1200 pF capacitor

[N4LTA]

I am in need of a good quality capacitor  - 1200 pF - for use in a 500 watt, 500 Khz transmitter. Needs to be good for high current at 500kHz. I am thinking a good high quality film cap should work or should I go with a high frequency ribbon or Vitromon type capacitor?  Voltage needs to be about 500 volts minimum - 1000 volts would be better.

Pat
N4LTA

[K5UJ]

There's several ways to skin this cat.   How much current?  How much room do you have to mount the cap?  How much $$$ RU looking to spend?

I have had good luck combining fixed vacuum caps from eBay like this just for example:

http://www.ebay.com/itm/RUSSIAN-VACUUM-CAPACITOR-B-300-pF-15-kV-20-A-25-MHz-/230505987503

but if the current is no more than a few amps continuous @ 1KV you could parallel 3 or 4 RF doorknobs.  My methods could be considered overkill in some cases but I don't like surprises.  Big tx micas can get pricey.

[KM1H]

Sounds like a job for any of those old style TX micas, just do a leakage test first.

OTOH 1200pf at that voltage is pretty much a 3 section BC variable.

[K3YA]

A big old TRF broadcast receiver multi-gang air variable? 

[N4LTA]

In looking closer - It appears W1VD used a 1000 volt silver mica in his.

Pat
N4LTA

[KM1H]

Depending upon where its used it may survive. OTOH the SB-200 used a 500pf 2KV mica for the 80M load padder and they still smoke at times. The same cap is in the SB-220 and smokes regularly with heavy use. Its a current issue and the 2KV size has a larger surface area.

[John K5PRO]

At 500 KHz, the broadcast TX micas are good. They are pricey, but 1200 pf is not uncommon size. You could look
around for CDE 271 or 272, depending on your current.
http://www.cde.com/catalog/mica/#hv

These guys stock them:
http://www.surcom.com/


 

[K5UJ]

Here's what you see on the surcom webpage:

When you have determined the part number and are ready to order please contact us for pricing and availability.

Translation:

Are you a rich ham?  You won't be when you get done with us!