deluxes ❤️❤️❤️,Without these videos they would out of my reach,!! Havent got in to oscilloscopeworld yet!just bough iwatsu synchroscope from fleamarket, what is difference between sychroscope and oscilloscope? My cat rudolf promised to help me ,but hes been so busy catcing criminals at night here in finland, so usually he has to sleep when hes home,
You're welcome, JJ. It's great to hear that you have applied the concepts in the videos to the creation and repair of amplifiers. I have no idea what a synchroscope is. Maybe you can find some info on the Internet ? Meanwhile, best regards to you and Rudolph from warm, sunny Texas, USA.
Thanks for the video. They are very informative and enjoyable. I am very familiar with the use and application of multi-channel DSOs (e.g., Snap On: Vantage, Vantage Pro, Modis, and Verus; and PicoScope) in connection with automotive diagnostics (injectors, ignition coils, fuel pumps, cam/crank sensors, in cylinder pressure diagnosis, et al.). The Snap On offerings evolved to be very good. However, the industry standard, in my opinion, has become the PicoScope because of its many capabilities. It is my understanding PicoScope makes a full line of DSOs. I don't know if these would be suitable for tube amplifier diagnostics, i.e., overkill, but having experience with their automotive version, it seems they would be a very useful tool. Cheers.
For those of you that are looking for an oscilloscope and like building things; I'd suggest a DSO Shell oscilloscope kit made by JYE Tech. You can purchase them from many places for about $20 dollars U.S.. I got mine from Banggood.com for less! They are easy to solder together in a couple of hours and make for a nice pocket sized scope. They are single channel but I don't see that being a problem checking anything presented in this video. I added a cheap $4 dollar 10x probe to mine as the voltage limit is 50 volts. With the 10x probe I'm safe up to 500 volts. Look up some of the review videos and some of the build videos for this scope and decide if it might work for you. They also sell signal generator kits for even less! My questions for Doug are, what's your scope voltage limit on 1x setting and will you fry it if you connect to plate voltage by mistake. My other question is; is there any time I would need more than a 500 volt limit scope?
Thanks for your helpful info on inexpensive scope availability, 10L. I believe the limiting factor is not the scope but the insulation within the probe. The 1Meg resistor at X1 will protect the scope innards, but an arc may occur in the probe at high enough voltages to destroy it.....and possibly your hand. I would think a normal probe could handle 500VDC, but I tend to avoid any voltages above 350V or so. Let's face it, there is really no need to attach a probe to the plate of a KT150
Love my tektronix 2232. Owned it first and after learning on the old-school I have a 200 MHz DSO that I use most of the time. But I love how the buttons click. The DSO is not the same. Wish that the modern ones had detents for the knobs.
Lo'der UD ! I smell an Honorary Diploma in "Ampology" coming soon ! Your dulcet tones and ageless wit and humor continue to both impress and educate. I'm only hoping you'll give my Vox clone design a look when it's ready and help me source the difficult bits like Diodes from Mullard for full wave bridge rectification. But in the mean time I will share with my friends and enjoy and wait for the video delights yet to appear. Robert aka jj Thanks ever so......
Greetings uncle D! Signal tracing has always been my favorite topic of your videos. Its always good to revisit your award -winning videos. They also offer hi level entertainment and make this subject fun and rewarding when we apply your techniques and solve problems. I want to thank you again.
Great videos Doug. I can now switch on my Tektronix T912 without trepidation ! Incidentally, I'm told my 'scope has a storage function - not sure how to use this yet. Another video perhaps ?
Thanks, Dave. I'm glad the videos were helpful. The majority of analog scopes, like mine, don't have a storage function, so it's not feasible for me to demonstrate it. Hopefully you can find technical assistance on the internet. Good luck.
Does this also applies to a stereo receiver? Meaning the information that you presented? i have a Tektronics 2245 150mhz O'scope that i am trying to learn how to use. So your videos are very helpful.
The general principles would apply, Rob, but if the stereo receiver is transistorized (and it probably is), the circuit details are quite different from the tube amps that I work on.
Enjoying this series. I sent you a private message regarding something I want to give to you. Don't know if you got it or not. Anyway, let me know. If you do want it, I'll need your shipping address.
Where is Jack. Silly Jack love that cat. If a cat really wants to hide you'll never find him until he gets out of his hiding place jack the good little black cat
I'm curious Uncle Doug like in a champ amp the on-off switch is in the return wire the fuse is in the hot side I wonder why Fender did that back when. Could it be that they were looking at less sparking in the contacts of the switch internally. I wonder what their reasoning behind it to the switch and fuse that way back then? What do you think?
@@dwightjt It's easier to wire when you have a lug for each of the primary wires, Dwight. In the modern wiring scheme, the white (return) wire connects directly to the PT primary with no lug.
Got a question. Looking at the waveform on the scope @~3:38, the sine wave looks symmetric, +&--. Looking at the trace @~ 23:30 - 23:48, the positive peaks look broader yet not like the input signal @3:38, and the negative peaks looks sharper, more pointed than the top of the positive peaks. Appears to be distorted. Why? You and Jack are like Kato and Inspector Clouseau, you never know where Jack is going to hide or how he is going to attack!
When approaching distortion levels, the sine wave is altered in shape. The sine wave at 3:38 is undistorted, while the later one is becoming distorted. I have no fancy explanation for this other than what is visibly evident on the screen.
Excellent video Uncle Doug. Also - I really like your 8 ohm load!! I have several smaller ones - but yours looks quite hefty and nice looking !! I looked on e-bay to find one like it - but couldn't find the same size/appearance load there. Can you tell me - what is the wattage rating of your load ?
