> If you take the grids to ground by a low ohmic resistor as a fuse with
> some high value cap in paralell, would that not add to parasite
> suppression? At the parasite frequency the cap, due to its inherent
> inductance, is no longer a cap and the grid sees only a resistor to
> ground?
The most common tendency for parasitics is caused when the grid
is no longer effectively grounded up in the tube. The system acts
like a TPTG oscillator.
If that is the case, and it usually is, anything that add impedance in
series with the grid to ground increases instability.
If you remove those silly capacitors you can peel about half the
turns off the suppressor and the amp will remain stable. If you try
that with the capacitors in line, the amp will oscillate.
A second problem occurs when the tube faults from anode to grid.
If the grid is floating, the HV can pass right through to the filament.
Grounding the grids and adding a HV fault resistor in the anode
makes the whole system better.
73, Tom W8JI
w8ji@contesting.com
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