[1000a]

Seriously I do need you guys help, thanks   I noticed a hum in my right speaker, trouble shot it down to the amps RT channel (not speaker or other gear)
Began checking bias on power tubes, sure enough something is wrong on RT side.

For the bias test I removed all input equip, I left both spkrs attached to amp
But I did remove the cables that go to the active subwoofer from the amp?- is that OK?  If so please continue

My power tubes line up like this
Back of amp

7    8         11    12
5    6          9     10

Front of amp
PP class AB Jolida  (EL34)

Tube V12  read .038  where it should be, all others +/- .001 to .002
Tube V10  read .003  no turning the bias pot could change it.

Next I tried a spare tube from my stash in the V10 position and it reads .003 and cannot adjust (?)  Placed this back in the tube collection box-

I decided to stay with what was in the amp at first and continued testing by:

Putting the V12 in the V10 postion it read  .003 I could not adjust. (makes sense)
Putting the V10 in the V12 position it read .003 I could not adjust.  (is this dead?)

Put V12  back into V12 position it reads .040  (good, V10 position did not harm it)
Put V10 back into V10 position it reads .003    (makes sense)

What is my next move?   It seems the V10 valve that was in V10 position is dead, cause it does not work in the V12 slot and the V12 after being in the V10 spot is still good in the V12 slot.  It seems the V10 part of the circuit is broken?

Or have I not gone far enough with the test?   Ideas feed back? thanks

[1000a]

caps and resistors all look good, so we will see I'll try a few other tubes in V10 and wait a few days for feedback before calling a shop.

the hum/buzz can not be heard from the listening seat but if I get within 12" of the spkr. I hear it and with the volume all the way down, with the volume full it increases only a tiny bit in level-all this is with the no music on - no inputs used?

anyway its usually very quite I have to really listen with my ear to the grills to hear much at all.

thought I would better describe what I am hearing and when, thanks in advance

[1000a]

OK tried 1 more tube in V10 slot  same reading .003

Can I play this thing without damaging it, as it is- still sounds OK ,
have no idea why-  or should I just box it & get it to the shop before something else goes wrong from using it in a weakened state?

[JohnR]

My wild guess would be that V10 shorted and somehow fried something else connected to it as well. Did you open the amp and do a visual inspection? (Leave it turned off for a long time before opening... best to check voltage on the power supply capacitors with a voltmeter before touching anything as well...)

[Audiovista]

It's really hard to diagnose, but to answer the question should you keep running it or not....it seems that you lost one or two tubes (or associated electronics). In the PP configuration you do need all tubes to carry bias current, otherwise you have imbalance on your OPT and that may cause hum you're hearing. The imbalance will also cause assymetric drive of the output transformer with increased non-linearity (distortion) and, in more severe cases, core saturation that may take out fuses and/or good tubes.

I would recommend taking care of it before repair gets complicated and expensive....

Boris

[Housteau]

My older VTL did something similar a while ago.  The one tube went out and took a resistor with it leaving that socket unable to bias the new tubes installed.  I just had to replace that one resistor and all was well after that.

[1000a]

Thanks guys

I am guessing any repairs to this unit require that the board to be removed and flipped over to make the soldering connections? (next time out I will avoid this pitfall- if it is such?)

anyway the only thing I can see is one tiny resistor has some clear glue looking stuff on its seam on the end of it (other than that it all appears as always)  I have since the photo removed those silver tube tension things on the power tubes.

called repair guy explained what the design is, mostly SS teritory here.
said he would check it out.

told him I would bring 2 extra tubes to trouble shoot with
I will also include the Jolda phone#
should I seek a electrical diagram of this unit to give to the repair guy?

thanks..