[ARC5] Re-furbishing BC band receivers...

[Brian Clarke]

Hello Ken,
I would like to (re)build a BCB Command Rx. I have a BFO and a new
RF coil set I got from Gordon White, and I have the chassis and tuning
gang from a stripped BCB Rx. What I lack and would ideally like to
find are three IFTs and a tuning dial. Can you help? I'm also short of
Rx antenna posts - they seem to get broken in transit, bending the
front panel, requiring removal of the tuning gang = pain.
I can't help with specifics of the IFT numbers, but I offer the
following comments from a design perspective. Usually the 1st and 2nd
IFTs can be interchanged (after swapping the base mounting flanges and
any errant internal taps) because they are only loaded by the high
impedance grids of 12SK7s. However, the 3rd IFT is designed for low
impedance feed into the detector. It is difficult to tell just by
looking - you really need an LCR meter to sort real 3rd IFTs from the
rest. I know because I bought some IFTs that had apparently been taken
from a BC-454 - but I was suspicious about the disturbed paint
on the screw-heads and mounting flange - the 3rd IFT was a
re-flanged ring-in.   73 de Brian, VK2GCE.

OnThu, 31 Jul 2014 00:28:40 -0000, you said:

 I've been going, slowly, through my stash of parts, trying to
identify to 
 which receiver each should belong, separating them into individual 
 storage "thingys" and labeling them.

 Today, I found several boxes of parts which I had forgotten about. In
one 
 of the boxes were four coil-boxes for BC band receivers, and 19 ea
239 kc 
 IF cans.

 Trouble is, 16 of those were for the 2nd IF only, 7269, one loose
single 
 was for the 3rd IF, 7270, in a BC-946, and there was exactly one
complete 
 set of IF cans for either the BC-946 or an R-24/ARC-5.

 I also found 10 each (what look like new) 239 kc BFO cans that I had 
 bought from Fair Radio Sales some time ago.

 I also found three complete BC band receivers, 2 ea BC-946s with
added 
 power supplies, and one ARA, relatively unmolested, and at least 4 
 "hulks", 2 of which could probably be "refurbished" enough to look
and 
 work "acceptably". The other two were simply hacked to ribbons.

 And I have one R-22/ARC-12, BC band receiver, which, without too much

 effort, could be made to work and look acceptably.

 Does anyone have any clear idea of the real difference between the IF

 cans? 

 The ARC numbers on the cans would be 7268 1st IF, 7269 2nd IF, and
7270 
 3rd IF in the BC-946 and in some R-24s. Other R-24s use a 7268 1st,
9635 
 2nd, and 9634 3rd IF transformer....at least according to the three 
 manuals I have so far examined.

 From what I can so far see from the drawings in the AN/ARC-5 manual,
AN 
 16-30ARC5-2 on pages 277/278, the 2nd and 3rd IF transformers appear
to 
 be identical internally, the only difference being the base plate.
Both 
 have both primary and secondary tapped, and both appear to be wired 
 identically.

 The first IF transformer (7268), however, is not tapped at either the

 primary or the secondary. But other than the orientation of the 
 baseplate, it is otherwise identical internally and is wired
identically 
 to the 2nd and 3rd IF transformers.

 Suggestions?

 BTW, the AN/ARC-5 manual I have (in PDF) contains very noticeable
errors 
 and missing information.

 Ken W7EKB 

-------------------------
Email sent using Optus Webmail