[Amps] SB-200 input.

Carl km1h at jeremy.mv.com
Thu Jul 24 21:20:43 EDT 2014

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.


----- Original Message ----- 
From: "Tom Osborne" <w7why at frontier.com>
To: <amps at 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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