[Milsurplus] Re: ARC-38/618S1

[Mike Morrow]

Ray wrote:

>The one that I picked out looks like a 38A except it dose
>not have the IF filters, and still had the AM modulator installed. Most
>of the radios had the 38A conversion with the new IF deck, no AM
>modulator and a big frequency deck with a PTO, would assume they were
>38A and good for SSB. 

That would have been the RT-594/ARC-38A, the RCA-modified for USB version of the RT-311/ARC-38.  This set does have an AMe (AM equivalent) mode.

>The one I bought was AM with a huge box with about
>a thousand crystals under a box shape cover. The tag says 618S-1

Yes, as I said in earlier postings the 618S-1 is in no way compatible with AN/ARC-38 components except on some modular levels.

>the head that I got with it is huge and has a lot of pre set
>channels and a mysterious set of thumb wheels in the center along with a
>flip up cover and little pins that look like they are for programming
>the channels. The head had been modified for a 38A with a stick on label
>for AME, CW, or SSB/FSK but it was the closest thing that I could find.
>They had lots of newer heads with direct frequency entry but assumed
>they were for the version with the PTO.

I'm betting that the direct-entry controls you saw were C-3141/TRC-75 boxes, which are NOT usable for any 618S or AN/ARC-38 installation.

You have the control head for the RT-594/ARC-38A.  There's a slot in the bottom for a frequency setting book that tells how to set the pins or dials to get a particular frequency.  Usually the book is missing, but it is vital because there's no easy obvious correlations of the settings to a particular frequency.  That's no loss in your case, though, because this control head has absolutely nothing to do with your 618S-1, and can serve no function for the it.

>Is that the huge old 618 that had the 813 PA tube? 

The Collins 18S series have a 813 PA, a couple of 811 modulators, and a big dynamotor all within the same size case as the 618S.  But it has only 20 crystal controlled channels.  The military version is the RT-380/AR, part of AN/ARC-59.  

I always regretted not getting a RT-380/AR when Fair Radio had them, but I do have a commercial 18S-4.  I was lucky enough to find a decent RT-311/ARC-38 in their new warehouse in 2002, long after they had stopped listing it in their catalog.

>And what's the difference between a 38A head and a TRC-75
>head? They both look the same. 

They are very very different!  The C-3141/TRC-75 is for a ground version of the Collins AN/ARC-58, a set used by the USAF for long range comms for SAC aircraft (and others) from the late 1950s to the 1970s.   I think it is identical to the AN/ARC-58 control box (C-1940/ARC-58 ??) except for the knob shapes and the "letter in a circle" control labels like you find on a lot of military ground gear.  The TRC-75 box is direct entry, and consists of a complex array of variable resistances.  It can not store preset frequencies.  The ARC-38A box requires setting code wheels or pins according to an enclosed book, and is an array of contacts and switches.  It can store 20 preset frequencies.

Is should be fairly easy to jury-rig a control box for the 618S, since it is mainly just a crystal selector.  That's something you could never do for the AN/ARC-38 or even less for and AN/ARC-58.

73,
Mike / KK5F