[Heathkit] How about the SB-220?

[Paul Baldock]

At 09:57 AM 8/22/2009, Carl wrote:


>Do not ground the grid pins directly to the chassis. The chokes DC
>resistance provides some degeneration and aid stability. Direct grounding
>increases gain, gives a bit more output and has led to instability. Nobody
>can hear the ~100W difference so why bother?

I'm not sure this is true. I have rebuilt two SB221's and grounded 
the grids directly. This does give more gain and allows you to turn 
the driver rig down. Turning the driver down from 100W to 90W on a 
12V rig greatly improves its IMD and more than the negative feed back 
that the amp "may" have with the Heathkit design.

I have had no instability problems and the output is very clean. I'm 
not aware of any modern 2 X 3-500Z amps that use the Heathkit method, 
they all directly ground the grids.

- Paul