How to Identify Amplifier Power Transformer Leads
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- Опубліковано 4 жов 2024
- This video is posted in response to a frequently asked question regarding how to identify the leads of an audio amplifier power transformer. Several methods are explained and demonstrated, including: Color of Leads, Twisted Leads, Wire Gauge, Resistance between Leads, Identifying Center Taps, and Voltage Output of Lead Pairs. Rusty and I hope this will enable viewers to accurately identify up to 11 different power transformer leads.
NOTE: Only 2-wire 120VAC primary power transformers are discussed. Diagrams are available at the Triode USA site for transformers with 120/240VAC primaries and four primary leads, which must be connected either in series (240) or parallel (120).
This is a great video; thanks Uncle Doug! Your videos are still helping people 8 years later!
Glad to hear it, NN.
They always will. :)
Love your laid-back tone and sense of humor. I've got a box of mystery transformers that I can now get to work mapping.
Thanks, MS. Good luck with your project :)
I have never seen such useful information in dozens of books and hundreds of magazines that I have read. Thank you very much
+agylub You're welcome. Please watch some of our other videos when you get a chance :)
Nothing like watching Uncle Doug using his Nicola Tesla channeling techniques. Great information!
Thanks, Doug. Glad you enjoyed it.
This is the clearest explanation i've found, thank you.
Glad it was helpful, PP.
Yes
Thank you very much for posting this. Us younger guys feeling our way through the dark with this appreciate all you more experienced guys, your knowledge, and your sharing this with us. I have surplus and junk PTs and OTs, and you really helped me out with identifying the unknowns and turning what were paperweights into useful electronics!
You're welcome, Jason. Comments such as yours make this process both rewarding and worthwhile. I'm glad the information within the video was useful and would invite you to watch the other 110 videos that I have posted, in hopes that they may be equally interesting and helpful :)
I just wanted to say that I have watched several videos online but yours 'clicked' with me. I identified the primary and secondary sides, center taps and which leads were the common, 4ohm & 8ohm on my output transformer! Thank you so much for your great videos!
Great instructional videos! Thank you. I wish you had been the instructor in my Freshman AC classes! To this day (many years later) I still have to use reference material for some very "basic" troubleshooting. I'm glad I found your videos -- and kept my old textbooks! Thanks again!
We're glad you found us, too, RO :)
Finally... a teacher who knows how to unlock these electronics mysteries, for us newbies. Thank you Uncle Doug for these many tutorials - the quality of which I have been unable to find elsewhere. In terms of your invitation for further topic requests - and related to this particular video on amp power transformers - I'd like to see another angle on this topic. That is where there is a need to replace an amp's power transformer with a new one, but the schematic [where available] does not specify windings values. I'm confronted with this exact scenario just now, whereby I would like to convert my 120V amp to 240V - and the current transformer does not carry a spare set of windings for the purpose. Exactly how do I confirm the power transformer specifications for my existing amp to a potential PT supplier? A topic for a further session, perhaps? Again, heartfelt thanks for these invaluable tutorials. Uncle Doug, you rock - and you are pretty handy with that ax! :)
This topic is covered in my Supro Tremo-Verb video series, Tony. You add up all the necessary voltages and current demands of your circuit and then find a power transformer that exceeds them all.
As always another great video! They will erect a statue of you and Rusty somewhere someday in remembrance of your undying posting of "the best" informational videos of all times. What a great pup! Thanks
I was just in the dining room (my electrical shop) inspecting a power transformer id bought. Your video came up and was very informative. Thanks for posting it.
You're welcome, Jay. I'm glad the video was helpful :)
@@UncleDoug Hey Doug I have a dandy Marconi-made boat anchor T1 in my 1953 Les Paul GA-40. I am mounting it in the bottom of the box - similar to the Estey Magnatone, which reverses any proof of concept. But Gibson's two chassis hanging bolts are not safe to carry with IMO.
Thanks to you I confirmed my pin 8 rectifier socket location as my B+ line start point - then saw the actual lead in the dress. Exciting!
That meant Gibson observed & used pin outs as per international standard. Whew. Had been wondering what other tricks of rectifier tubes wiring were out there - and of course this amp is a schematical black hole.
And indeed Canadian Marconi did ot go with international standard. foudnn that fuse blows when reds are applied to rect V8 pins 8 and 2.
Otherwise all the 6 volt starts in at V7, the trem circuit 6V6.
Looks like i have bias wire to pin 6 of V6s, other half of the power pair.
But yes indeed '50s Gibson GA series owners - the 5v4 in V8 may well be heated by orange - not red. Now it's for me to see what damage done if any before fuses went. Rectifier tube has not turned sooty black inside so perhaps it's still alright..
Happy New Year Doug & recalling Rusty fondly.
@@andrewgillis8572 Thanks so much for your interesting input and nice comments, Andrew.
@@UncleDoug I may ask Elon Musk to launch the Magnatone into space.My reasoning is that it already makes the right noise.
@@andrewgillis8572 I'll mention this to Elon, the next time he drops by the workshop, Andrew.
