[Amps] Odd Problem with SB-201

[Carl]

That really doesnt work very well as now there is no way to apply operating 
or cutoff bias without more work than it is worth. Plus anything that 
increases gain potentially reduces stability since neutralization was 
marginal to start with on 10-15M.

By simply adding a .01 to .02 1000V disc cap across the existing 200pf grid 
capacitors and replacing the parasitic suppressor resistors with Ohmite OY 
series resistors (use the original coil or wind a new one) the results are 
the same. High stability along with more output than is safe for Chinese 
tube which are only rated at 125W dissipation and have poor emission life 
when abused.

I also suggest no more than 75W drive unless a 10-12 Ohm non inductive NFB 
resistor is used at the input.

At 600-650W out the amp will last a lot longer and the signal difference 
wont even be heard.

Carl
KM1H



----- Original Message ----- 
From: "Jim W7RY" <w7ry at centurytel.net>
To: "Mike Baker" <k7dd at cox.net>; <amps at contesting.com>
Sent: Saturday, October 06, 2012 11:48 AM
Subject: Re: [Amps] Odd Problem with SB-201


>
> The SB-200 is a great amplifier. BUT, the girds need to be directly 
> grounded. To do this, you need to completely re-wire the metering 
> circuits. I've done that when I add my QSK board. With the grids
> grounded, it's more stable, puts out more power with less drive.