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

J. L. Trantham jltran at att.net
Wed Jul 7 00:43:33 EDT 2010

Just a wrap up on the 5061A that had a Beam I but no 2nd Harmonic

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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