R/E/P > Bruno Putzeys (Designer) - Dave Hecht (Master Tech)

Telefunken V72 output problem


industrial arts:
I have a couple of V72s on my bench for repair; the problem is low output.  I have traced the signal up to the output transformer but see nothing on the secondary side.  The secondary measures 10 ohms on both.  Seems a little low for an audio output secondary but since they measure the same, my first impression would be that the transformers are not bad.

I have disconnected the output transformers to make sure that there wasn't any problem with the wiring, so again it looks like 2 bad output xformers, but that just seems a little odd.
I have checked and double checked the units but with them both exhibiting the same problem (even though they are different vintages - besides the low output problem one of them has bad filter caps which appear to be older) I feel that I must be missing something.

My only other suspicion is that someone may have inadvertently plugged these into a hot phantom mic input and that's how both transformers got damaged in the same way, but that's just a wild guess.

I searched all over for bad or problems with V72 transformers, but have had no luck.

Any suggestions or advice would be appreciated.


Mark Springer
industrial arts

I'm here asking for V72 help myself. But I thought I'd at least ask what you mean by 'low output', because the V72 is not an especially high output pre-amp. And as what comes out is relative to what goes in, what is going in? If used with a low impedance mic with relatively high output, it should deliver a useful signal. As they both seem to be doing the same thing [as you noted] it makes me think they are OK and something else is wrong.

London John:
I've had the same problem, but with a V76. After much searching and testing, it turned out to be a tube....doh. Thankfully, I had two units to swap tube sets. Might be worth a try, otherwise Sonic Messiah in Belgium knows these units well.


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