[Amps] SB-220 6 meter conversion parasites

[Jim Thomson]

Date: Thu, 16 Jul 2015 14:38:15 -0600
From: Steve London <n2icarrl at gmail.com>
To: amps at 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