[Prev][Next][Index][Thread]
Re: 4,000 PF caps
Subject:
Re: 4,000 PF caps
Date:
Mon, 24 Mar 1997 00:12:50 -0500 (EST)
From:
richard hull <rhull-at-richmond.infi-dot-net>
To:
Tesla List <tesla-at-pupman-dot-com>
At 09:59 AM 3/22/97 -0600, you wrote:
>Subject:
> Re: 4,000 PF caps
> Date:
> Fri, 21 Mar 1997 18:03:14 -0800 (PST)
> From:
> "Edward V. Phillips" <ed-at-alumni.caltech.edu>
> To:
> tesla-at-pupman-dot-com
>
>
>Re: "those brown 4000 PF caps"
> Have used a lot of ones which sound the same. The actual
>capacitance is nearer 3100 pf, and they are quite temperature
>sensitive, with lower capacitance as they warm up (either from
>room temperature or due to self-heating when used in TC service).
>However, they are still compact and useful. Running a small
>coil from a 12 kV, 60 ma transformer with three of them,
>resonant frequency about 280 kc. Get 24" plus sparks which
>satisfies me for the moment.
>Ed Phillips
>
>Addendum to Ed's comments:
I have posted this advice and observation before. In Tesla service,
these
units will slowly and permenantly LOSE capacitance!!!! The action of
the
coil and the rapid discharging will blow the silver plate layer off of
the
Barium Titanate and thus the plate area decrease will cause the caps to
nose
dive in value. I had two 3600pf units in a coil for a year and was
tuned at
the 7th turn of a 10 turn primary. At the end of that time I was tapped
all
the way out and the sparks were dyin'. I remove the caps and each was
down
to 1300pf! I opened them up by machining off the exposy case and found
the
terminal not in concat with the plate material at all and much of the
material was burned away. If you use 'em keep a drawer full on hand!
Never again!
Richard Hull, TCBOR