I always used my tongue to test the 9V's. Thanks Uncle Doug for most the enjoyable educational episodes ever caught on video they are Gold. I do appreciate them & you I always learn something. Excellent teaching.
Hi Uncle Doug, thanks for going a long way to demystify the world of oscilloscopes. I don't think I am in a position to purchase a conventional scope, have you had any experience or opinion on digital scopes or ones which interface with PC's?
I have no personal experience, Colin, but would love to have a digital scope simply because they can perform most of the frequency and voltage calculations automatically. Likewise for the ones that interface with a PC......I'll bet they offer excellent results for a fraction of the cost.
I thoroughly enjoyed this video! It was just what I needed! I have a couple of scopes but my use of them is very basic. Many thanks to Uncle Doug and to the generous subscriber who donated the amplifier utilized in the making of this video. Using an oscilloscope and tracing a signal for grounding errors and failed components are what I need to see the most. I'm glad to have found this channel and this video - thank you very much Uncle Doug! I've subbed your channel and will become a Patron very soon! All the best - Luther
Plz help im new at all this and i was gifted a Tektronix 5110 to make my car amplifier repairs easier.. But i have been tryin for a week now to try to even calibrate it i can not get the split lines or even get it to stand Still im guessing i have a button pushed or unpushed in that needs to be if anyone one could help me or guide me in the direction i greatly appreciate it...thank you in advanced
I did my best to explain how to use an oscilloscope in my videos, Jose. If they are not sufficient, then seek additional info in other videos or find someone in your area to give you on site instructions. Good luck.
@@UncleDoug ty i apperciate it its just all new to me so i really domt have a full understanding of the buttons and their usuage.. It has tons ill keep trying and love u video very helpful and i will deff continue to stay subscribed
As a former math teacher, I'm embarrassed to admit that there is an error in my formula for the calculation of RMS power. The peak voltage should be corrected to RMS (i.e. multiplied by .707) prior to being squared and divided by the speaker impedance......not after :(
So, about 2.25 watts RMS?
Thats fine.....it makes some of us feel smarter lol.....another worthwhile video uncle Doug......I get all the young trainee's to watch these, its very helpful :)
Yes, Not Mark, the real value is a bit lower than my flattering portrayal of its awesome output power :)
Thanks, Harb. I always strive to make others feel smarter :):)
Thanks, Gianfranco. We will :)
Knowledgeable men such as yourself who are willing to take the time to share are rare, and absolutely beyond value to the rest of us . Thanks again sir. You will always have a willing and eager audience.
You're welcome, Ken. Thanks for your very nice comments.
I alredy know how to operate an oscilloscope, but I still watch these videos just because I love how you teach
Thanks, Michael. I am flattered that you would do so :)
DITTO! Besides we have to keep an eye open for Jack.
Like wise, uncle Doug really explains amps so well
Same!
Re: AC and DC co-existing within the same conductor.
I tied my brain into knots trying to follow and interpret tube amp schematics before I caught onto this principle. Finding that simple key removed the "magic" and suddenly there was light. :)) Years later, I think I still have marks from all the head scratching.
It does seem paradoxical........but truth is often "stranger than fiction" :)
CraftAero
Same here. I was reading the tube amp books I have, but nobody came out and said it; it was assumed you knew it. Then one day a few years back I was watching Uncle Doug being coached by Rusty (RIP Rusty, we miss you) on this, and BAM! , there it was! The mystery was solved. Thank you Uncle Doug for your great videos. Love the pet cameos too!
...no brains, no headaches(?)
Always appreciative of your shared knowledge. Didn't see Jack's new friend on this video. Miss Rusty very much. RIP
Thanks so much, Gil. Ollie was being demure during this production :) Yes, I miss Rusty also :(
This is the best oscilloscope tutorial I’ve ever seen. Took me way beyond what I learned (and taught) in Community College.
That's great to hear, Jeremiah. I'm glad it was helpful.
Awsome video, again clearly explained, thankyou for sharing
You're welcome, IG. Thanks !!!
Well Doug , I’m a 53 year old electrician who never got into electronics until watching your videos. When this covid thing broke out, I decided it was time for a new hobby. So I bought a bench scope, bench meter, a new solder station, a couple of power supplies, variac and a sig-gen. I’ve been watching your vids pretty religiously and you have taught me so much already. I really have to thank you sir. I doubt you’d ever need it but if you ever have mains or premise wiring issues, I’m all ears!
It's quite gratifying to hear that you have put the videos to good, practical use, Mike. Congratulations on your new hobby and best of luck with all your projects.
"It's not easy for a black cat to hide in a white sink." Sounds like some ancient piece of wisdom. On an unrelated note: I really appreciate your videos. I have learned a great deal. I am developing my own audio electronics bench for working on tube amplifiers and later I will work on ham radio rigs. I have a nice oscilloscope but I do not have a signal generator. I see them varying in price from $15 to $5000. Do you have any advice as to what features I should be looking for? Thank you. John
Uncle Doug+ Very professional. I love the fact you go into detail for the beginners. Most would overlook most of what you do, thank you! This is a real seminar, not the average UA-cam video.
You're welcome, Mr. B. I appreciate your nice comments.
Great video- WD9GNG
Thanks, Ken :)
Doug. I wish you had been my electronics lecturer! There were so many things that I didn't understand that It took me years to realise. This is probably, no definitely, the best simple introduction to a scope. Again it took me years to work most of this out.
