[ARC5] Sort of OT - Fuzzy VCs

[AKLDGUY .]

Must be 15 years since I worked on an acquaintance's Swan 350, so can't
remember whether it has a pi output circuit.

If it does, pay attention to the coupling capacitor from plate to pi output
tank. If the capacitor is shorted, you'll have RF peaks and troughs riding
on
top of B+ in the tank, a far higher peak RF voltage than designed.

There should be an RF choke across the pi output (antenna line) to short
circuit the DC that results from such a situation and draw attention to the
problem. Check that, if fitted, the RFC is not open circuit. You may have a
dangerous situation there, with B+ going out on the feedline, so take care.

If, with the PTT operated, you measure B+ or any DC on the antenna
socket, you'll know you have a problem.

Neil ZL1ANM


On Sun, Dec 3, 2017 at 2:30 PM, Jim Falls <radio-tuber at att.net> wrote:

> I have a Swan 350, and I have had fits with arcing on the tank VC from Day
> 1. It’s a 350pF Hammarlund-style straight line C unit and spacing is a tad
> wider than a BCB VC.
>
> The consensus on the Swan list was dust. It’d blow it out several times a
> week, filter the air going thru the Final cage, all to no avail.  Zapped
> and hissed like a feral cat after a day or two. Got disgusted. Put it away
> in the garage last year.
>
> Pulled it out yesterday. Under bright light, it appears to have metallic
> whiskers all over the place, especially on the stator plates. That thing
> was clean as a whistle when I put it away. Now it looks like I cleaned it
> with fine steel wool.
>
> I recall someone here or on the milsurp list posting a photo like that,
> but I don’t recall any cure.
>
> Is this “fixable”, or am I SOL?
>
> Jim K6FWT
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