[ARC5] 2 RX in rack with p/s and FL-8 Filter being worked on

[jcoward5452 at aol.com]

Go for it!
 Jay


-----Original Message-----
From: Tom Bridgers <Tarheel6 at msn.com>
To: arc5 at mailman.qth.net; David Stinson <arc5 at ix.netcom.com>
Sent: Thu, 25 Oct 2007 7:48 pm
Subject: [ARC5] 2 RX in rack with p/s and FL-8 Filter being worked on


Just purchased on Ebay, 2 ea BC-454 RXs in a 2-RX rack. Both RXs and 
the rack are heavily modified, with a power supply mounted on a shelf 
of "L" shaped aluminum plate attached to the rack. An FL-8 filter is 
permanently connected to the receivers on the back plane. 
 
Judging from the amount of dust, mouse hair, assorted other stuff, and 
crumbling condition of the power cord, I'd say these receivers, rack, 
power supply and FL-8 were modified and assembled in the early 1950's 
... then put away and stored in a barn or garage for some 30 or 40 
years. Everything is pretty dirty, grimey and greasy. 
 
So far I've been able to figure out: 
1. Power supply is working and under load it puts out about 255 volts. 
After running the RXs for about 5 minutes the voltage drops to about 
246 volts. There is an 800 ohm resistor (which gets very hot) preceding 
the capacitor input filter section with the choke being at least a 100 
ma Stancor model. 
  The power supply simultaneously supplies B+ and filament voltage to 
both receivers. 
2. The original owner had removed all 4 of the dynamotor shock mounts 
on each receiver and used them as access holes to feed wiring into and 
out of the receivers and to make connections between the receivers, as 
well as to the rack, FL-8, and power supply. The wiring is not neat and 
organized ... and in these situations, the term sphagetti comes to 
mind. 
3. Neither receiver receives signals. But the audio sections are 
working and I get a nice volume of static. 
  A. So far I've tested the current drawn of one receiver, and it is 
high. It's 55 MA, rather than the normal 30 MA. No doubt some leaky 
caps need to be found and replaced. 
  B. It appears that the BFO has been removed from one of the 
receivers. Which is a bummer. Why would the original owner do that, I 
wonder? 
  C. On the first iteration, after about 5 minutes, I noticed a 12SR7 
was cold to the touch. So I replaced it, and fired it all up again. 
4. Headphones plugged into the A-Tel jack on the rack are switchable 
between the two receivers. Never having used a rack before, I got very 
excited when I found out how the system of rack switches work. In 
essence, in this configuration, this arrangement allows you to "guard" 
one frequency and then cruise around and listen to any other freq's 
covered by the other receiver. Pretty neat. 
5. The FL-8 filter appears to be working, as I hear a difference in the 
static level when it is switched among voice, beacon , and both. 
 
Next Steps: 
o Clean the RXs, rack, etc some more! 
o Disconnect the wires to/from the power supply, to each receiver and 
to the FL-8, so the RXs can be removed from the rack for 
troubleshooting. Label wires so I can reassemble the dang thing. 
o To lower the operating voltage a bit (say to 150 to 175 volts), 
replace the 800 ohm, 15 watt resistor in the power supply with a 25 
watt resistor of resistance to be determined. 
o Reverse engineer the wiring modifications so they can be documented. 
 
That's it for today. 
 
I'm thinking this lash-up of receivers paired with a T-19 or BC-696 TX 
would be a VERY nice 80 meter station. And that is the direction in 
which I'm headed.... 
73's, 
-Tom KE4RHH 
 
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