SB-220 stabilization

AB5YG at AB5YG at
Mon Apr 8 06:03:54 EDT 1996

Th Parasitic Suppressor Kit for the SB-220 put out by Harbach Electronics
(407-723-7145),  replaces the 1mh grid chokes with  27ohm 1/2w carbon film
resistors and adds 820pf ceramic bypass caps (in parallel with original mica
caps)  to each grid terminal. The single capacitor from the RF input to one
side of the filament is removed and replaced by two .01uf ceramic capacitors
and in series with them are 10ohm 2w metal oxide film resistors - the
resistors connect to each side of the #12ga filament wires for a "balanced
feed".  The kit also includes plate parasitic coils/resistors.

Any comments on this approach??

73 - Bill,  AB5YG (ex K2MHJ)

>From Marijan Miletic <s56a at>  Mon Apr  8 15:06:14 1996
From: Marijan Miletic <s56a at> (Marijan Miletic)
Date: Mon, 08 Apr 96 10:06:14 EDT
Subject: SB-220 stabilization
Message-ID: <13055 at>

HI Bill, it was nice to read your nostalgia contribution to QRO debate. 
I strongly support your low voltage approach.  I did touch HV on my first QRO
with 4-400 in 60's and I keep my feet under the chair ever since
(unconfortable).  Regarding Measures mods, I prefer to make ground resistance
as low as possible and piece of thick wire does a trick for my 3-500ZG grids.
Cathode resistor surely improves stability at the expense of drive increase BUT
cathode impedanse changes greatly with driving voltage and I'd let tuned input
circuit to provide free-wheeling compensation and smooth the scene for solid-
state transceiver which enjoys pure 50 Ohms resistance after dealing with all
his nonlinearities including lowpass filters.  
I don't think good, old tubes self-oscilate as wildly as some authors wish us
to think in carefully engineered designs!
73 de Mario, S56A, N1YU.

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