[ARC5] "Curing Chirp in Command Transmitters" T-53 Self Heating/ Manuals

[AKLDGUY .]

>  3) Does applying AC to T-53 induce 60 Hz modulation into the VFO's
output?

T-53 is not air wound. There is an adjustable ferrite slug at the top.
Nobody
knows what the characteristics of that slug are at 60 Hz. However, I doubt
that it could act as a medium for transferance of 60 Hz hum by way of mutual
induction between the two windings. Anyone?

There could be another problem though:
Based on a tap-to-ground resistance of 0.3 Ohm suggested (as a maximum)
elsewhere on this forum and a heater current of 0.25 Amp, the heater voltage
appearing at the tap would be 75 mV, but is probably much less due to the
resistance being lower.

That voltage would amplitude modulate the RF flowing through the same
tap-to-ground path, but the effect is probably negligible. The 1626 is
called
on to deliver something like 75 Volts (not millivolts) to the grids of the
1625's
and you can bet there are quite a few volts of RF at the tap.

If there were say, 7.5 Volts of RF at the tap, the hum voltage of 75
mV would
be 40 dB down on that and scarcely worth worrying about. I'm not suggesting
for one moment that those are actual figures, just trying to give a sense of
proportion.

As to frequency modulation by the heater current, that's a pretty complex
question in light of the measures taken with the twin windings to minimize
frequency drift. Anyone?

73 de Neil ZL1ANM