How to Identify Amplifier Power Transformer Leads

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).

[@mickel7b]

This is a great video; thanks Uncle Doug! Your videos are still helping people 8 years later!

[@UncleDoug]

Glad to hear it, NN.

[@amimaster]

They always will. :)

[@missingsock18]

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.

[@UncleDoug]

Thanks, MS. Good luck with your project :)

[@agylub]

I have never seen such useful information in dozens of books and hundreds of magazines that I have read. Thank you very much

[@UncleDoug]

+agylub You're welcome. Please watch some of our other videos when you get a chance :)

[@gregglasgow9432]

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.

[@UncleDoug]

You're quite welcome, Greg. We're glad the videos are helpful.

[@tonywainhouse163]

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! :)

[@UncleDoug]

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.

[@lumpy2080]

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!

[@dougtaylor7724]

Nothing like watching Uncle Doug using his Nicola Tesla channeling techniques. Great information!

[@UncleDoug]

Thanks, Doug. Glad you enjoyed it.

[@pdimor]

This is the clearest explanation i've found, thank you.

[@UncleDoug]

Glad it was helpful, PP.

[@JjMn1000]

Yes

[@unhinged17]

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!

[@UncleDoug]

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 :)

[@rayfisher1564]

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!

[@UncleDoug]

We're glad you found us, too, RO :)

[@JimButler1234567890]

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.

[@UncleDoug]

Thanks for sharing these excellent safety suggestions and observations, Jim. We really appreciate your helpful input.

[@SPWoz]

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!

[@UncleDoug]

You're quite welcome, SP. I'm glad the videos are helpful. HNY to you all.

[@huberttremaine8343]

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

[@scottgoldsberry5203]

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

[@UncleDoug]

You're welcome, Scott. Good luck :)

[@jayivy710]

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.

[@UncleDoug]

You're welcome, Jay. I'm glad the video was helpful :)

[@andrewgillis8572]

@@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.

[@UncleDoug]

@@andrewgillis8572 Thanks so much for your interesting input and nice comments, Andrew.

[@andrewgillis8572]

@@UncleDoug I may ask Elon Musk to launch the Magnatone into space.My reasoning is that it already makes the right noise.

[@UncleDoug]

@@andrewgillis8572 I'll mention this to Elon, the next time he drops by the workshop, Andrew.

[@rudolfes]

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

[@UncleDoug]

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.

[@rudolfes]

@@UncleDoug In short, because I think you know what burn in such a case. What has to be done? Thank's

[@bullthrush]

A very clear and easy to follow explanation. Superb hand acting as usual, and good camera work from Rusty. Thank you.

[@UncleDoug]

Thanks, BT. We appreciate your kind appraisal :)

[@ollikivela2804]

Thank you Uncle Doug for all your informative videos. I watched all these before I started to build my first full tube amp.

[@UncleDoug]

Olli Kivelä You're welcome, Olli. Best of luck with your project :)

[@Willam_J]

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 KZbin 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.

[@UncleDoug]

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.

[@Willam_J]

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! :-)

[@UncleDoug]

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.

[@markwhiteley4149]

Thanks Uncle Doug!! My buddy just dropped off a nice GA23P from an old Gibson...your Rosetta Stone is magical!!

[@UncleDoug]

You're welcome, Mark. I'm glad the video was helpful.

[@sting1111]

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!

[@UncleDoug]

You're welcome, Sting. That's great news. I'm glad the video was helpful.

[@BenPrevo]

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...

[@Alext-wx7hr]

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!

[@UncleDoug]

You're welcome, LW. We're glad you found our channel and hope you enjoy our videos.

[@frankowalker4662]

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.

[@UncleDoug]

Makes sense, Franko.

[@RestoreOldRadios]

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

[@0tt0z]

Again, i find another one of your videos extremely helpful. You are a great teacher. Thank you very much! All the best to you!

[@UncleDoug]

That's great news, S3. Likewise :)

[@michaeldabrams]

Possibly the most helpful video Ive watched on youtube. Thank you Uncle Doug

[@UncleDoug]

+Michael Abrams You're welcome, Michael. I have posted over 125 other, similar videos that you may find interesting. Thanks for watching.

[@jaredkusner1137]

This was a big help to me with a couple of 1947 transformers. Thanks much.

[@UncleDoug]

You're welcome, JK.

[@amimaster]

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?

[@UncleDoug]

Apples and oranges, Ani. They are completely different components, subject to very different stresses and limitations.

