[Milsurplus] CU-1388, CU-5069 couplers?

[Steve Byan]

On Feb 6, 2007, at 4:35 PM, Jason White wrote:

> I'm busily making a home for an R390A and thought a perfect  
> accompaniment in the rack would be one of the older period  
> multicouplers so I wouldn't have to swap inputs from my various  
> receivers with switches. I've found lots of web pages on the  
> CU-1388, CU-5069, and CU-1020 from as recent as two years ago that  
> suggest these were readily available for very reasonable prices in  
> the surplus market, but as usual I missed out. Are these things now  
> scare as hen teeth?

I think so. I'd like to turn up another CU-1388/FLR-9 or two to mate  
with the one I got from Fair Radio back in the 1990's. I've gone  
through some effort to figure out how to maintain it; the stock power  
supply showed evidence of much ECO activity and when it gave up the  
ghost it took out the unobtanium PNP RF transistors. I suspect many  
of the 1388's are now probably dead.

I replaced the supply with an open-frame linear supply and paid some  
obscene price for some new 2N5160's to replace the fried transistors.  
I reverse-engineered the amplifier schematic at the time, but have  
since found that it is the same circuit as the amplifier board in the  
AM-4213/FLR-9(V), for which a scanned manual is available at The  
Bunker of DOOM <http://bunkerofdoom.com/lit/flr9/index.html>.

The amplifier circuit is quite interesting; it uses a Sziklai- 
connected PNP/NPN pair (aka complementary Darlington) <http:// 
en.wikipedia.org/wiki/Sziklai_pair>, which Lindsay Hood claims gives  
less large-signal distortion than a Darlington pair. I wonder if  
that's why the designer chose that configuration?

Regards,
-Steve

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