Hello Guillermo:
I have used the old WWII mica capacitors for many projects and they have
all worked fine and never failed. I have never experienced the shorting
problems that Rich mentioned with the mica caps.
Here in the Un.ited States, parts are readily accessible. But that is not
the case in some other countries where parts may be difficult to get and
tariffs high. So, use what you have.
There were paper capacitors made during WWII that looked like mica
capacitors. These are very poor and have a high failure rate. However,
the large mica capacitors are excellent. As a matter of fact, the only
mica capacitor failures I have had are modern ones.
The voltage rating is dc volts. They may be paralleled to obtain the
desired capacitance. Many of these caps have a current rating at a certain
frequency. They may be safely used at a higher frequency, although their
design adds a lot of inductance which may limit the use to below 20 MHz.
I have built an amplifier using an 813 and surplus mica capacitors and gave
it away to a friend about 20 years ago. It is still running and may have
been the most reliable amplifier I had.
Good luck on your project.
73, Colin K7FM
> [Original Message]
> From: Guillermo <nagato@arnet.com.ar>
> To: Amplificadores Lineales <amps@contesting.com>
To: <amps@contesting.com>
> Date: 7/13/02 6:35:11 PM
> Subject: [Amps] Mica Capacitors
>
> Hello all, I plan to build a small linear, with one 813 tube. I'm
> collecting all sort of junk box components, and in this search I found
> an old TU-6B (or 5B? don't recall exactly, range upto 3 MHz. or so),
> tuning unit from WWII BC 375 MOPA transmitter.
> There are several mica capacitors inside, Cornell Dubilier Type
> 871-15LS, rated as follows; 2A @ 3000 Kcs, 3000 Volts, values are 90 pF
> and similar.
> Can I use them as (in case of need) paralleled caps with plate tuning?,
> can they be used at 160 Mtrs upto 20.?
> I don't know also if this voltage rating is WVDC or what.
>
> TIA
> Guillermo - LU8EYW.
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--- COLIN LAMB
--- k7fm@teleport.com
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