Thanks so much, Darren. We're glad the video was helpful.
I appreciate your methodical approach to introducing us to a CRO. I particularly appreciated you saying things like BNC Connector, in a manner which could be understood.
I am working with model trains and considering purchasing an Oscilloscope. I am hoping that such a device could record a sequence of events, and allow me to play them back.
For example, a Capacitor Discharge Unit (CDU) charges a large value Capacitor (I'm using 10,000uF, 63Volts), by directing a supply voltage of 16VAC through a Non-polar 220uF 50Volt Capacitor, thence splitting the flow to two diodes pointing in opposite polarity, which charge the big capacitor. I wish that I could include the schematic, but you can probably get the idea.
After a couple of seconds, the big capacitor is changed to about 44VDC, and is ready to supply that jolt of power to a Solenoid, to change points.
I would like to be able to record that couple of seconds, and play it back in slow motion.
I am hoping that an Oscilloscope could do that for me.
Thank you for an interesting presentation. I hope that you, or one of your subscribers might respond to this entry,
Arthur
I don't own a digital oscilloscope, Arthur, but some models may be able to record and playback. You'll have to check on Ebay or the internet in general. Good luck. Thanks !!
Uncle Doug is the teacher that we wish we had in school. Thank you Uncle Doug!
Thanks so much, Ken :)
I like old style cro. I have also the same tech.I also love the frequency generator.You made a perfect combination of the limiter and the isolation transformer.I have enjoyed it and learned something usefull.
Another excellent video, you said nothing wrong but I think there may be some confusion regarding DC and AC signals on the scope and the use of the AC DC coupling switch. When the scope channel is set to AC it is capacitively coupled and blocks any DC on the signal, when the switch is set to DC in passes everything DC and AC and will display the AC signal riding on the DC level. Lastly the Add function is purely a mathematical function used to give the addition of the two channels, if is often use to provide a pseudo differential measurements between 2 points in a circuit as apposed to some point and ground. For example to measure the voltage drop across an resistor that is not tied to ground clip channel one probe to one side of the resistor and the channel 2 probe to the other side of the resistor (do not clip the probe's ground clips to anything, actually it is best to remove them from the probes) then set the scope to add channel one and channel 2 and set invert to invert channel 2
MK, I'm glad you clarified the AC/DC coupling switch here. It's a major point of confusion for oscilloscope users coming from a multimeter background.
Great video but I don't recommend leaving a light bulb current limiter hooked up to an amp when signal tracing or measuring output. The limiter will feed the amp a low voltage and all amp voltages and measured gain will be lower than normal. Once you verify an amp is powering up normally go ahead and disconnect the current limiter.
Thanks for your input, Rob.
Uncle Doug,how did I ended up here? I was trying to understand how AC is measured by 10x probes. Usually I'm here for amps, this is a bonus info video.
I'm glad it was informative, Sahin.
Uncle Doug, quick question. I just acquired my first oscilloscope, a Hitachi V-509. I wanted to check the phase of a sine wave at the speaker terminal. In other words, does the amp circuit produce a sine wave exactly like the input at the output or is it reversed. I wanted to use that info to determine if I should hook my speakers up in reverse. As far I know, a vintage Tweed Bassman 5F6-A circuit inverts the signal at the output. But, I want to check a 1959 Bandmaster. I don't know anything about scopes. I bought it to determine outer foils on capacitors. Not that reversing the speaker leads makes a huge difference in sound, I just wanted to see if it was a doable test. I don't want to use a dummy load, just keep the speakers hooked up. Also, other UA-camrs have me concerned about grounding and damaging the scope. One suggested using a ground lift adapter on the scope plug itself. Thanks for your advice.
You're welcome, MS. From my experience, the phase of the output sine wave is not a concern. Recall that even at moderate frequencies, i.e. 2000Hz, the phase is reversing 2000 times per second......far faster than your ear can detect.
A very nice practical demonstration, thank you. I tought I taw a putty tat!
Thanks, Andrew. I'm glad somebody can see him......I generally can't :)
Excellent video.....I bought a Sencore SC61 Oscilloscope and a Tenma 72-455A Signal generator like yours and followed everything you said on this video...I'm soon going to be one of your patrons cause I love your videos and the way you teach....I also like Mr Carlson's Lab videos but there soooo long and a lot of stuff he says goes over my head.
Thanks, Horst. I'm really glad to hear that the videos were helpful. Best of luck with your projects.
Moving along on my AC568 Bassman head, so many refrained questions but stumped: regarding both my speaker jacks I find all contact points have continuity to ground and to each other. Shouldn't "something" be isolated such as the Tip from the Ring? Whether plug is inserted or not everything connects.
The speaker receptacle has continuity through the secondary winding of the output transformer. The speaker plug has continuity through the speaker's voice coil.
Awesome stuff as always! Yes please more videos about uses and trouble shooting on amps like this! I just scored a similar analog oscilloscope to my tool kit, yay!
Thanks, CB. We will :)
My Oscilloscope only has one channel and is about as old as the amp in this video (not really... the scope is probably somewhere from the late 70's to early 80's)...... can i just switch between ac and dc instead of having separate channels for each signal?
I understand i wouldn't be able to mix the two signals and i'd have to take into account the different division settings but it should all be possible with a single channel scope right?
It's an old Sovjet made C1-94 analog tube driven Oscilloscope my dad gave me who got it from my grandfather so i'd really like to use it in my amp adventures.
Not knowing anything about your scope, TL, I can only guess that yes, you can switch between AC and DC.
