[ARC5] Questions for all - More info

[WA5CAB--- via ARC5]

Short answer to the original first question is "yess".  All of the single 
through quad receiver mounts (racks) are functionally interchangable and as 
far as the mounts are concerned, so are all of the receivers.  This applies 
to RAT, RAV, ARA, SCR-274-N and AN/ARC-5.  As Mike wrote, if you operate then 
in only local control, you will have to either plug in an MX-2/ARR-2 jumper 
plug or kluge up a jumper from pin 1 to pin 6 on each of the 8-pin 
connectors on the rear junction box in order to run 28 VDC into the receiver.

The AN/ARC-5 receivers differ from all of the others in that the RCV Audio 
is not run to the front box.  However, if you have a mount this is not a 
problem as you juse use one of the jacks on the mount.

One minor addition - the SCR-274-N "-A" version receivers only have 4000 
ohm audio output impedance.  All of the other receivers are or can be 
internally wired for 250 ohm (later called either 500 or 600 ohm).

Short explanation of the rational behind WW-II and earlier military audio 
source and load impedances - The two standard output impedances were either 
4000 or 250 ohms.  With the exception of the HS-30 Headset, standard 
impedances of almost all headsets and loudspeakers was either 500 ohms or 7000/8000 
ohms (some prewar headsets were as high as 20,000 ohms).  The apparent 
rational was that you could operate from one to four Hi-Z or Lo-Z loads on any 
source without noticable change in audio level due to the up to 2:1 mismatch.  
By the Korean War, there were no more Hi-Z sets being made and everything 
was called 500/600 ohms.  What it actually was I doubt anyone knows.

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

In a message dated 09/11/2015 21:04:03 PM Central Daylight Time, 
kk5f at earthlink.net writes: 
> The junction box at the back of the rack has an 8-pin connector for each 
> receiver, at the top of the junction box.  This connector goes to the 
> *remote* control box for that receiver.  Assuming that your rack and receivers 
> are still in original configuration, and you are applying power using the 
> normal rack 28vdc connector, you will need a jumper from pin 6 to pin 1 on 
> that 8-pin rack connector when the *local* control adapter is used on the 
> receiver.
> 
> Also...the AF output impedance of all ARA receivers is low, about 600 
> ohms.  The SCR-274-N "-B" version receivers may be wired for either high or low 
> AF output impedance.  Other than that, an ARA receiver is electrically 
> identical to the SCR-274-N equivalent.
> 
> Mike / KK5F
> 
> ------------------------------------
> 
> I responded earlier:
> 
> >Yes, any ARA, SCR-274-N, AN/ARC-5 receiver may be used in any receiver 
> rack from those three systems.
> >
> >Yes, the receiver local control adapters may be used regardless of which 
> rack is being used.  These receivers were *always* used in a rack, so any 
> accessory has to be usable to a receiver in a rack.
> >
> >At the wikipedia article on the "ARC-5" you will find links to 
> maintenance manuals, plus some background on them.
> >
> >Mike / KK5F
> >
> >
> >>. My question is, will all of the Command Set Receivers work in the 
> >>ARC-5 receiver rack mount? The reason I am asking is I have a set of 2 
> >>SCR-274-x receivers in a double rack, and a beautiful little ARA BCB 
> >>receiver I picked up for a song ($45) off the Bay. There were only 2 
> >>that bid on it and the other quit on $43.50. I have that set up in an 
> >>ARC-5 single mount. Another question is when they are in the rack, can 
> >>the local controls on the front of the receiver be used or do I have to 
> >>use the control box? Seems there is always a question bouncing in my 
> >>head. 73's ,,,,Joel  KB0FPT
> 
>