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

[Leslie Smith]

Dear list,
Thanks to the many members that replied to my question about heater supply voltage for command sets.  The general response provides an interesting "little" question - which follows.

Background:
I bought an R-24 set from a surplus shop in the USA about 2 years ago.  (The set was delivered by post to Australia).  With help from Mr. Ohm I figured the filaments were wired for 12 volt operation.  With help from the "toob" manufacturer, who diligently printed the valve type on the metal and glass valve envelopes, I saw every valve had 12V filaments.  With help from my eyes I figured the set was original, and not "hacked" . The set came with both the mounting rack and the shock mount, so I believe the set didn't come from an estate sale or field day (but that is a guess).  Hence my belief that the wiring (and 12V "toobs" in the set) are "as supplied" - ex assembly line.   I find it hard to believe a set from RAAF in Australia would bear the designation R-24 or R24 and get to USA, especially with the shock mounting frame.  Anyway, this set is black, wrinkle paint. 

I will inspect my R-24 later (photograph the nomen plate, wiring, & co) and document what I observe on this list.    I have run the set from 12V (I mean supplied the filaments with 12V) and I find it hard to believe a 24V set would run with 12V on the filaments - although I have never tried running a "toob" on 50% supply voltage.   The dyno is missing, so there is no clue there ...  

I was very pleased I took the time to measure the filament wiring resistance before I applied 24V.  (Phew, lucky!)

What is going on here?
Thanks to the various people who replied.


Les Smith


> ----- Original Message -----
> From: gordon white <gewhite at crosslink.net>
> To: Mike Morrow <kk5f at arrl.net>, "Discussion of AN/ARC-5 military radio equipment." <arc5 at mailman.qth.net>
> Subject: Re: [ARC5] Heater wiring - 12V vs. 24v
> Date: Sun, 27 Jun 2010 13:01:58 -0400
> 
> 
>      To my knowledge, the R-148/ARC-5X is the only AN/ARC-5 receiver
> built originally for 14 volts.  The R-148 and the ARA-2 (which is marked
> on the nomenclature plate as 14 volts) are not identical. The R-148 (as
> with the R-23/ARC-5 receiver) has the loop antenna connections and the
> front panel switch. The ARA-2 does not.
> 
>      My RAT receivers have no voltage markings on the nomenclature plate.
> Neither do my RAV receivers./I believe the plates are black, and if they
> are blue, the color has darkened up considerably until it looks black.
> 
>      Apparently the Navy still had 14 volt planes c. 1939 while the Army
> had gone to 28 volts.
> 
>      Of course the Type 12, which were built originally for postwar
> civilian use, were available in 14 volt versions.
> 
> - Gordon White
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