UD I am restoring a 1980 Marshall 100w lead, 2203 circuit. I had to use this video today to id the primary and secondary leads of the PT...This amp was a mess, no twisted pairs, all wires different colors and was a bit more complicated than your simple one here but Anyway this video helped a great deal. thank you!
You're welcome, Sting. That's great news. I'm glad the video was helpful.
I am a retired electrician with a smidgen of electronic knowledge and am enjoying learning more. Your method of explanation is excellent for novice or experienced person. Thank you for your succinct method of instruction and I am enjoying any of your videos that I can find. When I wrote my qualification exams, I was only allowed to use a slide rule as there were no calculators except 4 bangers at a very high cost.Whereas I have had an opportunity to study modern electronics, the basics are usually lost, especially tube workings. Thank you again.
You're quite welcome, Greg. We're glad the videos are helpful.
Thank you Uncle Doug for all your informative videos. I watched all these before I started to build my first full tube amp.
Olli Kivelä You're welcome, Olli. Best of luck with your project :)
Excellent video - thank you for posting. A few details that the novice may need to know: 1) After energizing the primary and when taking voltage measurements of each secondary, the voltages measured at each secondary will be higher than you may expect. The reason is because the transformer is not under load. Once the transformer is placed in a circuit and given the prescribed load conditions, the voltages will fall to what you would expect to see. For example, that 370v RMS high voltage, will load down to something closer to 350v when the transformer is placed in service. That 6.3v secondary will probably measure something closer to 7v RMS on the bench, but come down to right around 6.3v RMS under expected load conditions. 2) I will double-emphasize what Uncle Doug said about not getting into a big hurry, and to please use a current limiter.. If you goof and put line voltage on (for example) one of the filiment secondaries (like the 6.3 or the 5v secondary), the transformer will not have enough inductive reactance on that winding to limit the current. At best you will probably throw a circuit breaker in your house, or at worst you may over-heat the transformer and destroy it. 3) If you find an old transformer like this, it may be perfectly good, but it may also have been removed from service for a reason. One such reason might be that it already failed from over-load. When transformers fail from over-load, often times what happens is that either the primary or the high-voltage secondary will develop shorts between the windings. When this happens, it can draw excessive current just by having the primary plugged into the voltages it was designed for, unless the primary already failed open. If this happens, you will get excessive current even when you are doing everything correctly. It never hurts to put an amp meter in series with your primary so that you know what the transformer is doing. Also one caveat and disclaimer is that if you don't know enough about electronics to understand how to connect an amp meter in the primary circuit to measure the current, then you probably don't need to be dabbling with something like a supply transformer anyway, and should leave this kind of activity to people who possess the knowledge and skill to do this kind of work safely.
Thanks for sharing these excellent safety suggestions and observations, Jim. We really appreciate your helpful input.
Thanks again for sharing your expertise in the field - your postings save us individuals (who are new to the field) many hours of frustration - as well as keeping us safe. I did watch and build the current limiter, and it works like a charm... Happy New Year!
You're quite welcome, SP. I'm glad the videos are helpful. HNY to you all.
Again, i find another one of your videos extremely helpful. You are a great teacher. Thank you very much! All the best to you!
That's great news, S3. Likewise :)
This was a big help to me with a couple of 1947 transformers. Thanks much.
You're welcome, JK.
Thanks Uncle Doug!! My buddy just dropped off a nice GA23P from an old Gibson...your Rosetta Stone is magical!!
You're welcome, Mark. I'm glad the video was helpful.
Possibly the most helpful video Ive watched on youtube. Thank you Uncle Doug
+Michael Abrams You're welcome, Michael. I have posted over 125 other, similar videos that you may find interesting. Thanks for watching.
Thank you for the info. I never bought second-hand transformers because of the wireing. All the spare ones I had, I removed myself carefully and labled them as you do.
Makes sense, Franko.
Excellent info, expertly explained. Thank you, helped me out.
That's great to hear, WW.
A very clear and easy to follow explanation. Superb hand acting as usual, and good camera work from Rusty. Thank you.
Thanks, BT. We appreciate your kind appraisal :)
Hey uncle doug! stumbled across your channel recently because im a young person thats self taught in electronics, and i saw this video on how to identify transformer leads, Very informative and makes identifying the leads easier, i have a bunch of salavged power transformers and i thank you for uploding this vid!
You're welcome, LW. We're glad you found our channel and hope you enjoy our videos.
Very thoroughly explained. Thank you.
You're welcome, Ralph.
Thanks Doug,
I actually stripped the radio down to a bare chassis, and never considered attempting to use the circuit for an amplifier. The chassis is being set aside for a future amp build.I did a bit of reading about the heterodynes, and am aware of the dangers of power possibly crossing to the chassis. I will watch your output transformer video, and test the OT to verify readings of the wires (ohms/continuity).
Thanks again
You're welcome, Scott. Good luck :)
Absolutely brilliant video Unckle Buck!!
Glad you enjoyed it, Stephen.