[@toltec13]

Thanks VERY much for this video!!! I work on tube radios as a hobby and the transformer wires always mystified me

[@UncleDoug]

jorge hernandez You're welcome, Jorge. I'm glad the video was helpful :)

[@mixolydian2010]

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

[@JjMn1000]

I know I’m very late but this was a helpful vid

[@allhartfidelity]

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.

[@UncleDoug]

You're welcome, Charles, and thank you for your very kind and perceptive comments. Rusty and I have no idea why 1.) KZbin 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.

[@frankstone919]

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?

[@UncleDoug]

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.

[@benh7909]

Just wanted to say thanks. I'm sitting here with a tangle of transformer wires, think I've got it sorted now.

[@UncleDoug]

You're welcome, Ben. That's good to hear :)

[@WLguitarist]

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.

[@UncleDoug]

All is explained in my video regarding the Impedance Ratio, WL. Good luck.

[@UncleDoug]

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.

[@mostknownunknown1356]

😂 you dont know shit...

[@larryn1875]

@@mostknownunknown1356 Oh yes he does! Through experience I know.

[@airgliderz]

@@mostknownunknown1356 ignorance is bliss in your world. LOL

[@virpz]

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.

[@UncleDoug]

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.

[@worldwide1376]

Excellent info, expertly explained. Thank you, helped me out.

[@UncleDoug]

That's great to hear, WW.

[@westonb1384]

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.

[@UncleDoug]

+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.

[@thome1547]

Hi Uncle Doug, great video, good explanation and, as usual, solid Rusty camera work.Thanks for sharing.

[@UncleDoug]

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 :)

[@zaugitude]

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.

[@UncleDoug]

Thanks so much, BP.......for your nice comments and for subscribing :)

[@billmckenna7056]

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!

[@UncleDoug]

Thanks, Bill. That method will work, but it helps to do some preliminary evaluation to facilitate proper identification of the secondary leads.

[@billmckenna7056]

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?

[@joohop]

Nice 1 doug , so how do we go about building this ultra low noise amp then ?

[@UncleDoug]

+joohop Thanks, JH. It's a huge, complex topic. I suggest that you do some research at sites dedicated to low-noise amp design. Best of luck.

[@brianpotter7520]

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!!!!!

[@UncleDoug]

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 :)

[@roncarter2188]

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.

[@UncleDoug]

It sounds like all the essential ingredients for a really nice amp, Ron. Let us know how it turns out :)

[@td7456]

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!

[@UncleDoug]

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 :)

[@JjMn1000]

@@UncleDoug Hehe Also I’m a little late I know but very informative vid! Keep up the work!

[@100chuckjones]

I like your videos because you explain things very thoroughly. I thank you again for your efforts. have a great day.

[@UncleDoug]

chuck jones You're welcome, Chuck. Rusty and I wish you the very best :)

[@garyadkisson4790]

Always look forward to your videos. Full of good information. Thank You, and Rusty whose steady hand on the camera as always is commendable.

[@UncleDoug]

Thanks so much, Gary. Rusty gives you a "high four" (dew claws don't count :)

[@ralphmilner3347]

Very thoroughly explained. Thank you.

[@UncleDoug]

You're welcome, Ralph.

[@good_king_guitarman1334]

I'm watching in 2023 and this vid is now eight years old, i wonder if Rusty is still with us?

[@UncleDoug]

Sadly, he is not. He passed away peacefully at home several years ago.

[@good_king_guitarman1334]

@@UncleDoug That's a shame, thanks for letting me know Doug. He always seemed like a lovely dog with a big personality.

[@UncleDoug]

@@good_king_guitarman1334 He was indeed, GK.....and he is sorely missed.

[@phonotical]

This video was playing while I was asleep and it gave me one strange dream!!

[@UncleDoug]

Play the Super Organ Tone video with the outer space sounds, P......guaranteed great dreams :)

[@phonotical]

@@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

[@iamsuengas]

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.

[@UncleDoug]

You're welcome. I'll keep your suggestion in mind.

[@stephenwilliams1854]

Absolutely brilliant video Unckle Buck!!

[@UncleDoug]

Glad you enjoyed it, Stephen.

[@wcountyrednecks]

What a wealth of information. Thanks uncle Doug

[@UncleDoug]

You're welcome, Johnny :)

[@lindseymontana945]

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.

[@UncleDoug]

+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.

[@lucbelanger4951]

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

[@UncleDoug]

Thank you for your helpful suggestions, Luc.

[@jimtalltheislandbrothers6639]

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.

