[Hammarlund] B on SP-200 faceplate?

[Richard Knoppow]

     The BFO injection on mine was reasonable and I used it 
for both CW and SSB.  A product detector would help but I 
think you can improve injection by increasing the value of 
the coupling cap.
     The AVC system is such that the BFO is pretty well 
isolated from the AVC.
     The Geisler mods resulted in low gain. I don't remember 
what else. Unfortunately, the RF and mixer tubes used in the 
Super-Pro are very noisy especially the mixer. It taks some 
care if you want to re-design the front end that you don't 
wind up with overload problems and spurs.  Somewhere I have 
a Signal Corps technical manual (don't remember the number) 
which has details of all the receivers used at the time (mid 
1940s). One set of charts shows image and spurious responses 
of the Super-Pro and SX-28. The Super Pro has only one 
image, quite low, while the SX-28 looks like a corn field. 
I've been trying to find this book in my stored stuff with 
no success so far, but its there!
     FWIW, the RF amplifiers in the BC-1004, the 40 mhz 
version of the Super Pro, are shunt connected instead of 
series connected as in the other models. I think this was 
done to improve the Q of the coils by getting any DC 
magnetization off of the iron cores.  The Super Pro is also 
one of the few receivers that have genuine Faraday shields 
on the antenna coils. They are woven metallic cloth between 
primary and secondary of the coils. You can see them if you 
take the bottom cover off the coil compartment.
     The broadcast band and LF bands are also broad banded 
using resistors. Otherwise the bandwidth is not as wide as 
the IF.
     The Super Pro seems to be the most expensive receiver 
on the general market but the RCA AR-88 was probably double 
the price. Most, if not all, AR-88s were sold to the 
government.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com