Thanks VERY much for this video!!! I work on tube radios as a hobby and the transformer wires always mystified me
jorge hernandez You're welcome, Jorge. I'm glad the video was helpful :)
very informative and well thought out delivery. using size of wire, colors, number of wires ohms, to have a broad way to confirm that's what.
not sure why anyone would give the thumbs down like i see, nor why folks that do that dont post WHY they dislike.... whats not to like about Ole' Rusty!
thanks for posting, will look for more of your stuff. It was easy for me to understand, and that Sir, is no small feat.
You're welcome, Charles, and thank you for your very kind and perceptive comments. Rusty and I have no idea why 1.) UA-cam allows people to anonymously degrade the content upon which they depend to make their site functional.....especially without any explanation or justification. 2.) Why people would give a thumbs down to a clear, helpful, free, inoffensive video. If you don't like it, just move on.....no need to leave your stain behind. No doubt, many of these individuals will now give even more thumbs down, simply because I have dared to question their actions.
Just wanted to say thanks. I'm sitting here with a tangle of transformer wires, think I've got it sorted now.
You're welcome, Ben. That's good to hear :)
good to hear you again -- as you know with a 6.3 v winding with c/t some tube rectifiers can be used -- 6X5 EZ81 etc...
Uncle Doug, I don't remember if I were one of those asking but I will defiantly appreciate your knowledge! Busy testing an old phonograph type and was not sure about the power cable, as all the cable were open without there male or female plugs. Yes I could have tested the wire before I connect to the power, I track the wire at the back on the inside at the Transformer, but that wasn't the power cable, it was the speaker wire. So a little bit of smoke and there I made a big mistake with this 50's Phonograph with a Receiver. I would like to send you pic's, yes! SO after knowing about the awful mistake I took the other double wire and connecting it to the power after tracing it, I had to dismantle the whole system. Luckily, Luckily it is still power on, the only problem is that there aint any sound any more... I know now why and would of coarse love to fix it. Regards
Photos are of no benefit, Rudolfes. Your time would be better spent focusing on making the repairs yourself or seeking qualified help. Good luck......and be careful.
@@UncleDoug In short, because I think you know what burn in such a case. What has to be done? Thank's
Thank You uncle Doug!!!! I usually watch watch your video's a few times I have to take notes hahaha, I'm just a old guitar player and started trying to build my own amps or at least make the ones I have better. I really like your videos no bull, just knowledge thanks for helping the little people lol!!!!!
You're welcome, Brian. Rusty and I really appreciate your kind words and are glad to hear that the videos are helpful. Thanks for watching :)
another great video Doug! I have a pile of old transformers I've been hording for many years and always just plugged in the blacks and measured... good to be safer and more methodical!
Thanks, Bill. That method will work, but it helps to do some preliminary evaluation to facilitate proper identification of the secondary leads.
Thanks Doug, I re watched and am in the middle of a build of an old RCA reel player into a Suitcase amp. I was looking at the transformer it came with, on the schematic (and in the amp) and noticed it doesn't have the 5 Volt Heater typical of a 5y3 setup. They were using a 6x4 which used the 6.3 heaters from the usual heater winding. I was planing on a tweed era single end prinston. Question. Do you think I could get away with running the 6.3 heaters on a 5y3? or would this simply yield a burned tube and unhappy junior amp tweaker?
Thanks for the video Doug and Rusty. Nice logical layered approach from what is needed by the circuit to confirmation with both resistance and voltage. Great explanation as always. Take care. Colin
I know I’m very late but this was a helpful vid
What a wealth of information. Thanks uncle Doug
You're welcome, Johnny :)
I can't believe Rusty is 18 years old! That's quite a long run for a dog. I was also surprised when you said that you were 78. I believe that the key to growing older and keeping your mind sharp is to have hobbies, interests and things to challenge yourself. I became interested in electronics when I was 9 years old and I'm 48 now. I have had a very rewarding career as an electronics technician/engineer. It saddens me when I see young people that don't even know which way to turn a screw. It's up to people like you and me to get younger people excited about electronics. You do it through your videos. I have plans to start my own UA-cam channel at some point but, for right now, I have been teaching electronics to other people in person. I have nephews and sons of friends who play music. They often bring guitars, amps, pedals, etc. to me to have repaired. I always tell them that if they want it done for free, they have to "help" me. When they leave with a working device, they know more about electronics and have also learned the process of troubleshooting. Thanks for what you do here. Take care of yourself and I hope you have many more great years helping others understand electronics.
While I agree and applaud all of your comments, WJ, the single correction would be my age......I am currently 69 (until April) :) Your points about the need to inspire, educate, and integrate young people into electronics are of great significance. In my youth, we constantly worked on cars, dissected and repaired appliances, and knew which end of a wrench to hold. Last week one of my youthful neighbors had a dead battery, and asked my help......in not only diagnosing the obvious problem but also simply how to open the hood (the safety latch befuddled him). I believe that while there can be a limited group of experts in mechanics and electronics, ALL people should possess at least a modicum of knowledge in these fields.....for personal edification, if not personal safety.
