[ARC5] Heater wiring - 12V vs. 24v

[Leslie Smith]

Hello Mike/List Members,

About 3 years ago I bought a "command/ARC-5" radio from a surplus dealer.  The rack and shock mounting plate do NOT match the set below, as they are of Signal Corps, not Navy origin.

The Nomen Plate has the following information:

R-25/ARC-5
[Smudged & Modified] Volts DC
NOs 74912  2195 CBY

A brief explanation of "smudged and modified":  The plate background colour is the familiar blue, and the original voltage rating number (which I assume was 28) has been removed with abrasive.  In place of the erased information I see what is intended to be "12".  

The set is certainly Navy issue: it is painted in the usual "wrinkle" black and over the US anchor I see that this set was released 2-43.  The set HAS been unpacked between Stromberg Carlson and me - the "test" tuning knob under the lid is missing.  The wiring has not been modified.  ALL tubes are metal, and marked 12SK7, 12K8 and so on.  Beyond this, the type of valve in each socket is marked in silver lettering - all 12 volt series.  

The set has a feature seen less often - a 3 position rotary switch on the front "mod" box has a "vol" potentiometer and 3 position rotary switch marked (yellow navy paint) on-off-mcw.

The set is configured to operate in conjunction with a "loop" aerial.  

To conclude:  The filament wiring for this set assumes a 12 volt supply - confirmed by measuring the resistance of the filament circuit when cold and by measurement of filament current when running.  

I'm very lucky to have a set of this quality and age.

73 AR k

Les 
formerly VK2BCU


> ----- Original Message -----
> From: Mike Morrow <kk5f at earthlink.net>
> To: arc5 at mailman.qth.net
> Subject: Re: [ARC5] Heater wiring - 12V vs. 24v
> Date: Sun, 27 Jun 2010 21:14:27 -0500 (GMT-05:00)
> 
> 
> > What is the designation on the rack?  The single Rx 24v mount was the
> > MT-5/ARR-2 while the 12v one was the MT-7(?)/ARR-2.
> 
> The MT-5/ARR-2 is the shock mount.  The MT-7/ARR-2 and the MT-7A/ARR-2
> are 24-vdc single receiver mounts (The MT-7A has front-mounted phone jacks
> and an audio bus select switch that the MT-7 lacks.  The MT-7 requires the
> MX-2/ARR-2 plug at the back to make the proper audio bus connection.)
> 
> The 12-vdc single receiver mount is like the MT-7A, but is MT-411/ARC-5X.
> 
> Mike / KK5F
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