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

Didier Juges didier at cox.net
Wed Jul 7 06:29:36 EDT 2010


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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