[@UncleDoug]

That extra 50V tap is essential, Jim. It is rectified, filtered, and sent to the tube grids to establish their bias.

[@jimtalltheislandbrothers6639]

@@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?

[@jimtalltheislandbrothers6639]

@@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/

[@UncleDoug]

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.

[@jimtalltheislandbrothers6639]

@@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.

[@willlee5421]

Uncle Doug, will the limiter prevent me from getting absolutely zapped even if observing very careful technique? After watching many of your videos, I feel more comfortable embarking on my first build using my accumulated salvage. Nonetheless, I would like to take every precaution possible. Thanks!

[@UncleDoug]

The Current Limiter is primarily to protect the circuit itself from a short circuit, Will. You can still get shocked it you don't carefully follow all the rules for safe handling of high voltages.

[@jraimondi]

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.

[@UncleDoug]

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.

[@jraimondi]

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.

[@UncleDoug]

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.

[@theguitarguy777]

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!

[@UncleDoug]

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.

[@theguitarguy777]

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.

[@UncleDoug]

@@theguitarguy777 Thanks, Marc. Best of luck with your project.

[@idogepgyar]

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

[@UncleDoug]

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.

[@jteichma]

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!

[@UncleDoug]

You're welcome, John. Hearing from viewers like you makes it all worthwhile :)

[@jteichma]

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.

[@UncleDoug]

You connect to the two (outer) secondary wires, not the center tap.

[@robertmsmith7335]

Hi Doug great videos could you please tell me what the high voltage would be for a transformer for a 5w amplifier. thank you

[@UncleDoug]

Thanks, Robert. There is no way to answer your question. The HV is affected by all sorts of variables in each specific circuit.

[@danielayala9895]

Hey Uncle Doug, I recently got a rack power amp with a transformer issue, can you share me some links to where I can get a replacement?, TYIA, very pleasent to watch your videos and your pets :)

[@UncleDoug]

Thanks. I have no secret stash of links, Daniel, but use Google Search just like everyone else. Good luck with your project.

[@cctvfm]

Fantastic video! Could you make a similar episode covering output transformers? For example, how to identify output impedances and wattage?

[@UncleDoug]

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.

[@cctvfm]

Oops! Although I've already watched most of your videos, I seemed to have missed that one, thanks!

[@unboxedtravels]

Thank you Doug, your videos are priceless !

[@UncleDoug]

Thanks, Sebastian :)

[@RobertDaniels-v5g]

Very easy the way he presented it.❤

[@UncleDoug]

That's good to hear. Thanks !!

[@j.dragon651]

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

[@UncleDoug]

Thanks for sharing this with us, Jerome.

[@kennethiman2691]

Thank you for an easy to follow video.

[@UncleDoug]

You're welcome, Kenneth.

[@BravoColl]

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.

[@UncleDoug]

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 :)

[@stephenrioux6821]

Cheers, Uncle Doug-- Thanks for all the education. I got a question about old transformers, the type with 2 black primaries. Are they interchangeable when using a 3-prong cord having black (hot), white (neutral), and green (ground) conductors? Thanks again for all the info!

[@UncleDoug]

Yes, either of the black primary leads can be connected to the black power cord wire. There is no polarity concern.

[@stephenrioux6821]

@@UncleDoug Thanks, big time. Keep up the good work!

[@UncleDoug]

@@stephenrioux6821 You're welcome, Stephen. Will do :)

[@UncleDoug]

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.

[@ckhcvd6211]

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

[@UncleDoug]

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.

[@ckhcvd6211]

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

[@UncleDoug]

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.

[@rayhitchins998]

Uncle Doug

[@strangersound]

Excellent video, Doug. Serves as a great transformer primer, as well. Thanks!

[@UncleDoug]

+strangersound You're welcome, SS. Glad you liked the video :)

[@strangersound]

All your transformer videos are excellent. Thanks, again! ;)

[@UncleDoug]

You're welcome :)

[@scottgoldsberry5203]

Hi Doug, I just dismantled a c.1939-41 Philips CM23L tube radio...safely, I must add. I intend to use the salvaged chassis for a future amplifier project. But my question is regarding the output transformer. (This radio is a super heterodyne, so there isn't a power transformer) The output transformer only has markings 050-064. It has 5 wires (two for the speaker on one side, and three on the other side (white/red/black) I know based on the schematic, that the radio output to speaker has a range of 0.9 to 1.9 watts (lower wattage is for minimal distortion). My question is whether or not this output transformer would be a candidate for a low power guitar tube amp? And if so, can you suggest a circuit? Thank you, and again, your videos are inspirational and fun to watch.

