[Milsurplus] BC-9 Loop Test: Scratching My Head.

[AKLDGUY .]

On Sat, Feb 11, 2017 at 5:55 PM, Hubert Miller <Kargo_cult at msn.com> wrote:

> The receiver when boosted to full 120 B+ IS the transmitter.

Well, the regenerative receiving tube at left of diagram becomes an
oscillator when keyed.

> The audio stages are irrelevant to the frequency shift.

I wouldn't rule anything out. If there was a biasing problem as I suggested,
maybe the two audio stages become unstable when the key is pressed
and couple enough tone into the plate circuit of the oscillator to phase
shift it.

> You simply cannot change the operating point of the RF tube from 70 volts
to 120 volts and not expect a frequency shift. I might not have expected it
to be quite so large,
but there it is.

12 KHz is a huge change and makes two BC-9's unable to work together.

> The grid bias on the two audio stages, is reckoned, i think, by ½ tube
filament voltage + the drop across the filament dropping resistor. With
filamentary type tubes,
the ‘cathode’ point is reckoned at midpoint of the filament.

> One thing i find odd is that the B- is returned to the A battery + . Was
this done, i wonder, to boost the B batteries by another 4 volts?

73 de Neil ZL1ANM
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