How to safely test the Output Transformer on tube radio or amp.

The Output Transformer on a tube radio or amp is a crucial part of the design of the circuit, so a restoration's viability may depend on whether it is functioning or not. Finding exact replacements is not easy for equipment that is usually decades old.
The idea here is to create a series of 'Tube Radio / Amp Restoration Building Blocks' which will be added to in time. The Playlist link:
• How to safely check th...
See also my playlists on some other complete restorations.
Graetz Super 171W:
• Graetz Super 171W tube...
Loewe-Opta Magnet 3737W:
• Loewe-Opta Magnet 3737...
Loewe-Opta Truxa Stereo 4741W:
• Loewe-Opta Truxa Stere...
Braun Atelier 3:
• Braun Atelier 3
Graetz Musica 4R417:
• Graetz Musica 4R417 re...
SABA Freiburg W2:
• Saba Freiburg W2 (WII)...
Graetz Comedia 616:
• Graetz Comedia 616 tub...
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[@SBanas]

Thank you so much for those videos, I've learned so much, not only about radio restoration, but also about electronics itself! Greetings from Germany!

[@dr.frankenstrat2076]

Thank you so much-- this really saved the day-- ive been going in circles-- and remembered i watched this video a long time ago-- now i know its not output trans-

[@in.der.welt.sein.]

This is brilliant. Thanks for posting this video. It helped me determine that was transformer was indeed fine.

[@electronicsoldandnew]

👍

[@johnmcgiv1]

Mr Caldeira just what I needed great little tip many thanks very explicit, many thanks.

[@electronicsoldandnew]

John McGivern : glad to be of help.

[@dirtydon8661]

Awesome find for me! I work on cards for handset coms throughout oil and gas platforms in gulf of mexico. I have rigol similar to yours. I just tested a output transformer that i had removed. Got to love you tube and your time for making this vid!! Thank you.

[@electronicsoldandnew]

+DirtyDon RC : you are welcome.

[@kensvintagetoys873]

very clear and easy to follow

[@electronicsoldandnew]

👍

[@allthegearnoidea6752]

Hi I have just found your channel. I have used the same procedure as you many times but I really enjoyed your very careful and clear explanation of the testing method. Thanks keep up the good work

[@electronicsoldandnew]

+AllTheGearNoIdea : thanks for the kind words. Glad you enjoyed it.

[@Rush-gz9sx]

Watched the video about 5 times now and so wish I had a signal generator so I could do the practical lol.

[@electronicsoldandnew]

👍

[@2tallB]

So easy, thank you!

[@electronicsoldandnew]

👍

[@Leo6009]

Awesome? I am testing transformers in the Loewe Opta Hellas 3841 W at the moment. This is extremely valuable information and a fabulous reference and future guide. Explained in a straight forward, clear manner. Thank you very much Manuel! I am making a small donation.

[@electronicsoldandnew]

Thank you. Glad to help.

[@Leo6009]

@@electronicsoldandnew you only seem to have monthly coffee payment options now. I wasn’t able to find one off random PayPal coffee payment option via Patreon direction. It’s better to leave all options open for friendly relations. Don’t worry what the competition are doing. Just do your usual great work! Cheers. 😁☕️

[@electronicsoldandnew]

The patreon system doesn’t allow for one-off payment, which is why I added Paypal as an option. Thanks.

[@Leo6009]

@@electronicsoldandnew I have made several one off friendly contributions when you directed me to the Patreon link, where I made one off payments with PayPal. The payment link is no where to be found. Sorry to be a pain but it’s something I come across every time I want to make a contribution. I have clocked up thousands of hours in internet marketing, web design, search engine optimisation etc… A qualified observation!

[@electronicsoldandnew]

I’ll check it out. See why the link in the description is not working.

[@jimmccanna]

Hi, thanks for the informative explanation and vid. I am working on an Akai M8 right-side amp monoblock that has zero output. The left side works. The troubleshooting guide in the service manual suggests testing the output transformer. I have traced the wires from the speaker jack back to one side of the OT (output side) and traced the wires to the input side of the OT. I am using an IPad as my signal source with a stripped 1/8" cable with bare wires on one end connected with alligator clips. I am having trouble identifying where I connect the cable in my amp like you connected to the rectifier in the vid. I guess I am looking for B+? So, just guessing (with power off and unplugged) I connected one clip to the output side of the OT (a wire actually connected to speaker jack) and touched one of the two tabs on the input side of the OT with a probe and got audio. Then on the underside of the amp I touched the probe to the 7th pin on the EL84 socket (tube removed) which is hard-wired to other tab on the input side of the OT and got audio. Notably, I got audio from touching several of the pins and much better volume and bass from touching the underside center pin. I do not get audio if I touch the signal probe to each of the tabs on the input side of the transformer. I feel like I am doing it wrong. But, it seems like the signal has to be going through the transformer itself because I am connecting to wires on one side and completing the circuit on the other. I hope I am not being an idiot?

[@abeleballestri612]

A thanks for the tip you have shown how to test an output transformer . I would be interested to get a book from you telling us all these practical tests how to find out if they work?

[@electronicsoldandnew]

abele ballestri : I'm sure there are some books out there on the subject.

[@electronicsoldandnew]

abele ballestri : I'm sure there are some books out there on the subject.

