[Milsurplus] CU-1388/FLR-7 coupler

[Steve Byan]

On Apr 19, 2007, at 9:06 AM, Jason White wrote:

> If anyone has any information on the unit they could share, I'd love
> to hear it. When I get my grubby hands on it I'm sure I'll be able to
> figure it out, but why reinvent the wheel if I don't have to.

I haven't found a TM for the CU-1388 yet, but it turns out to share  
much of its circuitry, including the amplifier modules, with the  
AM-4213/FLR-9(V). The TM for the AM-4213/FLR-9(V) is available from  
the Bunker of Doom <http://bunkerofdoom.com/lit/flr9/index.html>.

Watch out for the power supply. Mine gave up the ghost and took out a  
bunch of PNP RF transistors, which are basically made of unobtanium  
now-a-days. When I opened the supply, the PC board had evidence of  
extensive ECO or FCO activity. I replaced the supply with a 24 volt  
open-frame linear supply, and the PNP RF transistors with 2N5160's.

I run mine with the cover removed; it's made for forced-air cooling  
from an external blower, but I didn't want to rig up the duct-work,  
so I just leave the cover off and depend on convection cooling.

Plug your DVM into the test points, set the switch to VDC1 and adjust  
the "voltage adjust" pot for a total power supply output voltage of  
20.8 volts. Diddle the "balance" pot for the best approximation to  
7.1 volts on VDC2 and 13.7 volts on VDC3. A3, A4, A6 and A7 should  
read 0.85 volts if the corresponding amplifier module is working  
correctly.

BTW, the CU-1388 uses silicon transistors, not tubes. It's an  
interesting circuit design; the amplifier is a push-pull design using  
a Sziklai pair (sometimes called a complementary darlington) <http:// 
en.wikipedia.org/wiki/Compound_transistor>. John Lindsay Hood claims  
the Sziklai pair is slight more linear than a Darlington pair and  
hence gives better distortion performance (although he discusses this  
in an audio power amplifier context). I wonder if that's why Sylvania  
used this circuit.

I think the "test" C connector is a -20 dB _output_ tapped off the  
input connector; it's for sampling the input rather than feeding an  
alternative input signal.

> The plan
> is to put it into service feeding my various receivers, but I'd
> eventually like to put it in a rack with a pair of R-390s.
>
> Looks like I should start buying stock in C connector manufacturers.

Fair Radio used to sell short RG-8 cables with a C connector on each  
end for pretty cheap; I bought a supply of them about 10 years ago. I  
salvaged the connectors and made up RG-58/A cables with a C connector  
on one end and a BNC on the other.

Regards,
-Steve

-- 
Steve Byan <stevebyan at mac.com>
Littleton, MA 01460