[Milsurplus] SCR-608

[WA5CAB at cs.com]

Ken,

Before you go looking for a BC-604-? nameplate, I'll point out two things.  
The bottom plate, with the schematic, is easier to change than the bezel 
with the nameplate.  And they never made a bakelite insert for the crystal 
tray that was different from the 0-79 one.  I think probably because with the 
BC-684 having 120 channels, you cannot load all the crystals into the tray.  
And how would you decide which 80 channel numbers were needed.

I had a look at the schematics of the BC-604 and BC-684.  Unfortunately 
there are no glaring differences other than if the transmitter is a BC-684-A 
there is no provision for Interphone operation and there is no 
RADIO-INTERPHONE switch.  The BC-684-B and -BM match the circuitry of the BC-604-D and -DM. 
 Except that in the BC-604-(*) the tube order in the RF section is 
Oscillator, Rectifier, Doubler, Tripler, PA whereas in the BC-684-(*) the Tripler is 
first followed by the Doubler.  The only relatively easy way (unless there 
is no RADIO-INTERPHONE switch) I can see is to couple a GDO to the output 
tank coils L-110 and L-111 and see whether they will tune up to about 40 MC.  

If anyone knows something I missed, please speak up.

In a message dated 5/2/2009 1:18:57 PM Central Daylight Time, 
scr274 at gmail.com writes: 
> Hello all,
> 
> I have had a complete set in my garage for decades, the whole shootin'
> match: 2 BC-683 receivers, the transmitter, the FT-327, the CH-74A metal
> chest with the canvas front flap, the MP-52 Mast Bracket, even an FT-285
> frame to rest it all on, plus lots of accessories and manuals. Even
> TM11-2701 "Installation of Radio Equipment in Car, Half Track M2".
> 
> So I pulled it out the other day to get serious with it, and to see what's
> what.
> 
> Everything looked in order, but I was suspicious... the transmitter
> nameplate (BC-684(*)) is mounted on the casting that protects the front
> panel controls. As with the receivers, this casting is easily removed and
> switched. So I pulled the transmitter out of the case and took off the
> cover. I was dismayed to see a schematic for the evil BC-604. The clincher
> was the crystal drawer with places for channels 0 through 79. There 
> appears
> to be no other way to ID the transmitter simply by eye-balling it. (The
> receivers are easy).
> 
> Obviously, years ago when I bought it, I relied on the nameplate (and the
> seller) to tell me it was the amateur-radio-friendly SCR-608.
> 
> Silly me.
> 
> I put primary power to it: The TX dynamotor struggles, one RX dynamotor
> runs, and one doesn't. No big deal. So I would like to get it up and 
> running
> before even thinking of trading it off or putting it up on you-know-where.
> 
> Now, I know I have some pieces here that are in demand by the vehicle 
> guys.
> These guys are sometimes more interested in putting their stuff together 
> for
> "static display" and not actually operating it.
> So I could probably get rid of it as-is. I certainly can't run it as a
> hermaphrodite. Breaking it up and selling the components is a decision 
> best
> left for later (the FT-327 should be worth something).
> 
> So here's the question... does anyone have a real BC-684 transmitter? Or 
> are
> they so hard to find that I should just give up? Or should I look for some
> BC-603 receivers and talk to my dummy load?
> 
> 73,
> 

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