[MRCA] [Milsurplus] [ART-13_Transmitters] Working on my ART-13's

[Ray Fantini]

You sir are the king of the Motor Generator, the world of the carbon brush, armature and re- pack able bearing. Perhaps because I was scared at a young age back in the seventies of having to learn what I thought was at the time completely useless information on the maintenance and operation of dynamotors to take the old second class radio telephone test I have always had a grudge against them and wet cells too. Looking at the responses that have been posted it appears that the cult of all original or not at all is in no danger. I am so inspired that I may revisit a abandon project to activate a 115 volt 400 cycle three phase rotary inverter that I have its just that initial testing once I was able to develop enough current surge to get the thing to fire up and run up to speed it sounded like it was going to take off and fly around the room.

________________________________________
From: milsurplus-bounces at mailman.qth.net [milsurplus-bounces at mailman.qth.net] On Behalf Of Meir WF2U [wf2u at ws19ops.com]
Sent: Wednesday, February 15, 2012 7:26 PM
To: art-13_transmitters at yahoogroups.com; 'MRCA'; milsurplus at mailman.qth.net
Subject: Re: [Milsurplus] [MRCA] [ART-13_Transmitters] Working on my ART-13's

Thanks to all who gave their opinions and ideas.

First of all, I realize now that testing the ART-13 could be done easier and
safer with an AC supply. This eliminates the dynamotor as the second
potential source of problems in the system so it's easier to troubleshoot
one assembly at a time.
I skipped the AC power supply route from two reasons: I didn't think the
dynamotor will have a problem - I'm using my ATD, ARB, ARC-2, several
BC-348's and Wireless Set 19 with their original dynamotors. Although I have
the original TCS AC supply, I also use the dynamotor supply with it
occasionally. None of the dynamotor supplies had any failures (should I add
so far?).
Incidentally, the oldest dynamotor is that of the ATD (1940)which I got NOS
3-4 years ago - incidentally the voltages are similar to those of the
ATC/ART-13 but lighter current, so the dyno is a somewhat smaller and
lighter than the DY-17.
The way I used to turn on a dynamotor for the first time is by removing the
HV brushes, I let it spin free just on the input voltage and monitor for
heat, and/or uneven running while watching the input current. I let it run
for about one hour. I have a surplus, non-current limited 24-28 V selectable
output at 50 A (or 12 VDC nominal at 100 A depending on the output
strapping).
Feeding a voltage equivalent to the output voltage to the dynamotor unit
without the brushes is a good idea and next time I'll definitely utilize my
adjustable HV lab supplies to do that.
The other reason for skipping testing the ART-13's with an AC supply is that
although I acquired a very nice homebrew supply together with the heavily
modified ART-13 I mentioned in my previous posting, I modified it to power
up my Canadian Marconi CM-11 transmitter (late WW2 ex- Royal Canadian Navy),
which requires 400 VDC for the low voltage (master oscillator,
multipliers/driver) and 1000-1200 VDC for the 813 output. This is a 100 W
output (on CW) transmitter, with screen modulation for AM. I removed the 15
A 24 VDC supply from it and replaced it with a 1 A 24 V supply - this
transmitter only needs 24 VDC for the relays, the filaments are supplied by
an internal filament transformer with 115 VAC 60Hz primary. The control
circuitry with the relays is different from that required by the ART-13, and
the negative sides of both high voltages are grounded. The metering is done
in the transmitter with internal sensing resistors.
So, I'll have to build an AC supply for the ART-13... There is enough
reference material on that and of course I'm aware of the external metering
resistor, it's placement in the circuit and its value.
For those who have the ART-13 and DY-17 schematics, the failure took out
L2702 and 2703 and the 3 section bathtub cap C2702 (rated 600 VDC) measures
short to the ground on all 3 sections. The 400 V and 750 V brush capacitors
are tubular, oil impregnated units, .12 uF each, rated 600 VDC and 1250 VDC
respectively which shorted (the 400 V one first) after it ran with the
brushes for a few minutes. I replaced them with mylar caps, which fit inside
the frame where the originals were.

73, Meir WF2U
Landrum, SC