[time-nuts] 10811 warmup (Jason Rabel)

[Daun Yeagley]

Hi Jason

I might have something for you on this.
All this talk about the 10811's forced me to get off my duff and get working on
two 10811's that I have and have been sitting on my shelf for several years
(like well before I "retired" from Agilent in '03).
One is a 10811-60102, and the oven heater was bad. I had opened it up several
years ago, and that was about as far as it got.  Now that Jack has made the PDF
of the manual, I had no excuses left.  It is now running after replacing the
10V. regulator, U1, and the two one ohm emitter resistors!
The second one is a 10811-60160, which was still in the original plastic wrap!
Well, I decided to power it up too, so I built the little test harness described
in the manual (this is the model with the edge connector).  Well, I couldn't get
the oscillator to draw any current!  I really didn't want to open up a virgin
unit, but I didn't see any other easy choice.  After pawing around for a while,
I came to the conclusion that there is an error in the manual.  Pin 2 is indeed
a ground, but it is only for the 10MHz output.  The "real" power ground for the
oscillator is actually on pin 4!  I tied pins 2 and 4 together, and it is
working fine. I would suggest that you check this out carefully... maybe that's
why it won't run.
At this point I need to make a run over to John Ackermann's and get them netted
in more precisely, as at the moment I don't have a better standard here at the
house (I'm working on it though!).  I can bring them to within 1 Hz using my
Spectrum Analyzer, and that is close enough for the two to injection lock, since
I'm currently running both of them from a common lab supply.
Next on the agenda is to get one of my FRS-C Rb's put together.

Daun 

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf
Of Jason Rabel
Sent: Sunday, January 21, 2007 4:36 PM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] 10811 warmup (Jason Rabel)

Thanks Bruce,

I think we have gotten a little off-subject here... My issue is not with the
oven, but the oscillator circuit itself. I'm not getting any signal on pin
1.

I removed the assembly from the insulation easy enough, I haven't gotten any
further yet, been troubleshooting my shera board today. I don't hear
anything rattling inside so I don't think the crystal is physically broken
like Chris mentioned. 

Jason



-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Dr Bruce Griffiths
Sent: Sunday, January 21, 2007 3:28 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] 10811 warmup (Jason Rabel)

Jason

As long as the thermistor is still within the oven mass and the 
temperature regulation circuit is functioning OK, the oven should 
actually be OK.
However the temperature control loop may oscillate as the thermal time 
constant for which it has been compensated has been drastically 
decreased by removing the insulation from the oven mass.
If the oscillation amplitude is sufficient it is conceivable that some 
damage due to excessive temperature may occur.
However, the dissipation of the oven heater transistors is limited by 
the control circuit so the temperatures reached may not be high enough 
to damage components.
The turn on current limit circuit limits the heater transistor emitter 
current to about 0.52A with a 24V heater supply, limiting the maximum 
dissipation in the heater transistors to about 12.5W with a 24V heater 
supply, which is probably insufficient for the inner oven mass to get 
very hot once the insulation is removed.
The principal problem is personal burn injury .

Bruce



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