Any updated opinions of these amps? Duggeh what's your overall viewpoint?
post #61 of 89
2/14/07 at 10:17am
Originally Posted by Dad
At least I now have an idea what the 2 preset pots on each channel do. The
one connected to the heaters is to balance the 6.3V a.c. heater supply
centred about ground which should help cancel hum. However adjustment of
this MUST be done with care as it seems that if both pots are mis-adjusted
then they could go up in smoke!.
The other pot matches the drive to the 2 output valves and will presumably
need adjusting to minimise distortion. ( or perhaps to get just the right
musical amount of second harmonic?).
Ok, I'll have to check in more detail later but:
1. double triode tube is 6N1 rather than 6P1
2. The trim pots for grounding the heaters was 50R, but I have replaced these with 2 x 100R to ground on all tubes (although I might just go to DC anyway)
3. The headphones output is taken before the output transformer through a 4K7 resistor. eh, I think anyway!
4. I have added in another 2 caps 220uF/200V in parallel with each of C1 and C2
Could you ask your Dad are the 2 other pots for biasing the output tubes? They read in the order of 50K (from memory) and would he have any idea of what they should be at, or how to adjust them (eg what do I measure whiole adjusting the pot?)