THX uncle doug n jack;-) now to find scope . thats all i lack. ANY 1 wanting 2 DONATE 1 out there? I see the fresh kitty water in the sink. mine wants fresh water in the sink also. ;-)
You're welcome, Ken. Best of luck with your quest for a free scope. It can happen :) Regards to your thirsty kitty.
Cats are shy they like
To hide +if that faucet
Leeks any he will drink
From it. What a beautiful funny black
Cat. Thanks for the vid
On the oscilloscope.
Dwight JT.
More poetry, Dwight.....Thanks :)
Wouldn't 1K hz technically be ULF and not VLF? VLF I believe is 3Khz - 30Khz
I guess, IN, but in the big scheme of things, does it really matter ?
In the old Pink Panther movies Inspector Clouseau had manservant, Kato who would hide out and attack when the Inspector was most vulnerable. Well, I just realized that Jack is your Kato. In this video he almost eviscerated your hand! Once a ninja is given a mission, it is very difficult to get them to backdown.
If you look closely at my hands in the videos, you'll see evidence of Jack's deadly claws......he is one tough little %@&?%@.
Doug, this video is very much appreciated. It clearly explains what I thought I knew already. Thank you so much..
You're welcome, Ron :)
Dear Uncle Doug, another excellent video, when these signals are mixed, is this the same concept of an AC signal riding on top of a DC signal. In other words, an AC signal being input to an amplifier where there is a bias placed on the amplifier. Thank you kindly...
Thanks, Mark. Yes, the AC waves ride atop the smooth DC, but never mix......just, as you said, like the AC music signal coexisting with the -DC bias voltage on the grid.
I wish I knew how you connected the 8 ohm load. Did you disconnect the the speaker wires and clip them to the load or maybe you used a 1/4 inch plug in a headphone jack that disconnects the speaker? Don't know what model amp this is so I don't know the available options...
You either connect the speaker wires to the load, or you disconnect the cabinet speaker and plug the load into the speaker output jack on the amp, if it has one.
.............Jack is an "Oscillo-Phobe" kittie & that's why he's hiding?
An excellent diagnosis, Floyd :)
Hi Uncle Doug! Your oscilloscope is plugged in your Isolation Transformer? Or in your wall receptacle grounded to earth? If it is plug in your wall receptacle, then are you connecting the chassis with the earth ground? thanks
The oscilloscope is always plugged into a grounded wall receptacle, ES. You never float an oscilloscope (it rhymes !!)
Thanks every so much for this - I've heard people say you can blow yourself up with oscilloscpes on amps but the same people will tell all sorts of old wives tales about valve amps! Thanks for explaining the sea of controls, fairly simple really. Much obliged Doug!
It's our pleasure, Prince. Don't let the lunatic fringe (we all know you're out there) interfere with your appreciation of vintage amps and oscilloscopes ;)
Got a Randall RG-100HG amp head for guitar. I get no sound at all. Got the schematic but sice they are a bit rare no troubleshooting available. Not a tube amp. Got any suggestions where to look? Powers up and transformer puts out power to the Bridge.
There are all sorts of reasons for it to be silent, David, and no one on Earth can guess the right one(s) without testing and examining it. You need to find someone locally to take a look at it.
Thank you, Uncle Doug! I wish I could be your apprentice. I guess in some ways, I am! Lol
Yes, you are, Shawn. Best of luck with all your projects.
Subscribed Sir...very informative. Thank you Sir.
Thanks and welcome to our channel, Julius.
uncle doug:
jack has been moonlighting at a channel called the truth factory. ;-)
So that's where he's been !!!
Thank you for the great education, now if you will explain hendrix feedback with the strat up agenst the marshal stack extortion
It's magic ;)
Superb Uncle Doug. Thank you. I still miss Rusty.
Thanks. So do we.
Sorry if I missed this, but should the oscilloscope also be plugged in to the same isolation transformer as the amp, with its ground lifted as well?
No, you never isolate the oscilloscope. It should be properly grounded.
Why do you not want the amp and current limiter grounded? Sorry, I know it's a dumb question for most, but I would like to understand why.
This is all explained in our video on Isolation Transformers, Steve.
If you don't want to listen to the annoying signal out of the speaker, just set the signal generator to 30KHz. LOL
Then your dogs will howl and wake up the neighbors, who will call the cops, and you will be arrested :)
O.K. then the calculation looks like this? RMS Output=(Peak V x .707)squared ? 6squared/8 x .707=3.18? I hope this is correct.It would be the first time for me.
Hi - I understand the isolation transformer bit and the lifting of the ground to the amplifier but I would have thought that as soon as you attach the Sig Gen which is itself grounded to the input that it becomes grounded that way and defeats the object. Of is the Sig Gen output floating?
If you want to isolate the circuit being tested from earth ground, you would have to ensure that no device, including the signal generator, provides an inadvertent earth ground.
Enjoyed your teaching active passive termonology also love bld race engines trying to apply this wave form todiesel injector trim scan great teacher
Thanks, William :)
My cats hoped this would be a how to hide tutorial from Jack, the plus side is they are both now oscilloscope experts. They still want to know when you will post Jack's tutorial though?
Jack is preparing a tutorial on cat box etiquette.....but I doubt that UA-cam will allow it to be posted.
Now I know why so many others rave about YOUR videos. Thank you!
Thanks, KP :)
I believe Jack is looking for the Goldfish!!🐠🐠🐠
You can be sure it's either food or trouble, if Jack is seeking it.
Interestingly in Trigonometry, a figure of .707 is the sin value for 45 degrees.
