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URT-12 AM/CW transmitter




 
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Author Topic: URT-12 AM/CW transmitter  (Read 734 times)
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Patrick J. / KD5OEI
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« on: May 27, 2018, 03:19:38 AM »

I'm selling my URT-12. No time to play with it and could use the space.

URT-12 AM/CW transmitter covers 2-30MHz and has an output of 100W on A1, 75W on A3.
With instruction book, hi-rez scanned manual, schematic, and many exciting internal images at its web page:
http://www.bunkerofdoom.com/mil/urt12/index.html

These were made by Radiomarine Coroporation of America (div of RCA) for the US Coast Guard only and are exceedingly rare.
This one made in 1955, #40, is probably the last one to exist in complete, unmolested form, anywhere in the world.
This was acquired from a surplus warehouse where it sat concealed by construction material in an unlit room since they won it on a bid in the early 1970s.

Audio:
Two 4-65s in AB1 modulating two 4-65s in Class C PA via the generous-sized 90W modulation transformer.
Audio input: Carbon mike via handset or 600 Ohms -20 to 0dB (0dB=6mW) level via input transformer.
Audio processing: limiter in/out, with additional separate high and low frequency EQ, and NFB from modulator secondary.
Hum <1% of 100% modulated level.

CW:
Keying speed up to 100WPM. Electronic keying.

RF Output:
Has provision for external master oscillator so is electrically simple to adapt and run coax out the back to a VFO.
Spurious Output -50dB ref 100% modulated signal.
Z range 5-1800 Ohms +/-2000 Ohms reactive via internal antenna coupler
(see diagram on its web page for understanding)


Mechanical:
120VAC power input 60Hz.
Dimensions 38.74H x 21.5W x 26.4375D Perfect deskside rig.
Weight 324 Lbs.


Readiness Condition:
One issue I know of: apparent lack of grid bias to the PA and modulator. That rectifier is a selenium stack, suspected not checked. The symptom is too much plate current and trips plate overload.
With tubes out, the HV of 1500VDC comes on with no evidence of shorting etc.
One fuse holder in the row at the bottom is physically broken but is electrically working.
All controls work freely. Bone stock. No evidence of hackery, repairs, or other surprises.

Included Items:
Still has original ten CR-18/U common-size 2-7.5MHz crystals in the internal holder.
Will include all spare 4-65's we can find. There are a few around.
Will include spare 3B28 Xenons and two FAA-rated solid state replacement sticks.
Will include furniture dolly it's sitting on so it is easy to move.
I do not have the handset or mike.
I do not have the test cables for servicing but the very simple plug-in wiring harness between them can be removed from the cabinet so the unit can be serviced on the bench. The connectors can to my understanding be ordered so a new service cable could be made.
Except for the above, the images on its web page show what is included.

$450 OBO
Pick up only in Dallas TX or will deliver by cargo van for reasonable amount. Shipping possible via craters-n-freighters.
Please inspect by appointment and/or ask any questions. Terms Cash.



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Opcom
Patrick J. / KD5OEI
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« Reply #1 on: July 01, 2018, 10:01:17 PM »

Asking $425 OBO
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Radio Candelstein - Flagship Station of the NRK Radio Network.
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