Sorry about the age! You mentioned your age in your "Chassis Fabrication" video and I mixed your age up with my neighbor who is 78 and very sharp, as well. I understand what you're saying about younger people and cars. While they shouldn't have to know how to do a valve job, they should know how to change a tire, check/replace their fluids, jump-start a vehicle, etc. As far as electronics goes, I find that one of the biggest hurdles for people is soldering. I have worked with MANY techs and engineers over the years that freely admit that they can't solder. Most of my other hobbies involve electronics in some way or another. I get known as the "solder guy" whenever someone needs something soldered. I used to do it for them, but now I make them learn. My local community college has "community learning" program. If you have a skill that you want to teach to others, you submit your subject, curriculum, cost, class size, etc. to the school. They will include it in their catalog that they mail to all the residents. If the class gets enough interest, they hold it and let you teach it. I'm filling out the paperwork right now to get my class started. I have given several classes, for free, to my model aircraft and ham radio clubs in order to refine my teaching style and discover how different people need to be taught. I'm really looking forward to teaching people this basic skill. If it is a success, I will move on to basic electronics. I want to give people the knowledge to repair simple problems and (sometimes more importantly) to identify when it's time to take something to a pro. Is this something you've ever done or considered doing? I think you would be great at it! :-)
Thanks, WJ. I was a classroom teacher for 18 years and retired several years ago, so I'm not real anxious to get back in the classroom. I feel like our videos are a more efficient way to present all sorts of (hopefully) helpful information to a world-wide audience. Base on the warm response, I think we are filling a niche.
This is excellent! So much insight and so well explained.
I paused at about 2/3 to check and was glad to see you are still making videos; subscribed.
Thanks so much, BP.......for your nice comments and for subscribing :)
This video was playing while I was asleep and it gave me one strange dream!!
Play the Super Organ Tone video with the outer space sounds, P......guaranteed great dreams :)
@@UncleDoug haha, well there was a group of us discussing the alien invasion situation and one burst in on us, we tried shocking it and then when one was on my back it was as though you were still giving the lecture about identifying the leads, and I'm lying there being attacked all like, just shock the thing! 🤣 Dreams are crazy
Hi Uncle Doug, great video, good explanation and, as usual, solid Rusty camera work.Thanks for sharing.
You're welcome, TM. Thanks so much. Rusty did a great job, but I wish he wouldn't run and hide whenever I get out the brush to groom him :)
Very easy the way he presented it.❤
That's good to hear. Thanks !!
Always look forward to your videos. Full of good information. Thank You, and Rusty whose steady hand on the camera as always is commendable.
Thanks so much, Gary. Rusty gives you a "high four" (dew claws don't count :)
Uncle Doug, thanks so much for making your videos. I know so much more about about guitar amplification electronics. What a fun introduction to electronics. I really appreciate your teaching style and sense of humer as well. Your workbis a great contribution. Thanks so much!
You're welcome, John. Hearing from viewers like you makes it all worthwhile :)
Uncle Doug. When you describe using a multi meter to check the voltage on the transformer wires which wires do you connect too? For example, on the high voltage leads, would I probe each lead and the center tap for that group? Thanks.
You connect to the two (outer) secondary wires, not the center tap.
Thank you Doug, your videos are priceless !
Thanks, Sebastian :)
Uncle Doug, you really are amazing. Thanks for all your educational and informative videos, and thanks for the wonderful dry humour (sorry, I'm Scottish and need the extra "u" in humor...).
I hope you, Rusty and Jack are all well.
Thanks again, Coll.
Thanks so much, Coll. Although Rusty is of Australian extraction, I am proudly of Scottish ancestry, clan McLane (sp?) I believe, although several generations back :)
I like your videos because you explain things very thoroughly. I thank you again for your efforts. have a great day.
chuck jones You're welcome, Chuck. Rusty and I wish you the very best :)
Thank you for an easy to follow video.
You're welcome, Kenneth.
Great info, thanks a bunch. I have a late 60's tube amp that I have been waiting to turn into a nice guitar amp. The tube layout are 2 - 6v6's, a 6x5 rectifier tube, a 12ax7 and 12at7. I'm a 5e3 Tweed board would be nice. The output trans has 4,8,16 ohm speaker connections. Time to get it going.
It sounds like all the essential ingredients for a really nice amp, Ron. Let us know how it turns out :)
That was just great. I'm an analog amp nut and I love your information.
Thanks, BK. Identifying the leads is sort of like a brain teaser puzzle.....kind of fun. We're glad you enjoy the videos :) ^. .^
Excellent video, Doug. Serves as a great transformer primer, as well. Thanks!
+strangersound You're welcome, SS. Glad you liked the video :)
All your transformer videos are excellent. Thanks, again! ;)
You're welcome :)
Thank you so much! Very helpful.
You're welcome, Bill.
Thank you, that was a very logical and useful explanation.
You're welcome :)
That was fascinating! And helpful!
