SCR-274-N Questions

[K3MSB]

My friend Dean K5DH suggested I ask my questions on this forum as there are some of you that are running authentic SCR-274-N systems.

I’m currently assembling an SCR-274-N system consisting of the BC-454/455 receivers and the BC-696/459 transmitters and associated racks.

The receivers are restored and work as does the 459. The 696 needs the two internal relays installed (which I have).

I also have the BC-442 relay, BC-450 Receiver Control Box and a BC-451 Transmitter Control Box.

Inbound (anxiously awaited) is a BC-456 with Dynamotor (not the one that recently sold on eBay…..wow, what a price….).

I'm ready to start cabling the system as I've acquired the necessary plugs. I would like some idea of the gauge of wire to use to interconnect these units. I can’t find this info in the manuals.
Is there any documentation that specifies how the cables were built?

I've been told that towards the end of the war years individual white cables laced with string were used for the connecting cables. Any idea if these were cloth covered or like today's plastic covered wire?

Thanks in advance!

[bdk]

I've been told that towards the end of the war years individual white cables laced with string were used for the connecting cables. Any idea if these were cloth covered or like today's plastic covered wire?

I can't say when synthetic materials replaced cotton insulation. Apparently Rayon was approved for houses in 1950, so it might have been around then.

This sounds like normal aircraft wiring harness practice where waxed string lacing was used to keep the wire bundles together.

http://www.aeroelectric.com/articles/ca ... _lace.html

http://www.casa.gov.au/scripts/nc.dll?W ... 9s2c08.pdf

[plankwings]

That would've been "uni-nyvin" Mil-W-5086 or similar number.
Does come in shielded

http://www.militarywire.org/singleconductor.htm

Gives off toxic fumes when smouldering, so no longer used by Boeing, Airbus, etc.


Plankwings

[Cvairwerks]

Mark: I ran thru one of my manuals looking for the radio wiring. I found the wire data, but it covers all the different radio boxes for the a/c, so I didn't get too specific. What I did find is that all the wiring is 10, 12, 14, 16 and 18 gauge, with one exception. All the audio input wiring is 22 gauge.

Hope this helps. I can dig a little more over the weekend if need be.

[K3MSB]

Gentlemen --

Thanks for your replies.

Mike Hanz KC4TOS emailed me the following:

“In T.O. 12R2-3SCR-274-2, Handbook Maintenance Instructions for Radio Set SCR-274-N,…Everything is contained in Figure 32. Look at CD-207, the twelve wire cable. You will see that it consists of ten #22 and two #16 wires. That defines the only two wire sizes used in the entire set. Then shift your eyes to the connectors to the right of CD-207...they show the pinouts of all the connectors, and on an exception basis, you will occasionally see "No.16" called out. The only thing they forgot was that the two conductor aircraft power cords to the receiver rack and modulator should be #16 as well. This ought not to be daisy chained, but come from a common point for both cables.“

BTW, Mike has a very interesting web site on WWII aircraft avionics: http://www.aafradio.org/ !!

The manual I'm using is Instruction Book for Operation and Maintenance of Radio Set SCR-274-N which doesn't contain this information. Yet another example of no matter how many manuals you have on your shelf, you always need one more