pentode/triode switch

[pdf64]

In theory there might be for an amp with plates sitting at 500V, but in practice amps aren’t that efficient. You can easily write off 10-20% of the hypothetical peak-to-peak swing once you factor in where p-pmax is on the load line. Also, the screen to plate voltage is in the middle of that plate peak-to-peak voltage, so you halve it again...

If using a 100:1 scope probe, it's possible to see the massive kV spikes on power tube plates of an amp overdriven into an inductive load; my concern is arcing across the switch body between the terminals with the plate connections; the p-p spikes will be twice as big as those between a single plate and 0V, 4x as big as the plate to screen grid spikes you describe; and I've seen similar arcing occur between the plate terminals of old OTs that have tagstrip terminations (rather than flying leads). And also arcing between those plate connected switch terminals and the chassis metalwork / toggle etc.

[nevetslab]

If using a 100:1 scope probe, it's possible to see the massive kV spikes on power tube plates of an amp overdriven into an inductive load; my concern is arcing across the switch body between the terminals with the plate connections; the p-p spikes will be twice as big as those between a single plate and 0V, 4x as big as the plate to screen grid spikes you describe; and I've seen similar arcing occur between the plate terminals of old OTs that have tagstrip terminations (rather than flying leads). And also arcing between those plate connected switch terminals and the chassis metalwork / toggle etc.

And, assuming the 100:1 Scope Probe doesn't have a max of 500VDC rating as most cheap X100 probes do.....the good Tektronix X100 probes are good for 1500VDC (I still have P6009 probes, older style. I forget the newer hi voltage X100 probe model #).

[J M Fahey]

Earlier I posted a 100:1 scope attenuator specifically to scope tube plates where the 10M input resistor is made out of 10 x 1M resistors in series, inside a transparent PVC tube, filled with electrical grade RTV or Epoxy.

As long as a BIC ballpoint pen, you will not easily jump an arc across it.

Too sleepy now, later will search for the schematic and reupload.