How to Construct a CHEAP Resistive Dummy Load Box for Guitar Amp (Hot Plate, Power Soak)
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- Опубліковано 11 бер 2021
- in this video. We'll discuss how to build your own switchable resistive dummy load box for use on your electronics testing bench. This load box is useful in allowing you to run a signal into an amp without fear of damage to the output transformer or tubes while testing, troubleshooting, or using the line out jack to a recording device, DAW, or mixer. This design allows the impedance to switch between 8 and 16 ohms at 200W and 100W respectively. This is not to be confused with reactive loads or attenuators, although we may do a future video on such a device also. Be sure to subscribe for that!
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CORRECTION: At about 11:20 I talk about total "power handling" of the load. I said, "with two resistors in series you don't increase your power handling". That is not strictly true. What I should have said was "you don't increase your TOTAL MAXIMUM power handling with two resistors in series". In the case of parallel resistors, they split the current between them, so the total maximum wattage that can be dissipated by the two resistors is increased, and if both are the same value, this figure is effectively DOUBLED. But in the case of series resistors, the TOTAL current through the series resistors is not split. The same current flows through both. Therefore, the total maximum power handling of this load cannot exceed the maximum wattage rating for the LEAST robust resistor in the series. I hope that clears things up somewhat. Got a lot of comments about that one, which is cool because it shows people are watching and thinking.
Brad, why couldn't you make a reactive load device by using a high wattage speaker... without the cone? (basically a Harry Kolbe "Silent Speaker"). You could run a line out to effects, that would then run into a power amp, or you could just use it as a stand alone device for repairing tube amps. It would certainly be better than running an output transformer into a bunch of resistors. Just an idea.
Watts equals current times voltage at any given point all ways but you can fool yourself with test gear mx false readings
2 power resistors of the same wattage and ohms value will double the wattage handling if they are wired in parallel or series. Ohms law dictates this. Current doesn't remain the same; it doubles when resistors are wired in parallel or it gets cut in half if wired in series. Voltage through each resistor does the opposite... Power dissipation (E*I or wattage) remains the same whether resistors are in series or parallel. So, two 100 watt resistors of same dissipation and ohmage will give you 200 watts dissipation whether wired in series or parallel
@@NoOne-sn2si thank you. It's pretty bad when somebody corrects themselves and still gets it wrong. Worse when they claim to have some technical expertise on the topic. And worst when they are teaching others with their incorrect information. Ohm's law is about as easy as it gets and Brad should know better.
@@JRFarmercom He really doesn't understand Ohms Law! Or circuit theory in general!
That’s what my dad said when me and all my buddies loaded into the back of the truck, “ well there’s a full dummy load!”
I sent you this concept almost a year ago. My suggestion was a little more elaborate allowing for 2, 4, 8, & 16 ohm loads but at least you have the start of something better than what you were using. Need to add a connection for your oscilloscope. Nice upgrade to your test bench!
Thanks Ray. I don’t specifically recall that, but the repeated calls from a lot of different viewers has led me here at last. I’m sure your suggestion was part of the overall inspiration to finally do it.
Power handling adds up with series resistors too, because one resistor only gets half the voltage, while in parallel circuits the current is split and the voltage is the same, but if you do the maths the power dissipation will be the same per resistor. You can also add a high impedance voltage divider in parallel to get line level out from the speaker.
I’m only looking at maximums. The maximum power handling (wattage dissipated) is unchanged in a series situation. Both resistors see the same current. I do understand what you’re saying and you’re right both resistors share the load, but the max handling for each resistor can’t magically go up when they see the same current.
@@TheGuitologist Yeah, you are still not understanding it. Let's say the output is 10V 10A, total power is 100W.
If your resistors are parallel they get 10V 5A each that's 50W per resistor.
If you put them in series that's 5V 10A each, also 50W per resistor.
But your resistors can handle 100 Watts, so they do add up in both situations.
I don't know where you learned electronics, but that's basic stuff.
@@szaki95 ????
@@triple_x_r_tard what is ????
We can go into how solid state and tube amplifiers act diffently to various loads, but that doesn't change that max. power in the circuit is the sum of the max power of all components (we are speaking about equal values).
If you have different power rating but same resistance values then max. is the weakest power rating * number of components.
If resistances are not equal you have to use Ohm's law for each component.
Just don't start calling yourself The Dynacologist.