It's no coincidence, Simon. In an isosceles rt. triangle (with 45 degree angles) the sin is the side opposite (1) divided by the hypotenuse (square root of 2). Thus the sin is the reciprocal of the square root of two......which is the same factor for RMS determination.
Hi, thanks for the video, very helpful, from UK.
You're welcome, Greg :)
Uncle Doug-A friend has asked me to look at his DOD Digital Delay R-908. I'm a hobbyist level guy. The sound goes in and the sound comes out, but the sound is not affected by the flange, delay, echo, switches etc. It just remains clean sound. I replaced all the electrolytic caps on both boards, and the op-amp IC's. I thought maybe I could see where the failure is by tracing the signal through the 2 PCB boards and maybe find the problem. I don't have an ocilloscope, so I thought I would ask you if there's another way to diagnose the problem. I've seen people use audio signal trace probes, some are home-built, and thought maybe that would work. What are your thoughts, and do you have a schematic, video, etc. that shows how to build and use one? Thanks.
I would like to fwd the cicuit diagram of my oscilloscope which has no horizontal sweep it is a national oscilloscope
I think you'd be better off seeking technical help from someone who works on oscilloscopes, Pete.
Don't you do something like this to figure total harmonic distortion? Are there scopes that measure root mean squared?
THD requires special instrumentation, as far as I know, Rusty. Digital scopes can provide both peak and RMS values. Analog scopes generally do not.
Hey Uncle Doug! Love all that you do and can’t stop watching video after video! I’m trying to follow this video to hunt down some noise and calculate my 1965 bassman’s output. I’m having success but one thing I noticed while putting test tone through my amp connected to the dummy load is that I can still hear quite a bit of test tone coming from what appears to be either the power tubes or output transformer! Is this normal or possibly related to one of the many issues that plague this amp currently? Thanks in advance! I always wish I had someone like you looking over my shoulder giving me pointers!
Thanks, Cody. It's uncommon, but occasionally components in the amp circuit will vibrate sympathetically with a signal input. Tighten the transformer screws and wiggle the 6L6's to see if you can identify the "canary" and maybe stop its duet with the output signal.
@@UncleDoug Thanks! It’s very kind of you to take the time to reply. If you’re ever looking for a real challenge this bassman has your name on it.
Thank you for that very detailed explanation and demonstration.
You're welcome, MMA. Glad you liked it :)
Why is there more "clipping" at the top of the wave form? Around 17:00 in video?
I don't know, Lizzie, but it's not unusual to see this.
Do you have an idea of what the input power was to get an idea of how much of the map was a bar heater and how much actually did sound amplification?
I honestly don't understand the question, TK.
Hello again, Doug.
Something's that confusing me is: Is the RMS output for an amp the same at all times or is it dependent on the input signal?
The same can be asked regarding what you said about putting a mark on the volume knob to mark the position where distortion occurs - is that irrespective of the signal strength?
I suspect it is but for a hifi amp different sources produce different signal strengths, right, or do they all max out at +1/-1 volts?
Please don't throw me a charged cap!
Great video. Thanks! Looks you lost a fight with a cat.....
Yes, a new feral addition to the family has been taking a toll on my hands.
Yes!!!! That was great. Thank you for doing it! More scope vids please!!!
You're welcome, GL. They're on the way :)
I second that!
These have been incredibly helpful thank you!
Glad to hear it, G :)
Uncle Doug, Love all of your work, I'm slightly confused on the final Peak volt output of 6V DC. Shouldn't that be AC? I thought all current in a sign wave was AC.
Thanks
I'm not sure where the "6V DC" statement was made in the video, but yes, all sinusoidal wave forms are considered AC.
@@UncleDoug @ ~ 27:16, it is written on paper, "Peak V= 6VDC"
Do you have any recommendations for isolation transformers?
I have never personally installed one, James, so I simply don't have the experience to offer any advice.
WOW Thanks I was just about to scope plate voltage This is so much better and safe r
If you ever apply a scope probe to a signal circuit, apply it AFTER the coupling cap, to eliminate the HVDC.
7:06...I'll have to remember that technique-!
Glad it was helpful, Dale.
Hi, I too miss your puppy. Question: I am learning to use my OScope and want to use it to diagnose a problematic SS preamp - a Solo 110. What I am confused about (among many other things) is whether I need to put a load on the preamp (output). If so, do I connect it to an amplifier? Then, the amplifier to a dummy load which I have?
So do I, James. I am no expert with SS gear, but to me, if you want to observe the performance of a preamp, it should be connected to a power amp and functioning as it does normally, which would also require a dummy load for the power amp.
Thanks for the reply. I learned from a SS electronics expert friend that a dummy load was not necessary - which does not make much sense to me. But, who am I to question right? Thanks for this video and all the others.
as always great info for old timers and new tube guys , thank you sir
You're welcome, R & R :)
Outstanding video finally starting to absorb enough of your lessons. If we don't have a scope how else can we measure the amplitude of the signal from tube to tube. My little 5F1 amp is now stable in heater and HV but no signal at all?? Great stuff Doug, Thank You, Dennis in Virginia
Thanks, Dennis. Since amplitude is a measure of voltage, you can try to use a voltmeter.....but since the signal amplitude varies constantly, you will never get an accurate reading. The oscilloscope freezes the wave so you can measure its amplitude.
Did anybody see Jack? I saw nothing!
See?........I told you so !!
Is signal generator connected also in the isolation transformer? Does it need to be connected if it does not?
