[Milsurplus] SC-901X answers

[Jim Whartenby]

NickI have a partial manual for the SC-901X which is pretty well beat and falling apart.  It is not a military manual by any means and there is no indication that it is a preliminary issue.  So my feeling is that this transceiver was meant for the civilian market.  The lack of a JAN designation is not really an issue since the Air Force used tons Collins KWT-6s Type 5 transceivers and never bothered to issue a JAN designation, AFAIK.  I did notice a pencil designation of 31R2-4-142-502 on the synthesizer module.  Not all that sure of the 142 part since it is somewhat blurred.

According to the 10 total pages of printing in this manual, the SC-901X was designed as a vehicular or man-pack transceiver so, if I understand this description correctly, it was designed with the Army in mind.  This helps explains the rubber seal on the mating surface of the front panel to the case which would not be needed unless the missile silo flooded!  
Looking at components, the few date codes easily seen show a range of late 1961 to mid 1963, no inspection stamps from government source inspectors were noted.  In doing this search I discovered a few transistors missing from some modules and broken leads on a top hat diode on the bottom of the main frame.  This radio has not been treated well.  I should also mention that when I got it, the case was also missing which explains the above damage and mud dauber nests!
The SC-901X is a distant cousin, at best, to the RT-618/UR.  It looks closer the first issue of the R-1051 with no finer frequency resolution then 1kc and of course, no meters.  The synthesizer six-pack looks similar but the RF module appears to be somewhat smaller in the SC-901X.  None of the other modules are the same in appearance.  There is a Noise Blanker module in the SC-901X and there is no power supply.  
The manual indicates that DC power is supplied by the RF power amplifier aka SC-901A.  This PA is powered by internal batteries or vehicular power but there is no mention of what this voltage level is.  The operators section mentions that the PA is a two stage vacuum tube circuit but other then this, there is no other info on this PA.
If the SC-901 is used alone, power was supplied by a SC-901S which gets it's power from the 115 vac line.  The SC-901S also provides interconnection of the SC-901X with either a 100 or 1000 watt power amplifier and an automatic antenna tuner.  There is no mention of the designations of these PAs or ATU.  Another unit mentioned of the system is a semiautomatic antenna tuner known as SC-905C.
So I hope this answers your questions and fills in some of the missing data on this receiver-exciter.Jim


      From: Nick England <navy.radio at gmail.com>
 To: Francesco Ledda <frledda at att.net> 
Cc: milsurplus at mailman.qth.net
 Sent: Wednesday, March 28, 2018 6:52 AM
 Subject: Re: [Milsurplus] SC-901X questions
   
Hue has the SC transceiver so the military “equivalent” is the RT-618/UR info found in the URC-35 manual. 
Speaking of which, if this thing was designed for the USAF, why the goofy commercial model number and not an AN/xxx compliant designation????
Has anyone got a dated component or inspection stamp to help figure out the chicken-egg history? I bet there is a good story here but I don’t know what it is. 
Yes sometimes the Navy will pay R&D costs on a project that has spinoffs or versions for other services. USAF used a number of Navy-developed equipments but I haven’t come across USAF to USN transfers. Army-Navy sharing was not common (R-390A being a notable exception). And of course USMC used lots of Army gear. 
I sure wish someone had written a history of all this procurement. 
Nick, puzzled as usual.    

|  | Virus-free. www.avast.com  |

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/milsurplus/attachments/20180328/e4527f16/attachment-0001.html>