[ARC5] [Milsurplus] ARC-2 Tags and Nomenclature

[Mike Morrow]

The meter was never removed by the modifications...just the ANTenna Current function and (usually) the ANT - PLATE toggle switch.  That left only the METER in service measuring PLATE current.

I'm not sure by your description what your RT-91 has, but it sounds like you are saying the original RT-91 METER circuit was left intact and your RT-91 still has selectable ANT current and PLATE current display capabiliity, unlike the RT-298.

Mike / KK5F

-----Original Message-----
From: jeepp 
Sent: May 7, 2018 1:33 PM
To: Mike Morrow , ARC-5 , milsurplus at mailman.qth.net
Subject: Re: [ARC5] [Milsurplus] ARC-2 Tags and Nomenclature

OK, I have a modified RT-91.  It has the fuses, spares, etc. but the meter and circuitry were not removed during the mod.  Nor were, of course, the changes to the output circuitry.  Mod # is stencilled on the panel.  K3HVG
-------- Original message --------
From: Mike Morrow <kk5f at earthlink.net> 
Date: 5/7/18  11:56  (GMT-05:00) 
To: ARC-5 <arc5 at mailman.qth.net>, milsurplus at mailman.qth.net 
Subject: Re: [ARC5] [Milsurplus] ARC-2 Tags and Nomenclature 

Dave wrote:

>Please see the close-up photo of the ARC-2A.
>Anyone have an insight into the white tag?

That documents the engineering modifications that have meen made to this set.  I don't know of any source describing them, unfortunately.  Doubtless, most of those shown sere related to the mods discussed below.

>Second:  This rig has all the features of an
>ARC-2A, but it has a nomen tag that says
>"RT-91/ARC-2."  I thought the -2A was a completely
>new run, not a modification of the -2?

After the RT-298 was introduced, the USN embarked on a program that gave the RT-91 as many of the features of the RT-298 as was possible, especially those related to operation.  These modified units have the front panel fuses and spare fuse box of the RT-298.

The RT-91 has a front panel METER toggle switch with ANT and PLATE positions.  The RT-298 does NOT...the meter always measures PA Plate Current.  So, most RT-91 units were modified to eliminate the ANTenna Current display and the meter switch was removed.  That is what happenned to Dave's unit, which has a panel hole filler where once there was the meter switch.

Some modified RT-91s did not have the RF amp function removed.  But confusingly, some had the RF amp function removed without removing the meter switch.  That can play a joke on a young and poor Navy guy like me, getting his first RT-91 from Fair Radio for $50 in 1975, who fires it up and can't figure out why no antenna current is shown even though a 40 watt light bulb connected to the antenna is glowing brightly!

An original RT-91 that escaped USN modification (and ham modification) is somewhat scarce.  IMHO, the RT-91 was better built than the RT-298, especially the late RT-298 which had hard plastic tuning knobs instead of the metal knobs of the RT-91.

So Dave, you have an RT-91 that the USN modified to behave as close as possible to the RT-298.

AN/ARC-2 and -2A units along with a R-23A/ARC-5 were still flying in TS-2A aircraft at NAS Corpus Christi in 1972.  When I asked about them following a flight, an aviation ET told me that it was harder than dammit to get spare parts for them.

Mike / KK5F