Also, MMCs let you adjust up and down in size as needed, and if one of the
caps goes bad, it is a lot less expensive than the single doorknob cap...
On Sun, Jan 15, 2023 at 10:53 AM Fabio Bragonzi.it <mcggyver@xxxxxxxxxx>
wrote:
>
> 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):
>
> https://www.ebay.it/itm/193245707970
>
> https://www.ebay.it/itm/284028401115
>
> https://www.ebay.it/itm/275420278203
>
> 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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