circuit board layout from a schematic

[Crackle]

I didnt change any components we just swapped the valves to see what effect it had. I cant say what sort of long term effect it would have on the valve, but they are only working at low power anyway. At audio frequencies the ECC83 would give more gain in the preamp stages, but I seemed to think it had only a minor boost in gain in the phase splitter stage, I think, it is quite a while ago now when we were experimenting with Sams JCM800 Marshall head.
But I seem to remember the best improvement in sound (for home use according to Sam) was when the amp was being driven hard at over 70 watts, into an 8 ohm power resistor on a massive heat sink, and with a 68 ohm and 6.8 ohm voltage divider driving the speaker.
Mike