[@UncleDoug]

Greetings, Scott, and thanks for the kind words. The term "superheterodyne" refers to the way the radio uses frequency mixing to convert a received signal to a fixed intermediate frequency (IF) which can be more conveniently processed than the original radio carrier frequency. It was a great improvement over the previous "tuned radio frequency" circuits. This particular radio runs the 120VAC directly through the filaments of the tubes, and therefore does not require a power transformer to produce individual voltages for each tube. As a result, it can present quite a shock hazard if the 120VAC manages to come in contact with the metal chassis. Also as a result, most of the tubes and components are not really suitable for guitar amplifier use, unless you chose to build a transformerless amp, which is not generally done because of the hazard described above, and the necessity of an isolation transformer to make it safe to use. I have posted a video addressing this issue. Looking at the schematic of the output transformer (OPT), the color codes of the wiring are provided, and it appears that the OPT might, depending on its winding ratio (see my video about OPT's), be usable in a single-ended guitar amp. You could use the blue and either the red or yellow (depending on the impedance you wanted) as the primary inputs, and the green and black as the secondary outputs to the speaker.

[@TheBoss1597]

Hi Doug! Your video's is such a great source of information, really appreciate it! I've got some questions which I hope u don't mind... I'm building a bass preamp and are researching about some things,I will use a hybrid tube/ss rectifier and as I understand there should be a limiting resistor between the ss rectifier and the tube, your thoughts? and I'm searching for a gain/sensitivity control which appaerntly should have been used in some of the matchless amps, do you have any tips for me there? Keep up the good work and give my best to ollie and Jack!/Peder J

[@UncleDoug]

I'm sorry, Peder, but I have no experience with either hybrid rectifiers or Matchless sensitivity controls. Hopefully there are sites dedicated to these topics that you can access. Good luck.

[@tommyausburn]

Thx! You've helped me. I'm dealing with a Solid State Fender FM212 DSP Amplifier w/out schematics. I'm curious to know if it's Power Transformer is good. Transformer info: (360w 120v 60Hz) C-056554 TCE-B3

[@UncleDoug]

I have no way to tell if it's good or not, Tommy, without voltage readings.

[@robertanderson8613]

Is there any problems using DC on the tube heaters? Great job as always

[@UncleDoug]

No problem at all, but in a properly built amp, it's not necessary.

[@carlrudd1858]

Excellent! I'm going to firm this knowledge in my brain...hoping it will stay there. Am I correct in assuming that you have created a similar video regarding Output Xformers?

[@UncleDoug]

Carl Rudd Thanks, Carl. Yes, there is also an output transformer video.

[@giulienk]

Great instructive video as usual! Do you think you and Rusty could make a video about the proper way to convert an old amp to three prong plug, i.e. adding a ground connection? Also, I scavenged this really heavy transformer from an old tube radio and I was thinking of using it for a small amp like a Champ but with solid state rectifier (as it only have wiring for high voltage ~300 volts and 6.3 v filaments). The "only" problem is I found out the transformer is really an autotransformer, not providing isolation from the mains. Would it still be safe to pursue the project? Worst come to worst I was thinking of adding 1:1 transformer just to add isolation between the mains and my transformer...

[@UncleDoug]

Greetings, G, and thanks for your kind words. I have been asked several times about the conversion to 3-wire cord, and, as demonstrated above, repeated questions often lead to a new video. Re the autotransformer-Champ project, as you have probably seen from my videos, I'm all for building amps and effects from crazy materials, but I would not be completely in favor of this project. As you state, there will be no isolation unless you add an isolation transformer, and then you will end up with a diode-rectified, 75 lb. Fender Champ. The charm of the Champ is its small size, weight, and (to some degree) tube rectification. For about the cost of an isolation transformer, you could buy a new, correct power transformer for the Champ (see Triode USA), and be much better off. I apologize for being so conservative, and you may well proceed with the project anyway, but having worked long and hard on projects that "just weren't meant to be", I wanted to provide an honest answer to your question. Regardless, I really appreciate your interest and input and wish you the best.

