Power Transformers: Basic Design and Function

In this video, I discuss the design and function of Power Transformers (PT), primarily those utilized in amplifiers. Topics such as winding ratio, output voltage, current limitations, and mounting characteristics are explained. Then, using a Fender Deluxe Reverb as an example, we analyze the voltage and current requirements of an amplifier. Using those parameters, we select an appropriate replacement PT for the amp. NOTE: These same parameters will also allow you to select the appropriate PT for a home-built amplifier project.
As if this weren't enough, star camera-hound Rusty appears several times, especially in some dramatic "Outtakes" at the end of the video.....so stay tuned until the end so you don't miss his Emmy-worthy performance.
If you enjoy videos featuring classic vintage amplifiers, jukeboxes, hand-built electronic projects, occasionally sarcastic humor, and (hopefully) clear, concise technical presentations, then please subscribe to my channel. You will gain immediate access to about 90 more videos, and (if you activate the service) you will be notified each time a new video is posted.
Thanks for watching !!!!

[@scottmcmurtrie]

I wish this channel existed when I first started in electronics. A wealth of information and easy to understand.

[@williampacatte9014]

Uncle Doug, every teacher should be as good. Thanks Uncle Doug.

[@VoidHalo]

I'm 34 and just got into electronics a year or two ago. I can only imagine how difficult it would have been to learn without channels like this, datasheets, educational resources at your fingertips, circuit simulators to visualize and predict how a circuit works, and not to mention dirt cheap Chinesium parts. I wouldn't imagine you could get a PLL or an op amp for a few cents in 1970.

[@VoidHalo]

KZbin wouldn't let me edit my comment, but I wanted to add that I never would have gotten into electronics if not for channels like Big Clive, Julian Ilett and EEVBlog. I only found this channel recently so it didn't get me started, but it's a great addition to all of my favourite EE channels.

[@robertkat]

In the 60s electronics was all tubes, you could actually see and test components, now monoblock amps, if it quits throw away.

[@jeffreyjhouser]

Thanks for this video, Doug! This helped me understand how to calculate the requirements of a power transformer.

[@UncleDoug]

That's great to hear, Jeff. Glad it was helpful :)

[@sigdaddy7377]

Someday I AM going to build my own "Champ" (from there, who knows), and when I'm able to, it will be very largely due to these videos. Thank you, both for the time you and Rusty spend sharing this knowledge, and for the ability to share it so clearly.

[@UncleDoug]

+sigdaddy You're welcome, SD. Rusty and I are glad the videos are helpful, and wish you the best of luck with your Champ build :)

[@StonyRC]

Wow, Dear Rusty is shaped like a BARREL. But he is probably the finest Canine-Cameraman I've ever seen. Another great video Uncle Doug - you are educating the world ;-)

[@UncleDoug]

Thanks, Stony. I'd like to report that it's all muscle.....but it isn't :) We thought about renting him out as a coffee table, but worried that it might interfere with his career in videography and poodle sniffing (his dual majors in college). Strangely enough, at 16 years old and admittedly rather "portly", he can still jump and chase tennis balls with the best of them......and, as you mentioned, is a maestro with the video camera :)

[@vikingmike8139]

Great info, thanks Uncle Doug. I must say also that I really appreciate the steady nature of Rusty's front arms for all the camera work. Thanks also to Rusty.

[@UncleDoug]

+Viking Mike You're welcome, Mike. Rusty studied at the UCLA School of Video Making, majoring in tennis ball with a minor in dog cookies. Steady camera holding was his favorite class :)

[@jaystern2130]

I don't know what is better... How awesome of a teacher Uncle Doug is, or what an amazing cinematographer Rusty is. Either way, your clear and well explained lectures are inspirational. Thank you!

[@UncleDoug]

You're welcome, Jay. Wow!.....High praise indeed, to be compared to Rusty, skill-wise. He is truly a master of his craft :) Either way, we both thank you for your very nice comment and are glad you enjoy our videos.

[@shawns735]

Can't say how much i appreciate you posting these videos... Found your tube amplifier videos, and I now have a very good general knowledge of everything you have covered. Excellent job, and many thanks for sharing your knowledge with the world.

[@UncleDoug]

You're welcome, Shawn. It's great to hear that the videos have been informative :)

[@bobsimard5591]

Thanks uncle. I’m a newbie to tube amps and I’ve learned quite a bit in 4 months obsessing. When I get in a rut and can’t absorb any more I always come back to the basics. The xformers and rectifier basics to sharpen up. I miss Rusty as much my Moxie. I’m also a retired pipefitter

[@UncleDoug]

You're welcome, Bob. Thanks for the nice comments. I'm glad the videos are helpful. Yay, Moxie :)

[@markrhine5809]

Dear Uncle Doug, Rusty sure is a beautful dog. I personal restore tube radios for my own enjoyment, and I have decided to watch all of your videos, I enjoy the way you present the material, it is easy to understand and very informive. Thank you kindly for presenting these videos. Have a great weekend...

[@UncleDoug]

Thanks so much for all your very nice comments, Mark. We hope you enjoy all our videos and wish you the very best.

[@markbteeps]

Hi Uncle Doug, I've watched your biasing videos today as well and they're all fantastic. Great, clear explanations and delivered really well. I've commented on this one because Rusty deserves it!

[@UncleDoug]

Thanks so much, Mark. I'm glad you're enjoying the videos. I will relay your kind words to Rusty :)

[@corralesdavid]

Great as usual. Thanks again Doug! It's great to see Rusty back in action :)

[@UncleDoug]

Thanks, David. Rusty and I are glad you enjoyed the video ^. .^

[@annehars6722]

great intro to power transformers. I have some old tube radios and one of them, a 1948 RCA, has a smoking transformer, so I'm watching a lot of videos about transformers and yours was extremely helpful.

[@samhafez]

Thank you uncle Doug I am new to electronic and learning everyday from this videos amazing teacher

[@UncleDoug]

You are very welcome, Sam :)

[@smasica]

Dude, you are a wealth of practical information and electronic ejamukashun. Love the simple, straightforward delivery and explanation. I'm learning a ton and you're clarifying stuff I was a fuzzy on. Thanks. Again.

[@UncleDoug]

You're welcome, TM. Thanks for all the nice comments :)

[@smasica]

No; thank you. Good, clear information is hard to come by. Too many self-styled experts can't easily explain that 2 + 2 = 4. I, and I'm sure many others, have no problem grasping the principles you present. It's refreshing and welcome.

