I'm referring to the value steps. Order whatever tolerance you choose. The NPO/COG tells you that the value isn't temperature sensitive. Those values are OK.
Alright, ordered some last night (not exactly that set, but what I thought were more common). I'll post results when I get them
Finally got back to this. Replaced all Cx13 & Cx15 with 7pF caps and I'm able to bias all channels normally.
As far as I can tell it looks good all the way through - at the least, it looks the same as the other 400a4 that hasn't been modified. Both seem to pick up a fair amount of noise from my power supply
Interestingly, I just picked up another 400a4, same revision 'E' as this one, and it is exhibiting the same behavior. It still had the factory seals, never opened, but was drawing 3A at idle, so I popped it open and tried to reset the bias, but it does the same thing as the other did (won't gradually increase, but instead jumps up and won't come back down).