[time-nuts] HP5065A S/N 0048-00131 - Worth repairing (and how to do it)?

Ulf Kylenfall ulf_r_k at yahoo.com
Sat May 6 05:49:01 EDT 2017

 HP 5065A S/N 0048-00131 
Repairing the heater...
I was able to get my hand on a faulty 5065A
that was left for dead.
The date codes on the semiconductors says 1968
so this unit is 50 years old... This instrument
has some provenance as it was
used in the European end during the very first
trans-atlantic VLBI (Radio Astronomy) 
experiments between Sweden and the USA.
The unit has the known problem with one of the
rubidium unit (s/n 05065-6001)
heater wires shorted to GND.
This failure was the cause of the decomissioning.
I managed to salvage:The transmitter lamp (fires up within seconds when connecting it to a 20V DC source),The Rubidium glass cavity, The photo-cell at the receiving end.
Having downloaded the "First-aid" documents
from KO4BB, I read a quote from Corby Dowson
regarding this problem and what to do about it.
I have been able to separate the TX/Rb/Rx assembly from
the magnetic shields but after this, I hesitate
about how to proceed. (why did not HP put more energy
in trying to isolate the magnetic winding from the shield?
Any scratch on the enameled copper wire and a short
circuit will be the result here as well?)
As far as I can see, the magnetic
winding has to come off. The rest of the
polyurethane (?) structure has to be removed
after which that structure has to be rebuilt
using some other material (PTFE?).
One other reason why I hesitate is that this unit is
v e r y old. It uses regenerative dividers
instead of binary (etc) and a lot of other
obsolete components.
I could use some suggestions about what to do next.
One other question is of course if it is worth
putting a lot of energy trying to repair
a 5065 as old as this. Perhaps easier to go
look for a working modern 5065A on the open market?
Comments invited.
Ulf Kylenfall

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