[@UncleDoug]

I'm glad to hear that, TM. Thanks :)

[@scottgibson118]

I have an old Marvel 35 [Valco, maybe?] combo which is essentially a clone of a 5c1 champ [octal 6S*7 preamp rather than 12ax7], and your channel has played an integral part in my identification of the circuit and current repair/restoration thereof. I really appreciate your thoroughness to the smallest of details; I don't even bother to seek out other users' videos of this nature anymore..

[@UncleDoug]

Wow, thanks, Scott. It's great to hear that the videos are actually providing useful information.....and that viewers are actually applying the principles to their own projects. I hope that Rusty and I can continue to provide useful information :)

[@troeteimarsch]

thank you so much for that whole series. you taught me so much in these 3 hours.

[@UncleDoug]

Glad to hear it!

[@tubical71]

Excellent Video, as always! Thanx for posting!

[@UncleDoug]

You're welcome, TC. Always good to hear from you :)

[@billdyke9745]

So size does matter. I always suspected my exes were just being kind. Superbly explained, sir, and great camera work from the much missed Rusty. Many thanks.

[@UncleDoug]

Good one, Bill :) At least your exes were diplomatic ;) Thanks so much !!

[@billdyke9745]

@@UncleDoug The thanks are all mine. When I was a kid I'd turn the radio to the wall so that I could watch those beautiful glowing things and wonder at the ingenious magic that was in there. 60 years later and it's still magic. But underlying it all is logic. And I'm starting to get an understanding of all those itty bits. A priceless series of videos which have edutained me while locked down on my boat in the middle of England. Keep well.

[@mlculwell]

Great Video!The thing that would help in understanding is take an amplifier and follow the schematic and put together the amp hands on as you put it together and explain it. You have the best videos on youtube.

[@UncleDoug]

Thanks so much, ML. I will keep your suggestion in mind for future videos.

[@andyracksthecams]

Best viewing on the Tube. Informative and comical. You are THE MAN! 👍

[@UncleDoug]

Thanks so much, Andy :)

[@lucasvechi1861]

I wish I could give more than 1 like in this video. Awesome explanation and easy to understand.Thank you Uncle Doug!

[@UncleDoug]

You are quite welcome, Lucas :)

[@joemcgraw5529]

wowsa its all making sense now your amazing doug what a teacher you are

[@vintageaudioworkshop]

Very helpful for a lot of people, will always recommend your videos to people interested in the theory....

[@UncleDoug]

Thanks, VAW. Rusty and I sincerely appreciate your interest and support.

[@skeeterbuck1355]

Hi Uncle Doug, I have used a Classic Tone Transformer like this one and IIRC when you connect it to the 120V line AC the white wire is connected to the white and the black/white wires on the primary side.( marked 1 & 3 on the spec sheet) The black wire from the AC line is connected to the black and the black/white wires of the primary side. ( marked 2 & 4 on the spec sheet) Basically when using the transformer for 120 volt operation, the primary windings are wired in parallel. When using it for 240 volt operation the primary windings are in series. Either way you need to use the complete primary winding for the transformer to function correctly. Keep up the great work and pet Rusty for me.

[@UncleDoug]

We will, Skeeter. Thanks for the helpful input and kind words :)

[@jimtalltheislandbrothers6639]

Your videos are such an inspiration to keep learning. Thank you.

[@UncleDoug]

You're welcome, Jim. Thanks for the nice comment :)

[@jimtalltheislandbrothers6639]

I am thinking about building a tube amp and your videos are worth their weight in gold. The concepts have been explained in such detail it is unreal. Much appreciated. I have done a bit of electronics in A level Physics, but doing more research into how things work together as I am fully aware of the very high voltages present and your videos are an excellent guide. Thank you.

[@UncleDoug]

We're glad you enjoy and benefit from our videos, Jim. Best of luck with your amp-building project.

[@djfrank59]

Hi Doug! Another excellent video! I've had several ordeals with new, off-brand replacement transformers. many of the replacement PT's I've used in the past were problematic, and unreliable...I've had many that had shown exceeding specifications (on paper) but in the real world, didn't deliver the goods (necessary current) I try to stay with only a few suppliers (Triode Electronics being one of them as per your recommendation) Tube Depot, and AES) so I know that the proper replacement will be delivered to me...Ah, I miss the days of Thordason and Stancor transformers...they were made to last...Mercury transformers so far, have been reliable...(keeping fingers crossed). I'm still in amazement how fast Rusty is at grabbing the ball in mid air :) Keep the videos coming, always great to watch :)

[@UncleDoug]

Thanks, Frank. Rusty appreciates your kind appraisal of his athletic prowess, which is pretty impressive for a 15-year-old dog ^. .^ I agree about Thordarson transformers. Way back in my jukebox days, they were the best !!!

[@tangotommi]

Hi Doug, I checked the Filter Caps with the Anatek Blue ESR meter, after calibrating to 0.00. 32uF 1.9; 22uF 1.3, 22uF 1.4, 200uF 0.31, 200uF 0.31; Grid Bias Cap 330uF 0.31 All test fine @ 450V Thanks for your time Doug, please say hello to Jack & Casey for me.

[@williambock1821]

I enjoy coming back and watching these tutorials on the basics that you make from time to time,UD. Just to make sure I’m not suffering from the Dunning Kruger effect if nothing else. There’s no WAY the Diane Kruger effect could happen to ME! ;-)

[@UncleDoug]

I've often wished that Diane Kruger would "affect" me some time.

[@thebloosman01]

Excellent work my friend! Very informative and highly educational! I must say that I have waited for this since your last instalment and feel very confident that my skills are growing further with your videos- thanks uncle Doug!! Great as always! Can I request another idea for a video? "I (and I'm sure others) would like to know why the pots in guitar amps are rated for different values & how these values are chosen to meet the requirements of the circuit". Also- the tone stack shaping caps and how they effect the first couplings in the tube preamps... Just a thought ! Thanks again. Great days!!

[@UncleDoug]

Thanks so much, TBM. I'm pleased to hear that the videos have been informative. I will take your suggestions to heart and will try to come up with an explanation for the pot values and tone capacitor effects.

[@johnzook7533]

Thanks again Doug for another great video. Power transformers are probably the most overlooked part of an an amp. It seems these days it's all about the tube used. I want to relate a situation I had many years ago with a Sunn Solarus amp I owned for several years in which the power transformer died. After confirming this, I ordered a new one directly from Fender/Sunn($37.00) and installed it without any problem as I had recently finished my schooling in electronics. The amp turned on ok and appeared to be operating ok except someone noted there was some distrotion when there shouldn't be at that volume level. I didn't think much of it at the time as I was still quite new to all this , however now I have reason to believe there was also another problem present that I failed to look for thus, did not detect. I wish I could get my hands on this amp again even after so many years...since 1978 and find out what was wrong, if the amp even still exists, as it was traded in for another Sunn at a local music Store in Traverse City, Mi. Sure wish I could find it again. It was a great amp.

[@UncleDoug]

John Zook You're welcome, John. Thanks for sharing this story with us. I think we have all sold items.....and then come to regret it later. My list would take several hours to type out :)

[@smstiao-tecnologia]

Hello friend, very good to his class on the power transformers and audio output. Enjoyed a lot.

[@UncleDoug]

Thanks, SS.....glad you enjoyed the video :)

[@smstiao-tecnologia]

Very instructive and very well explained friend. Congratulations.

[@shaunsanders9673]

Excellent tutorial. Thank you!

[@vincep8574]

Thanks for the info Uncle Doug as usual your videos contain some of the best content.

[@UncleDoug]

You are quite welcome, Vince.

[@markproulx1472]

Terrific presentation!

[@UncleDoug]

Thanks, Mark.

[@stefanvaneylen9488]

Really helpful video to determine which trafo to use. i dismantled a champ 12 totally and want to rebuild it without the PCB boards and without the reverb and switching unit for clean/dirty, so just 1 channel. thx Uncle Doug.

[@UncleDoug]

You're welcome, Stefan. Best of luck with your project.

[@Dan79istheman]

Doug, your a bloody legend mate! Cannot think of anything else to say....

[@UncleDoug]

Thanks so much, Dan. Kind words are, to me, what the tennis ball is to Rusty......highly motivational. ^. .^

[@jonnyhtown3806]

INFO IS GREAT I WATCH YOUR VIDEOS WHEN IM CLEANING MY HOUSE (WHOOP CAPS) I live in a 100 square foot place big yard for my pit bulls who have a tiny house with ac and a heater also then i have my little side kick and two cats that live in my house, then in the main house which is my folks ( i help them out with what they need, they let me live in my tiny house on their land and gave me half the yard for my dogs) they have 4 dogs in there house which were all from when i was rescuing dogs at my bigger place. anyways im a total dog and cat lover and full time musician who pays the bills selling gear. even though i feel my stuff is pretty good and guys from Warren Haynes to Craig Bartock use it but i always love learning and relearning and your videos keep me watching.

[@UncleDoug]

Thanks for watching and for your input, Jonny. Kudos to you for your service to animals.

[@jonnyhtown3806]

i just finished a red headed step child. i had a hoffman deluxe with vibrato from black face era amps it was missing an out put. i also had an early break up weber output laying here for el34 tubes and a 4x12 cab which was built by a shop to resemble a 40s record player cab. its got slotted wood baffle. last i set of jensen mods. I cut the 2x12 down and mad a back bottom mounted 2x12 combo. So i threw it all together which makes it an early break-up el34 tweed deluxe with the tone pulled and turned into a bass cut. going through 2 12 inch jensen 25 watt MOD speakers loaded in the cool cab. it actually mad a great middle volume amp. I go for tube saturation. although i sell pedals for a living ( and a little ghost building/designing) i only run a range master style boost to push my full volume amps harder. I have 4 amps all of different volumes so whether im at home or a gig i can play my amp full volume. anyways i have watched your videos a ton to get a handle on some of the things i had to change to make this basterd amp work. and also my silver face champ turned into a little monster with volume body treble mid bass controls killer little amps all choked up and everything thanks to your videos.

[@UncleDoug]

We're glad the videos were helpful, Jonny. Best of luck with your projects.

[@bullthrush]

Another excellent video! Camera work and hand acting are top quality.:))

[@UncleDoug]

Thanks, BT. Rusty's camera work was indeed superb for this video, and it's good to hear that my hand-acting classes (with Stella Adler) are finally paying off....:))

[@SassieHB]

Let's all just be honest for a second, Rusty is the real mvp in these videos.

[@UncleDoug]

Yes, indeed. He is definitely the chairman of the "bored" :)

[@SassieHB]

@@UncleDoug `Just kidding Uncle Doug, I`m trying to repair my rather complex H&K Trilogy amp and your in depth guides are amazing ! Literally the most clear info about tube amps I have ever seen

[@bluesman97]

Thank You Uncle Doug... Your a Scholar and a Gentleman.

[@UncleDoug]

I appreciate that, B. Thanks !!!

[@nusior]

Great video! Very useful stuff to know for future (hopefully) tube projects. For couple of months now I'm surfing thru websites like ebay and our polish equivalents of those auction sites to get some cheap elements or devices to salvage parts. Mostly solid state because I'm rather new to electronics. But now when I got "something" for tubes and finally understands basic of them I'm also looking for some cheap tubes like NOS etc. And now ALSO gonna try to get old transformers cause they seem so simple now! :D Anyway, to not bore you too much I'm glad that I found your channel. Thank you very much!:)

[@UncleDoug]

You're welcome, Nusior. Best of luck with your projects :)

[@nusior]

Uncle Doug I hope that someday I will do a tube amp and share it to get Rusty's approval :)

[@UncleDoug]

Rusty is very hard to please, Nusior, but I have faith in your abilities :))......Good luck with your project.

[@edwardhannigan6324]

Great video and introductory explanations of the functions of the power transformer..My head hurts, but awesome knowledge gained..Ed..U.K..😀

[@UncleDoug]

Thanks, Ed. Glad it was helpful.

[@r92g]

I subscribed, watched your videos on tube amps and this one and they're great!

[@UncleDoug]

+r92g Thanks for watching and subscribing, RG, and for the nice comment :)

[@tangotommi]

Hi Doug, Hope you are well. The Studio City 50R's problem where the current limiter bulb was glowing brightly when turning on just the Mains switch was diagnosed to be a bad diode in the full wave rectifier. So I replaced them all. I biased the EL-34s @ 17W PD. The hum is still there but fairly tolerable. Before the diodes arrived, I checked the power transformer and it checked out great, no problems. I went through all of the component values and they also checked out as being in spec. One solder connection on one filter cap was loose to my surprise and I took care of that in short order. I did reduce the hum to 0, but that occurs when either the Plate voltage was high and current too low for correct PD, also the opposite where the Plate current and PD was very high. As I also found out, and it makes sense, is that even though the Eurotubes "Pro One" Bias Probe enables us to easily bias one of the EL34s, when you change one tube bias, it will affect the other. So there still is some trial and error to bias them both to similar PD. Thanks again for all the great instructional videos! TG (Tom)

[@UncleDoug]

Thanks for this very informative follow-up on your initial problem and inquiry, Tom. We're glad you solved the problem and wish you the very best.

