Mainline trouble shooting help... [solved]

[bernieclub]

Just finishing my build and having a few issues.    The two LEDs on the B side of both C4S boards fail to light.    Voltage checks are good except IB on both boards is 218V, supposed to be 275V.  (This is assuming that the instruction to measure "IA on the B side C4S board" is a typo and should say "IB..)  Also, the bias pots seem to have no effect, and the voltage on the test points hovers around 216V, no where near 145V.    Any ideas appreciated.
TIA
Bernie

 

[Paul Birkeland]

Your 218V on IA isn't likely the problem.

Your 6C45's are drawing 0 current.  Are they glowing?  Can you check the black jumpers on the C4S PC boards? 

Somewhere long the way, there is an open connection... Photos may help in these cases.

 

[bernieclub]

6C45's are glowing....I checked all jumpers, solder joints, orientation of transistors.  I also removed and cleaned all tube pins.  I have 218V on the output caps, 217V on Pin 7 of both tubes, and roughly 3.6V on pins 1 and 6.  Center pins measure 25Kohm through the attenuator.    Odd that both channels have the problem, yet I can't see a common point.  What are the best things to photo....I'll try to make them as clear as possible.
Thanks,
Bernie

 

[Paul Birkeland]

Can you check the R1 values on the C4S boards? 

Does twisting the trimmer affect the voltages at tube socket pins 1/6?  Did you bend over the pot leads on the bottom side of the PC board (red instruction on page 28)?

 

[bernieclub]

Humiliation....The instructions in red, so as not to be missed.....missed it.  Thanks for your help!

 

[Paul Birkeland]

Yeah, that's an easy one to miss, even with the red writing.

 

[bernieclub]

I think what got me was that there was no separate step with a check box...ya moved my cheese!      The amp sounds fantastic.  With only a few minutes on it, it's more polite, yet way more powerful than my Crack w/C4S and film output caps.  ;D