[ARC5] OT: Hally Instability - Hammarlund drift.

[Kenneth G. Gordon]

On 15 Nov 2015 at 22:17, Richard Knoppow wrote:

> I wish I had known about the TC cap.

Well, it was mentioned in a bulletin which was printed, once, in QST 
magazine. Most hams of the time missed it. I have a complete copy of that 
bulletin here somewhere and could send it to you if you wanted it.

> My station receiver for years 
> was a modified BC-779.  It came extensively modified using the dual 
> triode amplifiers described in CQ. I am drawing a blank on the guy who 
> wrote the article.

Wasn't that Commander Lee? I think the title of the article was something 
like: "The Ultimate Super Pro". In any case, I have a copy of that article here 
too. The article, or one like it, was very extensive. The entire audio section of 
the original receiver was torn out and a power supply was built in in its place. 
I found very little in that article which would be useful. I do remember that 
there was one thing of use, but don't remember what it is right now.

One of my three BC-779s (in the queue to be restored) is one of those 
"Ultimate Super Pro" jobs. I intend to restore it to operational condition 
simply to find out if all that hacking was worthwhile. I seriously doubt that it 
was.

> Anyway, I didn't like the way it performed and 
> restored it to its original circuits.

Ah! Interesting!

>  I think experimented a little. I 
> wound up using 6BA6 RF amps and a 6BE6 mixer with the original LO 
> changed to an electron coupled circuit copied from a General Radio 
> frequency meter.  I used adaptors so that restoring it original was 
> easy. I eventually did this and found the dial calibration was closer 
> with the original LO.

I don't doubt that...

>  One mod I found helped a lot was the use of a 
> voltage regulator tube on the oscillator.  The B+ of this receiver 
> changes with the RF gain so there is frequency pulling by the AVC or 
> manual gain.  A 150V regulator fixes that. Hammarlund certainly knew 
> about both temperature compensation and voltage regulation by the time 
> the HQ-120-X came on the market. It is actually a quite stable 
> receiver.  Whey they didn't apply this to the Super-Pro, their premium 
> quality receiver is beyond me.

Me too. Perhaps the contigencies of wartime requirements precluded it.

>  FWIW, my modified BC-779 was a very good 
> receiver, quiet with the modified circuits and quite stable. However, I 
> let run all the time.

My experiences are almost the same as yours: my BC-779 was an excellent 
receiver.

Ken W7EKB