[ARC5] OT: Hally Instability - Hammarlund drift.

[Todd, KA1KAQ]

On Mon, Nov 16, 2015 at 1:10 PM, Kenneth G. Gordon <kgordon2006 at frontier.com
> wrote:

> 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.


Here you go, gents:

http://amfone.net/Amforum/index.php?topic=15703.0

Ralph/W3GL posted this on AMfone.net some years back after we had discussed
the early Super Pros in a Tech section thread. I think Ralph is 89 now and
used these receivers in WWII.

Be sure to read down further as someone else included info on another
change of that time that involves adjustment of the variable cap for
additional warm up drift improvement.

You're right on the money, Ken. I need to look through my manuals again to
find the actual quote from Hammarlund about leaving the sets on for
extended periods to stabilize. Few folks ever really understood much less
appreciated the process of thermal stabilization.

Probably most noticeable is the lack of drift or frequency jump from
bumping the panel, thumping the desk, etc. Mechanical stability is top
notch, for its day and well beyond.

~ Todd/KAQ

BTW, I've heard from some folks who claimed the addendum changes made no
big improvement. Upon questioning, it seems they hadn't gone through and
changed out bad caps, checked for out-of-tolerance resistors, done an
alignment, or even checked tubes in one case. These changes were intended
for a well-performing receiver, not a tired, old carcass limping along on
its original 75 yr old components.