On Jul 26, 2005, at 6:13 PM, Greg S wrote:
> Well, the saga continues. Please see my initial
> description of the problem, and note the following
> found tonight:
>
> There is an arc occurring upon power-on somewhere on
> the Zener Diode ZD-1. The HV is coming up, and it
> appears the tubes begin to draw plate current in
> receive mode. (not good.) Hmmmmmm...... any more
> ideas?
Definitely not good. Ip in Rx means you likely have a grid-fil short,
probably in V2. The short is the result of an intermittent parasite at
c. 110MHz. In a stock SB-220, a grid-fil. shorted tube also shorts the
unfused +110v PS -- which will destroy T2 if left on for very long in
Standby, The fix is to determine which tube shorts when the fil is hot
and replace it. This can be determined by plugging in one tube at a
time and shutting it OFF quickly when Ip is drawn on Rx. Odds are that
the other tube is okay, so there is likely no need to purchase two
tubes. To avoid an instant replay with the new tube, reduce the VHF-Q
of both parasitic suppressors.
>
> Will keep the list informed as I go along. Time is
> short, so sorry I cannot get into it as often as I
> would like. Will let you all know what I do next.
>
> Thanks again-
> Greg, KC8HXO
>
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Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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