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

[Mark K3MSB]

Hi Leslie (Bloke).

Thanks for your comments.

I don't believe that I ever stated my HB PS is regulated, as it is not.
For CW operation regulation is typically not needed, and it was not used in
the BC-456 modulator.  My PS uses the same simple resistor divider network
that is used in the 456 which is the same as Dave Stinson recommends.    I
believe I told you I was considering regulating the Oscillator voltage, but
I have not done that.

I believe my PS is "stiff".   It only supplies the HV.  I have a separate
28V supply for the TX and another 28V supply for the receivers.   The
reason I don't use the dynamotor on the 456 is because when I key down I
definitely see a voltage drop, as the 28V TX supply is not stiff enough.
The other reason is that the dynamotor gets hot, it's summer here, and my
shack is not air conditioned.....

I don't believe there is any sag when I key down, but I will check again.

When restoring the SCR-274N I used my business cards soaked in DeoxIt to
clean relays etc as recommended.  I can always do that with the cap wipers
I recently cleanred with wet/dry sandpaper.

I will check issue with the plate caps disconnected.

73 Mark K3MSB

On Sun, Jun 28, 2015 at 11:32 PM, Leslie Smith <vk2bcu at operamail.com> wrote:

>
>           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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