Chuck I suspect it actually is for you. As you say you now have a great deal of insight that you did not before and as I have often read here. Its funny how we have all learned about the nasty effects of age. Ahhh I mean equipment that is. So I would bet you could get it going. The RB elements in the 5065 seem to last a long time its worth a shot. Kind of like the HP 5060/5061 was worth a shot and I learned a lot. Can't help that it actually works now. That was unexpected. Bythe waythat effort sort of cured me of the I want a CS. :-) Regards Paul WB8TSL
On Sun, Aug 2, 2015 at 6:36 PM, Chuck Harris <cfhar...@erols.com> wrote: > The main oven on my 5065A was made with a bifilar winding of enamel > covered nichrome wire wound directly on the aluminum oven. To cancel > the magnetic field, the far end of the coil was shorted, making the > heater a hairpin loop.... No twist that I recall... The enamel was > compromised somewhere along the winding, causing it to put the oven > into thermal runaway, thus toasting the lamp assembly. > > (this was my first exposure to how stupid HP could be with some > of the designs they made...) > > The runaway oven got hot enough to reflow the solder, and cause > several parts to fall out of the lamp's circuit board... the board > was turned into just plain old fiber glass matting, as all of the > epoxy... or whatever it was, turned to charcoal. > > When I did this stuff, I was fresh out of EE school, the web didn't > yet even exist as an idea, and I knew nothing about how rubidium > standards worked.... I knew they were special, so I called up HP, > and ordered a $300 manual... but I digress... > > My first fix was to disassemble the oven, and wrap it with a solenoid > of teflon insulated heating wire. It worked nicely, except that it > made a magnetic field, and shifted the frequency with temperature.. > > <Whack!>... DOH! > > Next, I found some thin coaxially shielded nichrome wire meant for > I know not what... maybe electric blankets? And put a crimp on > connector at the far end to make a coaxial hairpin loop. I tightly > wound that around the oven, and used "great stuff" urethane foam > to replace the oven's insulation. > > It worked quite well, until the next thing went wrong, and I put the > reference on my to be fixed someday shelf where it has lived ever > since. > > Back then, I didn't know anything about capacitor plague, and carbon > composition resistor drift, and all the usual failure modes of HP > equipment... I ought to take it off of the shelf and give it a go > once again... should be easy... for an engineer that now has 35 years > more experience... Right? > > -Chuck Harris > > > cdel...@juno.com wrote: > >> Hi, Just thought I'd share some info on repairing a defective HP 5065A >> lamp oven. >> These ovens can fail either shorted to the oven cylinder >> or have interwinding shorts. >> I have repaired three optical units so far with this failure. >> The original winding was insulated twisted pair wound >> directly onto the Aluminum oven cylinder. >> I used teflon insulated heater wire, Pelican P2332ADVFEP.009BL. >> It is approx. 5 Ohms/ft. and I use a 50 Ohm length doubled and then >> twisted tightly. >> This is then wound onto the oven cylinder which is first covered with a >> single layer of kapton >> tape. >> The original thermistor is replaced with a DigiKey 615-1007-ND. >> The thermistor MUST be surrounded by heat sink compound. >> I also install a digiKey TO220 100 degree thermal cutout switch for >> future >> protection. It is mounted to the top of the lamp assy. using one of >> the 3 original mounting screws. The thermistor and heater wires are >> brought out tie wrapped along the original cable and then soldered >> to the appropriate pins on the db9 connector. >> >> Cheers, >> >> Corby >> > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.