[Milsurplus] Questions about the Collins 18S and 618* equipment

[Mike Morrow]

Michael wrote:

>I have an 18S-4 but lack a schematic and information on the coils &
>output network to move it into the ham bands.  (None of the crystals
>that came with it were even close.)

The military version of the 18S-4 is the RT-380/AR, part of AN/ARC-59.
Somewhere I have a manual, but it may be a while before I can find it
since most of my manual collection is still packed up after a move I
made last year.

>Next, is the 618M-1 the same as a 618S-1/MC?

No, the 618M is a VHF-AM aviation-band unit, introduced in the 1960s, IIRC.
I'd bet some are still flying, just like the contemporary 618T HF set.

>What (if any) modules are interchangeable between the 618S-1 &
>RT-311/ARC-38, the 618S-1/MC & RT-594/ARC-38S and between the two
>groups?

No doubt some modules are common in these four units.  There are many
differences between the contemporary USAF 618S-1 and the USN RT-311/ARC-38,
but the major one is the use of 144 crystal channels in the 618S-1 versus
the use of a Stabilized Master Oscillator (SMO, O-215/ARC-38) to generate
frequency in the RT-311.  The USAF's AM crystal-controlled 618S-1 was
modified by RCA to the Collins/RCA 618S-1/MC, which provided USB and
incrementally tuned operating frequency.  The USN's already incrementally
tuned AM RT-311/ARC-38 was likewise modified by RCA to create the USB 
Collins/RCA RT-594/ARC-38A.  All four of these variants have significant
differences between them, but also many similarities.

I made an error a few weeks ago when I said that the Collins/RCA 618S-1/MC can
be tuned by a direct dial-up of the desired frequency on the CSC-1 control
panel.  I was incorrect.  Even though the CSC-1 has four frequency select
switches, the positions are alphabetic, not numerical.  One must use a
table to find the four characters that must be dialed in for the desired
frequency.  A pain, akin to the design of the RT-311 and RT-594, but somewhat
different too.

>The same question exists between the various versions of the 618T and
>the military versions thereof.  Also, was there any restrictions on
>the sets that wouldn’t allow them to operate in CW or data mode or was
>that simply a function of the control head?

The military version of the 618T-2 (400 Hz power) is the RT-695/ARC-94.
The military version of the 618T-3 (28 vdc power) is the RT-698/ARC-102.
There are also several other variants, such as the AN/ARC-105.

At least as far as the AN/ARC-94 and -102 go, they both used the
C-3940/ARC-94 control head that allowed full mode selection capability.

The 618T-series has my vote for the best airborne MF/HF set of all time.
I just wish I could find a PP-3702/ARC-102 mounting rack and inverter
for my set.

Mike / KK5F