[Amps] A Meeting Ground

[Vic Rosenthal]

Bill Fuqua wrote:

> I have noticed some homebrew amplifiers I have purchased have the plate 
> tuning capacitor grounded to the front panel. This is bad. Since all the 
> fundamental and all the harmonic currents from the plate of the tube 
> flow thru this ground path and can produce a good deal of radiated TVI 
> off the front panel.
> 
> Also, it is bad when the plate capacitor return path to cathode on the 
> chassis is common to the input circuit. Even though the circuits are on 
> opposite side of the chassis there can be a good deal of coupling.

This is extremely important, since the return path is part of the parasitic 
tank, as Rich has pointed out.  In a 3-500z amp I insulated the plate tuning 
capacitor frame except at one point, where I used a wide copper strap that goes 
to a copper ring around the tube socket hole.  Grid terminals (and various 
bypass capacitors) were connected directly to this ring.  The less inductance in 
the parasitic tank circuit, the less inductance you need to use in the parasitic 
suppressor and the less power that will be wasted on 10 meters.

-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco