[time-nuts] 5061A Problem Child - It Lives!

[paul swed]

Completely agree congrats and thanks for the update.
I may be getting back involved with my 5061a soon now that I have a HP
pico/femto amp meter.
By golly I will go hunting for the elusive I beam current ghost directly off
the tube or at least learn that I can't.

On Wed, Jul 7, 2010 at 6:29 AM, Didier Juges <didier at cox.net> wrote:

> Congratulations Joe!!!
>
> Didier
>
> > -----Original Message-----
> > From: time-nuts-bounces at febo.com
> > [mailto:time-nuts-bounces at febo.com] On Behalf Of J. L. Trantham
> > Sent: Tuesday, July 06, 2010 11:44 PM
> > To: 'Discussion of precise time and frequency measurement'
> > Subject: [time-nuts] 5061A Problem Child - It Lives!
> >
> > Just a wrap up on the 5061A that had a Beam I but no 2nd
> > Harmonic indication.
> >
> > I was originally stymied by swaps of modules with another
> > 'functioning unit'
> > with no help.  I then swapped CS tubes with A4 Harmonic
> > Generators attached and A11 Cesium controllers at which point
> > neither unit worked.  I added an
> > A15 Power regulator swap and still neither unit worked.  I
> > undid the swaps, got the 'functioning unit' working again
> > (found a leaky A11C2, a 2.2 uF film capacitor with a
> > resistance of about 1800 ohms, that prevented the 2.8 KHz
> > Control Oscillator from oscillating), then went through some
> > tests of both units, assembly by assembly and found A7
> > faulty.  Problem was a 'weak' Q1 (1854-0023, the input
> > transistor in a 3 transistor amplifier)) with a Beta of about
> > 20.  An identical transistor at Q2 had a Beta of about 200.
> > I installed a 2N2222A that had a Beta of about 150 and all
> > was well.  The 2nd Harmonic came up normally but the Alarm
> > light would not go out.  However, when put in Operate, the
> > Continuous Operation light would come on and the unit seemed
> > to 'lock' normally.
> >
> > I found an open Q20 and a shorted Q22 (both 1854-0003's) on
> > the A14 Logic Assembly causing the Alarm light to stay on.
> > Replaced these with 2N2222A's and now all seems well.
> >
> > I can't explain why swapping A7 modules early on did not
> > resolve the 2nd Harmonic indication problem unless both A7's
> > were 'weak' allowing them to work with a stronger signal but
> > not a weak signal or all the swapping of tubes, back and
> > forth, in and out, etc., fixed a dirty connection.  On
> > reflection, probably the latter.
> >
> > In any event, it works and seems to be one of my stronger tubes.
> >
> > I could not find any cross reference for either of these NPN
> > transistors but the 2N2222A seemed to do just fine.
> >
> > Thanks for everyone's help.
> >
> > Joe
> >
> >
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