[Hammarlund] Bias supply zorching the audio driver transformer

[Kenneth G. Gordon]

On 25 Jul 2012 at 13:08, Todd, KA1KAQ wrote:

> I do have a
> pre-war 200SX here that someone started to gut the audio section from.
> Fortunately the iron is still in place. Have seen a few with the audio
> section complete gone, no way of knowing if a roached transformer was
> the reason or the typical mod-of-the-day approach promoted in the
> 50s-60s.

That undoubtedly is the beginnings of a project from an article in some ham 
mag, I don't remember which at the moment, entitled "The Ultimate Super 
Pro". 

The entire audio section was hacked out, leaving a 1/4" lip around the space 
on which a piece of aluminum was placed and on which was then mounted 
an internal power supply and a really wimpy single-6AQ5 audio stage.

There were other, much more "destructive" mods included in that article, 
along with one possibly valuable or useful one. 

I cannot understand the thinking in that article.

I have one complete example of that "Ultimate Super Pro" here in the form of 
what was once a very nice BC-779.  In addition I have one completely 
untouched BC-779 with original power supply, and a pretty beaten up one 
which is restorable and which was given to me by my nephew who found it in 
a dump in Butte, Montana.

I have always considered the Hammarlund receivers to be unusually good 
receivers, and rather forward-looking for their various time periods. They 
were always more expensive than most other receivers of their time periods 
too.

Back in the 1960s sometime, I was given a completely unused BC-779 with 
original power supply. I mounted it in a nice rack I had then.

I suspect now that there was something wrong in the BFO or its 
interconnections to the following stages since the BFO injection was horribly 
low, making it almost impossible to copy CW, let alone SSB.

I converted the 6N7 noise limter tube into a triode product detector, and was 
amazed at the resulting improvement (as I have mentioned many times).

The sensistivity and quietness of that receiver after that mod (despite that 
crappy, noisy 1st mixer stage) was literally startling to me!

I could hear signals I didn't even know existed before that, and used that 
receiver for several years afterwards as my main RTTY receiver.

I never turned it off, and it would drift back and forth a few Hz on 20 meters 
all the time. I thought even that made it sound pleasant.

vy 73,

Ken W7EKB