[@lelandclayton5462]

I don't have a Function Genator so this is how I test transformers for power or output for speakers I use a little AC Train power supply that is varible from 1volt to about 6volts. I typically try not to go over 2 volts. Then on the output will just use a voltmeter to get a voltage reading. A friend of mine does the same test but with a higher voltage and a light bulb.

[@electronicsoldandnew]

+Leland Clayton : that's just fine. All you need is any source of AC voltage, and try to keep it low, so you don't get any nasty surprises.

[@adrielrowley]

I have looked for one of these with no success, are they called by something else? There are one or two found at 6 volts, nothing adjustable and nothing at the lower voltages. TIA

[@worldwide1376]

Thank you for posting this, very useful for a novice like me. I'm working on a Knight signal tracer that has no audio. All tubes are good, I replaced all electrolytic and filter capacitors and spot check several resistors and replaced a couple that tested out of spec. The output transformer tests good using your test method. Can you point me in the right direction, would else would be the most probably reasons for no audio?

[@salossi]

Repairing basically guitar amps, I must say that this procedure is unfortunately not enough to verify that an output transformer is really okay. Problems could be caused by insulation problems, caused by internal sparks if amps have been driven hard without a load being connected. Those issues might only appear, if the ot is tested under proper voltage-conditions. I usually use my variac plus a connected powertransformer out of any tube gear and use the 6.3V heater coil to get an adjusteable ac between 0 and around 7V.. I then connect this voltage to the secondary winding of the ot and make my measurements at the primary coil of the ot. I've already found dead transformers that seemed to work fine with the other checkup procedure... But thanks for your great videos!!!

[@electronicsoldandnew]

salossi : thanks for your input.

[@daleburrell6273]

...that's clear as mud to me-!!

[@BKGoldDetecting]

Another great video, very concise clear instructions. I successfully tested my power transformer using your other video as a guide, but unfortunately I don’t have a signal generator. Could I use a Variac set to low voltage to test the output transformer? Thanks again. Also, would be great if one day you could do a video explaining how to connect an external device such as an iPhone to the PU plug so we can listen to online radio as an option. :)

[@electronicsoldandnew]

E careful of using the variac. It has very high current capabilities which could do more damage. As for your request for a video, I have actually done one. I believe it was the stereo to mono cable video.

[@BKGoldDetecting]

Electronics Old and New by M Caldeira Thanks, just watched the suggested video for stereo to mono, exactly what I needed. Thanks also for the advice on the Variac, I’ll have to come up with another way to test the output transformer, or just take a punt that it works after recapping my Schaub Lorenz. :)

[@buddha65281]

I appreciated your video... I am not working on a tube radio but a lamp with sound and animated parts. I would like to test the secondary windings to figure out the Voltage output but do not want to desolder the connection. The windings go into the board where the RR(4 diodes) meet in the middle of them. Then there is a capacitor (smoothing cap I believe it is called). the voltage at the RR is 1.5v but at the capacitor 2200Uf/16v is 9v... How can I test the output voltage correctly as I need to order another transformer for a 2nd lamp that is no longer working? Thanks!

[@sinecure45]

THank youi for the very instructive video. How would the procedure differ for a push-pull configuration?

[@electronicsoldandnew]

Do exactly the same thing from both driver tube anodes, one at a time.

[@sinecure45]

@@electronicsoldandnew Much obliged for the response.

[@pahaahv]

Hello. I've got help from You many times, thank you for your answers and detailed videos. Another question here though. When one does not possess a signal generator, what would be the approach then to test the output transformer? Is there a way?

[@electronicsoldandnew]

You could use a signal from an mp3 player or even you phone.

[@waynegram8907]

I'm confused how the output transformer BLOCKS the 300vdc to 600vdc DC voltage apply to the power tubes on the anodes. I know that capacitors block DC but inductors pass DC and there is high DC voltage on the primary side to the output transformer to the secondary side of the output transformers must have very high DC voltage or the output transformer RATIO is what BLOCKS the high voltage DC ?

[@pahaahv]

It's an old video but can you give an explanation how to do the same procedure on Push-Pull output transformers? I have a soviet hi-fi radiola that I'd like to test, it has EL84s in push pull.

[@electronicsoldandnew]

Exactly the same. Do it one winding at a time and the signal should be heard at the output in both cases.

[@philshifley4731]

I put the positive lead from my signal generator to the correct pin and heard a signal without placing the negative lead on the circuit. Just that mean the circuit is grounded?

[@electronicsoldandnew]

Your signal gen is grounded through the mains earth, and if your unit is also using mains earth as a ground, then you have the system using the same ‘ground’

[@SuperSeanXXX]

What if it's a center tapped output transformer......can you go across the whole primary

[@electronicsoldandnew]

I’d try each half separately. You should hear a tone (albeit a little distorted) in both cases.

[@torybosher9079]

thanks for your informative info, but I dont have radio tube Transformer. I have electrics organ I couldn't find good inf on how to tested. my transformer have 4 wire in primery and 6 wire secondry. could you please performe vidoe on how to test this kind of transformer. many thanks

[@electronicsoldandnew]

+Tory Bosher : is it a power transformer or audio output transformer?

[@torybosher9079]

I really appreciate ur reply. Unfortunately there is no way to show u my transformer but believe It is audio transformer. Many thanks

[@pronoysarkar4073]

Please call me output transformer winding formula

[@daleburrell6273]

Years ago, there was an article in the September 1970 issue of Popular Electronics magazine, about winding your own output transformers. You can find this magazine on the internet at no cost.