A one in a bazillion chance, 2 years of searching.. asking members of Greenkeys, Armyradios, Radiomarine, MRCA, GB, MRC, R390, and indeed the Coast Guard at various maintenance and salvage and historical installations, the Dept. of the Navy, Library of Congress, many hams, Martians, and old Coasties.. Pestering anyone and everyone..
Thanks to W7TFO and WA6OPE I have an original "Preliminary Instruction Book" for the "RADIO TRANSMITTING SET AN/URT-12".
Printed in 1955, it is a good read. The whole schematic is pretty legible and I will have to scan this asap.
RF range 2-30MHz continuous using 10 crystal channels and/or an external VFO.
The AM circuits provide high level mofulation as 2*4-65x2*4-65.
The secondary of the mod iron also provides negative feedback loop for the audio and screen modulation of the IPA, and 807. PA screen is choke self-modulated.
Keying for low speed (old buzzard manual key) is done by clamps and relays, and high speed keying up to 100WPM is done by clamping the IPA only leaving the TX in the transmit mode. I do not know at what WPM the transition occurs but it is automatic and apparently transparent to the user, except that break-in may not work as well when it goes all-electronic in case any RF escapes the cabinet.
Above 70% modulation, compression is used so that a 10db increase in input level results in a 3db increase in modulation level. MOD is rated for 100%, so there might be a better way to express that. The unit also has a switchable in/out switch for the audio limiter.
RF Output impedance is adjustable from 5 to 1800 Ohms resistive and +/- 2000 Ohms reactive, inclusive. I think this means bedsprings can be used.
Hum and noise <1%.
Frequency response flat from 200-2500Hz +/-3dB ref 1KC.
The audio bandpass is accomplished by a frequency compensating network including active stages with separate adjustments for HF and LF audio . I believe this is called an equalizer today.
HV is 1500VDC via two 3B28's coming from a 3500VCT 0.25A HV transformer.
There are 14 steps to "starting" the transmitter.
There is a "Battle Short" switch to be used in case of damage by gunfire.
I'll post the schematic, I think this will be a fun one to look at. Also have to tell KF4TXQ-Sam, Dadeville, AL since he seems to have one, maybe two IIRC, of these rigs as well.
http://amfone.net/Amforum/index.php?topic=3720.msg27614#msg27614
