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Hi Jordan and all!
I personally had some excellent results either with MMC capacitors
(using MKP or KP type caps) or big ceramic capacitors (flat disk or
hollow tube type) but i struggled to get proper results with doorknob
capacitors (molded in plastic) or mica capacitors (molded inside a
bakelite or ceramic case).
For a better explanation, the doorknob i tried wasn't working as
expected (quick overheating, resulting in a shift of resonant frequency)
and all of the mica capacitors i tried worked just fine for a short
period of time.... until they fail.
I strongly suggest an old Soviet ceramic capacitor because are very
strong and also quite cheap (something like these):
Please note that these capacitors almost always have the maximum
reactive power rating printed on the case, but most sellers never give
you this information
(FYI, the cyrillic writings "kBAp" means "KVAr")
The rated voltage of the grid leak capacitor shall be equal or greater
than the max voltage ratings of the plate;
almost any kind of capacitor (except electrolytic) is adequate for the
purpose.
Ciao!
Fabio.
Il 10/01/2023 18:11, jordan simmons ha scritto:
Hey All,
I have been looking for a while to find some suitable doorknob caps for a
GU 81M VTTC. Running ~350kHz probably around 1kW, 1.5kW if I really push
it. C-tank between 1.8-2.5nF.
Is it worth it to get doorknob caps? Or is it more wise to roll with an MMC
tank?
And what about the max voltage ratings on the grid leak capacitor? Is it
critical for it to be plate supply rated, or derated to the tube's
datasheet?
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