[@233kosta]

Always love a good technical video 😁

[@UncleDoug]

Thanks, 233 :)

[@MichaelRusso]

The video I have been looking for!

[@UncleDoug]

We're glad you found us, Michael.

[@BourneAccident]

Whew! That was scary. I stayed tune to see the Rusty outtakes and for some reason I "thought" you were going to play "tennis ball" using that gigantic transformer! Thank God cooler heads prevail. Oh, and while I'm at it, this lesson was superb. I will watch it, and others, several times. I take it that you and Rusty must have been teachers at some point because I can't imagine better electronic lessons. I have a hard time learning new things like this, but I am having no trouble following along. Lately, I have been refurbishing my old Fender amps and it's going quite nicely. Next project? Building an amplifier from either a kit or from scratch. Thanks so much for all you do.

[@UncleDoug]

Bourne Accident You're welcome, BA, and thanks for the very kind words. Rusty was a tenured professor at an obedience school....and I taught math and science for 16 years, so your guess was correct :) Rusty was probably up to retrieving the transformer, but the prospect of throwing it didn't appeal to me, so we settled on the traditional tennis ball. We're glad you enjoy the videos. By all means, follow through on your desire to build an amp. If you're careful....and it works well....it's a very rewarding experience :)

[@mozilla2576]

Another outstanding video. My pal Frisco says a big Austin hello to Rusty. Bark, bark!

[@UncleDoug]

Back at you from Jack and KC :)

[@adamscottmccomb]

Thanks so much for these videos Uncle Doug, I learn more and more from each one. This information is not explained in such a digestible form anywhere else that I have found. A lot of effort have clearly gone into creating them so if you have some sort of paypal donation set up I would be more than will to contribute. How is Rusty going? I hope he is still well and happy. All the best and thanks again!!!!

[@UncleDoug]

You're welcome, Adam. If you'd really like to show your support, you can make a one-time donation to our PayPal account, [e-mail], or become a patron on Patron. Thanks so much :)

[@adamscottmccomb]

Will do, thanks again Doug!

[@ConvoysToNothingness]

Hi Uncle Doug. First off, thanks so much for taking all the time and effort to make your videos. I wish I had professors in school who were as concise, clear and easy to understand as you. Secondly, I have an old (1968) clone of a Traynor YBA-1 Bass Master (and by extension, patterned after the 5F6A Bassman). It's a Lifco Model 1000. Information on the net is extremely hard to find when it comes to details. I'm trying to figure out if it'd be possible to do a few mods on the amp since it didn't cost me much and likely doesn't have much residual value left. It's currently running a pair of 7027A's in the power section, and three 12ax7's in the preamp. There is a spot for another preamp tube, unused. I was thinking of adding another 12ax7 and converting the power tube sockets to run EL34s like a JTM45, however I cannot find any identifying marks on the transformers, nor can I find any information about Lifco transformers online. Is there any way I can figure out or calculate the ratings on the power and output transformers without knowing anything about them?

[@UncleDoug]

+ConvoysToNothingness You're welcome CtN, and thanks for the kind words. Unless there is a part number on the transformers that can be traced to a data sheet, there is no way to know for sure. About the best you can do is make an educated guess based on the current requirements they fulfill in the amp circuit they came with. In addition, most amp builders use transformers that offer some leeway above the circuit requirements, so it's generally possible to add a fairly-low-current-drawing pre-amp tube to an existing circuit.

[@68MalKontent]

Another fine explanatory video, done as Einstein prescribed: as simple as possible, but not simpler :) If only Rusty didn't snatch those written comments from the screen so quickly... They disappear so fast, that paying attention to what's shown *and* reading them when there's a good moment is impossible, I have to pause the video. Of course, it may be due to my poor reflexes :-D

[@UncleDoug]

Thank you for the kind words and very flattering comparison, Stan. I understand your plight. I'm the same way with closed captions on DVD's......having to pause the disc continually so my wife and I can read them, before we move on....to the next caption. It takes us about 3 hours to watch a 2-hour movie :)

[@warywolfen]

I am a Certified Electronics Technician (Audio Specialist), a confirmed audiophile, and a lifelong member of the "Fraternal Brotherhood of Goldenears" (such an organization does not officially exist :), but it should!) And I LOVE tubes! Ah! How did I end up subscribing to a channel dedicated to GUITAR amps!!! :)

[@UncleDoug]

Clyde Wary I'm not sure, Clyde, but Rusty and I would like to welcome you to our channel. Thanks for watching and subscribing :)

[@rádiosantigos1958]

Great explanation and very didactic. Thanks again.

[@UncleDoug]

You're welcome, RA. Thanks !!

[@peterhutchinson3424]

Awesome thanks Doug.🤘

[@UncleDoug]

You're welcome, Pete.

[@alvagoldbook2]

Another excellent video! And that is one massive power transformer at the end of the video!

[@UncleDoug]

Thanks, Alva. Yes, that transformer is from a Baldwin organ amplifier that used about a dozen tubes, so it's windings have substantial current capability. I'd love to use it to build an amp, but would probably need a fork lift to move the amp around.

[@alvagoldbook2]

Uncle Doug I wonder what the HT voltage rating on it would be. It might make for a good tube bass amp. I've played around with the idea of building a tube bass amp, but it would be quite expensive and hard to find the right transformers for it. I've read that a pair of KT120 tubes can get you as much as 150 watts in push pull, so my idea is to use a quad of KT120's, so you could get a 300 watt bass amp like those old SVT Ampegs.

[@UncleDoug]

It drove a pair of 6L6's, so the B+ would probably be around 450 to 475 VDC. I also have the filter choke and output transformer from the amp (both are quite stout). It is definitely tempting to build an amp around them......but they are so darned heavy. I can't imagine the PT that could handle a quartet of KT120's, or the cooling system you would need to dissipate 240W of Plate Dissipation. Wow !!

[@alvagoldbook2]

Uncle Doug If I ever get around to building such an amp, I will probably just use a pair of KT120's. They're tempting to use for a tube bass amp, because you'd get a tone of clean headroom, and I've heard very good things about their clear bass response from those who use them in HiFi applications. But man oh man, I know the transformers alone are going to cost a fortune.

[@UncleDoug]

They are definitely "current hogs" and thus would require a big, expensive PT. I wonder about the possibility of using two, smaller PT's in parallel, each one individually rectified. You might get the current, but It would probably cost about the same, and you still would not get the outrageous plate voltage that these tubes need.

