[AMPS] [Fwd: Heath sb200/201 amplifiers]

[Rich Measures]

.....
>Does any one know the reason why Heath would chose to float the grids
>above
>ground on the 500z tubes. they are bypassed for rf thru a couple of chokes
>and capacitors, it seems to me it would make more sence to ground them
>directley to the chassis, for better isolation and stability. 
I have tried direct-grounding the grids and grounding the grids through 
3, 200pF capacitors.  The grid's self resonant frequency is not 
significantly different either way.  Amplifiers that use 
directly-grounded grids seem to oscillate occasionally at VHF, as do 
amplifiers that use the C-bypassed grid approach.  If you want to improve 
VHF stability, you might try decreasing the VHF-Rp of the parasitic 
suppressors.  
cheers, Dick
Rich---

R. L. Measures, 805-386-3734, AG6K   


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