[@UncleDoug]

twangzilla Rusty and I watched the video and thought it was good, but we have the following observations: 1.) In the video, the conversion is complicated by the presence of the Fender polarity switch. If you're not working on an older Fender amp, this will not matter to you. 2.) It might be easier to simply remove all wires from the Polarity Switch, i.e. bypass it, but leave it in place for originality sake. It serves absolutely no purpose after the conversion. 3.) The black (hot) wire, not the white (common) wire, should always go to the main power switch.....otherwise, 120VAC will be present in the circuit even if the amp is turned off. 4.) Rusty is not so paranoid about the "Death Cap". If it were to become shorted to the chassis (exceedingly rare), the resultant current flow would cause the fuse to blow.....otherwise, what is the function (or value) of the chassis grounding wire?

[@JCHaywire]

Greetings UD. I have a rather specific question that you or anyone similarly knowledgeable may wish to field. I have built a 5F4-style amplifier on the chassis of a Conn 430M organ amplifier. I chose that amplifier because the existing 5U4 and pair of 6L6's, and trio of 12AX7's already resembled the Fender 5F4--and it seemed simple enough to assemble. I have discovered, however, that the Woodward-Schumacher 606041 PT that lived on the Conn chassis may not be compatible. I got everything wired up and discovered that there was no red/blue wire to supply the bias voltage to the 1N4007 (through a 6.8K resistor). The PT leads and voltages, supplied with 121.1VAC are as follows:(I clipped all leads and re-measured these voltages for this note.) RED 825; Rd/Yl Tap 415 Green 14.0; Gr/Yl Tap 7.1 Brown 7.1 Yellow 5.6 Is this PT simply not compatible with the 5F4 circuit's needs? Or can I derive the correct bias voltage by another means? Thanks for your insights--you may wish to google the Weber 5F4 layout diagram for reference. I can't put the link here. I have a fair supply of power resistors and know how to heatsink them against this chassis. Thank you!

[@UncleDoug]

JC, I have seen several amp circuits where the bias voltage is simply taken from one of the high voltage outputs from the PT. For example, check out the schematic for the AA764 Fender Princeton Reverb.....the bias circuit connects directly to one of the 330VAC PT outputs. The 100K (series) and 27K (to ground) resistors bring it down to a half-wave rectified -35VDC. A second, very clever method to derive bias voltage is provided at the following site: education.lenardaudio.com/en/14_valve_amps_6.html This method utilizes a 6V to 120V transformer at the end of the 6.3VAC filament circuit to produce and then rectify a usable bias voltage (probably 45 to 50VDC or so). As long as your 6.3V winding could stand a little more current flow, this would be a good way to go. Don't give up. There are several ways to solve your dilemma. Good luck :)

[@robb4545]

I didn't want to ask any more questions but the voltage you read on the secondary 372 seems low for such a big transformer where the other PT you talk about had 660 from end to end. What tubes would only need such low voltage especially after being center tapped to half 372? Or was 372 the center tapped voltage on just one side? Great video on figuring out the wires though. That was really beneficial and a great video.

[@UncleDoug]

It's been a long time since I made this video, but I believe the 372V is between one high-voltage lead and the centertap.

[@robb4545]

OK thanks Doug. Just watched about 3 more of your tutorials. Really good instruction. You can't pay a college ransom and get better. Thanks for answering my questions. I try not to ask too many unless I just get stumped and you make it easier to understand with your answers. Much appreciated. Really cool of you to do so.

[@sawyer7271]

An oldie but a goodie! Question: any way to determine or estimate the VA rating or the approximate amperage rating for the 6.3v and the high voltage leads?

[@UncleDoug]

Thanks :) Other than simply estimating based on the gauge of the output leads, I know of no way to determine the amperage capability.

[@sawyer7271]

@@UncleDoug thanks. I will look into that, see if I can find a way! I am thinking there are a couple of options: load the outputs (not to failure) and use the transformer temp to be my indicator... I.e. over a period of hours apply a load and track the temp. I would expect that as the load limit is approached, the temperature will rise in a nonlinear way. The other option I am thinking is to track voltage drop/sag as an increasing load is applied, which might also allow me to estimate the losses in the transformer ... anyway, I will do my research and report back. I have recently come into possession of quite a few vintage power transformers of varying size... it would be great to know their limits so I can build amps that will be reliable. . .

[@stephenquail3168]

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.👍🏻🔉🙀🐶

[@UncleDoug]

You're welcome, Stephen. Yes, indeed, Jack is a stern taskmaster ;)

[@marisonuratani]

hi uncle Doug, learnd a lot from your videos, thank you very much. I just built your tremo verb e Im having current leak from chassis to ground of about 2.5 volts ac. already tried everything from changing transformer, filter caps a a lot of capacitors on the ciruit, but it remais leaking 2,5v to ground. Im out of ideas. what whoud you think coud be happening? Thanks a lot for you videos.

