There are 3 different Tune caps used in the SB-220 family.
The first was a Johnson 154-7 which will have a label on the rear; these
have all the plates staked in place.
Next came a cost reduction using the OEP cap which is put together with
spacers and nuts and bolts, the ceramic insulators are different. This will
have the Heath part # on the rear.
Both above fit the same mounting holes but the OEP required washers to raise
to the panel hole center.
The SB-221/HL-2200 used a wider spaced cap as mentioned and were also sold
as 220 replacements.
Since voodoo parasitics have nothing to do with switch failure the Tesla
effect in the tank now found the switch an easier path. This can be
eliminated by adding a 10-12 pf 1000V silver mica or a RF doorknob directly
across the 20-40M contacts. Since this cap is added to the Tune cap minimum
C it may be necessary to spread the 10M coil turns slightly.
Carl
KM1H
------ Original Message -----
From: "Martin Sole" <hs0zed@csloxinfo.com>
To: <ham_amplifiers@yahoogroups.com>; <Amps@contesting.com>
Sent: Monday, October 18, 2010 10:07 PM
Subject: [Amps] SB220 tune capacitor
> Perhaps a question for the Heathkit history buffs.
>
>
>
> Did the tune capacitor change during the life of the SB220 or perhaps with
> similar amplifiers? SB200 HL220 etc.
>
>
>
> I have received a replacement capacitor, well it's in UK awaiting onward
> shipment. From a picture of the actual part sent to me it appears to have
> two differences with the original part, these being that the ceramic
> insulators are mounted outboard of the aluminium end plates whereas on the
> original they are inboard and secondly that the number of fixed / moving
> vanes is 21/22 as opposed to 18/19 on the original part. I am awaiting
> confirmation of mounting hole spacing which might be the most significant
> issue, assuming the min C is not now too high.
>
>
>
> Any thoughts?
>
>
>
>
>
> Thanks
>
> Martin, HS0ZED
>
>
>
>
>
>
>
>
>
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