[time-nuts] Aging 5065A ?

[paul swed]

Will agree I would hack something in. The same for the synthesiser. I could
swear someone on time-nuts already has. The phase detection circuit is
audio and it would take some experimentation. I think Corby supplied an
alternative approach on the A7 opamp so a lot of good work.
But the charcoal problem mentions really would be the worst problem to deal
with. I guess it would be ebay parts. $$$ Whats a dead 5065 go for chuckle?
Regards
Paul
WB8TSL

On Tue, Oct 6, 2020 at 6:27 PM Bob kb8tq <kb8tq at n1k.org> wrote:

> 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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