[@UncleDoug]

If I understand properly, you measured the potential between your (ungrounded) chassis and earth ground and found that it was 2.5VAC. I assume, however, that when you ground the chassis with a 3-wire power cord (thereby eliminating the 2.5V potential), the amp works just fine and no fuses blow. If this is true, I don't think you have a problem. It's not uncommon for a small potential to exist between a chassis and ground. Most people never notice it because the 3-wire power cord eliminates the potential.

[@marisonuratani]

Thats right,,the amp is working fine, very little hum. Thank you for the help Uncle Doug, Your channel on youtube made it possible. I always wanted to build my own tube amp and you explain things so easily that I finaly gave it a try. Thanks from Brazil.

[@UncleDoug]

You're welcome, Maris. Congratulations on your successful project.

[@markbrooks7257]

Uncle Doug, thanks again for all your videos and this one especially! I'm in the process of converting an old Hammond organ amplifier into a guitar amp. I pulled the transformers and choke off last night. Fortunately, I made notes about where the leads went from the power transformer (and everything agrees with what you've said here). But I forgot to write down where the output transformer leads went. Do you have a video like this one, but for output transformers? Like you I'm unlucky and I can't find any info about the specific output transformer. It has 5 wires total (two green, two black, one red) and I believe that the organ only had a 8-ohm output originally. Any ideas what the wires could be? Thanks so much for all you do! I'm taking videos as I go along on this build, so hopefully I can contribute those to the same people who love your videos so much.

[@UncleDoug]

You're welcome, Mark, and thanks for your nice comments. A double-ended OPT should have 5 wires, as yours does. Three wires for the primary....one to each tube plate and a center-tap to the B+. Use your ohmmeter to see if the red wire has continuity to the green wires.....if so, then the red is the CT and the greens go to the tube plates. The remaining two wires (black, if they have no continuity to the red wire) go to the speaker.

[@markbrooks7257]

Perfect! Thanks so much for your response. I'll do exactly what you said here. I found your output transformer video a moment ago and it seems great as well. One final question; when purchasing a variac, what should I look for? I know little about them, but my gut says that I should make sure it ranges from 0-130ish AC-volts and it is rated for 5 amps (since some amplifiers I would theoretically work on have 4 amp fuses themselves. Does that sound right?

[@UncleDoug]

You're welcome, Mark. With regard to Variac's, 5 Amps should be plenty of current for just about commonly encountered tube amp. Best of luck.

[@andrewgillis8572]

@@UncleDoug Deep into these comments Doug and this - incredibly - may be your most helpful video ever. And that my friend is really saying something.

[@UncleDoug]

@@andrewgillis8572 Wow.....thanks so much, Andrew.

[@Barnekkid]

That was just great. I'm an analog amp nut and I love your information.

[@UncleDoug]

Thanks, BK. Identifying the leads is sort of like a brain teaser puzzle.....kind of fun. We're glad you enjoy the videos :) ^. .^

[@ncilmo]

Thanks Uncle Doug. This was very helpful.

[@UncleDoug]

+Dr. Arthur D. Kemp You're welcome, Dr. Kemp. It's always good to hear from you :)

[@alvin10388]

Thank you so much for all the educational videos and as a newcomer to amp building,i have a quick question ,if i use 240 AC Power transformers on circuits thats match to USA power ratings do i have to change the capacitors and resistor values? i ask you this because i have found some great vintage schematics on internet.but most of them compatible to USA power ratings .your feedback is really appreciated(i don't know if i explain enough the subject)

[@UncleDoug]

Alvin s Greetings, Alvin. Amplifier power transformers with 240VAC primary windings produce the same secondary voltages as those with 120VAC primary windings. The transformers have different winding ratios that compensate for the difference in voltage input. Many power transformers have primary windings that allow you to use them with either voltage, simply by connecting the primary wires in the proper configuration (instructions generally come with them).

[@vhm14u2c]

Hi uncle Doug. I wanted to mention, I have an gdr8514 airline amp that has no 5 volt coming off of xformer, plus no diodes for rectification. Instead uses a 6x5gt as rectifier, and uses 6.3 volts ac as heater. I was not sure if you came across one of those in the past. And I have a question unrelated to rectification. - Do you have any vids that demonstrates how to lower B+ voltage using Zener diode and mosfet? I have a db115 bogen xformer that outputs over 550v dc when rectified and capped, and was hoping to tame that beast to use with one of the fender clones I’m working on. Unrelated, That bogen original chassis also uses a 6.3v heater rectifier too (6bw4)

[@UncleDoug]

Yes, some tube-rectified circuits avoid the need for a 5V winding by using a 6V rectifier. No, I have never made a video about Zener diodes, but they definitely can be used to reduce voltage. They produce a lot of heat, so they often must have a heat sink. Hopefully, you can find videos on YT by other people which will cover the topic. Good luck.

