[ARC5] that one cent command receiver - (long reply)

[Leslie Smith]

On Fri, Apr 11,  Bill Cromwell wrote:
> Hi all,
> I have just completed the entire transaction for the one cent 160 meter 
> command receiver that was listed on the bay.  [...] - Bill

Hello Bill (and others),
I looked at that set, (the R-25) and my fingers hovered over the "bid"
key for a micro-second; I'm glad I didn't bid, because I know you'll get
a lot of fun from bringing 'the beast' back to life!  

 Great description of the condition of the set as received!

I recently got a set similar to yours - it is a BC-946 (Colonial) and a
bit knocked around - but it can be made to go, I think, just like your
set.  The detector/AF amp has been replaced by a 6H6 and a 6J5 triode
sits in the 12A6 socket.  The 7 pin connector on the rear panel has been
replaced by a rather ugly and out-of-place tag-strip.  I think the
heater wiring has been 'messed with'.  I really do prefer the 24v
filament system; although I understand that 12 volts supplies were
easily got in the late 40's and early 50's 

The B.F.O coil-box is missing in 'my' set, and I'm rather grateful to
Ken (KG) for the idea I can get a new one from Fair Radio.  I'll do
that.  The output transformer is missing.  Ditto for the
noise-suppression choke in the B+ line.  

"My" set isn't too dirty.  In the past I used "Dot's bath and tile
clearner" on really dirty sets.  This is a quaternary ammonium foaming
cleaner and I spray it into the set until the thing looks like it's full
of cream - like a cream bun you might buy at the bakers.  Then I work on
this with a paintbrush to loosen dirt and crud.  Others have described
this process, so I'll not repeat that here, except to say it seems to
work a treat.    

Now I must make some interesting decisions about what I need to do to
make this set go.  Since the complete deck is missing under the dyno
plate I'll cut a 3mm aluminium plate to replace that and bolt it in the
hole.  If the other hole around the 7 pin connection is smaller than 1
1/8 inch (I think this is the size of an octal s ocket) I'll use an
octal socket on the rear panel for power etc.  

The bottom plate is missing - and I think I've got Buckley's chance of
finding a replacement.  I don't know what I'll do with that, but the
bottom plate seems to have the very important function (long term) of
keeping the under-chassis clean.   I'll need a bottom plate of some
sort.  

Since my set is already a junker I'm going to use it as an experimental
I.F. 'back-end'.   I'll use it on 525, 715 and 1500kHz and experiment
with breakthru from the BC band.  I've always wondered about BC
break-thru when the I.F. is in the middle of the BC band.  (The BC-348
seems ok, so maybe it can be done.)  The band-width in the '946 will be
broader than I might get from a BC-453, but even on 40m I think the
selectivity will be good enough for this beginner.

I bought a DC-DC converter from eBay (12v to B+).  I can select any B+
voltage from 45 to 180 volts by changing a single resistor.  I hope I
can keep the switching noise out of the '946.  I plan to experiment with
the performance of the set as I vary the B+ supply.  I'm certain others
have done this already, but I haven't.  I'm curious to investigate the
effect of different B+ supply voltages on set performance.  I'll need to
make a calibrated signal source to get an objective reading; I have an
HP 606 but I'll need to repair it.  I bought the 606 as working - but
when I turned it on it took about 10 seconds before a cloud of smoke
dispensed with that illusion.  Shorted caps took out a RFC in the B+
supply and gave that delicious (not) smell of burning electronics.  

After that I'm going to build a front-end for my BC-946 - just the
RF/mixer/oscillator part of a simple convewrter.  Nothing elaborate, but
good enought to work as the front-end of home-brew receiver on
160/80/40/20.  So - I was more than interested to read about the work
needed on your 'one-cent' receiver, and your plans to make it go.  My
long term goal is to use this set during the 2015 Remembrance Day (RD)
contest here in Australia.  Contacts made with a genuine WWII rig earn
double points.  I'm not sure if my 1/2 vintage 1/2 homebrew rig will
pass the 'genuine WWII' test.  

The RD contest is a memorial to the end of WWII (the contest date is the
weekend after the end of hostilities in August) and using a 'command'
rig should be a real 'hoot'.  I hear AM stations calling CQ (using
Collins gear) and the quality is really 'nice'.  When I hear it - it's
like "wow"!  I think I can make a T-19 sound good too!  So - this is
August 2105.  Doing this will keep me busy until then.

Some say home-brew is dead, but I believe this is THE age of home-brew. 
Test gear is abundant and cheap.  Good test gear.  When I was in my
teens a 20k-ohm per volt multimeter cost 15 hours wages.  Recently I
bought a meter (a real cheapie with only 1% accuracy) for about 2 hours
wages, so home-brewing is much easier now than in the 50's and 60's.  

As for your set - I read your posting with great interest.  Thanks for
taking the time to write.  Keep us posted as your set comes to life!


  73 de Les Smith
  vk2bcu at operamail.com


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