[ARC5] "Curing Chirp in Command Transmitters"

[AKLDGUY .]

Let me explain it once more, then I'll give up.

The VFO tube (1626) has two heater pins, 2 and 7.
Pin 7 is connected direct to cathode (pin 8) and the reason is given in the
manual:

*"...so that variations of cathode-to-heater capacitance within the tube*
*will not affect the frequency of operation."*

Pins 7 and 8 are connected to a tap on the VFO coil (it's a type of Hartley
oscillator).
Now, obviously the cathode and heater currents flow through part of the VFO
coil,
from the tap to ground.

Since DC *was* used for the heaters, the only voltage that could be induced
by the
heater current into the secondary would be that due to a noisy 28V line.

I believe that to counter the effect of the 28V line going noisy, the
designers incorporated
another winding, winding B, through which the other heater pin, (pin 2), is
fed.

Now if I'm correct, any noise voltage induced in the VFO coil secondary due
to noise in
the tapped winding will be cancelled by the noise in winding B.

The two heater wires flow through two different windings that oppose each
other, so the
noise cancels.

Now, using AC for the heaters is simply using a form of noise on a grand
scale, so there
should be no hum or any other noise in the secondary.

If I'm right about the phasing of the windings to minimize noise, there
should be no adverse
effects from using AC for the heaters as long as the original coil and tap
connections are
retained for heater pins 2 and 7.

If the heater pins are rewired some other way, the benefits of
noise reduction will be lost,
*even for DC heater operation*.

73 de Neil ZL1ANM