[time-nuts] AN/URQ-13 FE-15a oscillator question

[Bob kb8tq]

Hi

Indeed the outer oven (as a minimum) needs to be 5 to 10 C above
the maximum ambient. If it’s not it goes out of regulation (runs away)
and you loose any benefit from it. ( = it now works against you ). 

The inner oven as a minimum needs to be 5 to 10 C above the outer
oven. Again if it is lower, you can / will get into the same runaway 
issue. 

Those offsets are dependent on the way things are insulated. If you are
using a dewar flask, 5C is probably not going to work for you. 

Your inner oven *also* is impacted by the turn temperature on the crystal
being used. This *might* have a 20C range. That would put the maximum
inner oven temperature at 10 + 10 + 20 = 40C above the maximum ambient. 

Needless to say, if the max ambient is 85C, this will get the inner oven 
components up pretty hot. That’s not a real good idea. Derating the heater
is pretty easy, derating *everything* in there is much more complex. You
do not often see 85C upper end double ovens ….

One *could* also ask: “is all this worth it?”. List members *have* written 
papers addressing that point :) 

Bob

> On Feb 11, 2021, at 10:05 PM, Paul Alfille <paul.alfille at gmail.com> wrote:
> 
> Shouldn't the outer oven be cooler than the inner oven except during
> warmup? I would think the inner electronics would be generating heat.
> 
> Paul Alfille K1PHA
> 
> On Thu, Feb 11, 2021 at 9:30 PM paul swed <paulswedb at gmail.com> wrote:
> 
>> 50C is what I have sort of seen over the years. Just wondered could there
>> have been a lower temp version. That made no sense. But then this beast has
>> never made a lot of sense. The $20 mystery from Frequency Electronics.
>> Thanks Bob
>> Paul
>> WB8TSL
>> 
>> On Thu, Feb 11, 2021 at 8:08 PM Bob kb8tq <kb8tq at n1k.org> wrote:
>> 
>>> Hi
>>> 
>>> Even for an outer oven, anything below 60C / 140F would be low enough to
>>> run into significant problems. On a mil device, an upper end temperature
>>> on
>>> the equipment likely would be over 70C. The outer oven would need to be
>>> 5 to 10C above that.
>>> 
>>> Bob
>>> 
>>>> On Feb 11, 2021, at 5:55 PM, paul swed <paulswedb at gmail.com> wrote:
>>>> 
>>>> OK I have had several responses and 110F is low as I expected.
>>>> Wonder if I am being faked out? Perhaps by an inner oven and I am only
>>>> reading the outside of the outer oven. The Older URQ10 and newer URQ23
>> do
>>>> have 2 ovens. The meter switch for test is only labeled 1-9. no other
>>> clues
>>>> to the function. I noticed 2 positions change with warm up. Sort of
>>>> supports the 2 oven theory.
>>>> Really do not want to take what might be the outer oven off to put the
>>>> probe in.
>>>> Thanks everyone.
>>>> Paul
>>>> WB8TSL
>>>> 
>>>> On Thu, Feb 11, 2021 at 5:32 PM Bob kb8tq <kb8tq at n1k.org> wrote:
>>>> 
>>>>> Hi
>>>>> 
>>>>> 110 F makes very little sense unless you are in a very cold climate.
>>>>> For military gear (or any gear for that matter) 43C on the oven just
>>>>> doesn’t work.
>>>>> 
>>>>> 110 C would make sense in a very high temperature environment.
>>>>> (think of 85C upper end ….).
>>>>> 
>>>>> Bob
>>>>> 
>>>>>> On Feb 11, 2021, at 2:18 PM, paul swed <paulswedb at gmail.com> wrote:
>>>>>> 
>>>>>> Hello to the group.
>>>>>> I have had a AN/URQ-13 or FE-15a oven oscillator for years.
>>>>>> Its never worked correctly and in reality some early alpha build.
>>> (Funny
>>>>>> that its labeled 15a)
>>>>>> Looking online there is no documentation that I have been able to
>> find
>>>>> over
>>>>>> the years.
>>>>>> However in another discussion on a AN/URQ-23 that does have a manual
>>> and
>>>>>> schematics I realized my guesses on power could be totally wrong.
>> Using
>>>>>> voltages like the URQ23 the URQ13 actually behaves fairly well. I was
>>>>> lucky
>>>>>> that I didn't destroy something with my original guess.
>>>>>> That said what I find odd is the internal crystal oven runs at
>> exactly
>>>>> 110
>>>>>> degrees. Its repeatably warms to that level with a range of supply
>> from
>>>>> +/-
>>>>>> 12-15V.
>>>>>> Does 110 degrees F make any sense at all?
>>>>>> Thank you
>>>>>> Paul
>>>>>> WB8TSL
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>>>>> 
>>>>> 
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