That's a good point, MP. If the frequency generator is not isolated, it will provide an earth ground to the DUT through the cable that connects the two devices. If you want complete, pre-first-ground-clip isolation of the DUT, then, yes, the FG should be isolated.
I learned something new today. Thanks!
Glad to hear it, CB :)
Jack's a beast!😂😂
Yes, he is, DEC......but a lovable one :)
@@UncleDoug Indeed!😊
I have a nice older tektronix 453 but no practical experience. Thanks for a very clear explanation amd demonstration of the basics I needed to see.
Hi Uncle Doug, i am following your video for a long time and i am learning a lot of things, thank you a lot. But after watching this one there is a thing i did not understand and it is about isolation transformer: i am operating on my 100 watts marshall 2203, testing with multimeter and oscilloscope and i would like to understand if, when, how and beacuse an isolation transformer is useful to me. Can you help me please ?
If there is a private channel (email) where i can ask some amps stuff please tell me !!
I have posted several videos on isolation transformers, Matteo. I'm sure they will answer all your questions. I prefer to keep all correspondence in this format or on my FB page: Uncle Doug's Vintage Amps.
The clipping point is also dependent on the strength of the input signal. Electric guitars don't output anything near +/- 2V, so that's why it went into clipping at such a low volume as the signal generator is overdriving the input compared to what it was designed for.
Another great video, Doug, thanks again!
That's a good point, AQ. I thought my input signal was +/- 1V, but you may be right about it overdriving the circuit. You're welcome.
I've always operated under the impression that typical guitar signals are 300mV pk-pk and line-level signals are 1V pk-pk. This is something that I think I picked up from Craig Anderton's book.
I tested a pair of humbucker pickups several years ago (both activated) and got a 0.7V output. To me, 1V is a close approximation that allows for easy numerical comparison.
Is it true that if youre connecting your oscilloscope (3 prong, grounded ac cord) probes to a solid state amp (2 prong ac cord) that you do not require an isolation transformer for safety?
I.e. isolation transformer is only needed when the device under test has a 3 prong ac cord?
I don't work on SS gear, V, and honestly don't know the answer to your question.
@@UncleDoug Not a problem sir, truly appreciate your time. My regards to Jack as well!
Thank you... would the signal tracing for a radio RF be the same procedure from the antenna?
Heck if I know, LD. Maybe another viewer will be able to answer your question. I'm strictly a vintage tube amp guy.
LestonDr; Yes, could very well and I have done just that as do many, many repair techs. Of course, when you get to the converter and IF stages you will be on a different frequency than the incoming signal, like 455KHz for AM or 10.7MHz FM. Most scopes can "see" those frequencies if they have the bandwidth like Uncle Doug's is 40MHz. 10 to 20MHz will probably work OK too but more bandwidth is usually always better and more expensive, new or used, but just for broadcast bands not that necessary. Also, the very low signal level of regular radio programing may be a little low for some scopes. Of course, if tuned to a station, the signal may be out of the bandwidth of the scope. If you're going to use a radio station broadcast try using a station at the lower end of the band to start with.
You'll want to use your 10x probe so it won't load the circuit especially if the radio is solid state, but you may be tempted to your a 1x probe on the first RF amp or at the converter due to low signal level or pushing the bandwidth limits of your scope. That may load the circuit and cause a little confusion about the signal strength. You may not want to connect the RF generator directly to the radio. You can couple it to the radio by using a simple coil of wire to induce the signal to the antenna input, or use a capacitor. By varying the output level of an RF generator connected to your antenna input, The signal level can adjusted so you can get a decent waveform on the scope. And, of course, you can modulate the RF from the generator with an audio generator (many RFGs have a 400 or 1,000 Hz audio oscillator built in for that purpose) so you can see a modulated envelope in the RF and IF stages. So yes, you can use the same technique as Uncle Doug shows here, comparing input and output to look for distortion or loss of amplification, any differences, etc.
Just one more thing, since I have time to type. If you inject a known signal into the front end, and have a dummy load connected instead of a speaker (Always a good thing! Don't drive yourself and anyone else in the house nuts.) start with the scope probe in the middle of the signal path. If you see distortion, low or no signal, go half way towards the RF input from where you started probing, maybe output of the converter. ~OR~ if you see good, clean signal, head towards the dummy load, perhaps halving the distance again, like the output of the detector or middle of the audio amp. This will help to quickly isolate where the trouble is, considering the power supply is fine. Check the PS first! Always! Just like Uncle Doug shows. Don't listen to Jack.
There are other You Tube videos on this somewhere, maybe not quite like Uncle Doug's, though. Mr. Carlson's Lab, Radio Mechanic, the Radio Shop may be places to try if you're not already scribed up with them. They're very good, too.
Hope that helps a little.
LestonDr as Cavemannspace said, you can, but don't expect to see a whole lot right off the antenna because the RF signals will be very small (most will be too small to see on an oscilloscope) and all them will be present at the same time so it will look like noise. If you pass the antenna through a narrow band pass filter you might be able to see the stronger signals but you will start seeing things after your first IF stage, just be sure to keep your probe on 10x because you don't want to load down the signal path.
...an oscilloscope probably isn't sensitive enough to detect signals in the microvolt range- that's what you are dealing with.
looks like I have to hunt down the elusive ocilloscope/ signal generator.. this looks pretty straight-forward , just have to have plenty of original Taco Doritos and some light beer and a nose for smoke :^)
It sounds like you already have the most important "tools", Malcolm.
Mmmmm. Original Taco Doritos!
Excellent video. Great information here. Explained better than what I have found elsewhere. Just curious did this include before and after of all tubes? I am unsure of how many times were in this amp. Schematic may have helped. Thanks again.
