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 <[email protected]> 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/mailman/listinfo/time-nuts and follow the instructions there.
