On Tue, 2008-03-04 at 09:55 -0500, Jack Mandelman wrote:
> I made a similar mod to my 229B tuner. However, instead of using
> doorknob caps I replaced the originals with 6KV 470pF Y5P ceramics.
> These capacitors are physically larger than the originals, having a
> thicker dielectric for increased breakdown voltage and larger plate
> surface area for increased current carrying capacity. The drift problem
> was nearly completely, but not entirely, mitigated.
Y5P ceramics are still fairly drifty. The large physical size of the 6
KV caps is a benefit. It would be better to look for high voltage NPO
temperature coefficient disk ceramics. Perhaps 3 of the Sprague
561R10TCCT15 from Mouser in parallel for each 470 pf. Just 1KV but NPO
which also makes them large and most temperature stable.
> Complete
> disassembly of the tuner was unnecessary, since I was able to work in
> the tight space around the switch with small forceps.
>
> Now, I'm considering using the doorknob caps. Would appreciate any
> suggestions about disassembly of the tuner for easier installation of
> the doorknob caps.
>
> 73,
>
> Jack K1VT
>
73, Jerry, K0CQ
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