Absolutely brilliant!
😂😂
I made two attenuators that also work as dummy loads with several 20w resistors :D
you should expand on this and show us how to make a home made attenuator
Ok.
Tremendous idea !!!
In its most primevil form: remove 1 resistor for desired ohmage. Run wires from where the resistor was to a 1/4 inch jack. Plug stuff in. In series/parallel, expect about 75 pct Wattage attenuation of low frequencies. Highs will be attenuated based on reactive loading. Highly variable by speaker type.
That would be seriously valuable video!
Reminds me of the Scholz Power Soak I had back in the 80’s. Worked just fine for its purpose especially back then.
Thats funny you say that, because I just did about 30 minutes ago! :D take care!
Lots of people fried the output transformer on their amplifiers back in the day using a "Power Soak" or similar resistive device... output transformers were never designed to operate into anything other than a speaker (reactive load). Read; "The Trainwreck Pages" by the late Ken Fischer... he was adamantly against using these *resistive" load type devices.
Regards 🎸
@@scottdunn2178 Well, back in the 80's I used one for 7 straight years, gigging 4 days a week with it on a 1977 Marshall 100 watt twin combo and it worked fine. Believe me it was cranked rock n roll 4 hours a night. Not one single problem with the soak or the amp. Sure, I agree its not the greatest thing for the amp/transformers, but it worked and got me that cranked kick ass Marshall sound. There are much better soaks now like the Rivera rock crusher.
@@Superjet113 Yes, some people used a Power Soak without a problem, but tons of people fried their amps too, it's the luck of the draw... but I wouldn't risk it. Use a REACTIVE load type device... your output transformer "sees" these as a speaker, and won't cause any damage. Purely resistive load type devices are only asking for trouble.
@@scottdunn2178 Pretty sure their were no "reactive load devices" back in 1981 when I bought that power soak. But I appreciate your input. I have a rivera rock crusher these days, works great.
Damn. Destroying a nice vintage Dynaco. As a vintage audio lover, that hurts. I hope that amp was beyond repair.
Agreed. Dynaco amps were the cream of the crop in the 70s and available in kit or built form. They were often called the poor man's Marantz but a few audiophiles I knew thought they were every bit as good.
Ya - my sentiments exactly. And ... to house some load resistors !!!!!!! OMG
This wasn’t a highly regarded model. Parts will be salvaged and put to use. And it needed a lot of work.
What a waste of early amp!!!!!! You could of went to home depo and got cheap 6-7 dollar metal box for this as I did for one I made years ago to drain RC car battery's. Sorry a total waste. Z.K.
11:17
Power handling also doubles in series, as they get full current, but drop only half the voltage.
However keep in mind that those power resistors also have a maximum temperature rating. With purely passive cooling, you can calculate the approximate temperature rise per watt for your heat sinks. I think you need surface area, cubic content and thermal conductivity but don't ask me for the formula. Only if they stay below the max operating temperature they'll dissipate full power with no damage. Just by looking the heat sink is probably too small, but you're not gonna need that for guitar amps anyways, so you're fine.
Several others are saying this as well, but it’s a misnomer, I think. So, yes, the voltage drop per R gets divided between the two Rs, so all other things being equal, two Rs in series are better than one, but that doesn’t raise the max power rating of the circuit as a whole. The proper way to look at it is the two 8 ohm Rs in series at 100w max rating each together are the equivalent of one 16 ohm at 100w max.
@@TheGuitologist
That would be 40V 2.5A
(40/16)*40 = 100W
40/16 = 2.5A
20V drop per R @ 2.5A
20*2.5 = 50W dissipation for each R.
Great job brother. How about designing a pedal using 6 volt tubes like a tube driver
Awesome, was watching this while wearing my teal/purple Squishy wrist band and seen your black one! They sent me 2 instead of 1, so I gave one to my G/F, and donated another $20. More power to Squishy little girl.
Cool project Brad, this kinda reminds me of the inside of my 80's Tom Sholz power soak... lol Great video, thank you!
Made one of these years ago with 4 16 ohm 100 watt resistors, gives me 100 watts of 16 ohm, 200 watts of 8 ohm, and 400 watts of 4 ohm. I use a much more massive heat sink than you but still I have contemplated water cooling because it get's scarry hot when soaking an amp. For testing and intermittent use it's fine.
