[Amps] SB221 Low Power Help

[Paul Playford]

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 at gmail.com>
To: <amps at 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
>