That's good to hear, Brent :)
Nice presentation! Thanks.
You're welcome, RA :)
As always great video and a good lesson for us tube-o-holics :)
Thanks, Nusior. I hope all the ampliophiles liked it :)
Thanks Uncle Doug. This was very helpful.
+Dr. Arthur D. Kemp You're welcome, Dr. Kemp. It's always good to hear from you :)
Thanks Uncle Doug, another great informative video plus....a grand appearance by Rusty! He's probably a little upset about being on the "end" of the vid! LOL!
You're welcome, Tim. Rusty was hesitant to appear on camera, worrying that his scruffy (seasonal fur shedding) appearance might disappoint his fans......but he STILL won't let me get near him with a brush :)
@@UncleDoug Hehe
Also I’m a little late I know but very informative vid! Keep up the work!
I really enjoy your videos and have learned so much from you , thank you. A few months ago I had just built my first amp , out of a old tape deck. These things seem to reproduce now there are 5 and they make me buy test equipment. I'm not addicted to the smell of old tape recorders , I can quit anytime I want.
When I hooked up a power transformer to the current limiter , without a
load on the transformer I got nothing. Using a small Craftsman digital
VOM. Then I hooked up another transformer I knew was good and nothing.
It's good I didn't put my tongue on it. lol When I hooked it up direct
to AC ..... I got power?
Greetings, Frank. You're welcome for any assistance provided by our videos. Recall that current limiters, as evident in their name, are purely current-dependent devices. When you connect a PT primary winding to the CL, with no secondary load, virtually no current flows. Thus, there is no current to illuminate the bulb or to be measured in the secondary. For this reason, CL's are best used for monitoring current flow in completed circuits, such as operating amps. Best of luck.
This video is gold
Thanks, Z1 :)
Thanks very much for excellent video's explaining both the "power" transformer and "output" transformer funtion in a tube amplifier. Very helpful information. Will need to rewatch videos a few more times before passing any test but great information I failed to find in other sorces. This the type of information I need to learn and really understand how a tube amp funtions. My eventual goal being to (diagnose problems) and repair tube amps for personal pleasure and hobby. I have more questions as well as answers now. Good thing you made more videos covering other tube amp components and their funtion. One question however, can any other tool perform the funtion of a variac? Seems I am going to need one. Thanks again for all.
+Weston Bennett The first tool you need is a Current Limiter (see my video on how to build one). A variac is primarily used to gently power up electronic devices that have not been used in many years, and is the only way to do this task. To me, however, the CL is more useful on a day to day basis.
Doug,
Great video and excellent tutorial.
David U Juarez Thanks so much, David......glad you liked it :)
Thank you Uncle Doug. I needed to know that and it helped a lot.
That's good to hear, Thomas. You're welcome.
Doing a refresher course.
I hope it's helpful, Mike :)
you are back to making at leat the occasional video that is awesome sir
Thanks, Wes. It's good to hear from you :)
thank you so much for your kindness--
Alvin s You're welcome, Alvin. Rusty and I are glad you enjoyed the video :)
@@UncleDoug I’m 6yrs late but I am very happy that you made this video.
Excellent video! very informative.
Thanks, Rob :)
Very helpful thanks!
Glad to hear it, Tony.
Best videos on the WEB! Thanks Doug....
Great instructional video and easy to follow. You mentioned hum is reduced by twisting the associated secondary leads around each other. I would appreciate you expanding on this. In addition, is there a simple method for establishing the max current ratings for the secondary windings? Thanks again for sharing.
Don
great information doug, i've quite a few unknown transformer's, now i can figure out what goes where,
p.s. say "hi" to rusty,
That's good to hear, Paul. I'll convey your regards to Rusty.
Thank you very very much for posting this :-)
I'm glad it was helpful, CT.
Great video! I'd like to add, look for a short to the iron core from any of the winding's, I've seen this problem a few times, and it will make for a nasty shock!
Thanks, FS. You make a good point. In my experience, an internal short within a transformer is far more likely to energize the chassis (and create a significant shock risk) than is the so-called "Death Capacitor"......yet no one cowers in fear of "Death Transformers". :) :)
Ha Ha! If people really knew how dangerous their amps could be they would probably never use them, in theory! In actuality, very few people get shocked by their systems. My first experience with a shorted tranny was when I was testing a surplus store power transformer and when I plugged it in, there was a blue flash from under the tranny to my metal desk! Kind of scared me into paying more attention! It also taught me to put a layer of plywood over the grounded metal desk!
Good move, FS. The only good use for metal tables is in morgues and welding shops :)
I'll say! I was young then, back in the 70s I think. A metal ground plane is great for cutting down electric noise on your bench. For a time I had old safety glass from 60s television cabinets on top!