You're welcome, LF. I honestly don't recall. Was the answer not evident in the video ??
@@UncleDoug From my notes, :) it stated +/- 1 volt for the frequency generator. +/- 8 volts for the first stage of amplification and +/- 50 volts for the second stage of amplification. When I looked at the back of the amplifier it appeared to be more than just 2 tubes. One could be a rectifier tube.
Also what is the range of amplification for vacuum tubes? Haven't found any info this. Also is there a limit on the number of stages? Is a preamp actually required? These questions also not found anywhere.
Ever think of making a video on the different types of amplifiers? It took a lot of studying to find out there are three types(I could be wrong here, just started studying) 1 tubes 2. PNP or NPN and 3 Op Amps. Thanks again.
Yes, the extra tube was a rectifier. The highest amplification factor I have seen is 100, found in the 12AX7. No limit on the number of stages, but diminishing returns sets in rather quickly. Yes, the pre-amp is required to step the voltage up high enough to drive the output tubes. There are more types of amp, LF. Look up Types A, AB, C, etc.
Doug, I don't see how you can keep track of Jack. Maybe you should have named him Houdini.
Yeah, thanks for the reminder, U.D. Learn the functions and take advantage of the options(8-).
About everything resembling a signal is riding on some dc level in a tube amp...including that
pesky ac hum you may have to track down.
You're welcome,Tom. If I can find Jack, I'll give him your message.
I've got two dual-channel Oscilloscopes in my collection of test equipment, one is a solid-state 20Mhz DSE Q-1804 I bought back in the late 90's, the other is an old Telequipment D33R 15Mhz Tube Oscilloscope that needs a new CRT and some restoration work done on it, they really are useful pieces of test equipment to have, once you know how to use them properly, having the ability to see how a circuit is actually behaving is like the difference between working blind and working with 20/20 vision.
That's a good analogy, Simon. Being able to see wave forms and "noise" eliminates the majority of guesswork involved in electronic repair.
Once again, thank you for the clear/informative video's. For Christmas i'm getting a Siglent 4 channel 100 Mhz scope and I just won bids at work (Zoll Medical - Leader sig gen, Fluke DMM and a 10A/20V power supply) so, I'll have a fairly well rounded home lab bench in a few weeks. Having successfully build and gig with 2 tube amps, it will be nice to finally "see" more deeply into what is going on in each gain/transformer stage of subsequent builds, mods, and some day designs. Thank you!
Congratulations on a fine acquisition, Phil. We hope it serves you well for many years.
Great video again,thanks!!!! Because of youre videos ive been able to fix many amps and build bassmans and tweed deluxes ❤️❤️❤️,Without these videos they would out of my reach,!! Havent got in to oscilloscopeworld yet!just bough iwatsu synchroscope from fleamarket, what is difference between sychroscope and oscilloscope? My cat rudolf promised to help me ,but hes been so busy catcing criminals at night here in finland, so usually he has to sleep when hes home,
You're welcome, JJ. It's great to hear that you have applied the
concepts in the videos to the creation and repair of amplifiers. I have
no idea what a synchroscope is. Maybe you can find some info on the
Internet ? Meanwhile, best regards to you and Rudolph from warm, sunny
Texas, USA.
Thanks for the video. They are very informative and enjoyable.
I am very familiar with the use and application of multi-channel DSOs (e.g., Snap On: Vantage, Vantage Pro, Modis, and Verus; and PicoScope) in connection with automotive diagnostics (injectors, ignition coils, fuel pumps, cam/crank sensors, in cylinder pressure diagnosis, et al.). The Snap On offerings evolved to be very good. However, the industry standard, in my opinion, has become the PicoScope because of its many capabilities.
It is my understanding PicoScope makes a full line of DSOs. I don't know if these would be suitable for tube amplifier diagnostics, i.e., overkill, but having experience with their automotive version, it seems they would be a very useful tool.
Cheers.
Thanks for the interesting input, JW. I have no familiarity with PicoScope but I'm sure there are sites and videos that do. Best of luck.
For those of you that are looking for an oscilloscope and like building things; I'd suggest a DSO Shell oscilloscope kit made by JYE Tech. You can purchase them from many places for about $20 dollars U.S.. I got mine from Banggood.com for less! They are easy to solder together in a couple of hours and make for a nice pocket sized scope. They are single channel but I don't see that being a problem checking anything presented in this video. I added a cheap $4 dollar 10x probe to mine as the voltage limit is 50 volts. With the 10x probe I'm safe up to 500 volts.
Look up some of the review videos and some of the build videos for this scope and decide if it might work for you. They also sell signal generator kits for even less!
My questions for Doug are, what's your scope voltage limit on 1x setting and will you fry it if you connect to plate voltage by mistake. My other question is; is there any time I would need more than a 500 volt limit scope?
Thanks for your helpful info on inexpensive scope availability, 10L. I believe the limiting factor is not the scope but the insulation within the probe. The 1Meg resistor at X1 will protect the scope innards, but an arc may occur in the probe at high enough voltages to destroy it.....and possibly your hand. I would think a normal probe could handle 500VDC, but I tend to avoid any voltages above 350V or so. Let's face it, there is really no need to attach a probe to the plate of a KT150
Love my tektronix 2232. Owned it first and after learning on the old-school I have a 200 MHz DSO that I use most of the time. But I love how the buttons click. The DSO is not the same. Wish that the modern ones had detents for the knobs.
Thanks for the input, AT.
Lo'der UD !
