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

[Ian Wilson]

Thanks, Ray. Normally it's easy to trace the circuitry but in this case the
two submini tubes are plumbed into a separate subunit that doesn't
dismantle (well, I can't see how to without breaking the tubes). I have
checked the continuity on the coil assembly, seems OK.

73, ian K3IMW



On Fri, Dec 13, 2013 at 10:42 AM, Ray Fantini <RAFANTINI at salisbury.edu>wrote:

> 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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