Mike:
Your experience is exactly what I have seen in the many SB 220s that I have
repaired and modified. I think to upgrade the blower is wise at these power
levels, and I think you need to change out the switching to avoid eventual
hot switching problems with EBC and vacuum relays. The amps are beautiful
as silent switchers operating QSK and much more pleasant while operating
VOX.
With these upgrades, I doubt I will see this level of operation "take its
toll". I've been operating since 1967 and only replaced leaky filter caps
in both units. I did once loose a string of diodes in the SB 200. Pretty
good service I would say. These are wonderful economic designs, perfect for
the amateur market and sensible upgrading.
73 and Happy DXing,
Mike
W2AJI
----- Original Message -----
From: "Mike K6BR" <noddie@comcast.net>
To: "'Mike Schatzberg'" <cherokeehillfarm@earthlink.net>; "'Roy Koeppe'"
<royanjoy@ncn.net>; "'Amps Reflector'" <amps@contesting.com>
Sent: Sunday, July 16, 2006 7:25 PM
Subject: RE: [Amps] transformers
My SB-221 also does the same, about 1500watts PEP with 80 watts drive. I
drive it with 60watts and the output is around 1300 watts or a little less
depending on the band, just my observations. I think it is one of the best
value amps you can buy used to be honest. I got mine as a partially built
kit, so actually it is brand new with the original tubes.
Mike
______________________________________________________________________
This discussion doesn't seem to match what the SB 200 and SB 220 have
produced since I built them.
My SB 200 produces 700 Watts PEP, with about 50 Watts PEP drive, and my SB
220 produces about 1.5 KW PEP (both amps on 20 meters) with about 80 Watts
PEP drive.
Yes, I have some modifications, such as RF negative feedback, restrapping of
the grids, grid equalizing resistors, etc., but no changes in the
transformers in either unit.
I built the SB 200 in 1967, and only have changed the finals once, when I
had an open filament. The second pair are still in there. The SB 220 now
runs Chinese triodes, probably made by Pride, and runs very cool, with an
upgraded blower.
I always thought of the two units as double one another. The 2 KW PEP input
(the SB 220), and the 1 KW PEP input (SB 220). Both produce clean signals,
and don't eat their finals. The output is cross checked by Bird and Nye
Viking PEP wattmeters. How could these amps produce such output, if they
weren't capable of such input?
They both tune smoothly up to these output levels, with nominal grid
current. I pulse tune both amps for peak power, and over couple slightly.
Just my observations.
73 and Happy DXing,
Mike
W2AJI
----- Original Message -----
From: "Roy Koeppe" <royanjoy@ncn.net>
To: "Amps Reflector" <amps@contesting.com>
Sent: Sunday, July 16, 2006 3:06 PM
Subject: Re: [Amps] transformers
>
> > "The SB220 transformer was designed for a kilowatt INPUT
> > DC,
> > which was the legal input when it was designed. This was
> > about 450 mA at about 2200 volts. It was...(etc)"
> >
> >
> > If this is so, why should anyone ever have bought an
> > SB-220, when the
> > SB-200 was also rated at that exact same power, with a
> > much lower price?
>
> Because the SB200 was not rated at a kilowatt input power,
> as measured on the meters, on SSB.
>
>
> But this seems wrong. When we tune up for maximum output with resulting
> readings of 450 mA at 2200 volts on both amps, equaling one KW input
> power key down on both, we can't drive the SB-220 any higher on its
> plate meter than we can on the SB-200's plate meter during SSB voice
> use. The higher peaks of current would result in instantaneously lower
> plate Z which would not be properly matched by the pi-net setting
> adjustment. The only way we could achieve increased PEP would be to not
> tune for the 450 mA previously stated. I assume this is what was really
> meant.
>
> 73, Roy K6XK
>
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
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