[@GScott50]

Thank you, that was a very logical and useful explanation.

[@UncleDoug]

You're welcome :)

[@onemancarnage]

I have a good question for you uncle Doug . Another carefully explained video by the way. Now my amp has 6l6 tubes . They draw 900 ma. I started to convert over to el 34 and hit a problem. One my heaters are wired in series . Two it seems it only allows for 1 amp draw. Would I need a different transformer to get 1.5 amps for the 34's . And how would I know which one to get ? If it would be too much trouble to explain I understand . Worst case I just buy another set of 6l6 's . Thanks in advance .

[@UncleDoug]

Thanks, Bryan. Your 6L6's draw 900mA each for a total of 1.8A. Your power transformer (PT) has a 6.3VAC winding that can probably handle a little over 2A. Tube heaters in conventional amp circuits are wired in parallel. The only exception I can think of is in the economy series-filament amp and radio circuits that don't have a power transformer....and they don't use 6L6's. I tend to think that your tube filaments are wired in parallel, but that's not the problem. EL34 heaters draw 1.5A each for a total of 3A, which is probably beyond the capability of your PT. Also, they operate at higher plate voltages than 6L6's. I guess you could try to use the EL34's, but don't be surprised if the PT fails....which will be expensive to replace. Your best bet is to either stick with 6L6's or install a higher-capacity PT before converting to EL34's.

[@onemancarnage]

Thanks for the reply . Believe it or not they are series at least the power tubes . And dc to boot . Peavey does this allot . But the rest I didn't consider. So thank you and I'll just stick with the 6l6 tubes. Thanks again.

[@UncleDoug]

You're welcome, Bryan. I think you made the right decision. Good luck !!

[@jackallen6261]

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!!

[@UncleDoug]

You're welcome, Jack. Thanks for your testimonial :)

[@jaysgr]

Thanks for the great video! I have a question for you. Trying to repair a solid state guitar amp which has a noise (a grounding noise), I came across this : - The ground from the ac socket is connected to the amp chassis. - A black wire coming out of the transformer is connected to the ground of the pcb ( where the sleeves of the jacks are also connected) But, there is no connection between the sleeves and the chassis. Does this mean that the transformer is faulty? And is it ok to connect these two grounds (the jack sleeves & the chassis) with a cable? Any help would be much appreciated!

[@UncleDoug]

You're welcome, Jay. I am no expert on transistorized gear, and without actually seeing the chassis and a schematic, it would be virtually impossible to answer your question definitively. I would suggest that you use an ohmmeter to see if there is continuity (i.e. 0 ohms of resistance) between the sleeves and the chassis, with the amp turned off. Sometimes a connection may exist but is not readily visible. This connection, or lack of connection, should not be indicative of a problem with the transformer. Be careful.

[@johnboleyjr.1698]

I wonder if it might be worth going over the different classes of multimeters? Personally I wouldn't test a power transformer with anything less than a class IV multimeter due to the potential for higher voltages coming from the secondary winding.

[@UncleDoug]

It might be, John, but I'm not sure if the majority of viewers would be interested in a rather esoteric topic such as this. I've had great luck for many years with my moderately priced multimeter.....and I'm not even sure what class it is. I will, however, keep this suggestion in mind for the future. Thanks for your input.

[@andrewdarnley4608]

Hi Doug, I've just finished watching your video and it's been extremely helpful. What I'm not sure of is if I'm searching around for a power transformer for an 5F1 type amp project, what do I look for in a transformer ? Are there any readings I can take with a meter to find a suitable transformer for the 5F1 circuit ?

[@UncleDoug]

+Andrew Darnley You're best bet is to go to the Triode Electronics Internet site and see what power transformer they offer for the Fender Champ. They will also provide the specifications for the PT.

[@andrewdarnley4608]

I was wondering about the possibility of salvaging a power transformer from an older amp. Would you advise against this for a newbie like me ?

[@UncleDoug]

Not at all, as long as you can determine that it will meet or exceed the voltage and current requirements of the circuit you intend to build.

