Great news and what a deal a dead 5065 lives. I don't think its that critical and not sure how you would test it. But do get a good stable high temp. As I recall the rn70 series was pretty good. For the moment you can reassemble it and see if the rest works the resistor should hold up for a 30 or so minute run. Don't push it if its a plain old cheapy carbon. Best of luck, though I think you have had plenty so far. Regards Paul WB8TSL
On Tue, Feb 21, 2017 at 7:56 PM, David Scott Coburn <[email protected]> wrote: > I installed a 10 ohm 1/2 watt carbon resistor and the Rb lamp came right > on! Woo-hoo! > > > I will get a better quality, high temperature resistor to replace this > one. (RN70?) > > > How critical is the resistance value? 10 ohm? 12? Is there a way to > test for an optimum value? > > > Scott > > > On Tue, Feb 21, 2017 at 10:01 AM, paul swed wrote: > > Totally agree with the try a 12 ohm resistor. Nice simple and low risk. >> If thats actually the issue then you do need to obtain a high quality >> resistor that can live in a hot environment. Anything will work for a test >> run. >> Regards >> Paul >> WB8TSL >> >> On Tue, Feb 21, 2017 at 2:22 AM, timeok wrote: >> >> >>> Hi Scott, >>> the emitter resistor have to be in the range 9 to 15 Ohm. Probably the >>> high temperature and current have burned it out. >>> Replace it with a 12 Ohm 1/2 W resistor, It will work. >>> Luciano >>> www.timeok.it >>> >>> >>> From "time-nuts" [email protected] >>> To [email protected] >>> Cc >>> Date Mon, 20 Feb 2017 19:25:37 -0500 (EST) >>> Subject [time-nuts] HP5065A Rubidium questions: some progress >>> Hi All, >>> >>> >>> Thank you all for the very helpful suggestions! >>> >>> >>> I will try to reply to you all in this one post. >>> >>> >>> I opened up the A12 assembly and was happy to find that the lamp, >>> windows, and reflector all appear to be in good physical condition. >>> There is some very light corrosion on the aluminum reflector, all of >>> the windows are clear, and the photodiode is very visible at the >>> bottom >>> of the oven. >>> >>> >>> The Rb bulb looks very slightly darkened, maybe like a pair of very >>> lightly polarized sunglasses. >>> >>> >>> I measured the resistance of the 20 VDC supply line to the lamp >>> oscillator and it is 3350 ohms, just as Corby said and as I see it >>> should be from the schematic. >>> >>> >>> I measured the current to the lamp oscillator and it is only about 13 >>> mA. Paul mentioned that if it was about 15 mA it was probably not >>> working. And, Poul-Henning mentioned that it should draw about 3W >>> when >>> working, which at 20 VDC would be 150 mA. >>> >>> >>> I powered up the lamp oscillator with it on the bench and I do not see >>> any light from the bulb. I am assuming that it should be visible, but >>> I'm not sure! What is the spectrum from these lamps like? Visible, >>> UV??? >>> >>> >>> I measured the resistance of the small coil wound around the bulb, it >>> is >>> about 0.3 to 0.4 ohms, which seems reasonable. >>> >>> >>> (It looks like someone has been in this assembly before. There is >>> solder flux on the transistor leads, the 20 VDC connection, and the >>> bulb >>> coil leads.) >>> >>> >>> One odd bit is that the resistor in the transistor emitter leg >>> measures >>> about 350 ohms (this is R3 in my schematic). The schematic says it >>> should be 10 ohms. This resistor is on solder posts, so it looks >>> like a >>> 'selected at assembly' item. Corby: it this the 12 ohm resistor you >>> mentioned? >>> >>> >>> The voltage across this resistor when the power is on is about 1.6 V. >>> >>> >>> The base voltage is about 2.2 V (this is across CR1 also) and shows >>> "flat-lined" on my scope with the board powered. >>> >>> >>> So, I'm betting that the collector of the transistor is cooked. (The >>> base-emitter drop of ~0.6 V probably means the base and emitter paths >>> are still OK.) >>> >>> >>> But, it is also possible that the R3=350 ohms is way out of line?? >>> >>> >>> Comments welcomed. >>> >>> >>> Corby: the serial number for the unit is 0968A00302. It has a >>> 105-6012 >>> quartz oscillator, and a mechanical PP clock. The A12 unit is a >>> series >>> 1220, and is green in color. (The OCXO and the bands around A12 are >>> blue.) The A12 unit has a warranty expiration of 30 April 1978. It >>> has >>> had its "Mag Filed" and "Thumbwheel" blacked out with marker and new >>> values written in. >>> >>> >>> Cheers, >>> >>> >>> Scott >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to https://www.febo.com/cgi-bin/ >>> mailman/listinfo/time-nuts >>> and follow the instructions there. >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to https://www.febo.com/cgi-bin/ >>> mailman/listinfo/time-nuts >>> and follow the instructions there. >>> >>> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/m >> ailman/listinfo/time-nuts >> and follow the instructions there. >> >> _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/m > ailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