Okay that makes sense. All resistance readings across primary and secondary windings on both the PT and OT pass inspection. I may have to move on to more advanced testing for both units. My main reason for testing these is that I feel the guitar amplifier should be much louder. I feel that I shouldn't be able to set both the channel volume and master volume to full on a 100 watt guitar amp and driving only one 12" 65 watt 8 ohm speaker. In comparison, my friend brought over his 60 watt Fender amp and we could only get that Master Volume to 2 before it was shaking the house. My amp does sound great and is not weak sounding at all. It has 4 new matched output tubes , New preamp tubes and filter caps.
jraimondi JR, If your amp is truly 100W, it should be able to simultaneously pulverize a single 12" 65W speaker and deafen your neighbors.....at less than
full volume :) One of the main culprits would be a shorted OPT, but if the resistance between the primary CT and either of the end windings is around 100-200 ohms and equal with no continuity to ground, and the secondary is measurable and shows no continuity with ground, then it must be OK. I assume that it has no built-in attenuator or power-reduction switch, and that you are feeding in a guitar signal with a good cord and no effects, loops, etc. are attached. The speaker should be of appropriate impedance to match the OPT. You mentioned replacing all the tubes, but how about the phase inverter ?? Have you checked the value of the Channel Volume and Master Volume pots? It appears that either the signal is being partially lost to ground or there is a partial failure in the chain of amplification. I would suggest getting a schematic and tracing the tube voltages and resistance to ground along the signal path. If the wiring to a tube socket is bad, changing tubes would make no difference. Best of luck.
Uncle Doug So measuring the OPT in circuit I came up with 36.3 ohms from CT to one end of Primary and 37 ohms from CT to othe end and 73 ohms across both ends. The reading across the secondary is .9 ohms with no continuity to ground.
I don't own any four-output-tube amps to compare these measurements with, JR, but they definitely seem OK to me. I guess it's time to focus on the other suggestions I made above. Good luck.
thank you, sir!
this is really shed a light to my sight :)
Glad to hear that, JiV. You're quite welcome.
very informative I just ran across your Channel, I only have one thing to add , next time please can you show us the actual readings and the identification of each pair with the multimeter, it would greatly help my learning curve thank you.
You're welcome. I'll keep your suggestion in mind.
I'm watching in 2023 and this vid is now eight years old, i wonder if Rusty is still with us?
Sadly, he is not. He passed away peacefully at home several years ago.
@@UncleDoug That's a shame, thanks for letting me know Doug. He always seemed like a lovely dog with a big personality.
@@good_king_guitarman1334 He was indeed, GK.....and he is sorely missed.
This was delicious. I ate every bite.
Thanks, Jeff. Glad you enjoyed the meal :)
Loved this video. Keep up the good work
Thanks, Ideal. We will :)
Didn't help me, but I gave a thumbs-up anyway, based entirely on the fact that you used a compass and straight-edge to make your diagram.
I'm sorry you weren't helped, Russell, but appreciate the thumbs-up :)
Thank you for explaining everything so clearly, as always. One question that I couldn't find anywhere is: Why a common way to test power transformers is to measure their unloaded voltage at the secondary, but switching on an amplifier without any load connected is strictly forbidden as it would fry the output transformer? Is there something that makes power transformers different or more resilient? Or the output tubes play a role in that?
Apples and oranges, Ani. They are completely different components, subject to very different stresses and limitations.
Learned some more here. I started to build the current limiter with parts I have around. Got done, it wouldn't work. The ceramic bulb holder I had was brand new, never been used, it has one of those chain pull switches in it, the switch is no good. I been carrying it around for years!
Thanx
Thanks for sharing this with us, Jerome.
Fantastic video! Could you make a similar episode covering output transformers? For example, how to identify output impedances and wattage?
Thanks so much. I already posted a video on Output Transformers: Output Transformers: A Discussion of Basic Principles Check my channel index for over 100 videos covering vintage gear and all sorts of basic technical topics.
Oops! Although I've already watched most of your videos, I seemed to have missed that one, thanks!
Great Video
Thanks, Greg.
Great Video!
Thank you.
You're welcome, L :)
Thanks
This video has been very helpful!
You're welcome, Mike :)
Hello Doug!
Are you planning to do a video about the basic safety tips associated with tube amps? Your videos are such a fun and easy way to learn!
Thanks,
András
Greetings, Andris. Thanks so much for your kind words. I generally try to include safety recommendations on most of my technical videos, where appropriate. I have not yet produced a safety video, but may consider doing so.
Great video as always, I am new to your channel and enjoy your videos.
Thanks, OG, and welcome aboard. We hope you watch and enjoy all our videos :)
3:47: Uncle Doug: What's going on here? You have the center-tap of the high voltage winding connected to ground. Then you have the center-tap of the 6.3 V filament winding connected to ground. HEY! I thought you can't do that. Now the windings are connected together and not independent as they should be. PLEASE ANSWER MY TEXTS.(You never respond to me).
Echo, I cannot reply directly to your inquiry. Hopefully, you will see this response. If your amp is operating properly at the moment, I honestly would not recommend changing to a Mercury power transformer. Others may disagree, but I really don't think the benefits would be worth the (substantial) cost.
😂 you dont know shit...
@@mostknownunknown1356 Oh yes he does! Through experience I know.