[@miguelortega7112]

Thank you for the video Uncle Doug. I have seen it like a thousand times. I still have 2 doubts if any of the people around could help, would be great. 1 how to know the current capabilities of a given power transformer 2 I have a bias wire as shown in the video. But it has no ohm reading, but when applying voltage it works as a volt splitter between the center tap and one on the high voltage leads. This tip is in working condition? Greetings to all tube amp lovers

[@UncleDoug]

Greetings, Miguel. There is no way to accurately determine the current capability of an unknown transformer winding. The best you can do is estimate based on the gauge of the output leads. If your bias output lead shows an output of around 50 to 60VAC, it is working.

[@miguelortega7112]

@@UncleDoug Thank you very much for taking the time to answer.

[@victorsalcedo8127]

Thanks Uncle Doug. Uncle Doug, what is the proper gauge size of the ground wiring for the vintage radios. Thanks in advance.

[@UncleDoug]

That's hard to say, Victor. I would think that 18 to 20 gauge would probably be adequate.

[@el_arte]

best explanation ever; I do have a transformer that seems to have a 120VAC primary, a 130VAC secondary with CT, a 345VAC secondary with CT, a 5VAC secondary without CT; are those common?

[@UncleDoug]

Thanks, Laurent. The 130VAC secondary is strange......there is no need for it.....and you are missing a 6.3VAC secondary with CT. Are you sure the 130V is not really 6.3V ?

[@el_arte]

@@UncleDoug I'll take a picture of it, maybe I am confused www.dropbox.com/s/x8ejta6o5mge5dm/transformer.jpg?dl=0 it's clearly a Chinese model, so the color-coding tends to be misleading... I remeasured again and I did confuse myself. I have: 7 ohms between red and red, 76 ohms between brown and brown, 0.3 ohms between yellow and yellow, 0.6 ohms between blue and blue

[@brentgilbert4208]

That was fascinating! And helpful!

[@UncleDoug]

That's good to hear, Brent :)

[@ianbrereton4783]

Hi Uncle Doug, very informative and comprehensive video as always! Now, I've got a question for you on reusing old mystery transformers: Often I'll run into the following kind of scenario: Original radio/organ/tape/record player amp is for instance single ended, 1 6v6, 1 6x5, 1 12ax7, nearly perfect for a Champ!? OR similar scenarios for AB style amplifiers..The problem is the transformer secondary only has 4 leads, two heaters, and two for the rectifier/Hivoltage B+, So the trouble is twofold, A: there doesn't seem to be a center tap to ground on the rectifier-HiVoltage winding, what am I missing here? even the schematic calls for a grounded centre tap? and B: the 6.5v heater leads would be shared between the audio circuit and the power supply rectifier, and not an independent heater winding, is this safe for a guitar amp?

[@UncleDoug]

Ian Brereton Greetings and thanks, Ian. Since full-wave rectifiers (like the 6X5) require a center-tapped high-voltage winding to function, I'm not sure how one could not be present in the power transformer. Perhaps there is an internally-grounded high-voltage center tap within the transformer itself. This would be easy to detect with an ohmmeter. As far as the safety of amplification tubes sharing a filament winding with the rectifier, this is commonly done in many amp circuits, particularly in early National amps.

[@ianbrereton4783]

Uncle Doug Thanks for the reply! You were right, I tested it out on an old Webcor transformer, and sure enough resistance between either hivoltage rectifier lead to the transformer casing was about half of the resistance found across both leads. So it must be internally grounded. Good to know I can use the same heater lines. Working with, different rectifier tubes is still a bit of a mystery to me, I'm not sure if it's better to use the rectifier original to the transformer, or to attempt to modify the circuit in order to swap in a different rectifier more appropriate to a given schematic--assuming they're full-wave. For instance the 6x5 has significantly lower plate voltages (running at 220v in the previously mentioned transformer) than say a 5Y3, or 5U4 (which run over 300v in a champ, princeton, or deluxe). I suppose I'd also need to drop the heater voltage, but are these tubes even operable at such lower plate voltages? I'd assume the filter section would need modification in order to achieve an adequate result? Or should I just work with the original 6x5 tube?

[@UncleDoug]

You'd best stick with the 6X5. It draws only 600mA of heater current, while the other rectifier tubes you mentioned draw 2 to 3 Amps. The power transformer you have cannot cope with these higher current demands. Perhaps you could use diode rectification and get some increase in plate voltage, however, if the original amp you disassembled used a 6X5, 6V6, and 12AX7, then apparently they work just fine with this power transformer and rectifier.