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

Telefunken V72 output problem

(1/1)

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.

Thanks

Mark Springer
industrial arts

LSA7:
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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