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 _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