@@mostknownunknown1356 ignorance is bliss in your world. LOL
great video
Michael Moore Thanks, Mike. Glad you liked it :)
Thanks Doug .Give Rusty a little more responsibility,I think he is ready.When I see the cat supervising,I know that there some serious quality control going in over there.lol.👍🏻🔉🙀🐶
You're welcome, Stephen. Yes, indeed, Jack is a stern taskmaster ;)
thank you sir, helpful as always
You're welcome, Kyle.
Great video. I fear electricity greatly! Just as a PSA I guess (Public Service Announcement) I have been working as an Industrial Maintenance Technician for about 22 years. Granted we are only talking about 120 VAC input here and single phase BUT the output of this transformer is well over 300 volts...PLEASE PLEASE be EXTEARMLY careful in dealing with transformers of this type (300 plus volts output voltage) I have seen the result a dead short in action and when a transformer blows up from a dead short it is not a good day. Please listen to Uncle Doug when he says use a current limiting device to do your tests...the life you save could be yours!! Thanks for the video!!
You're welcome, Jack. Thanks for your testimonial :)
Hi Uncle Doug, I hope you, Rusty and the fam had a wonderful holiday season! I've been sitting on my hands, eagerly awaiting your next excellent video.
In the meantime, I've carved out a new work space, installed some functional lighting and a permanent, wall mounted current limiter, using one of several vintage mogul base 300 watt bulbs I got from an old hardware store that recently gave up the ghost.
Here's my question: I'm rebuilding a 1957 Les Paul Jr. GA-5 circuit from scratch and the original PT is blown. I have obtained a vintage PT absolutely free, so I'd like to use it. Trouble is, it seems a little big. There's tons of literature about running amps with small PT's, but it's hard to find info for those of us blessed with too many volts and plenty of current handling.
My free transformer measures out at 375-CT-375 (750V); 3.8-CT-3.8 (7.6V) and 5.8V. The original circuit was for some sort of antenna array, which used a type 80 and a type 83 rectifier. Those tubes are supposed to have 5.0 volts, same as a 5Y3.
So, I'd be interested in your opinion, can I run 7.6v instead of 6.3v on the 12ax7 and 6v6? Is 5.8v instead of 5.0v is OK for a rectifier such as a 5y3? And if not, would I reduce the voltages with power resistors in series? Thank you.
+Lindsey Montana I think you'll find that the voltage measurements will go down to "normal" (6.3V and 5.0V) values once the transformer is operating in a circuit. The only one that may be excessive is the high voltage, so I suggest that you check the output tube bias immediately after you get the amp operational. Good luck with your project.
Hello Uncle Doug, this is uncle Luc (French Canadian here, call me Luke)... I am a retired industrial electronic tech and I find your channel very interesting as I am starting to build tube amp... My take on a Princeton Reverd has started to sing yesterday!
Anyway...
I would like to comment on something here, the technique with the ohmeter is of course the way to go but it could get tricky at times, so may I suggest a few more ideas?
Like you do, I will bundle the wires by who conducts with who... and I try as hard as I can to locate mostly the primary. 1,8 ohm can not be always trusted, sometimes there can be 240 Vac primary, or there can be 2 primaries to be set in series (240V) or // for 120Vac... in industrial we also had many Hi-V secondaries... says for a 3 phases motor etc....
And also I really don't like your idea of using a lightbulb in series with the 120Vline, the secondary at 300 or 400V will get you if touched....
So what I do instead is I use a small 12V transformer, say 100ma or so, connected to a variac and adjusted to give exactly 12V out and I feed 12Vac to what I think is the primary. Then I can safely measure the voltage at all the secondaries without fear of zapping myself!
12V is a 1 to 1/10 ratio of the power line, so if there is a second primary, I will measure 12 V across its wires, 5V will read 0,5V... 350V will measure 35 Vac and so on....
There is another method also but trickier involving an audio generator and a scope... but that's for another time
I truly enjoy your site and your deviant sense of humour! :)
Cheers, Luc
Thank you for your helpful suggestions, Luc.
Hello Uncle Doug your videos are helping me a grear deal. I just recieved a huge haul of hammond iron. One piece has 2 pairs of 9 wires each with same 9 colors on each side. Weighs 22 pounds. Curious what you would do with it. Thanks for being such a good teacher. Im a guitar maker at heart but love tube amps and thanks to you am on my way to building a scratch amp from Hammond organ parts. May the lord bless you!
Greetings, Marc. To be honest, those huge organ transformers are just not desirable. They are too much of a good thing. Stick with the smaller ones for guitar amp use. Best of luck to you.
Uncle doug. Watched another of your videos and got a good hint at what my transformers from the organ haul are. 606 .....schumaker made. I got two super reverb outputs and a power with 340 volts and center tap. I really want to do a 5E3. I realize the outputs might not be best choice because of the 2 ohm output. The power tranny appears that it will work. Thanks for the great hint about Schumaker codes. LOVE THE INTERNATIONAL TRUCK.