[@rcmoot]

i am so glad you are our teacher on amps. do you have a video on the tech instruments we need to check or build audio tube amps ? next would be , Do i need a math degree to figure out to build an audio amp? do you have a video on just how to read all the specs on a tube sheet and break it down into understandable jargon?

[@UncleDoug]

Thanks, RC. I have no video dedicated to the necessary instruments, but they are generally evident in the repair videos. A good meter to test resistance, voltage, current, and capacitance is a necessity to get started. No, you don't need a math degree, only a strong desire to study and learn. I have not yet produced a video on interpretation of tube data, but it would be an interesting topic. You don't really need to fully understand a tube manual to build an amp. I think the best way to start out building amps is to buy a kit for a simple chassis, like the Fender Champ, and build it. As you do, try to understand the function of each of the components (using the Internet as a resource). After that, you might try building your own amp by downloading a schematic, selecting and buying the necessary components, and assembling it without instructions other than a schematic itself. Good luck.

[@endrestory4345]

I just love thes videos, its supernice learnings videos for me. Thanks

[@UncleDoug]

You're welcome, Endre :)

[@UncleDoug]

Smokinone951, your question did not have a Reply capability. It sound to me like the On/Off switch is faulty. Next time it delays coming on, wiggle the toggle switch and see if that helps. If it does, you need to replace it.

[@alvarogeorg]

Great explanation! Thanks.

[@UncleDoug]

Glad you enjoyed it, Alvaro.

[@scottmezei5523]

Great video. Thank you!

[@UncleDoug]

You're welcome, Scott. Glad you liked it :)

[@TheLeetfrog]

I love that doggo :)

[@cpchris2]

Thanks so much .. I changed my transformer on my fender twin and works beautifully thanks again

[@UncleDoug]

Glad to hear it, Chris. You're welcome :)

[@davewilson6324]

Great job! It would be helpful to have a video going through some of the common problems that cause a power transformer to fail.

[@UncleDoug]

Thanks, Dave. I think the best way to protect a Power Transformer (PT) is to have it properly fused, i.e. with the lowest-possible-amperage fuse that will still allow the amp function. The fuse value may even be lower than what the factory recommends, since they were more interested in "fire" protection than the protection of a (now priceless) vintage transformer. I am not a big fan of slow-blow fuses. People don't realize that a slow-blow fuse can tolerate twice its rated amperage for over 10 seconds before opening the circuit......by then, the PT is most likely fried. Any internal shorts (i.e. shorted filter caps) or running the amp with output tubes biased way too hot (excessive plate current) are probably the leading culprits in PT damage. You can tell if the PT is overheating simply by placing your hand on it after 10 or 20 minutes of use. It should be warm to the touch but never uncomfortably hot.

[@endrestory4345]

Nice video.Thanks From Norway

[@UncleDoug]

You're welcome, Endre :)

[@craigrobichaud2354]

Hi Uncle Doug!!... Absolutely love your videos...I wish I had teachers, while getting my BSEE & MSEE, who explained the technical issues as clearly and precise as you do...I'd like to ask, which video(s) you recommend that clearly explain the power amp operation, from the point after the phase splitter, as clearly as you have with the preamp...It obviously doesn't matter how many degrees a person has, it's the experience and hands-on that truly develop your technical know-how...school is great to get a solid base of technical knowledge. I would just love a better understanding of the power amp section, as a whole...Thanks again for your time taken to share your solid understanding of amps. Rusty has a very steady paw while filming....and I love Jack's occasional walk thru during filming, it's just like the ring ladies showing which round it is in between rounds!!

[@UncleDoug]

Wow, high praise indeed, Craig. Thanks so much. Have you watched the output transformer video ? As I recall, it goes into some detail regarding how the two out-of-phase signals from the phase inverter drive the output tubes, producing greatly amplified high-impedance (voltage) signals that are united in the output transformer and converted to a low impedance, high current signal to drive the speaker.

[@craigrobichaud2354]

Thanks Uncle Doug!

[@timsmith5021]

Ham radio and guitar player, thanks for the awesome video!

[@UncleDoug]

That's a good combo, Tim. You're welcome.

[@KleyDeJong]

When you were looking at the transformer from Triode you mention in the annotation that it is not the correct mounting style. Could you explain why that is so? What is the difference between mounting horizontally vs. vertically - other than the practical consideration of how your chassis is routed?

[@UncleDoug]

In horizontal mounting, there is a large square hole in the chassis that accommodates a portion of the transformer body. This is the type of mounting that is generally used in chassis that hang from the rear roof of the cabinet, like a Fender Champ. The vertical-mounted transformer is more commonly found in chassis that rest upon the floor of the cabinet with the transformer pointing upward.

[@mariocopete4417]

Hey thanks For your video, it was very usefull, grettins from Colombia.

[@UncleDoug]

Glad you enjoyed it, Mario :)

[@BjornBlomstrand]

Thanks for today lesson. I wich you a Merry Christmas. ps if Rusty are still around give him some goodies from me. Bjorn

[@UncleDoug]

You're quite welcome, Bjorn. I wish I could......but he is no longer with us.

[@BjornBlomstrand]

@@UncleDoug It is sad to hear.

[@jamespaterson7597]

very interesting uncle doug thank you

[@UncleDoug]

Glad you enjoyed it, James.

[@javijap424]

Hi Uncle Doug, very instructive video, thanks for sharing. In the Princeton Reverb-Amp AA1164 schematic they use a 125P1B transformer. The 5VAC secondary (that supplies up to 2A) is used to feed a 5U4GB rectifier tube (that needs 3A) and the 6.3VAC (also 2A) is used for the rest of the tubes (that needs a total of 2.1A)... Do they use this transformer in order to save money (although it runs hotter and reduces the component's life) or my maths are wrong?

[@UncleDoug]

You're welcome, JJ. Your math is just fine. I have wondered about this too, and guess that the power transformer must have a fairly large built-in current reserve (especially for the rectifier filament). It seems unlikely that Fender would risk a bunch of warranty problems just to save a dollar or two. I generally switch to a GZ34 and solve the problem.

[@sigdaddy7377]

Hello Uncle Doug! Your advice about reinforcing my tracing repairs on the tube socket PC in my Blues Jr. was right on, but I discovered more issues and decided to discard the whole thing and fabricated a new plate, with new sockets, all hardwired to the rest of the amp. It's not as visually tidy as I would wish because I left ample wire to facilitate removal of the main PC, but I'm far more concerned about the proper functioning of the amp. Should I have been careful to makes these 23 wires as short as possible, as long as the aforementioned removals could still be done?

