Greetings to all,
I usually do not comment on topics like this but could not resist
this time. I, also, have been repairing amps for about 40 years -- have
probably worked on 100 SB-220's. I think it is the best watt/dollar
available in an amplifier today. However, as it was originally designed, it
is just an accident looking for a place to happen.
I use nichrome wire (nichrome ribbon in larger amps) in the anode
suppressors, not because it is the best material, but because, as Richard
Measures said nearly thirty years ago, it is relatively easy to work with,
readily available, inexpensive, and does the job. In all my years in
working on amps, I have never had, even one, come back for service, of
parasitic related problems, after installing Measures parasitic suppressors.
I personally think that input network changes are as helpful, or more, than
the anode changes.
After parasitic suppression, I think the most important modification
is the bias mod. I do not know how many filament transformers I have
replaced in SB-220's over the years, but it is safe to say that not one of
them would have needed replacement if the bias mod had been done. If you
want to really make a nice amp out of your SB-220, you might want to
consider Richard's QSK mod. It is relatively cheap, not too difficult to
install, and really works.
Another great amp is the Kenwood TL-922. Of course, it is nothing
but a cleaned up SB-220, but, it is even more parasitic prone, due to
placement of components in the final compartment, than the SB-220. It,
also, needs the bias mod and a soft start mod. QSK makes this amp a
pleasure to operate.
I have known Richard Measures for nearly forty years. He is one of
the real thinkers in the Amateur Radio field. I do not agree with
everything he says, but I have never, not even once, found him to be wrong
wrong. No one else has either. Remember, they almost burned Galileo at the
stake for saying that the world is round.
73 de Lon, K5JV
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