[Hammarlund] BC-779s and mods (was HQ-129 serial number list)

[Kenneth G. Gordon]

On 23 Mar 2020 at 10:03, Richard Knoppow wrote:

>     I have to cudgel my memory. I think it was published about 
> 1948 and want to attribute it to Paul Lee but am not sure.

Yes. That is correct. Title was something like, "The Super, Super Pro." I have that complete 
article in PDF format if anyone would like a copy. Just let me know and I will send it to you.

I have three BC-779s here. One was COMPLETELY modified according to the above 
mentioned article. As far as I'm concerned, it is a complete mess. I intend to get it working 
so that I can run some tests on it to see what "damage" those mods made to it, and I am 
sure they are extensive.

I also have at least one complete (with original power supply) BC-779 which is in original 
condition, and a third one which, although mostly complete, is in very bad condition. I do 
think that one is restoreable, though. In fact, I intend to restore them all.

I was given a complete, almost new, BC-779 with power supply many years ago. When I 
first got it, the BFO injection was terribly low. I modified the 6N7 noise limiter into a 
triode-product-detector and was amazed, I mean REALLY amazed (!), at how much the 
apparent sensitivity and quietness improved!!!!. I loved that receiver. I turned it on and 
never turned it off. I used it for RTTY for many years. On 20 meters, it would slowly drift 
back and forth, very slighly, a few cycles. It was a real pleasure to listen to.

BTW, that TC cap one adds in parallel with the HFO section of the main tuning cap is a 2-3 
pfd N-1500 as specified by Hammarlund in a service bulletin I have here. If anyone wants a 
copy of that, I have that as a PDF also. Just let me know.

>     The mod used cathode coupled 6SL7s I think. A type of circuit 
> developed by Keats A. Pullen.

Well, Pullen's design was for MIXERS not RF amps. A poor choice for an RF amp, but a 
superb mixer. It NEEDS a good RF amp stage ahead of it, though, and the BC-779s two 
tube RF amp is excellent.

>     I don't think you need to article, just restore the circuit 
> to the one in the schematic. Hopefully, the original sockets are 
> there.

Well, if the complete mod has been done, then the entire audio section has been removed 
and a power supply built into its place. As far as I'm concerned, if that entire mod has been 
done, then the receiver is ruined.

What I would suggest is that you simply replace bad caps and resistors and run it as is. It 
would take WAY too much work to restore to original condition. I wouldn't bother.

vy 73 for now,

Ken W7EKB