[@UncleDoug]

+sigdaddy Signal leads are like antennas that pick up stray EM "noise", SD, so keeping them short as possible generally results in a quieter amp. I guess you could complete the job as-is and see how it sounds.....maybe you'll get lucky......but short and/or shielded signal leads are the best way to go.

[@tangotommi]

Hi Uncle Doug, Hope you are well. Well, I was finishing up the restoration of the Studio City 50R, 50W amp head, and replaced those out-of-spec components; filter caps, plate resistors, etc., and had set the PD of the 2 EL-34s several times. First, to about 70% of the max 25W, then and lastly to ~19-20W to achieve more head room. During the intermittent testing after the installation of new components, tubes included, I noticed a low to mid level amount of hum from the (4) 12" speaker in my Marshall Cab. (Impedance of the cab 16 ohms Mono as was the amp set at 16 Ohms) In the course of audio testing without the current limiter (for the first time since all other testing showed no excessive amount of current being drawn, Please note however, previously, the bulb filament was glowing a faint orange. I considered this to be normal since the amp is 50W. I recall a similar situation in one of your videos). I chose a different outlet in a different room to see if perhaps there was some "ground loop" causing the hum. Perhaps this level of hum was acceptable, IDK. Shortly after, I turned the amp on again and the 3A Mains fuse blew. Took the amp back to the bench and after installing a new fuse, turn the Mains switch on and was blinded by the current limiter 300W bulb! Whoa! I immediately shut the amp off and am diagnosing the problem. I'm just looking for some feedback during this process. Maybe you may have an idea why this could happen. After looking at the primary and secondary sides of the Power Transformer, I measured some resistances. Q1: Are the resistance values I measure valid without disconnecting those leads from the amp? One resistance I measured was the resistance across the Hot and Neutral leads of the power cord so as to measure the resistance of the primary winding. I got 5.7 Ohms, seems low to me. Q2: The Secondary Filament leads seem to have continuity to chassis ground at 0.2 Ohms And with respect to each other from the winding to be `0.2 Ohms! Same resistance , that is , practically no resistance. This seems Very wrong! As a note about being careful during component replacement, I was very careful to take pictures and draw diagrams beforehand, so I could refer to them. Also, I never got too far ahead of myself during replacing so as not to make a mistake during replacement. Any thoughts are appreciated! Thanks Uncle Doug

[@UncleDoug]

I wonder if one of the new filter caps failed, causing the initial hum and then, possibly due to an internal short within the cap, the final dead-short indication from the CL ???

[@tangotommi]

Uncle Doug Thanks Doug, i will check them out. If you are correct, and 1 of them had shorted, would that be detrimental to the power transformer? See, the current limiter lights up when only the Mains switch is turned on and the amp is only in Stand By mode. I think the FCs are only energized when the Stand By switch is closed to permit current to energize the FCs and remainder of the circuitry. Initially, since the hum wasn’t responsive to volume, i thought 60Hz hum, and realized the filament circuit wiring lays on the tube side of the chassis (wierd), holes are drilled through the chassis on either side of the tube socket to allow attachment to the sockets. Not very efficient as the twisted configuration i see in the Fender and other amps you’ve worked on. So i moved around the 12AX7s and then bought a matched Quad of Tung-Sols. I’m sad because i was just getting ready to test it with my Scope and Tone Generator. ::( Even my dog Spunky is melancholy! Maybe i let him give out candy to the treat or treaters tonight to cheer him up.

[@UncleDoug]

@@tangotommi As I have noted many times, TG, it is virtually impossible to troubleshoot long distance, without the ability to observe and test. If the short only appeared after your repair work, then the cause must relate to the work done. I would focus on every solder joint, component value, and connection made during the repairs.

[@tangotommi]

@@UncleDoug I understand completely. It really wasn't working well when I got into it. Terrible sound, dirty pots, some wiring incorrect for biasing properly, Reverb driver 12AT7 in the wrong socket. Then I made it sing for a while. Cest la vie. That's ok. It's a tough one for my baptism/initiation into Ampaholics Unanimous.

[@tangotommi]

@@UncleDoug I just wanted to thank you for Not suggesting anything more. You're an excellent instructor. It's the best way for Anyone to learn is by Doing. I just turned 68, and in retirement, this a perfect hobby to keep my mind sharp by problem solving. Yes, even though I Feel confident on what I've been able to accomplish on this amp, and don't see the error I've made, it doesn't mean it's not there. I Will find it and I will be the first to admit any oversight on my part. I'll keep you in the loop when I find the problem since you may find my predicament pertinent to bring to the attention of my fellow subscribers. Thanks for all the projects and subject matter you convey to us! I remember upgrading a Hickok 539C with a kit supplied by Bill Eccher, a retired electronics expert from the Navy. I asked him if he could recommend something for me to learn about vacuum tube technology and he sent over the Navy training manual. I got swamped in the first 30 pages. That was about 5-6 years ago. However with the videos you've published, I've learned So much more practical knowledge to help me understand electronics of vacuum tubes and amp circuitry. Thanks again! Keep 'em coming!

[@michaelfolchetti736]

Love RUSTY!

[@muybridge3961]

this is what we call in the UK An "old school" electrical installations lecturer, he covers everything you need to know and just that, no fluff. and no rubbish. Usually guys like this have a long history of "Trusted Person" roles in the large scale Electrical installations industry. And a dodgy knee or something from the one time they had an accident which was not their fault involving high tension Electrical systems, by trusting someone they should not have trusted to lock off the supply properly, or something similar. From that point on they develop a need to pass on quality knowledge and a healthy distrust of less qualified/experienced people.

[@UncleDoug]

Wow......quite an analysis, MB. I do indeed have 2 bum knees, mostly from kickstarting old British motorcycles....and an occasional wreck or two, after they started ;)

[@GenerationGap69]

I can’t believe it took me 10 videos before I subscribed

[@UncleDoug]

Neither can I, Wayne......but at least you finally did :) Welcome !!!

[@charleswoolbright6933]

YOUR Great i have a 68 fender dual showman sounds great now/THANK YOU !

[@UncleDoug]

So glad the video was helpful, Charles.

[@zep136]

Would the Fender Deluxe transformer you used in your example have about a 1: 3 ratio then? Love your videos, thanks!

[@UncleDoug]

You're welcome, Zep. Each of the voltage outputs has its own winding ratio, i.e. the 6VAC filament winding would be about 20:1 with 120VAC primary input. To produce 660VAC from 120VAC input, the high voltage winding ratio would be about 1:5.5 by my calculations.

