At 11:39 AM 6/23/99 -0500, you wrote:
>
>Make sure you have an RF choke accross the output
>of the amp because is is just a matter of time until
>those "TV" type doorknobs are going to smoke. They
>are not RF rated for 1500 watts.
>
>(((73)))
>Phil, K5PC
Sorry Phil, you are completly off base here. I have never seen a cap with a
"power rating". Those caps are rated for 20 kv breakdown voltage. They have
very low leakage. Like most ceramic caps, the current handling capability
sux. If you were foolish enough to use one as a tune-C padder cap in the
output tank where the RF current was 10's of amps there would be a problem.
(I keep a fire extinguisher handy when doing these experiments, it saves
911 calls)
In anode DC block use, with 4 in parallel, the RF current in each of them
is on the order of 200 to 300 milliamps. Even a crummy ceramic cap can
handle that.
Those pictured caps were pulled from a dumpster TV's around 1963. Two of
them were used in a TZ-40 amp for a couple of years before they were put in
the pictured amp chassis. It's just a matter of time until any component
smokes, but I'd say that more than 30 years is a fair MTTF!
You are more than welcome to give the surplus bandits your money, but for
me, I'll use the free stuff whenever I can.
Have fun & 73,
Larry - W7IUV
w7iuv@arrl.net
http://www.axtek.com/w7iuv
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