[time-nuts] 5061A Problem Child - It Lives!
didier at cox.net
Wed Jul 7 10:29:36 UTC 2010
> -----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.
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