[Milsurplus] Looking for info: ARC/38 250kHz PTO (Collins 147A-1)

[Ray Fantini]

Recall that there is a varacap diode in the PTO and they did some correction by biasing that. If I have a chance over the weekend can pull the TM for the radio and get more information. Not much different than a regular PTO in running at 150 Vdc and filament.
I have one SMO chassis that I gutted everything off of except the PTO and wired it so the assembly fits into a 618S and allowed you to turn the PTO by hand and QSY that way, much better than the old 144 crystal pack the radio came with.

Ray F

-----Original Message-----
From: milsurplus-bounces at mailman.qth.net [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of Ian Wilson
Sent: Friday, December 13, 2013 1:23 PM
To: Military Surplus net List
Subject: [Milsurplus] Looking for info: ARC/38 250kHz PTO (Collins 147A-1)

I have figured out the power connector (not difficult, since there are only 3 leads <g>). The submini tube filaments light OK.

However, the unit doesn't oscillate. There is some internal diode switching that seems to be related to the INPUT (a mini coax connector).

Any suggestions for what needs to connect to INPUT (or better, a schematic) would be helpful. The OUTPUT connector pin connects via a 470k resistor to one of the PTO coil terminals. Doesn't 470k seem high for an output connection?

I've looked at the Collins 618-S manual but the circuitry around the 250kHz BFO is not very similar to what I see in this PTO.

73, ian K3IMW
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