I smell an Honorary Diploma in "Ampology" coming soon ! Your dulcet tones and ageless wit and humor continue to both impress and educate. I'm only hoping you'll give my Vox clone design a look when it's ready and help me source the difficult bits like Diodes from Mullard for full wave bridge rectification. But in the mean time I will share with my friends and enjoy and wait for the video delights yet to appear. Robert aka jj Thanks ever so......
I can tell that you're an honor graduate in the making, Robert. You're welcome. Thanks for watching :)
Greetings uncle D! Signal tracing has always been my favorite topic of your videos. Its always good to revisit your award -winning videos. They also offer hi level entertainment and make this subject fun and rewarding when we apply your techniques and solve problems. I want to thank you again.
You're quite welcome, Mr. K. Thanks for the nice comments :)
Great videos Doug. I can now switch on my Tektronix T912 without trepidation ! Incidentally, I'm told my 'scope has a storage function - not sure how to use this yet. Another video perhaps ?
Thanks, Dave. I'm glad the videos were helpful. The majority of analog scopes, like mine, don't have a storage function, so it's not feasible for me to demonstrate it. Hopefully you can find technical assistance on the internet. Good luck.
Does this also applies to a stereo receiver? Meaning the information that you presented?
i have a Tektronics 2245 150mhz O'scope that i am trying to learn how to use. So your videos are very helpful.
The general principles would apply, Rob, but if the stereo receiver is transistorized (and it probably is), the circuit details are quite different from the tube amps that I work on.
“10 minutes of theory, and 16 minutes of hands on...” Don’t forget the minute spent looking for Jack! 😻
Yes, and it was a minute well spent :)
Enjoying this series. I sent you a private message regarding something I want to give to you. Don't know if you got it or not. Anyway, let me know. If you do want it, I'll need your shipping address.
Thanks, Chuck. I'll look for the message.
UA-cam doesn't seem to be supporting private messaging any more, Chuck. If you give me your e-mail address, I'll contact you.
chuck.mac.leamon@gmail.com
Where is Jack. Silly Jack love that cat. If a cat really wants to hide you'll never find him until he gets out of his hiding place jack the good little black cat
True enough, Dwight.
I'm curious Uncle Doug like in a champ amp the on-off switch is in the return wire the fuse is in the hot side I wonder why Fender did that back when. Could it be that they were looking at less sparking in the contacts of the switch internally. I wonder what their reasoning behind it to the switch and fuse that way back then? What do you think?
@@dwightjt It's easier to wire when you have a lug for each of the primary wires, Dwight. In the modern wiring scheme, the white (return) wire connects directly to the PT primary with no lug.
Got a question. Looking at the waveform on the scope @~3:38, the sine wave looks symmetric, +&--. Looking at the trace @~ 23:30 - 23:48, the positive peaks look broader yet not like the input signal @3:38, and the negative peaks looks sharper, more pointed than the top of the positive peaks. Appears to be distorted. Why?
You and Jack are like Kato and Inspector Clouseau, you never know where Jack is going to hide or how he is going to attack!
When approaching distortion levels, the sine wave is altered in shape. The sine wave at 3:38 is undistorted, while the later one is becoming distorted. I have no fancy explanation for this other than what is visibly evident on the screen.
Excellent video Uncle Doug. Also - I really like your 8 ohm load!! I have several smaller ones - but yours looks quite hefty and nice looking !! I looked on e-bay to find one like it - but couldn't find the same size/appearance load there. Can you tell me - what is the wattage rating of your load ?
Thanks, Donald. Mine is 100W.....but it does get hot. I would recommend a 200W version for fairly low-wattage amps, and a 500 to 1000W for large amps.
I always used my tongue to test the 9V's. Thanks Uncle Doug for most the enjoyable educational episodes ever caught on video they are Gold. I do appreciate them & you I always learn something. Excellent teaching.
You're welcome, W4. Thanks !!!
Hi Uncle Doug, thanks for going a long way to demystify the world of oscilloscopes. I don't think I am in a position to purchase a conventional scope, have you had any experience or opinion on digital scopes or ones which interface with PC's?
I have no personal experience, Colin, but would love to have a digital scope simply because they can perform most of the frequency and voltage calculations automatically. Likewise for the ones that interface with a PC......I'll bet they offer excellent results for a fraction of the cost.
I thoroughly enjoyed this video! It was just what I needed! I have a couple of scopes but my use of them is very basic. Many thanks to Uncle Doug and to the generous subscriber who donated the amplifier utilized in the making of this video. Using an oscilloscope and tracing a signal for grounding errors and failed components are what I need to see the most. I'm glad to have found this channel and this video - thank you very much Uncle Doug! I've subbed your channel and will become a Patron very soon! All the best - Luther
You're welcome, Luther. Best of luck with your scope education.
Plz help im new at all this and i was gifted a Tektronix 5110 to make my car amplifier repairs easier.. But i have been tryin for a week now to try to even calibrate it i can not get the split lines or even get it to stand Still im guessing i have a button pushed or unpushed in that needs to be if anyone one could help me or guide me in the direction i greatly appreciate it...thank you in advanced
I did my best to explain how to use an oscilloscope in my videos, Jose. If they are not sufficient, then seek additional info in other videos or find someone in your area to give you on site instructions. Good luck.
@@UncleDoug ty i apperciate it its just all new to me so i really domt have a full understanding of the buttons and their usuage.. It has tons ill keep trying and love u video very helpful and i will deff continue to stay subscribed
That's great to hear, Jose. It takes some time to learn a new skill, but you'll succeed. Good luck.