@@theguitarguy777 Thanks, Marc. Best of luck with your project.
Thanks a lot Uncle !
You're welcome, Shy :)
Pin point as always.
Uncle Doug, may I have a question ? I scored a B&H 385 and while testing it's power transformer ( Gramer Halldorson - november 1955. Learned that here too. Ty ) I got the readings as follows:
feed by 120V AC
Primary DMM Re: 4 Ohm's
6.30V Reads 6.735V AC
DMM Re: 0.3ish Ohm's
5.00V Reads 5.320V AC
Re: 0.2ish Ohm's
High VAC Reads 645 VAC
Re HVAC 1 to CT: 89 Ohm's
Re HVAC 2 to CT: 104 Ohm's
Re HVAC 1 to 2 : 193 Ohm's
Now, my question is more about the resistance of the primary and high VAC as both measured higher resistance than what you did mention in the video. Also, within maybe 30 seconds of metering voltages the transformer got warm already. Do you think this transformer is safe ?
I hope Jack and Rusty can forgive any mistakes I made with my english.
Greetings from Brazil.
There is so much variation between different transformers, that you can't really judge them by the DC resistance of their windings, V......in fact, the DC resistance is really of very little use in that regard. Simply go by the voltages that the windings produce, and a little heat is to be expected from any transformer.
CKHC VD: Your inquiry had no Reply capability. Hopefully, you will see this. Testing the transformer is rather simple. Once you identify the primary and secondary leads, you can determine if the leads pairs have measurable resistance. If a winding is open, the resistance will be infinite. Finally, you can connect the primary to a current limiter and (very carefully) measure the voltage across the matched output leads.
thank you for the lesson. i measured; with current limiter, 744VAC = 2 Reds, 5.37VAC = 2 Yellow, 6.83VAC = 2 Green. 5.9 ohm = 2 Blacks; O.L. ohms to grnd. 365.7ohm = 2 Red; 190.4/175.5 ohm to grnd(?). 00.3 ohm = 2 Yellow; O.L. ohm to grnd. 00.3 ohm = 2 Green; 00.3 ohm to grnd.
is this a good power transformer?
sorry for the "no reply" I'm not sure how to enable that function.
thanks Uncle Doug
It sounds like a good one to me, CKHC. The 2 blacks are our primary AC input, the reds are your high voltage, yellows for your rectifier tube filament, greens for your amp tube filaments. The reds should have a center tap (CT). Perhaps the CT is what you are calling "ground". The CT would probably be red with a stripe (usually yellow), and it is usually grounded.
Uncle Doug
Yes, the transformer is mounted in a chassis and there is a red w/yellow stripe to ground as well as a green w/yellow stripe to ground
the yellow wires look as though they got hot at one time, the insulation is very slightly burnt(dark yellow) where they where twisted together, this made me think i had better check it out further
thanks so much for your time Uncle Doug and happy holidays to you your family and rusty of course
The green with yellow is the 6.3V centertap, which, when grounded, reduces tube hum. You're welcome, CKHC, and happy holidays to you as well.
Uncle Doug
Hi Uncle Doug. I have got myself a princeton reverb reissue circuit that has been gutted out of a new princeton reverb. I have purchased upgraded transformers for it and at the stage of starting to wire it up. The Power transformer I got is a Hammond 290BEX. On the diagram it is showing an extra 50V blue tap in the cetre of the 330v secondary. I take it that for a princeton reverb type amp I will not be using that and just isolate it. Thanks for reading.
That extra 50V tap is essential, Jim. It is rectified, filtered, and sent to the tube grids to establish their bias.
@@UncleDoug Thanks for a quick reply. I think I just saw that on the schematic. my first attempt at building. So the centre tap 0v on the high voltage is not used and tapped off right?
@@UncleDoug On the schematic I downloaded below for the 68 reissue princeton, there is nothing showing with regards to the centre tap 0v line.
guitarampblog.wordpress.com/2017/01/26/fender-65-princeton-reverb-schematic-vs-68/
I don't work on reissue amps, Jim, because they are often hybrids and absurdly complex. In every tube rectified amp I have ever dealt with, however, the high voltage centertap has to be grounded.
@@UncleDoug thanks for your reply. I checked again and it does go to ground. However in the original design fender took a branch of the high volt secondary and fed to the bias circuit. I could do the same buy i would be wasting the 50v line. If i do use the 50v line then i guess i will have to change resistor values to match 50v and not 325v. I do agree with you that they are overly complicated.
Hi Uncle Doug, I've put together a few guitar tube amp kits but they were neatly labeled with directions especially the leads for the PT. I recently purchased a tote of old organ parts which includes many PTs and OTs, and other goodies. I really want to build a guitar amp with these PT but their leads are not labeled so I came across your video . My question is, when your measuring each lead, how do you setup/connect your current limiter and to the PT, so that you can get the correct readings on your multimeter? I totally understand how dangerous this process can be so I want to make sure this is clarify prior to doing it myself. Thank you.
All is explained in my video regarding the Impedance Ratio, WL. Good luck.