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 1 
 on: Today at 03:19:38 AM 
Started by Opcom - Last post by Opcom
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://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.
To my knowledge three exist. The other two have been modified removing part of the antenna tuner.
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.
Note this is a plate modulated rig and will not run SSB. At all.

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.
Will include spare 3B28 Xenons and two FAA-rated solid state replacement sticks.
Will include furniture dolly it's sitting on..so easy to move.
I do not have the handset or mike.
I do not have the test cables for servicing but the connectors can to my understanding be ordered.
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.

 2 
 on: Today at 01:58:13 AM 
Started by ka1tdq - Last post by ka1tdq
I'm just posting the G rated stuff, like this one.  The other stuff stays in Vegas. 

I got new matching probes and the amplitudes are the same.  This shot was taken also at 13.8 vdc on the drains.  I'll do an atmospheric dummy load (75 meters at noon) test sometime soon at full power. 

Jon

 3 
 on: Yesterday at 11:26:27 PM 
Started by Steve - K4HX - Last post by Opcom
to go visit my Dad. Mom's there too.

 4 
 on: Yesterday at 10:55:22 PM 
Started by vk3alk - Last post by vk3alk
The LTC6992-1 arrived and so completed Nigels PWM...
All went well and no problems at all....
Just have to be mindful of the audio input levels thats all.....

Nigel recommends the PWM generator circuitry been away from the output board currents but will leave that up to future builders etc:....

Have attached 3 photos...one of the quickly assembled unit....the output from the LTC6992 and the output from the LPF with an audio tone....
Also ran an audio sweep with 100 volts to the board and all went fine....

Its probably only me but are not keen on using motor controllers as PWM generators...
So if anyone is interested will build one of my own and replace the existing one on Nigels Board and post the results......


Wayne

 5 
 on: Yesterday at 10:54:42 PM 
Started by ka1tdq - Last post by PA0NVD
The vegas pic has been viewed a lot more than the scope pic Huh Roll Eyes

 6 
 on: Yesterday at 09:18:47 PM 
Started by K6JEK - Last post by Detroit47
Nesting Falcon

 7 
 on: Yesterday at 08:34:52 PM 
Started by Steve - K4HX - Last post by Steve - K4HX
This topic has been moved to Wanted.

http://amfone.net/Amforum/index.php?topic=43942.0

 8 
 on: Yesterday at 08:34:11 PM 
Started by w7gs - Last post by w7gs
I have a very clean 51S1 receiver for sale. It come with the original manual and rack mount. It is installed in a KWM2 cabinet for desk use which is included. SN#8566 asking 1500.00 plus shipping pictures on request contact at w7gsw9hli@embarqmail.com

 9 
 on: Yesterday at 08:33:34 PM 
Started by ka1tdq - Last post by Steve - K4HX
I though what happened in Vegas stayed in Vegas?

 10 
 on: Yesterday at 08:27:18 PM 
Started by Steve - K4HX - Last post by Steve - K4HX
Remember.

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