Wey hey! No more tremolo! Thanks for the heads up, Sean (and Rick's advice to blackface007, which I'd clearly missed...). Now I just need to get to the bottom of the measly ~62V at the end of the charge pump, cos, how can I put this? - it's a bit quiet!
which diodes are your using? some drop more than others, can you post your voltages for each drop measured off C2, C4, C6 ect...
charge pumps work by packing electrons in to the capacitors, by oscillating, the capacitor dumps across the diode, when packing more electrons across the diodes you get more voltage. With this design its a latter where you get a voltage with no load, once there is a load there are not enough electrons left to = said voltage and you see the voltage drop.
you could have a power supply that is not supplying enough current causing this supply to SAG.
Also this tube puts out 65mw. I have built amps using 12k5 which have the same power output and they are quite, this is not a jam with the band amp, but a tone amp. add an inefficient speaker and its worse. I use a Red Coat Wizard which is a 103db @ 1watt. In a similar amp I get 70db at one foot, according to my meter. 70db is quite, but loud enough to record or mic.
if you built off the board design, you could try some things, different wall wart, or use 13v supply. this is over the chip rating, and with Rick's voltage drop raises the heater voltage on the power tube. So is not a great option .
Schottky diodes will drop less voltage, giving you a slightly higher voltage at the end. A BAT41 is rated at 100 peek inverse voltage and 100ma. so it should work with no issues. the 1N5711 can be used also up to that last two diodes in the chain. Then your getting to close to its 70v max inverse voltage.