I can always add another heat sink on top of each heat sink later. And I can add a fan as well, which will help. A cool video might be frying some bacon and eggs on it. :)
@@TheGuitologist :)
I'm doing the same thing at the moment , this is perfect timing for more ideas for my project.
Great video. I made one of these for high discharging RC batteries for racing (they sell for $180 USD which is the same thing you built with a fancy brand label on it). RC guys would appreciate this build, I will pass it on to them.
Wow Brad. What a way to treat a Dynaco 120. That was my first ever amp project kit circa 1974. Ran my floor wedges until I blew up one side during a gig. Ooops! That aside, 2 x 100W - 8ohm resistors in series or parallel will handle 200W. Even though when in series the current is equal in each R, the voltage divides across both. Similar to when in parallel the current divides, but the voltage drop is equal across both. You can do the math as I x V , or I^2 x R, both = same W. As long as the resistors are equal this will hold true. It's when you have unequal resistors that things get sporting; you have to calculate voltage and current through each leg and determine power handling requirements for each R (that's when I^2 x R is best formula to use). Have fun with your load, but don't do electrics loaded!;-)
I feel like everyone is confused on the issue of series resistance. Two 8 ohm 100W max Rs in series yields the equivalent of one 16 ohm at 100W max. The max wattage rating of the pair does not technically increase.
Could have probably had better thermal properties if you had put like 1/4 as much thermal paste, it is just meant to fill in the imperfections of the metal, very thing layers work excellent - after that you start to insulate it as the metal (copper and alum) will disperse it better than the paste will.
I used to have one of these Dynaco ST120 amps---HATED IT! The tube amps I had were MUCH BETTER! Stayed with them and sold the ‘120. I built it from a kit-just one afternoon to build. When I attended college at the University of Springfield,South Dakota in 1971-1972-the Dale resistor factory was in Yankton SD just a few min from Springfield Sd. The Dale folks donated several of those chassis-heat sink mount resistor to the school. Some rated to 500w! Later in life as I worked on AM broadcast transmitters had to make a dummy load for a 10Kw AM transmitter modulator was 5kw of audio into 6kohm. Used a bank of 1 Kohm 200W ‘dog bone “ resistors in series parallel.worked great. The modulator had a pair of 12BY7 tubes in the font end-they drove a pair of 6CA7/EL34 as drivers for a pair of 4CX3000 ceramic tetrodes via a mod transformer-that ou-led to the RF PA stage.Most of the time could test modulators in the transmitter as is with the Tx feeding the antenna or dummy load-often the stage had to be isolated to troubleshoot noise issues or crossover distortion that could be caused by a shorted turn on the mod transformer primary. Like the output transformer in a usual tubed PP amp the mod transformer has a high resistance single end secondary wing to couple to the single end RF PA stage. Fortunately the mod stage was ok and it’s mod transformer. Glad of that mod transformers are expensive and heavy at 600 lbs¡ your dummy load made me think of the one for a modulator stage.
Now that's a real cool use of existing heatsinks and chassis, Brad. Thank you. If you use your pairs of 8's in parallel to make 4's, you can then parallel those pairs to give you 2ohm (Bassman and Super Reverb). You now have a couple of options on getting your 16ohm. I use the Weber Tru Load, which is excellent 90% of the time. It has a BNC for my scope, but sometimes the inbuilt speaker coil can cause oscillations. That's when I need to pull out my Guitologist dummy load. :-)
I will definitely be adding more options to this. Ideally, I need another one exactly like this wired to 4 and 2. I could get there with switching too, but switches are a failure point I’d rather avoid where possible.
Brilliant. Not only the engineering, but the reclamation of parts you had and a few purchased items.
That chassis could not have lended itself any better to this project! I love when stuff falls together. Nice job!
Hey Brad! Love the video.
Could you do a series on Guitar Tube Amplifier Design where you tackle the basics (somewhat like Uncle Doug) but go much further, explaining how each design type, component values affect the end result, the tone. All the while you would be showing Schematics to illustrate how the topics you're covering are implemented, with some chassis pictures and real demos as an added bonus when you can get your hands on the appropriate amps!
I have learned a lot following your channel, and I know you're already kind of doing what I've talked about, but I would LOVE (and I think that a series like this would be VERY POPULAR) it if you could structure your teachings in order to help people like me in their quest to build tube amps, effects pedals, etc.
