[Collins] Re: {Collins] Colpitts oscillator

[David Knepper]

We are so pleased and honored to have Dr. Johnson, technical advisor to the
CRA, on the QTH.NET mail list.  Dr. Jerry has been so generous in taking his
precious time to respond to questions, etc. from all of us.   We certainly
owe him our debt of gratitude.  Jerry was a former employee of Collins
Radio, if you did not know.

Thank you, Dr. Jerry, on behalf of the membership of the CRA, now some 1600
strong and those on this mail list.  What we need to do - all of us who read
this post - is to spread the word that the QTH.NET Collins mail exists.  All
one has to do is to go to www.qth.net and sign up.  Perhaps, a donation to
Mr. Waller who owns this Internet service would also be in order.
It seems quite odd that there are some who would suppress the word!

Thank you.

Dave, W3ST
Publisher of the Collins Journal
Secretary to the Collins Radio Association
www.collinsra.com
Nets:  3805 Khz, Monday/Wednesdays 8 PM EDST
          14250 Khz Saturday, 12 Noon EDST

----- Original Message -----
From: "Richard Keller" <rkeller at ij.net>
To: <geraldj at ispwest.com>
Cc: <collins at mailman.qth.net>
Sent: Saturday, September 04, 2004 1:53 PM
Subject: [Collins] Re: {Collins] Colpitts oscillator


> Wow! What a fine refresher. I was looking back at my electronics school
> notes also from 40 years ago (Whew, can't believe it has been that long)
> and you did a  great service by reminding me of the intricacies of the
> shunt fed Colpitts. I also learned some new things that only someone of
> your experience would present.
>
> I did as you suggested for reducing stray C and the difference was small.
I
> give high probability to your suggestion that the silk screening may be
the
> biggest culprit. I noticed that the ganged capacitors are slightly
> different in value. The feedback path is 410pf and the signal path is
400pf
> but I believe that is by design for proper feedback function.
>
> Thanks so much for the help and willingness to do the back and forth
> discussion. Your knowledge and experience is invaluable to us who still
> need a teacher from time to time.
> 73, Dick KF4NS
> St. Petersburg, FL 33714 USA
> Keep the glow!
>
> ----- Original Message -----
> From: "Dr. Gerald Johnson" <geraldj at ispwest.com>
> To: <rkeller at ij.net>
> Cc: <collins at mailman.qth.net>
> Sent: Friday, September 03, 2004 10:48 AM
> Subject: Re: {Collins] Colpitts oscillator
>
>
> | You could reduce the inductance of the coil by adding a shorted turn
near
> | the coil. Either a turn of copper wire or a brass or copper washer will
> do a
> | small amount. Adjust its position for the inductance you wish. But that
> will
> | bring up both the low and high frequency points on the dial.
> |
> | You might work to lower the stray capacity that set the minimum C for
the
> | oscillator, like being sure the oscillator tube is the right one with
> small VHF
> | geometry, then being sure that the leads from band switch, variable
> | capacitor, and tube socket are not pushed neatly down against the
> | chassis. You get band width of tuning only by square root (Max C/ Min C)
> | and a higher minimum from strays can limit your coverage.  You might
> check
> | that the capacitor rotor plates are centered and that there's no
> | accumulation of dust bunnies around the stators to add C (and R).
> |
> | And you might just have to live with the fact that what the engineers
> | designed and drew up for the front panel / dial silk screen were with a
> | different part for the variable capacitor than what production bought.
> I've
> | read that Collins had some difficult moving the S-line from prototype to
> | production because the manufacturing department wanted longer leads on
> | everything, especially the wiring harness and those longer leads made it
> | oscillate well. The engineers had to convince manufacturing to use the
> | shorter leads of the prototype to make a saleable radio.
> |
> | 73, Jerry, K0CQ, Technical Advisor to the CRA
> |
> |
> | --
> | Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
> | Reproduction by permission only.
> |
> |
> |
> |
>
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