[time-nuts] HP5065A Rubidium questions: some progress

[paul swed]

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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