You have a very dynamic and clear, concise way of explaining things with a lot of insight.
Thanks for considering this proposed project!
Nice of you to say. I typically don’t script things verbatim, so I slip up a lot and I don’t think I’m a very good teacher. My stuff should be viewed as entertainment with some practical applications for hobbyists.
Brad gave a nice reply to your request for a component-by-component explanation of how it affects the sound of the amp. The request is so easy to state, but does not have a simple enough answer to be meaningful to a novice, or even intermediate builder.
Extremely interesting. I never thought of using a dummy load for an amplifier other than on transmitters in our radio business.
had a line out that didnt have a dummy load but worked on standby and was not affected by master volume, wanted to know if i could connect a speaker cable to a 100 watt 8 ohm resistor and have that plugged in just incase i accidentally switched it from standby to on with volume at 0, and this video was super helpful.
I learned i can run the two 8 ohms i have in the 4 or 16 configuration since the head has both options and it will probably be fine ayyy time to go make my first thing and see if I understood this at all.
The ambient music and time lapse electronics work is hmm, very relaxing haha. More importantly, I now know what I need to do to build a dummy load! I'm going to be repairing an old Fender silver face Bassman amp, so this is perfect, thank you!
Have you considered adding terminals to the dummy load so that you can connect your scope easily?
Man, those 8RJ resistors are giving me Navy flashbacks. Actually really glad you posted this, though. Been considering how to go about this exact project.
I mounted four 300W / 4R on a huge heatsink for testing PA power amplifiers more quietly.
I made two pcs for a total of 2x1200W. If i need more power, i just connect them in series.
Works great!
I need to build a load for a 5 watt blackheart, how much resistance do l need to bring a low power 5 watt TUBE amp down to line level?
Great video Brad I’m always learning something new from your videos I love how you repurpose things we have become a throw away society and it’s sad hope some of the young viewers watch because they can learn a lot from them thanks for all your videos.
My ears perked up at the title, this one was fantastic. Will definitely have to make one of these someday.
What are the chances the holes line up you might want to play the lottery
Great truly useful project. Could you make a cheap power brake?? Please.
It's good to show simple ways to make a home brew speaker load..
Many years back I used heater element.
Now use fan cooling just to push the load resistors a littler harder.
Nicely done. I've done the same thing. I like your chassis. My dummy load is in plain view on a huge heatsink. Cheers
Fella I grew up with who was sort of an electronics savant had an idea that used an ordinary lite bulb base and regular lite bulbs of varying wattages. I don't know the other components, but the idea of drawing off various wattages with different lite bulbs seems interesting. Just a thought.
A regular space heater on "Hi" ( 1650 watts) is quite near 8 ohms and can dissipate.... well 1650 watts. Just change the plug. Best to use one without a fan. If it has a fan you can disconnect it if you don't drive it near the max rating. The fan is inductive instead of the resistive load of the heater coils. It wont hurt anything but the impedance will vary a little with frequency and will have a reactive component. A lower setting on the heater will give higher impedance ( a 900 watt setting would be 16 ohms). If you have a 1000 watt setting it will be a little lower than 16 ohms. You can calculate the impedance of the heater from the listed watt draw at a particular heat switch setting by the formula 14400/watts=impedance.... assuming 120 volt ac line voltage. You can hear the guitar sound from the heater a little too. A bonus...
Hmm. I’ll have to try this sometime.
Nice....!!!....background music is relaxing too. A Made in USA label, some probe jacks for a meter/scope and a fuse could be handy additions.
Very cool. Can you do a video on how to test a speakers impedance and it’s power handling capability? I have speakers with no labels and don’t know where I can use them.
Another dummy load I used that type of resistor in-just thought of it. This load was used to test cook a broadcast console mixer power supply-+ - 15VDC thThe console power supply would fail intermittently-cooked it under load until it died. Then was able to fix the supply.-funky regulator chips.re-laced them-cooked the supply again and it was OK . Had to make a “HOT DO NOT TOUCH’ sign so others in that shop would not touch the load. Mounted it on a rack panel to work as a heat sink and chassis. The load served it’s purpose-probably still in that shop-the VOA maintenance shop in Wash DC. Sometimes folks like to touch resistors being used for test. Your load has the cover to prevent. That.
