Tony, From various reports, use of the dynamotor may well be better than a.c.
supplies in that the dynamotor MAY provide better regulation than external
supplies. If your a.c. supply is stiff and capable of not sagging under voice
peaks, etc. it will be just fine. Personally, I use one with a pair of 6336B
regulators. That really helps the residual FMing of the signal. Also, try
the "San Luis Obispo" fine tuning procedure for the frequency you intend to
use the most. That will also quiet things down a bit.

Regards Jeep/K3HVG

OK Jeep, thanks for your advice.

I would not like to build a stabilized power supply, as that would be quite a
huge machine. Anyway I shall give a look to the diagram and see whether there
would be any simple way to feed just the oscillator tube with a separate
stabilized HV.

With regard to voice peaks, using big output capacitor should help.

I am more worried about CW because, even with a big output capacitor, voltage
will tend to decrease along the duration of a dash or a dot, and this may cause
chirp.

Going back to my original question, the first test I shall do is to feed the
filaments with a transformer, while keeping the dynamotor for the HV. I want to
be sure that powering filaments on AC (instead of DC) does not cause an
unacceptable hum on the audio.

By the way, I have been looking for a spare VT-25 (10Y) tube, but I could not
find one for less than $70. Apparently that tube is one of those that had the
disgrace to fall into the esoteric hi-fi aficionados circuit, who are prepared
to pay almost any price for the promise of a "warmer" sound.

73

Tony I0JX