Hi,
Me, I personally prefer to use transmitting mica capacitors in the tank on
my VTTC's as they work great and they run much cooler temp. wise as long as
they are sized properly and they pretty much have a near unlimited life
span.
But doorknobs caps will work also, but I would make sure it has some "heft"
to it, physical size wise. This is needed, as doorknobs are a ceramic type
of cap, and they heat up more in tank service, the larger physical size
will help dissipate heat build up. The nature of the ceramic dielectric is
it heats up more in RF tank use versus some other dielectrics. Even better
would be true transmitting type ceramic caps. They are a bit different in
construction. An example of one type of several, is some tend to be a
flatish disc like, varying in sizes depending on power levels it can
handle. These are better able to dissipate heat in this construction style.
(Actually, I have seen these stacked up MMC style on some really big VTTC's
because of much higher plate voltages involved here.)
Basically you always want to avoid any excessive heat in any capacitor. It
will greatly shorten it's life to failure. Some types of caps, even though
it may match or even greatly exceed the voltage you are applying just are
an unsuitable type of dielectric and will not last in a tank.
I suppose a MMC could be possible, and I am assuming you are thinking of a
polypropylene caps. But I personally do not have any experience ever trying
this. I can only recall seeing a video or two online somewhere of a MMC of
this type on a VTTC in the past several years. I am not sure of the heating
possible here and life span of the caps here. There is of course well
documented recommendations for SGTC and DRSSTC use, but VTTC's are a bit of
a different "beast".
Maybe some more knowledgeable others can chime in here.
And for the grid leak cap, it does not need to be plate supply rated. I
prefer a minimum 1200V rating usually, but commonly use 2500V, as I am
running some pretty high plate voltages at times. Depends on how you are
set up. I guess roughly you could say a third of the plate voltage used.
Any extra here or even the tank itself is always beneficial.
Hope this helps some and others could chime in also.
Chris Reeland
Ladd Illinois USA
Sent from my Lenovo Tablet
On Tue, Jan 10, 2023, 1:36 PM jordan simmons <simmonsjordan999@xxxxxxxxx>
wrote:
> 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?
>
> Thanks for any input.
> _______________________________________________
> Tesla mailing list -- tcml@xxxxxxxxxxxxxxx
> To unsubscribe send an email to tcml-leave@xxxxxxxxxxxxxxx
>
_______________________________________________
Tesla mailing list -- tcml@xxxxxxxxxxxxxxx
To unsubscribe send an email to tcml-leave@xxxxxxxxxxxxxxx