Brad I used to use my ex as a dummy load but she kept complaining about it, I couldn't convince her it was pre-menopause thing. Good stuff here as always!! Dynaco! How kewl is that!! Them Ohmites were built for mucho watts and I still have them in use today!! Ohmites were never pussyfied - also I still have and use my Ohmite 194X variac just not very fancy as todays stuff. Take care!!
Dang! You completely dismembered a vintage Dynaco stereo amp just to make something to dissipate some extra heat? You big dummy!
Nah. This thing needed a lot of work. Lots of leads already disconnected on it, one power resistor was rattling around inside it. And generally I have no use for it. I have tube amps for stereo use. Plus, this model isn't generally that well regarded.
Is it possible to make a dummy load with a line out jack?
If you can find the time I'd love to see a video showing how a reactive loadbox circuit works.
Thanks Brad for making video's that bring so much happiness.....
The resistors you have used are metal clad wirewound resistors.
These will be an inductive load to the amp, you realy need to use
high wattage carbon film resistors, this is what Hughes & Kettner
use in their valve amps as dummy loads.
Great tutorial Brad! I dig these style of instructional videos--great info and footage editing.
Thanks for the clarification. I have been looking into this idea mostly because I want to go Cab-less, but want to keep my amp head.
You know I'll be building one. Thanks Brad!
Brad I loved this one. I assume you are making the music in these videos, I want to hear about it!
Not this one. This is a UA-cam library track.
Thanks Brad. Your videos are top of the pops buddy.
I've actually been wanting to build one of these from an old paint can filled with cooling oil for a ham radio dummy load for the radio, has to be able to handle high wattage. I like this for that idea much better, never thought of it for some reason.
I would also like to see about using this as a laod for the tube amps as well.
Great video's as always!
Can you make a video showing how to make a Line Out Box because some Line out Boxes use an isolation transformer and the line out box needs to convert speaker level signal to instrumental level or line level signal. The amplifiers output is going to have an impedance of 4 ohm, 8 ohm or 16 ohms which the signal is not an audio signal level because its a speaker signal level which needs to get converted back to instrument level or line level signal. It would be nice to learn how to do this correctly.
Excellent tutorial. Thanks Brad. Can't wait to see you back in the amp world. Though I'm sure your other stuff is just as impressive. I understand that a person must evolve, especially a creator.
Hi this is very informative. What do you with the Ground connection that is tied to the TS connector sleeve ? Thanks.
Hi! great project! I´m testing an 8 Ohm prototype made of 2 pairs of 8ohm 100W resistors, and I´m making initial tests with 3 amps, 24 volts and making augments of 1 volt. I have noticed two things, I will appreciate if we can share some info about it. Here is what I found:
1.- Do you have any specific test to confirm it´s working? I made this calculation:
To get the maximum input values:
P= 124 [W] @ 1k [Hz] (info from manufacturer, hand made amplifier)
Z= 8 [Ohms]
=> I = sqrt(P/Z) which is a bit less than 4 [Amp]
=> Vout max from amp = 4*8 = 32 [V]
So with this I decided to make the system stable for a DC signal of 32*sqrt(2) = 45.3 [V], and an AC signal, 1k [Hz], V peak = 45.3[V]
2. - The resistors gets VERY hot : I ´m making measurements, and just got a thermometer to confirm but I could estimate about 80°Celsius by touching it. Do you know if there is a wat of estimating or calculating that? I´m concerned with loosgin resistance stability due to heat in the long run. I´m building an enclosure with a 1590 C Hammond box, a fan underneath the resistors, and CPU dissipation and vents on the outside of the box.
Have a great day!
I have a speaker 1000w in to 4ohms can 2 resistor of 4ohms 100w in parallel to make 6ohms to my speaker can the resistors handle thank you
Wicked, I was just about to whip one of these together. CPU coolers should work great for the application. Super- cheap (or even free) for 80 to 100W dissipation each.
Biggest down side is the 12V requirement for the fans. I used a PC PSU in my last dummy load. Built it in an old Dell chassis.
This makes me wonder if you can use an old punctured speaker that still has an intact voice coil. Basically a speaker that doesn't make much noise. Maybe put it inside a sealed box. I can't remember if this is already a thing or not.
Hmm... maybe I'm confusing a dummy load with an attenuator.
With a dummy load for troubleshooting, measuring etc on workbench, if the dummy load is not used when playing, does less than full power handling do the job. Say being enough for a bass amp, since you don't introduce power spikes with transients when you're not playing it?
