[Collins] Collins ARC-2 Question - power supply

[Dr. Gerald N. Johnson]

On 10/3/2010 4:29 PM, Greg Mijal wrote:
> Hi:
>
> Got a couple of question on the Collins ARC 2 am
> transmitter-receiver.  I'm about to lite the candles to the one I
> recently acquired. It looks pretty good inside with only a few
> modifications.  It was modifed in the past to operate without the
> dynamotor.  The power supply I built up load checks ok for plate and
> B plus load but I'm not sure about the 24 vdc portion of my supply.
> I can get 5 amps out of it on the low end of the 22-28vdc spec and
> it's the source of my question.  Do I have enough current to lite the
> pilot lamps inside the tubes and spin the channel selector motor at a
> reasonable speed, all at the same time? I can live with slow motors
> but get a bit antsy about the possibilty of dragging my DC voltage
> transformer into oblivion.

Transformers don't usually fry instantly from overloads like twice rated 
current, they have considerable heat capacity so heat up slowly. 
Utilities figure intermittant loads at twice rating cut the life 
(figured at 40 years or so) in half. What happens is that the heat cooks 
the paper insulation and eventually it lets the wires vibrate and wear 
the insulation off and short turns. Then is when that shorted turn gets HOT.

The motor will probably chug away at 12 volts, but the tubes will loose 
emission and plate current as the cathodes cool. If you can wait a bit 
(20 seconds or so) before transmitting after making a channel change it 
will probably recover, the VFO may take longer to get back on exactly 
the same frequency.

I don't know the power requirements of the ARC 2. Had one in MARS once, 
don't think I have it now and none of my surplus manuals admit it 
existed though I did find a reference to a 73 magazine article but 
didn't turn up that 73 last I looked.

Here's another thing I noticed,  I'm
> reading 15 ohms from the power cable wires to the distribution points
> in the rig.  The set does have series chokes in the supply lines but
> read only 6 ohms. so where's the 10 ohms coming from.

There might be another choke, I presume that's in the low and high B+ 
lines, not the heater and motor circuits.

The last time I
> fired up a major piece of aircraft radio stuff, I was 14 years old
> and the old ART 13 caught fire out in the garage.  My parents nearly
> killed me over that! Thanks a bunch Greg WA7LYO Kinston NC
> ______________________________________________________________
>
73, Jerry, K0CQ, Technical adviser to the Collins Radio Association.