[Amps] Air Variable Spacing Question

[Jim Garland]

Hi All,

I'm trying to decide which air variable plate tuning cap to use on my
forthcoming 160m monoband amplifier. The one I'd like to use has .080" plate
spacing, and I've tested it and it works up to 3200 VDC on my tester before
sparking across the gap. My question is whether that's enough of a safety
margin to use with 2500V plate voltage on three GU-74Bs? Not that it matters
particularly, but the plate impedance of the three tubes is about 740 ohms.
There'll be no DC voltage on the cap.

 

I also have several air variables with .075 in spacing, and one with .140"
spacing. The latter I've tested to 6kV, but want to save it for a different
project. In principle, I'd like to use one of the .075" caps for my
monobander, because of their convenient size, but I think that's cutting it
a bit close for 2500V. Whaddya think?

73,

Jim W8ZR