It can work for som troubleshooting, but I wouldn’t want to push it too long.
Hey Brad, great video today. I still have no idea what it’s for, but I really enjoyed watching you build like always. Keep up the great work.
Watt a cute little low tech load bank and a great use for a dynaco 120 horrible amp my load band is rated conservatively at 1,000 watt a side it’s forced air conked and water cooled the resistors used are Dale250 wt nonindutive with switching between 2, 4 or 8 rack mount with tempature switchs to control the fan speed and pump for cooling
I have load envy.
You could slightly enhance this as noted and then market this! A handy tool for amp work.
Question... 😊 if I build one of these... I could hook up my marshall head without a speaker and play to my DAW without the worry of killing my head even if I used it full blast for an hour... I have a marshall jcm 900 50w it has a couple of line outs (direct out and recording compensated)
You need a speaker load on the speaker output of any tube amp to run it. You could probably pull your output tubes out of the amp and use the line out though with no problem then. I assume that, but I don’t have your schematic in front of me atm.
You do know that some people love those amps, right? My jaw is on the floor, scrapping a decent Dynaco for the case! That said, thanks for the tip on the Dummy Loads! I'm going to build one, but try not to destroy a classic amp in the process.
This model is pretty universally loathed for sound quality. Plus I don't have any use for it as an amp, even if I serviced it, which it needed. It was non-working.
@@TheGuitologist yes, not as much love as the st70 but they’ve been gaining popularity as a cool looking retro amp for people building 70s rigs. While I winced, I’m over it - somehow seeing it trashed activated my hoarder ocd!
The parts will all be salvaged.
Hi! Awesome video!
I just ordered 4 of the resistors. I am just now realising that my Engl head is only 50w. If I build it the way you have, will there be any negative effects or is it just more headroom?
I guess what I'm asking is, are the resistors 100w "max".
Thanks to anyone who helps me out!
Yes. 100w max
@@TheGuitologist oh cool. So as long as I get the serial/parallel wiring correct, I can run my Engl Sceamer 50 into it.
Thank you so much for this video. I was going to try to buy some kind of solution for this but I like to tinker and prefer to build cool stuff myself.
Thanks Brad. I fried 2 pots the other day trying to make an effects loop attenuator. I need to up my soldering game. Ill give this a go.
Can’t put too much heat on a pot terminal. You risk melting the internal plastics in some of them. It’s the prolonged heat that does it. So make sure your iron is nice and hot. Clean the tip, pre-tin it, and remember to heat the work before trying to apply the solder.
@@TheGuitologist i use plumbers paste flux , i use very tiny amount , i also REMOVE the flux when i am finished . its my little thing that i do that makes my life so much easier until i admit using it online then ... oh boy the pros techs and experts line up to tell me how wrong i am . thing is i started doing this in the 90s and all that stuff i built and repaired is still kicking ass so ... maybe some rules are meant to be broken . i use it on everything .
Tip: I use a Badcat amp attenuator... but it's used to lower the volume of your speaker not eliminate the speaker. So... long story short: Dummy load it...instead if using speakers. Now the output goes straight into mixer. Magic!
Will not work if this isn't done, the attenuator does not sound the same unless you use "loud enough" which is way too loud for my bedroom.
Don’t forget a 2 ohm load for the occasional Super Reverb/Concert/Bassman full bore power test!
Nice job. I am looking at building an attenuator for my Mk IV. Boogie. I have come up with a T topology resistive pad that should give about 20dB and an impedance of 8 ohms. I’d be interested in hearing your thoughts.
whoua man thanx I will build it for sure !!
Good luck! Have fun!
Thanks for the video. I have 2 dummy loads of 4.2 and 8.4 ohms, can I use for load testing of 4 and 8 Ohms? What's the maximum tolerance? Thanks.
Yes. Those are close enough.
can i use speaker cables for the internal wiring?
Very cool to watch and learn thank you.. Question what was wrong if anything with the transformers on that are they salvageable ?
Im wondering who would rewrap those type transformers these days ?
Well Brad, I think I know someone who also read and used the Forest Mims Engineer's Mini-Workbooks. ;p)
These power resistors in aluminum case have heat sinking built in, that's why they are finned, extra sinking can't hurt but it seems like overkill to me.
Sweet Brad, been needing a dummy load thx.
