[Milsurplus] SCR 269 test set (reply to Ed)

[boeing377 at aol.com]

Ed,

I have the test set for the ARN 7 which will also work with the BC 433 
SCR 269. Not really much better than some ordinary test gear and a 
manual. A lot of the test set deals with the loop functions. Unless the 
LP 21 loop is internally corroded, it will probably work even after 
years of storage. Loop slip rings (silver plated) may need attention if 
you get noise when the loop turns. Don't forget a short whip sense 
antenna otherwise you will get poor ADF performance with 180 degree 
errors. Don't pay attn to all the manual stuff about critical 
parameters for the sense antenna. I have found that just about anything 
works fine.

Getting one of these old ADFs running is not too hard if you have a 
manual, 28 VDC and a source of 110 VAC @ 400 cps. I have found that bad 
tubes and bad caps are the main problems and luckily the bad caps have 
been located on the underside of the chassis where they are easily 
replaced.

The only thing that is really tough is if you have bad components (caps 
or resistors) inside one of the big cans that you see from the top of 
the receiver chassis. They surround the bandswitch, IF xfmrs, etc and 
are a bear to access internally for service.

If you use square wave 400 cps expect audible shreeking from the 
bearing indicator I 81 or I 82, really annoying. The loop servomotor 
works fine with square wave AC and so do the selsyns, with a slight 
selsyn repeating  inaccuracy which can be adjusted for in the 
inidcator. it's almost worth building a small 26 VAC 400 cps sine wave 
supply for the selsyn system. It takes very little current.

These sets have really incredible AM BCB performance when hooked up to 
a long wire antenna. If you use the loop do not expect great weak sig 
DX, but the loop can be VERY useful in nulling out an interfering 
station that is off axis from the one you are trying to hear.

Good luck. These are historic radios that led many a B 24 and B 17 back 
home.

73,
Mark



Today's Topics:

   1. RE: Re: Identify this WW2 DF? (Ed Zeranski)





  Ed,

  SCR-269 is an airborne radio compass.


    [Ed Zeranski]
        Yes it is, I'm trying to collect the parts. A couple of years 
ago we
exchanged email when I found a manual and you said nobody was 
interested in
the things. Well, I came up with an antenna and some parts so would 
like to
put together a working SCR-269.  Crap, if nothing else you would know 
where
the ball game was coming from ~8^)

  EdZ


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End of Milsurplus Digest, Vol 25, Issue 14
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