[time-nuts] HP5065A Rubidium questions: some progress
paul swed
paulswedb at gmail.com
Tue Feb 21 15:01:33 UTC 2017
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 <timeok at timeok.it> 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" time-nuts-bounces at febo.com
> To time-nuts at febo.com
> 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
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