[ARC5] Collins 18S-4

Mon Dec 3 21:14:15 EST 2012

I have to admit that I'm a glutton for punishment - also, something in that
ugliness attracted me - and gave the seller an offer, which I think was a
very generous one, considering he has 5 units to get rid of. He accepted so
I'll have another box in my aviation radio collection. (In the worst case,
I'll have spare parts, dynamotor and some tubes for the ART-13! I'm
gathering all the info available, and also asked the seller whether he might
have a manual or copy thereof. I'm sure (but still researching) that the
shockmount is close to unobtanium...
Since I work on a number of nets, it shouldn't be a big problem to have the
inconvenience of crystal control on those. Receiver selectivity for my
purposes can be improved by an external DSP box (hidden of course) or an
active filter. This way I can use even my RT-91/ARC-2 on CW which of course
has a receiver section much wider than anything... 

Wish me good luck :-) !

73, Meir WF2U
Landrum, SC

-----Original Message-----
From: arc5-bounces at mailman.qth.net [mailto:arc5-bounces at mailman.qth.net] On
Behalf Of D. Platt
Sent: Monday, December 03, 2012 7:34 PM
Cc: ARC-5 List
Subject: Re: [ARC5] Collins 18S-4

On 12/2/2012 10:03 AM, David Stinson wrote:
> Forgive me if this has been discussed to death-
> if it was, I didn't see it.
>
> What experiance is there in our community with the Collins18S-4?
>
> http://www.ebay.com/itm/271112883477
>
>
Dave,
I know that myself and K4CHE have gotten them on the air.  As history, 
and with some anecdotal information, in hand, from those who (tried) to 
use them in USAF aircraft, let me provide the following.  The 18S-4 
consists of two basic units, the R/T unit which is sort of a re-packaged 
ART-13 (sans autotune) and a fairly broad, single-conversion receiver.  
Its all crystal controlled with 20 channels "dualed up" via having 
channels set up as close pairs. Each channel requires a set of plug in 
L/C modules and added/changed fixed capacitors in the output circuit.  A 
chest of modules originally came with each set.  It is these modules 
that are a real bugaboo, not that one cannot (and must) re-create them 
for each transmitter stage and receiver.    The rig runs, of course, an 
813 in the final.  The antenna tuner is the 180K-3 or 180-L3.  The 
receiver runs on 28v DC for plate and fils.  The Tx requires the 
standard ART-13 DY-17A dynamotor (sans base) for B+ and is internally 
mounted in the T/R unit.  The tuner requires DC voltages and the typical 
400 Hz for the servo system.  If anyone gets one of these units, books 
are available.  I have an original Collins factory manual (dated Aug 
1954) and an 18th AF FTD training outline book (dated June 1956).

The 18S-4 was one of the first units to try and comply with the RTCA 
requirements from the early 50's.  Arguably,  I suppose the first try 
was actually the Comco crystal mod for the ART-13.  Anyway, the USAF 
maintenance troops hated the 18S-4 owing to the laborious tuning and 
setup tasks required every time a frequency was added or changed.  The 
18S-4 did make it into civil aviation but did not last very long.

That said, the transmitter does not sound bad, at all.  The modulation 
iron is all ART-13.  The receiver is very broad and captures about 15 
kHz worth of bandwidth.  But... it is a nostalgic rig and a sign of the 
times........ Getting one set up for, say 3885, and leaving it there is 
not too bad.  One may pay more for the crystals then for the whole 
unit.........  The one pictured on Ebay DOES have a suite of L/C 
modules, so that's a real plus.  I wish the seller luck as to asking 
price, however.  I paid about $95 for mine and it was clean!  I don't 
know if Bill Perry has the rear panel connectors, but he may well.  A 
rack is a real find.  The seller says his units were overhauled in 
1978.  If that's correct, they must have come from a non-MIL source as 
they had been long replaced by the ARC-38 and onwards and thence to 
SSB.  Anyway, that's my take on the subject...........  I've tried to 
find a reference to when ICAO transitioned to HF-SSB, and what the grace 
period was, but can't locate the correct proceeding, here.... yet.

Jeep - K3HVG

add'l info:  http://www.aviation-radio.com/collins18S4.html
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