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

[Bob kb8tq]

Hi

……. You have just discovered why we all depend on hard working Corby so much. Repairing these
old beasts is not as easy as it first seems !!

The traditional theory about mag wire on a metal tube was that they both have very similar
temperature coefficients (maybe) and that there is no motion between them (maybe). With 
zero motion, the insulation (maybe) goes nowhere even if it degrades. For heater windings
the theory was that the direct contact gave you better heat transfer. That works for round
cavities (like the 5065). All of this falls apart a bit for square cavities (think OCXO’s). There 
the wire hits on the corners and floats as it goes over the broad sides of the part. 

Lots of fun !!

Bob


> On May 6, 2017, at 5:49 AM, Ulf Kylenfall via time-nuts <time-nuts at febo.com> wrote:
> 
> 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
> SM6GXV
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