A couple of things to check Rahul:
1. Plate idle current should be 120-150 ma in the SSB position.
2. One of the grid chokes is open from a tube arc or short.
3. If it has always been this way since built the coax cables going to the
input bandswitch may be reversed.
Input VSWR is a function of plate current & voltage so with one defective
tube it will be quite high and out of the networks tuning range.
Dont go ripping things out, that 100W should be more than enough at 1000W
out.
Also, unless it is a European built/kit amp from Heath UK, or supplied with
a 50 Hz transformer it will have to be run at reduced power to keep the
transformer from burning up.
Carl
KM1H
----- Original Message -----
From: "Rahul Sathe" <vu3raz@gmail.com>
To: <amps@contesting.com>
Sent: Tuesday, September 08, 2009 11:32 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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