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" time-nuts-boun...@febo.com
To time-nuts@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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