[time-nuts] hp 10544A and 10811A ovenized oscillators

Neville Michie namichie at gmail.com
Fri Nov 2 20:06:40 EDT 2018

HI I have had experience with two 10811 oscillators which turned out to have the same problem.
Inside there is a gold plated ferule mounted in teflon at the junction of the tuning diode and 
the transistor, obviously considered a very high impedance point, or may be just sensitive to leakage.
In both cases the joint was not soldered. A touch of solder and they behaved perfectly. Before, 
they did not respond to the adjusting voltage.
Thinking about it again, maybe the diodes were variable, so they assembled the oscillator so that 
the oven could operate, to see if they covered a tuning range test. If they did not they could change the diode.
If they forgot, they did not go back and solder the joint.
I have been feeling bad for some years as I bought a 10811 from a ham on the popular trading site, and when 
I complined that it was out of range and would not tune he refunded my money. A few months later, when a 
previously good unit failed, and I did a post mortem, I found the problem, and checking the first bad unit 
it had the same problem. When I looked for the ID of the guy who sold it to me I could not find it,
and I feel I owe him the price. After all he was a ham, not some shonky dealer.
So if two samples in four units I have had the fault, it is worth checking if troubles appear.
Neville Michie

> On 3 Nov 2018, at 06:15, Bob kb8tq <kb8tq at n1k.org> wrote:
> Hi
> The change is suspiciously close to the electrical tuning range of a typical HP OCXO. 
> The answer may be a failure of the bias on the EFC line …..
> Bob
>> On Nov 2, 2018, at 2:51 PM, Walter Shawlee 2 <walter2 at sphere.bc.ca> wrote:
>> I have several of these as the -010 high stability timebase options
>> in my various HP counters, and generally they work very well, with
>> usual errors under 0.01Hz and very minor drift over time.
>> a few months ago, I had a power interruption, and black out for a few hours,
>> along with the usual erratic restart from the power company. shortly afterwards, I built a nice little
>> homemade TM500 plug-in OCXO unit to fit on my bench, and without giving it much thought, used
>> my bench standard (an hp 435B-K26 power/frequency reference with an internal 10544A) to cal it.  all seemed good.
>> soon after, I was working on an hp 5334A counter, and added a 10811A as as upgrade from my
>> spares and suddenly, I had a big 1.3Hz error at 10Mhz when I cross checked it to my bench references AND a rubidium. I brought over my recently cal'd rubidium from the upstairs lab, and yes, there was now clearly a big step error. my upstairs 5335A with a 10811A had the same step effect!
>> these 2 units are always on for stability, so both got cycled the same way during the power failure.
>> it seems that the power failure cycle had bumped the internal 10544A oscillator inside the 435 by that amount, as well as the 10811A inside the 5335A. I have never seen that effect before, both the ovenized osicllators from hp have been very reliable for me, so I thought I would put that info out in case anyone else has seen this effect and knows the cause.
>> using the rubidium (which I keep off until I need it, and wait for at least 2 hours for best settling), I reset everything back to a flat 10Mhz, and all was well, except that the first 10811A I put in the 5334A conked out (oven still fine, but the oscillator went dead, giving the dreaded "no osc" message on the counter). another spare fixed that, and two days of drift testing to get everything back where it belongs.  anybody want the bad 10811A?
>> anyway, just thought the information might be handy for others.  the EFC range on the 10811A/10544A is *only 1Hz*, so such a big jump is unusual to say the least. it required the main coarse adjustment to fix.
>> The 435B-K26 is a pretty remarkable widget if you ever see one, it makes a great 10Mhz reference and 1mW power reference in one little box, very useful for an RF bench. One of hp's rare and forgotten treasures.
>> all the best,
>> walter
>> -- 
>> Walter Shawlee 2
>> Sphere Research Corp. 3394 Sunnyside Rd.
>> West Kelowna, BC, V1Z 2V4 CANADA
>> Phone: +1 (250-769-1834 -:- http://www.sphere.bc.ca
>> We're all in one boat, no matter how it looks to you. (WS2)
>> All you need is love. (John Lennon)
>> But, that doesn't mean other things don't come in handy. (WS2)
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