[time-nuts] Aging 5065A ?

[Bob kb8tq]

Hi

Replacing the synthesizer with something more modern is certainly possible. I have
a project (slowly moving along) to do just that. There is nothing crazy on the logic board,
it could easily be replaced with something more modern for not a lot of money.

The phase detector / photo amp / modulator chain is a bit more problematic. My guess is that
a replacement of both the photo amp (preamp) and the phase detector at the same time
would make sense. Both are “audio” circuits. There is nothing in them that makes them
totally nutty to replace. 

The physics package *is* the long term question. When the lamps die, I doubt we can find
( or fab) replacements. If the temperature controller fails in a fashion that the entire “tube” 
turns into a chunk of charcoal, that would be a long tough fixer upper. 

Fun !!!

Bob

> On Oct 6, 2020, at 3:39 PM, Ulf Kylenfall via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> 
> Having been shut of for several months I fired up the
> refurbished 5065A a few weeks ago. 
> 
> It has since been equipped with a new AC-amplifier
> (A7) and a new Rubidium cell with the repaired lamp
> (thanks to Corby Dawson) and a receiver with a 
> TED that was connected according to HP instructions.
> 
> Also the 5 MHz original crystal oscillator has been replaced
> with an 10811 upgrade kit.
> 
> Almost immedeately, the FET's in the 60 MHz Multiplier A3
> not replaced during the first repair all failed. 
> They were replaced with metal can 2N4416 and all was well. 
> 
> The next thing that happened was that the amber 
> pilot light "Continuous Operation"
> went out. From just a single event, the lamp started
> going out just every time I turned my back on the 
> instrument. Since there were no sign of out-off lock
> conditions and I had no clue other that removing the
> logic assy A14 and checking the lamp driver Q18
> (1854-0003, selected from 2N1711) I found the transistor
> to be leaky. After replacing it with a 2N1893, I have
> only had one single such event in a week. Looking at
> the 1854-0003 from the bottom, the TO-5 package is most
> likely sealed with brown epoxy. And the A14 board
> is littered with them.
> 
> I could of course replace all these
> small signal transistors, be it NPN or PNP with modern
> types  but contemplating on this, I wonder how long a 5065
> can be operational if the heater windings in the Rb cavity
> remains OK and the synthesizer with its unobtanium
> logics are OK. From the records on the inside
> of the meter and switch parts on the front panel, I can
> see that the photo current of the original unit
> slowly decreased over the years. I have one more
> Rb TX unit but the Rb bulb in that one is really "brownish"
> and not in any way clear as the one presently used.
> 
> Standard "non-critical" semiconductors can of course
> be replaced, even the integrator IC. But what about
> transistors in the phase detector assy A8? There
> are some oddly looking packages and trying to find
> data sheets only returns bad photocopies from
> years ago, not really detailing what criteria 
> I should be looking for. 
> 
> Many web-pages from time nuts displays modern
> versions of the 5065 (digital clock). The one
> in my lab dates back from 1968 so it is over
> 50 years old.
> 
> Any research made on possible replacement
> types for those exotic semiconductors used
> in the critical parts as eg. the phase detector?
> Best Regards
> Ulf KylenfallSM6GXV
> 
> 
> 
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