[@treborheminway1196]

As always, great video UD. You always have a barrel full of practical info in these videos. Have you ever considered a deeper dive? I would like to suggest explaining whats going on in the magnetic core of the transformer, but am reluctant to ask.....(pun intended). Did you ever teach Maxwell's equations? My guess is that you did - at least the amperes law portion. I would love to hear you cover Maxwell as you just have a way with your explanations and analogies that really makes sense to me and evidently many others here. I can understand you have better things to do, but maybe Jack can handle it if he's not too pissed at the Physics crowd over the whole Schrodinger's cat thing. Thanks again.

[@UncleDoug]

Thanks for the suggestions, Trebor. I'll keep them in mind for the future.

[@mercyseateffects]

Hi Doug! Excellent video. I’m working on a WEM Copicat tape echo machine, tube powered, and I’m only getting 1.7V on the secondary that feeds the diode rectifier. It should be 250V. Does that sound like a faulty transformer or is the circuit simply not pulling enough power? Maybe bad smoothing caps?

[@UncleDoug]

Does the secondary output remain 1.7V when you disconnect the diode rectifier? If so.....bad PT. If it goes up to 250V, then look to the rectification stage for the problem.

[@mercyseateffects]

Uncle Doug yep, unfortunately it still reads 1.7v That’s a shame. Thanks for the help!

[@conjering]

Uncle Doug, I need your help. How do I figure out the secondaries 4 ohm, 8 ohm, 16 ohms and the center tap on a unknown Heyboer output transformer? Thanks

[@UncleDoug]

The safest way is to look up a wiring diagram for the Heyboyer OPT on their Internet site. The part number should be stamped on it. If that's not feasible, then you can try another approach. On the secondary side of most OPT's, the common wire is usually black. If you have a good ohmmeter, you can then measure the resistance between the black wire and each of the other three wires. The wire with least resistance to the black wire will be the 4-ohm connection and the one with highest resistance should be the 16-ohm connection. The remaining wire should be 8-ohm. I'm not familiar with secondary center taps in OPT's. Perhaps you meant the common wire (usually black). Good luck.

[@mikebarney]

hey Doug I'm just curious, I see that there is a fuse connected to the primary of the PT. How do amp manufacturers determine what size fuse is needed for the amp?

[@UncleDoug]

You can measure the current flow to the amp with an AC ammeter and install a fuse that is about 25% to 50% higher value.

[@martinlundberg5413]

I have a power transformer which has more than enough current headroom on the 5v and 6.3v taps but it puts out 450 on both the high voltage taps. Am I able to just put in a 5y3 or would I have to find a way to drop the voltage first? Thanks for any help and for the awesome videos!

[@UncleDoug]

If the high voltage secondary is center tapped and you are getting 450VAC between each lead and the CT, then a 5Y3 should be able to handle it since its PIV rating is 1400V......however, after rectification and filtration, your DC voltage will be over 600V. The only output tubes that can handle this type of PV would have current demands beyond the capability of a 5Y3.......so it may not be a wise choice for rectification. You might consider diode rectification, as in the Fender Bassman.

[@martinlundberg5413]

Uncle Doug thank you! I'll have to look into that then. Might not turn out to be the amp I initially was envisioning but it could be a fun experiment!

[@jlucasound]

It is better to have more current capability than not enough. Current is "as needed" and you have more problems (many actually!) with too little current available. Also, mechanically, a transformer is not affected by its orientation to the "floor". Mounting it sideways, so to speak, gives more "headroom". (The physical type). ;-) Do I have this correct, Rusty? Uncle Doug, please let me know what he "says". :-) I am learning so much from you two. Thank You!

[@UncleDoug]

I awakened Rusty from his (fifth) nap of the day, and he responds: "Yes, indeed, JL, it's always better if your PT can exceed the predicted current draws by a safe margin, say 25%....otherwise it will run hot and possibly go up in a cloud of (expensive) smoke. Regarding the orientation of the PT, we tone (and nap) purists always prefer the horizontal orientation whenever possible.....zzzzzzzzzzz"

[@atta1798]

Excellent!...Uncle Dough if a 5C3 or 5E3 were to be modified to have both a tube rectification and a diode one......what would the best way be to add the diodes this for optimal tone/headroom?.and which configuration a full bridge one?..

[@UncleDoug]

atta1798 There is an easy way to do this, atta, simply unplug the rectifier tube and plug in a Weber Copper Cap replacement module. Here is a forum that discusses the pros and cons of conversion from tube to SS rectification: www.thegearpage.net/board/archive/index.php/t-363649.html

[@atta1798]

Uncle Doug I read about it....thank you I will check it out!

[@shaunsanders9673]

Hi Uncle Doug. I have sometimes used old transformers in amp builds. Even though I try to make sure they're up to the task before using them, they sometimes become rather hot. So I wonder, how hot is too hot? The PT in a mojotone 5E3 kit I build a couple of years ago seems to hit about 126 degrees f inside the cabinet, which seems hot, but I figure mojotone know better than me. At that temp, you can't keep your hand on it for long. Do you have a temperature limit before you consider the PT dangerous to use? Thanks as always for the great teaching.

[@UncleDoug]

The extreme heat indicates that the current flow through the transformer may be approaching or exceeding the level it was designed to handle......however, most transformers are rather robust and can handle a bit of overage. I would say keep using it until it fails and then replace it with a PT with higher current capability.

[@jackytangahheng]

very like you video,clear n clear explanation..

[@UncleDoug]

Thanks, Jack. Glad you liked it :)

[@robertkat]

Electronics goes back along way, 1957 at12 years old, I build my first triode receiver, antenna coil, metal earphones.

[@UncleDoug]

You've been at it for a long, long time, Robert.

[@craigrobichaud2354]

Uncle Doug....Love YOUR videos, as I've praised in the past. But my main question is, where do you start...Do you pick the power tubes your planning to use and design, electrically, around that.....Should I pick power tubes then create a.load line to determine operating thresholds??...Any input would greatly help, because I'm ready to begin my design. Thanks Craig Robichaud

[@UncleDoug]

Thanks, Craig. I begin by selecting a vintage amp that has the tone, effects (if any), and power that suit my interests and needs. If the circuit is unusual or utilizes unusual tubes then so much the better, but my primary consideration is its utility. I then study the schematic of the desired amp, make some improvements if possible, order reasonably priced components, and build it. If you check my videos featuring handbuilt amps and effects, you'll find several types of tremolo, reverb, the first Fender amp (Model 26), the Supro TremoVerb, various Champs and VibroChamp, etc. I like low to moderately-powerful, compact, tone-rich vintage tube amps.....so that's what I build. Almost all use 6V6 output tube(s) and tube rectification, but each has its own special voice. Bottom line, don't try to impress others with intricacy or cleverness, or focus on using some weird tubes you found in a Dumpster, simply build what you love.