Am I crazy or did you not do anything with the ground (tip?) of the speaker plug?
thx 4 ya vids brad hope you have a great day!!!
Hey Brad, my amp guy says that nothing will truly substitute a speaker cabinet for a tube amplifier and that any dummy loads otherwise will end up damaging it. I would normally look at the fact you're making one, as well as the fact they are sold everywhere and seem to be widely used as evidence to the contrary. However, this guy is definitely has some weight behind his opinion as he's worked on stuff for big names for a long time (more on the vintage synth end of things, but he's done many amps).
Is there any truth to it, or do the resistors truly serve the same function that the speakers do in a cabinet?
Looks like a Dynaco ST120 60 watt stereo amp. I used to have one. Easily upgradedable... that is if you don't destroy it to make a stoopid load.
Is this also “reactive”? What’s the difference and should I care?
Can you show us how to make an attenuator?
@@electrofrying1685 awesome thanks!
I have a lot of rheostats lying around. I was also thinking of maybe building a silent speaker. I’m ruminating on it...
can u power a fan off the power amp current?
you can , more importantly a neon lamp so you can see the throngs of women coming to mate with you .
yes but not directly, you'll need a rectifier and some sort of voltage regulation. a 100w amp will produce 40V plus peak.
Can you build a attenuator dor a 100 watt tube amp?
Seems 4 ohm would be good for bass amp heads.... you could parallel that 4ohm with enough of those handle a bass amp... drill a different hole pattern and put 4 of those on each side of the heat sink....4 ohms and 400 watts handling.
But Brad, there's a glaring problem with the video; where's the demonstration?! That's my favorite part haha
Excellent work KOOL
You're a gifted musician and electronic engineer
More of a jack of both trades.
Really informative , love the simplicity 👍🏻☮❤peace and love brother 😊
Using the dummy load, how to you then hear the amp ?
In theory you’d go out through the line-out of your head and into recording interfaces.
You can also use a speaker cab parallel to this load on the amp output and it’ll cut the overall power to the speakers in half.
Thank you for the info Brad. Love your vids!! 💚🎸
Big dummy load 🤠
Phase Plasma rifle in the 40 watt range.
Straight forward but effective. Wonder if you have any thoughts on the differences between a purley DC resistive versus an inductive dummy load. It would seem a resistive load offers negligible inductive reactance and so serves mainly as a load for the DC component but an inductive load has both impedance (inductive reactance for the AC component) and DC resistance. Maybe not an issue with most tube amps as far as basic troubleshooting and maintenance goes but it takes me to one of those ..'Hmmmmm'...moments. Cool video once again. Cheers!
I made one with an audio tap. I can run a 5150 head and then use impulse responses in my DAW. I think I have the schematic. Also, you're using too much thermal goop. I used to design battery chargers for Yuasa/Exide and we found if there was too much thermal grease it screwed up the heat conductance into the heatsink(Large diodes on a flat plate). Little dab a do ya.
And where the output should be for daw recording?
Very interesting video never knew what it was or used for thanksfor your time
Love the background music! Zen as fuck! Cool Project Sir!!!
Fine work,brad👍🎸🔊🎶
Does reactance come in to play at all?
at 8:44 did you put a hex on it? mojo?
Hi Brad I was wondering if you could help me. I have a 16 ohm Hotplate and my amp is 8 ohms output into the 16 ohm hotplate which I know is fine with that one step mismatch BUT what about the output coming from the 16 ohm attenuator does it have to be a 16 ohm cab or can I run an 8ohm cab? I remember calling THD years ago and asking them about this and they said no problem going from an 8ohm amp into 16 ohm Hotplate but going out of the 16 ohm Hotplate you want to run a 16 ohm cab. I can't remember if they said it was not a good idea or it would ruin the Hotplate but I don't always have a 16 ohm cab and more commonly have 8ohm 2x12 cabs so I have been going into a 8ohm 2x12 out of the 16 ohm hotplate but my amp is always 8ohms into the 16 ohm Hotplate. You think it's hurting the 16ohm Hotplate by running out into an 8ohm cab?
I would trust their take on it. Not sure how their product is wired, but if they say stick to 16 ohms out, I'm sure there is a good reason. If you have an 8 ohm speaker, you should sell the 16 ohm hot plate and buy an 8 ohm one instead to match your rig.
@@TheGuitologist thanks Brad. I might pick something up that is switchable.