The SB-200 was designed years before untuned SS rigs became common and the
input networks were approximations for pi net tuned tube finals that didnt
mind a 2:1 VSWR, especially on 20 and up.
Tuned inputs provide the flywheel effect that makes the tubes easier to
drive and improves IMD 5-10dB.
There are a couple of web sites that change a few components for better
matches. One is just a bunch of hot air but I dont remember which but the
best one just increases the cap values a bit on 10 and 15.
The PA0 site is another one thats a bit off the wall.
Melted output wafer contacts will often destroy the inputs as they attempt
to act as 100W dummy loads. Stuck slugs are often a sign that it has cracked
from heat.
Carl
KM1H
----- Original Message -----
From: "Tom Osborne" <w7why@frontier.com>
To: <amps@contesting.com>
Sent: Thursday, July 24, 2014 8:17 PM
Subject: Re: [Amps] SB-200 input.
I know the SB-200 has tuned inputs. Two of the coils in this one are bad.
One of the caps is bad.
Can you give me a source where I can buy new coils for the inputs? I need
the ones for 15 and 10 meters.
Maybe some people shouldn't go off on a tangent on why people want to do
something until they know the circumstances.
On 7/24/2014 5:12 PM, Louis Parascondola wrote:
The SB-200 amp has individual tuned inputs for each band. Most bands can
be adjusted to near perfect input swr with slight adjustment of the
coils. Other bands can be made to have decent input swr with some work
if need be. I see no need whatsoever for a total remake of the input
circuit. I have no idea why so many people have to go off on such
tangents to try and modify what experienced engineers have designed.
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