See the link below to my build thread. Having issues with the input tube plate voltage.
Long Overdue SE Build
Long Overdue SE Build
So I think found the problem. I have bad cap values for c4, c2/3, and c6. I am gonna pull the board and check via the schematic. I am not sure it jives with the parts list for caps. Or I built this when I was not sober. Which could be possible. 
. C4 is my fault. I added a 0 to it so it’s 470uf.
Thanks for the input.
. C4 is my fault. I added a 0 to it so it’s 470uf. Thanks for the input.
All through checkout. Need to order 300b tubes and had the rectifier tube go bad.
B+ Is 430v
B- is -290v
Grid V is -131 & -143v but pots ran out of room to adjust.
Input tube is @170v but pot ran out of headroom to turn.
Time to order output tubes and do some final assembly.
Thanks for the help.
B+ Is 430v
B- is -290v
Grid V is -131 & -143v but pots ran out of room to adjust.
Input tube is @170v but pot ran out of headroom to turn.
Time to order output tubes and do some final assembly.
Thanks for the help.
So new issues; been chipping away at this guy.
I can not adjust the voltage on 5842 over 165. My pots run out of throw.
The other issue is my 300b bias gets to over 65ma at start up with the lowest voltage.
The voltage goes to -165v for both channels.
I also found out 1 of my meters will not read mA even though it has the settings. I was using voltage instead.
I can not adjust the voltage on 5842 over 165. My pots run out of throw.
The other issue is my 300b bias gets to over 65ma at start up with the lowest voltage.
The voltage goes to -165v for both channels.
I also found out 1 of my meters will not read mA even though it has the settings. I was using voltage instead.
We are dealing with 5842 tubes that are old and were pretty widely scattered parameter wise when built. It is possible that yours are a bit outside the range of the current board setup. The easiest way to fix this is increase the value of R10 and R21. If you have a 620 ohm in there now go to an 820 or even a 1K. This will give you more adjustment range.
Not quite sure what the grid voltage can go to, but -120 volts should run a true 300B to near cutoff (under 10 mA) even with 450 volts on it's plate.......but what is a true 300B? Many current production 300B's tubes are a bit different from the WE spec, so maybe your tubes need a bit more negative voltage.
This can be accomplished by increasing the value of R11 and R22, or reducing the value of R13 and R24, whichever is most convenient. Change the value about 10%.
Neither of these problems should prevent the amp from operating. Run some music through it and make sure everything works before changing lots of parts.
Thanks for the advice.
I measured voltage across R29/18 in the picture shown.
~.5v across both resistors with -130v bias voltage (measures w/o tubes).
Got sound from 1 channel. Got some awkward squawking from the amp so now I powered down and am working to find why only 1 channel works. Swapped all tubes and the problem didn’t follow.
Back to troubleshooting.
I measured voltage across R29/18 in the picture shown.
~.5v across both resistors with -130v bias voltage (measures w/o tubes).
Got sound from 1 channel. Got some awkward squawking from the amp so now I powered down and am working to find why only 1 channel works. Swapped all tubes and the problem didn’t follow.
Back to troubleshooting.
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