I bought a project DSL 40c 1st test revealed v8 bias OL

[bfglp]

Amp powered but was weak and trebly. It has new tubes all test as new and a new cream back speaker that sounds great with my Boogie.
Tried to bias it and v8a was OL and v7a 42mv plate voltage is was 474 and 475.5
Found a test recommended by Mad Scientist and ohms between pin 4&5 stoped 515 v8 & 517 v7
Following circuit from bias point I see that r67 has lost a good portion of its coating the bias pots respond to adjustment smoothly

So I believe that I found the issue is r67 but can only speculate the cause was someone frequently using the 1/2 power switch without putting the amp on standby first

 

[Jon Snell]

R67 will fail as the EL34 valve flashes over internally or draws excessive current due to an internal fault.
R67 will withstand quite a lot of abuse before it fails.

 

[bfglp]

R67 will fail as the EL34 valve flashes over internally or draws excessive current due to an internal fault.
R67 will withstand quite a lot of abuse before it fails.

Thx for your insight, a faulty valve makes sense. I know very little about its history, previous owner said it was at a reputable repair shop that I’m familiar with twice for issues with intermittent power loss and received a full set of Groove tubes. It’s in really good nick tip to toe.

 

[bfglp]

So I replaced R67 and was able to properly bias the el34’s I tested the 1K resistor that I removed and it read as 22.66 M ohms - TOASTED
Cleaned all the switches and circuit board but stayed clear of the board with the processors. Much quieter now but to late for a good test run

 

[bfglp]

Powered amp up let it warm up and a big whoosh of white noise when I turned on the standby switch
Clean channel has low volume adding gain the volume swells switching to crunch sounds better but no tone stack or reverb
Channel 2 lead one lead two and ultra switches work but no tone stack or reverb
Turned off standby and another whoosh of fading white noise
I’m thinking the white noise is from faulty power tubes? Have a new pair I’ll throw in and re check the bias
No idea what’s up with the tone stack and reverb