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
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