[Milsurplus] A Little on the ARC-2

[David Stinson]

The AN/ARC-2 doesn't get the attention it deserves;
it was a big techno-leap forward for a WWII rig.
The WWII vet is the RT-91/ARC-2; the RT-298/ARC-2A
is a post-war version with several circuit improvements.
I have both sets here and will probably be selling
the -2A model in the near future.
Other than the obvious addition of a fuse block on the front
and removing the meter switch, the main changes are
in the receiver front end and the variable IF.

While both receivers are "broad,"
the -2 is much broader than the -2A.
Both ARC-2 sets use small caps to couple between
tuned circuits in the IF strip.  In the earlier ARC-2,
these were 12 pFd, which loaded the circuits and
reduced Q, making them broad.  The ARC-2A design
changed these to 5 pFd, giving a marked improvement.
Changing them to 2-3 pFd with improve it more.
The -2 IF strip is tuned using the coil slugs.
The -2A has trimmer caps, making the tuning less "touchy."
In the -2, the forth IF uses degeneration to
try and "flatten" the gain response of the IF strip.
The -2A removes degeneration and does this with
extra tuned circuits.
There are also changes in the mixer designed to
"flatten" its freq response and provide better shielding,
but I don't think that's as important as the IF changes.

There are some differences in the transmitter output networks-
neither model will tune a 50-ohm antenna without external help-
but the transmitters are otherwise electrically identical.

A couple of tips, learned the hard way:
To get the cover off the rig, you first must remove the
round "air filter" vent covers.  If you have the "C" shaped
spanner wrench on the back, that's its purpose.
Yes- I did waste an hour trying to figure it out.
My only excuse: I didn't have the manual at the time.

The dynamotor mounting is a Rube Goldburg thing-
it will give you grey hairs.  The dyno comes out
easy enough, but it has this off-set connector,
flush with the dyno body, which goes out at a
45-degree angle to plug into this bunch of tilted
connector posts.  That wouldn't be so bad, except that
the center of gravity of the long axis forces the connector
down away from the plug when you try and reinstall it
and there's no room for your fingers.  In other words-
when you try to engage the connector, the dyno rotates
away from the plug and you can end up "boogering"
the connector if not careful.  I don't know how
to do this better- it took me awhile
to get the blasted thing back in place.

It's a very cool set.  If you have one,
you should try it out sometime.

73 Dave S.