[Amps] SB-220 6 meter conversion parasites

Steve London n2icarrl at gmail.com
Thu Jul 16 16:38:15 EDT 2015


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


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