[Heathkit] How about the SB-220?

[Carl]

----- Original Message ----- 
From: "Paul Baldock" <pbaldock at verizon.net>
To: <heathkit at mailman.qth.net>
Sent: Saturday, August 22, 2009 3:32 PM
Subject: Re: [Heathkit] How about the SB-220?


> 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.


Not all rigs show an IMD increase at reduced power., some actually increase. 
What sort of levels do you see with a spectrum analyzer?


>
> 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.


Again, what does your spectrum analyzer show?

Carl
KM1H



>
> - Paul
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