Hello all,
attached is the latest schematic, I've added an EM87 magic eye for show! It's a bit underrun and dim at 115V but works ok. Just have to work out how to power its filament, might have to add an extra winding on the mains Tx
I'd now like to raise the cathode and grid leak about 20V above ground, I was going to use a simple resistor / capacitor arrangement but this is now no good as tuning the tank circuit has a big effect on the standing current.
So my other options are:
- rectify the heaters (~50V rms) and use some of that as a bias voltage.
- zener diodes I've got plenty of these!
- A string of LEDs
- A Potential divider from the HT line suitably decoupled
- any other ideas?
I'm guessing a PD would have to pass a lot of current (and dissipate a lot of heat!)
If using zeners is it the peak current or the standing current that matters when chosing parts? They'd be bypassed by a big capacitor I've got plenty that'll stand the 2-15mA standing current but the peak current is pretty high!
Dom