Date: Thu, 16 Jul 2015 14:38:15 -0600
From: Steve London <n2icarrl@gmail.com>
To: amps@contesting.com
Subject: [Amps] SB-220 6 meter conversion parasites
Finished the SB-220 6 meter conversion, but it seems to have major
parasitic oscillations.
A little background - I basically followed the 2008 QST article, except
I have the original relay in it. I don't have a source of nichrome
ribbon, so I made parasitic suppressors recommended by another avid VHF
guy - a copper strap U, and a 300 ohm resistor straddling the U. No
difference with or without those parasitic suppressors. The tuning
capacitor is bigger than the one in the article - Surplus Sales is sold
out of the smaller one. However, the tank does resonate on 6 meters.
Just to be sure, I'll describe the symptoms: engage the T/R relay with
no input signal. Grid current, plate current and RF output ! I can
change the level of these from 0 to potential disaster by adjusting the
tuning capacitor. The RF chokes in the grid circuit have not (yet) fried.
Sources for small quantities of nichrome ribbon ?
Other suggestions ?
73,
Steve, N2IC
## Get rid of the grid chokes. Get rid of the grid caps. Bond the 6 x grid
pins
to the chassis with wide copper strap, 6 x straps in all.
Jim VE7RF
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