[@emanoelraiffnobrega7419]

Uncle Doug I believe I forgot to specify that this 68' custom vibrolux reverb is the new one the fender "reissue" in 2014 (but the schematics is far far away different from the original 68'). It has no rectifier tube and the transformer (165v-165v no center tap) have not the secondary 5 v. So I imagine that to install a socket for the 5U4 I have to drill a new hole and I also need a PT with three secondaries. So I'm a bit confused about how much the current would be in the end. Could you clarify me, please? Thank you for the videos and the attention!

[@UncleDoug]

My advice would be to sell the amp and buy one that better suits your needs. Changing power transformers, adding tube sockets, altering circuits, etc. would represent a whole lot of work and expense to gain a little "sag", and, to be honest, I think you would be disappointed by the result. You would need a PT with a center-tapped HV winding, probably around 325-0-325, and a 5V 3A filament winding. If you watch my videos on the Supro Tremo-Verb, I explain the selection of a PT and the high voltage DC you can expect. If you still choose to proceed, good luck.

[@emanoelraiffnobrega7419]

Uncle Doug thank you for the advices. I think you're right, maybe it could be expensive.

[@richclayton5785]

Got a Baldwin just like yours! Need to find a project for it.

[@UncleDoug]

Good luck, Rich.

[@millerviz]

I'm interested in building using unknown transformers. I get how to calculate voltages and impedance ratios; is there any way to gauge current capabilities?

[@UncleDoug]

To my knowledge, you can only guess at the current capabilities of unknown transformers, based on mass and wire gauge......neither of which is particularly accurate. Another approach is the Kamikaze method, in which you simply install the transformer and hope for the best :)

[@millerviz]

Thanks Uncle Doug. I thought as much. If a transformer fails what might I expect to happen? Any prospect of fire or other damage? Btw, I love your videos. Clear and concise. The pace could be a little faster for me, but I love the detail and clarity.

[@UncleDoug]

When a power transformer fails, the amp simply ceases to function. There may be some light smoke and a burning smell, but if properly fused, there should be no fire risk. Glad you like the videos.

[@millerviz]

Thanks again, Uncle Doug. Truly can't praise the videos enough.

[@emanoelraiffnobrega7419]

Hi, Uncle Doug! Nice video! I have a Deluxe Reverb and I want to mod the tremolo to Princeton 6g2 specs. But in the 6g2, the bias comes from red wire HV because this section does not have a bias tap. So, I would to know if I can isolate the bias tap and take a red wire to make a bias like the Princeton 6g2. Thanks.

[@UncleDoug]

Greetings, Emanoel. The wire from the bias tap in the DR has a 470 Ohm 1W resistor, while the higher voltage plate-circuit wire used for bias in the Princeton has a 100K Ohm resistor. I would think that you could simply use the bias tap wire and 470 Ohm 1W resistor for your Princeton conversion. After wiring it, check your rectified bias voltage to see if it is in the neighborhood of -35VDC and fine tune it if necessary.

[@emanoelraiffnobrega7419]

Uncle Doug, thank you very much for you help! :)

[@UncleDoug]

You're welcome, Emanoel :)

[@JoeBlow-px4ng]

Uncle Doug

[@smokinone951]

i have a question i hope you can help me with. i have a kustom hv65, its a great lil amp and i only paid 100 for it. problem is when i turn on power sometimes immediately turns on other times it can sit for up to 30 min before it pops and turns on. didnt do this before, any ideas what could be? im thinking power supply because once amp is on everything works great

[@UncleDoug]

I agree with Lefty. You could try bypassing the (possibly bad) on/off switch to see if the amp comes on at once. If not, then start looking deeper......like power supply components and loose connections within the PS. Good luck.

[@smokinone951]

awesome. thank you for the tips. will definitely be looking into it this weekend when i have time to methodically break it down. will let you know how goes

[@UncleDoug]

Please do, Smokin', and best of luck.

[@guitarbackingtracks4386]

Excellent stuff as usual Doug. Any chance of direct dialogue regarding amps etc?

[@UncleDoug]

Thanks, Brian. Due to the amount of correspondence we receive daily, we are unable to engage in such private discourse, but will try to answer basic questions via this format.

[@guitarbackingtracks4386]

Uncle Doug fair enough Doug. Fancy doing a video on integrating a magic eye into an amp circuit showing output power? Frivolous, but eye catching!

[@meneses1947]

very good

[@UncleDoug]

Thanks, Manuel :)

[@NasirAli-lu4it]

You are unique Sir.

[@UncleDoug]

Thanks, Nasir :)

[@frankstone919]

I've never used a new power transformer. I wonder how much transformer size is low voltage winding? Just curious , I've got a Thordarson 26r46 370-0-370vac 190mA 5volt 3A two 6.3volt taps 7.9A & 1.2A It is in the 1966 catalog. Weighs over 11lbs. Building my version of a Matchless Clubman 35 (ef86) with it (thread on el34world frankenxtein) , now I know why people like to build Fender's. Mature Iron leads to some interesting amps though. Really enjoy your videos , thank you.

[@UncleDoug]

You're welcome, Frank. That Thordarson sounds like a real beast. You'll never be at a loss for 6.3V power :) Best of luck with your project.

[@annomaus8386]

Uncle Doug: FB vid. coupla questions tho, On the example xformer, the HV secondary is 660V and the 5U4 plates need 330V. The bias taps appear NOT to be centered. I would expect to need a true CT for the HV supply, so I wonder if the proposed replacement is really the right one. Or is that just an incidental graphics error? Also, I have a Triad R-26A I want to use for RF power amp PS. The HV secondary is marked 880V with taps for 720V, sharing a center tap. Each winding is marked 200ma. Is this xformer rated for pulling 200ma/each out of both windings concurrently, or is it likely an either/or situation? tnx! woof to Rusty from Buddy the WonderLab.

[@UncleDoug]

One of the taps in the diagram (#6 Red/Yellow) is the center tap and the other (#7 Red/Blue) is the bias tap. If you look at the diagram, the center tap is indeed centered. Generally, the current rating for a power transformer high voltage winding is the total HV DC current available after rectification, i.e. 200mA. It is not the current for each winding. Regards to Buddy :)

[@rondobondo6600]

Thank you very much....

[@UncleDoug]

You're welcome, Ron.