[ARC5] Suppressor connection in ARC-5 receivers.

[Ian Wilson]

Hi Ken,

I would guess that connecting the suppressor to the cathode
provides a path of low inductance, removing one possible
configuration of the tube as an oscillator. I think that DC
considerations would be less important, since the influence
of DC suppressor voltage is small in most normal operating
regions.

In most pentodes there is some operating region where there
is negative gm between the suppressor and screen grids (look
at the Transitron to see this in action). So if the suppressor is
not at ground with respect to the cathode, this can set up the tube
as an oscillator if the conditions are right (external circuitry has
high enough Q, etc).

I seem to recall that one of the Hallicrafters uses the technique
of lifting an IF tube suppressor above *AC* ground to add
regeneration and provide a very low cost BFO function. The diode
just acts as a DC-controlled resistor (turning on the diode provides
a low impedance path to ground for the suppressor).

73, ian K3IMW