1) Turned round the negative voltage sources so as not to confuse.
2) Is it better to drive the screens with high impedance by increasing R14, R15 or low impedance and use resistors to ground to reduce the screen voltage. What works better when the 6ej7's are not matched? R13, R16 would be a 100R pot for DC balance.
I choose the 6ej7 just because I have a load upstairs and I can match a few. I used them for 10.7MHz FM IF stripe before finding the gain was too high. I now use 6bw7's here. I have 6ba6, 6ac7, ef80, and a few others but don't think they are suitable - all seem lower voltage than the 6ej7 ratings some variable mu.
3) trying to find a spice model of the 6528. They don't seem easy to obtain in the UK. Does look easier to drive. Probably not as visually attractive. Given I have a collection of 6550 amps would be nice to have something look a bit different.
Tried a 12BY7 in simulation. This works too but needs the screen lowering with resistors to ground. Its important to keep R19. Without it the screen goes to near 0V and this causes a much higher saturation voltage on the plate which limits the drive range.
2) Is it better to drive the screens with high impedance by increasing R14, R15 or low impedance and use resistors to ground to reduce the screen voltage. What works better when the 6ej7's are not matched? R13, R16 would be a 100R pot for DC balance.
I choose the 6ej7 just because I have a load upstairs and I can match a few. I used them for 10.7MHz FM IF stripe before finding the gain was too high. I now use 6bw7's here. I have 6ba6, 6ac7, ef80, and a few others but don't think they are suitable - all seem lower voltage than the 6ej7 ratings some variable mu.
3) trying to find a spice model of the 6528. They don't seem easy to obtain in the UK. Does look easier to drive. Probably not as visually attractive. Given I have a collection of 6550 amps would be nice to have something look a bit different.
Tried a 12BY7 in simulation. This works too but needs the screen lowering with resistors to ground. Its important to keep R19. Without it the screen goes to near 0V and this causes a much higher saturation voltage on the plate which limits the drive range.