[ARC5] BC-459 Drift (summary of postings & my comment)

[Leslie Smith]

          Drift (and rough tone) in a BC-459.

I went thru the postings for this thread and made the summary below. 
Then I added my comment at the end.  The quotation marks don't enclose
actual words - just my idea about the intent of the writer.  I use the
quotation marks to understand how the other person sees the situation. -
Les

Background:
Mark (K3MSB):  "When I restored the [BC-459], I did general cleaning,
replaced the bathtub capacitor, and re-soldered all the joints I could
get to.  I still  had some chirp which I wasn’t too concerned about, and
drift was minimal.   This weekend it got to the point that I decided to
pull the 459 off the air (and since 80M was dead, brought my operating
fun to an end……)."

Mark's Power Supply:  He's using a bench PSU with B+ applied to the dyno
pins.  Privately Mark told me:  "P.S.U. has good regulation.  Stiff
beyond suspicion".  (My words, despite the quotation marks."

Dennis M: fixed a problem like this in his set by cleaning the
bearings/connection in the tx cap.

Wayne said:  "Check the caps."

Mark:  Reported "found the problem."  Cleaned behind the wiper arms on
the variable caps.  Used de-oxit on the caps.  Mark's report: "I put the
transmitter back in the rack and the tone sounded good with no drift
..."

More recently Mark posted to say: "Took the tx out for the weekend.
Problem is NOT licked."  Then:  "I got drift (on key down) and a rough
note, but not as bad as before I did the cleaning as mentioned in my
earlier post."

Then he asks: "I suppose it's time to go in a replace components in the
Oscillator section?"


MY CONCERN OBS:  (1) Any kind of sand-paper (or method) that leaves
debris behind (eg in relay contacts or the cap wiper) has a potential to
produce an intermittent fault.

(2) I would like to hear what happens when you run the V.F.O. with the
B+ "off" the finals.  I mean listen to the tone when only the 12J5 is
running.

(3) I think your original work (cleaning the capacitor wipers) may still
be correct.  Maybe the cleaning was partly effective, but not complete. 
(See #1).  My vote: re-clean the wiper - but use brown (wrapping) paper
with a touch of de-oxit as lubricant.

On point #2 - I'm answering your suggestion that you may "replace
components in the oscillator section."  I would leave ONLY the
oscillator section running for days and listen to the tone.

One more question:  With "key down" for a long time - how does the tone
sound?  Is the problem only apparent when keyed for a short time?  If
the drift/chirp occurs only at the moment of keying - then the
oscillator lacks gain; it takes a moment to stabilize (due to low gain).

Les

P.S.  Here, in Australia, Leslie is a bloke.  That's what my mum thought
when I was born, and I think she was correct.  In USA I understand
"Lesley" is a bloke.  It's all very confusing to a very ordinary Aussie
bloke.





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