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

[Richard Knoppow]

    You are now reminding me. My receiver had only the RF mods. I 
do remember reading the rest. I don't think he removed the audio 
amp but converted it from triode to pentode connection and may 
have changed the bias around. about doubled the output power. 
Completely unnecessary. The Super Pro audio is just fine as it is.
    I have seen Super Pros modified in the way you describe, push 
pull audio removed and replaced with a single ended amp and power 
supply on the receiver chassis. Very bad idea.
    I used my SP for SSB with no mods. The BFO injection was 
adequate. One has to run the AF gain high and RF gain low. I 
wanted an HC-10 for mine but couldn't afford one.

On 3/23/2020 10:59 AM, Kenneth G. Gordon wrote:
> 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

-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL