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

Tue Jun 30 01:21:22 EDT 2015

If I understand correctly, you intend to operate your xmtr with the plate caps removed, from the 1625s. That is probably not a good plan---You may destroy the tubes, in a flash---the flash coming from the vaporizing screen grids, of your 1625s.
 You should remove the screen grid voltage, or simply remove the tubes from their sockets.
               73 & Gl de Ron                       

------------------------------------------
On Mon, 6/29/15, Mark K3MSB <mark.k3msb at gmail.com> wrote:

 Subject: Re: [ARC5] BC-459 Drift (summary of postings & my comment)
 To: "Leslie Smith" <vk2bcu at operamail.com>
 Cc: "ARC-5 List" <arc5 at mailman.qth.net>
 Date: Monday, June 29, 2015, 12:21 PM

 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.
 >
 >
 >
 >
 >
 > --
 > http://www.fastmail.com - Access your
 email from home and the web
 >
 >
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