I have the ART-13's 1950s descendant, the Collins 618S (ARC-38). This
has the same dynamotor behavior as the ART-13 - it runs continuously
when in CW mode. This is quite normal; when in AM mode the dynamotor
runs *only* in xmit mode. In the 618S B+ voltages for the xmit and
modulator
are generated by the dynamotor, B+ (and B-) for the rest of the system
is derived from the 115V 400 Hz supply. On my 618S I run the filaments
from a filtered 27.5V DC supply, the dynamotor from raw DC. This is
accomplished by minor rewiring of the 416W-1 power supply; it's
probably easier on an ART-13.

John VK3XAO

Yes, looking to the schematic diagram, I see a relay that interrupts high
voltage (+1250VDC) on the modulator tubes plate circuit when one runs CW. So
having the dynamotor continuously running is no problem, because the modulator
tubes would draw no current anyway.

When in AM instead, there would in principle be two alternatives:

- to have the dynamotor running continuosly. But they should then have a relay
which removes plate voltage from the modulator tubes during receive, so as to
avoid a useless power consumption from the battery. Such arrangement could cause
high voltage spikes in the relay and/or modulation transformer

- to instead have the dynamotor running only during xmit

Evidently they selected the second one.

As to the power supply, I preferred to build a power supply fully replacing the
dynamotor which is too noisy. Anyway feeding the dynamotor with raw (unfiltered)
DC seems to me a good idea if one wants to use the dynamotor without a battery.

73

Tony I0JX