Richard Measures, AG6K, has done a lot of work on SB-220s and talks about
the input circuit at:
http://www.somis.org/SB220ci.html
FWIW, Richard has his detractors however I have applied his modifications to
several SB-220s and a Henry 2K with great success.
de Paul, W8AEF
ZF2JI/ZF2TA FO8DX/FO8PLA 8Q7AA XZ0A VU7RG TX5D
----- Original Message -----
From: "Rahul Sathe" <vu3raz@gmail.com>
To: <amps@contesting.com>
Sent: Tuesday, September 08, 2009 8:32 AM
Subject: [Amps] SB221 Low Power Help
> Hello Experts,
>
> My name is Rahul call VU3RAZ. This is my first post to the list. I am
> seeking help on fixing my old SB221.
>
> as such the amp works on all bands, no arc or parastatics, tuning and
> loading is smooth and easy.. I am not able to load the amp to full rated
> plate current even with a 100 W drive with my 756 Pro3. Input VSWR is
> high,
> I tried tuning the input tuned circuit but no luck on few bands (20, 15).
> With the 756 ATU the things improve but I can not get plate current beyond
> ~
> 400 mA. Even tried disconnecting HT from each tube to see if one if the
> 3-500 is dead... both work but even with single tube I am not able to load
> the amp fully. Am I looking at dead (weak) tubes ... can both of them show
> exact same behavior? Or I am missing something I am not sure if I need to
> re
> build the PSU (replace caps)
>
> Please help...
>
> 73
> DE VU3RAZ
>
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