[MRCA] MRC-55/GRC-14 Radio Set-Up: Anyone have any history on this unit ?

Sat Jun 24 14:11:04 EDT 2017

I have working examples of both the GR-19 and GRC-14 (in an M38A1 as an
MRC-55), and can say for certain that there is no appreciable difference in
power output.  The GRC-14 will make a solid 100W carrier with full
modulation on AM, which is what the GRC-19 does.  The T-195 falls down a bit
at the upper end, to perhaps 90W, whereas the T-631 will make 100W out to
30MHz.  The scales are evened up when the T-195B is used, as the SS HVPS
allow for a bit more B+ under load.  I would estimate that the Brute for AC
supply does indeed add probably 100# to the power supply, not sure why
Federal didn't go with a B+ supply and a lower current 28VDC supply, Running
that crazy huge dynamotor on AC leaves me scratching my head.  The packing
density in all units of the GRC-19 is much higher, so cooling may have been
an issue in hot climates.

Clearly, the GRC-14 was designed with RATT in mind, but even with the
outboard converter and FSK modulator, the GRC-19 is a comparative
lightweight.  Given that the design kicked off a good five years after the
GRC-19, I would have thought it would have been refined a bit more, save for
the frequency synthesis in the transmitter, which was fairly novel at the
time.  I have had four GRC-14s go through my hands over the years, and all
were in pristine condition, which is indicative to me that they were not
widely used. Most radios used by the USMC tend to be "well used" by the time
they leave service, as witnessed by the TRC-75s and PRC-47s released beck in
the late eighties.

I have a hard time with the notion that the GRC-14 was intended a
replacement for the GRC-26, since the GRC-14 is tactical, both in its
packaging and in the component selection and construction.  It may, however,
worked out that way, since as a tactical piece, it was pretty useless, and
was only in service a few years before the GRC-106 appeared (BuShips TM
dated Dec 1958, I believe the earliest GRC-106 TM is dated1962 or 1963)
Interesting that ITT, the parent of Federal, also had their hand in the
GRC-106.

Scott V. Johnson W7SVJ

5111 E. Sharon Dr.

Scottsdale, AZ 85254-3636

H (602) 953-5779

C (480) 550-2358

 <mailto:scottjohnson1 at cox.net> scottjohnson1 at cox.net

 <mailto:scott.johnson at ieee.org> scott.johnson at ieee.org

From: mrca-bounces at mailman.qth.net [mailto:mrca-bounces at mailman.qth.net] On
Behalf Of WA5CAB--- via MRCA
Sent: Friday, June 23, 2017 10:40 PM
To: mrca at mailman.qth.net
Subject: Re: [MRCA] MRC-55/GRC-14 Radio Set-Up: Anyone have any history on
this unit ?

Much of the weight difference between AN/GRC-19 and AN.GRC-14 can be
accounted for by the fact that the former operated only off of 28 VDC
whereas the latter operates off of that plus 115 VAC.  Secondary reason is
that the T-631/GRC-14 has a rated output power of 400 watts AM compared to
only 100 watts for the T-195/GRC-19.  Tertiary reason is that AN/GRC-14 does
FSK whereas AN/GRC-19 doesn't.  For that, you have to have AN/VRC-29 or
AN/GRC-46.  When you really get down to the basic specs, the comparable
Signal Corps sets of the period are SCR-399-B or AN/GRC-26(*), not
AN/GRC-46.  A few of you may have had the pleasure of helping move a BC-610
or a T-368.  :-)  AN/MRC-55 (the mobile version of AN/GRC-14) included an
M38A1 whereas SCR-399 and AN/GRC-26 included one of several different types
of 2-1/2 ton trucks and a 1 ton trailer.

Based upon nomenclature and (which was normally assigned in chronological
order when development was approved) and manual dates (which were written
around the production prototype stage), original authorization of AN/GRC-14
occurred earlier than AN/GRC-19, say 1952 versus 1953.  But serious
development work on the AN/GRC-19 must have started immediately whereas
development work on AN/GRC-14 probably didn't start until 1956.  Remember
that component nomenclature isn't usually assigned until about the
production prototype stage.

So although I have little doubt that some of the impetus behind AN/GRC-14
and AN/MRC-55 came from Not-Invented-Here, it would appear to have been
aimed at the GRC-26, not the GRC-19.

Robert Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480

In a message dated 06/23/2017 19:19:34 PM Central Daylight Time,
<mailto:scottjohnson1 at cox.net> scottjohnson1 at cox.net writes: 

I think they are about a half generation newer than the GRC-19, which was in
development in the 1951 timeframe.  Given that it has transistors (a few),
It seems to be a rather poor response to the GRC-19.  It will make a few
more watts, and has dual receivers, but it weighs more than two complete
GRC-19s.  It is clear the GRC-19 was a winner, given its length of service,
and the fact that it eventually got solid state power supplies, servos, and
blower inverters to extend its useful life.

Scott V. Johnson W7SVJ

5111 E. Sharon Dr.

Scottsdale, AZ 85254-3636

H (602) 953-5779

C (480) 550-2358

 <mailto:scottjohnson1 at cox.net> scottjohnson1 at cox.net

 <mailto:scott.johnson at ieee.org> scott.johnson at ieee.org

From:  <mailto:mrca-bounces at mailman.qth.net> mrca-bounces at mailman.qth.net [
<mailto:mrca-bounces at mailman.qth.net> mailto:mrca-bounces at mailman.qth.net]
On Behalf Of DSP3
Sent: Friday, June 23, 2017 4:14 PM
To:  <mailto:mrca at mailman.qth.net> mrca at mailman.qth.net
Subject: Re: [MRCA] MRC-55/GRC-14 Radio Set-Up: Anyone have any history on
this unit ?

I don't have an official history but the GRC-14 was the Marine Corps answer
to the Signal Corps GRC-19, both RATT rigs.  The receiver with the GRC-14
had the RTTY converter built in and supplied the loop current to the
terminal unit.  What looks like an S-meter is the tuning indicator for RTTY
signals.  The receiver is "fair" and pretty broad.  The whole mess is much
heavier than the GRC-19, I think and a bit more complicated.  I've had some
of the equipment, to include a couple of receivers.  They are all gone, now.
They are post Korea and appear to be about the same vintage as the GRC-19.
I never did see any real quantity of GRC-14 gear on the market or for sale
by DMRO or GSA, etc., just a few receivers.

Jeep - K3HVG

On 6/23/2017 1:20 PM, Doug Hensley wrote:

Anyone have any history on the MRC-55/GRC-14 heavy duty but mobile RATT
setup?  I have seen one standard military catalog picture showing the whole
thing rigged &fitted onto a Jeep vehicle.  Also have heard they were
installed in shelters.  But I know very little about quantity made, when
made, whether they are Korean Era only or were also used in Vite-Nahm ?  If
you know alot about these or have any stories, I for one would enjoy reading
about them.

Thank you,

Doug W5JV

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