>Subject: [AMPS] SB-220 IMPROVEMENTS
>Sent: 3/30/1997 9:01 AM
>Received: 3/30/1997 9:36 AM
>From: T. A. Russell, n4kg@juno.com
>To: amps@contesting.com
>
>The SB-220 is a near optimum design for it's intended power and size.
>
>Trying to obtain higher power seems to run one right into the limits of
>other components such as the power supply filter capacitors, variable
>capacitor breakdown, and bandswitch breakdown. Adding 160M operation has
>been done, but is not easy. The plate and filament
>chokes are a bit small for optimum low band operation.
The filament choke works well on 160m by adding C to C2 in the tuned
input to cancel the choke's X.
>Power output on 10 and 15 meters is down from other bands...any
>solutions floating around out there?
Sure, but would the guy on the other end notice a db? When 10m is open,
it's hard to tell 100w from 1000w.
>It has occurred to me, as an owner of several SB-220's that an
>interesting alternative would be to create an optimum designed
>high band amplifier (20/17/15/12/10) with 1200 watts output on all
>5 bands, and an optimum designed low band amplifier for 160/80/40/30/20
>meters, using the SB-220 as the basic chassis.
The problem with the stock chassis is that it is not quite deep enough to
put in the extra bandswitch wafer needed for 160m operation. This was
why I had to go with two vacuum relays for the "Adding 160m.." article in
the January 1989 QST.
>I've never gotten sufficiently motivated to do this but think the idea is
>worth developing.
I agree, Tom. This idea was in the back of my mind when I wrote "The
Nearly Perfect Amplifier". Heath's design has a lot going for it.
Heath's simple but ingenious 3-500Z cooling system has not been
surpassed. It would be nice to have a more capable core in the HV
transformer---but with a secondary winding cw tap---instead a primary
winding cw tap, for increased efficiency, like the TL-922. High speed
switching is hardly an option nowadays due the switching speed of modern
radios. Fully adjustable tuned inputs would be good. ........ For
another 120 1972-dollars in parts, Heath could have had a first rate
machine.
R. L. Measures,ag6k,805-386-3734
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