[Milsurplus] Fair radio

[Scott Johnson]

OK, corrections

Mike Morrow wrote:
> Scott wrote:
>
>   
>> The 618S-4 = RT-311
>>     
>
> Er...that's perpetuating the error that the Collins 618S-1 and the USN RT-311/ARC-38 are the same.  They are not.   I have both the 618S-1 (military contract) and the RT-311.  Externally they look almost identical.  Internally most of the modules are the same.  But the 618S-1 is crystal controlled.  The RT-311 has the stabilized master oscillator instead of the crystal bank assembly as the principal difference.  But because of this, the 618S and the RT-311 and related support components are in no way equivalent or interchangable with each other.
>
>   
>> It seems that most USAF installations used the 180-L3 couple, whereas the
>> USN installations used the CU-351, which has a MS power connector, rather
>> that the legacy K connector that dates back to the 18S installations. 
>>     
>
> This makes sense, because the USN's AN/ARC-38 is NOT part of the commercial 618S series.  It has its own CU-351/AR coupler (using the same type of connector as is used through the AN/ARC-38 system), while the commercial 618S uses the commercial 180L coupler.  It would be really unexpected to find the 180L used with the RT-311, or the CU-351 used with the 618S.  In addition, the RT-311 was developed after the 618S. 


> My guess is the reason that the 180L-3 was still used with the 618T-1 retrofit is because the USAF saw little need to upgrade to the 490T coupler.  Most USAF installations (C-130A, B) originally had two 618S-1MCs, and two 180L-3 couplers.  From the early seventies, the B were modded with two 618T-1s, retaining the 180L-3s.  Some A models were only given one 618T-1, retaining the 618S-1MC in the #2 position.  We started replacing the 180L-3s with 490T-9s in the early eighties on B models, and I believe most E models were built with 618T-3's and 490T-1's from the beginning.  I have never seen or heard of a control head for the 618S that has direct readout of frequency, so I believe this must be for a different set, perhaps an ARC-58. I do wonder wheter all SSB mods were made from AM radios, or were there "new" RT-594s manufactured?  Probably not, since it was an RCA mod, and by the time the mod existed, so did the 618-T.
>   
> There's also a military version of the 180L-2 coupler, the CU-991/AR.  This was used with many AN/ARC-94 (618T-2) and AN/ARC-102 (618T-3) installations on into the 1970s, even though it had a 25 mc upper frequency limit.   I have one for the AN/ARC-102 that I'm trying to assemble.
>
> 73,
> Mike / KK5F
>   
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