[time-nuts] DIY FE-5680A lobotomy (disable temp compensation)
EWKehren at aol.com
EWKehren at aol.com
Fri Jul 4 07:11:02 EDT 2014
Good Morning Angus
Let me start out by saying the FE5680A project was intended for time nuts
and the unit will not be part of our bench, so the work on it is limited. As
far as Rb's are concerned our focus is on FRK and HP5065. Looking back I
would most likely not suggested it, had I known how much time it took up.
How ever it also made us take an other look at Rb control, switching from
analog to digital and resulted in looking at the FE 405 B. So it is worth it.
Using heat pipe for the FE 5680 was the outcome of many test with heat
sinks and other heat pipes. The big advantage of the heat pipe is the ease of
removing the heat but it also has its limitation. Its biggest limitation is
the fact that it works on the principle of converting a liquid to a vapor a
process that takes a lot of heat. so you can not expect it to bring the
temperature down to 20 degrees. And to much heat pipe is not good either. In
the one you see in the picture I may have to deactivate one of the pipes.
The ALU p;ate is 3/16" and the LM335 is on the back. I took out the bottom
plate of the 5680 and between the two mounting holes of the ALU spine is
plenty of room to install a SMD version of the 335. Temperature is 40C but not
that critical but range is limited by the function of a heat pipe.
You may want to experiment and if you are going to do some serious work
contact me off list, not secrets, but the pictures can not be attached on this
list because of file size limitation.
When I first got the 5680 I did a crude temperature control using a fan a
heat sink from an ATT Rb a LM335 along with a bang bang op amp circuit. I
previously published picture and schematic. Temperature stability was better
than 0.1 C. We have done extensive work on controlling the back plate
temperature of a FRK and now get 0.01 C. We learned a lot and I like to share it
since it will also apply to the heat pipe. The biggest problem is the fan.
We do not have speed control but vary the speed by changing the fan
voltage. We use a linear controller also previously published but have to be
concerned about fan starting voltage. We want to be able to hold constant
temperature over a 10C ambient change. Found that 12 V fan is best and at the
same time looked for low noise. Learned also that more heat from the back
plane helped with the operating range. Now all voltage regulators and the fan
power transistor are along with heat sinks are mounted on the back plate.
Side benefit is more stable voltage out of the regulators.
This would be an ideal project for time nuts, since the results will apply
to other Rb's not only the 5680 and benefit the community. I will stay out
of the discussion since we have our hands full.
In a message dated 7/3/2014 9:37:27 P.M. Eastern Daylight Time,
not.again at btinternet.com writes:
I am thinking about testing a heat pipe on a fan cooled setup I use.
The first temp controlled chassis I did used a peltier and works very
well, but was a lot more work to do and is much more power hungry.
The main problem I find is not the temp controller itself, but rather
the change in the temperature across the chassis as the ambient
changes. However good the temp controller is, it only controls a
single point, but other points further away from the sensing
thermistor can vary a lot.
I noticed you posted a picture of a heat pipe cooler a couple of weeks
ago - did you happen to compare the temperature across the unit with
direct fan cooling and the heat pipe cooler, or with different heat
On Sat, 28 Jun 2014 12:37:37 -0400 (EDT), you wrote:
>Will someone beside us use heat pipe. Would love to have an impendent
>input. What does it take to get a test going. Scott has done a lot of
>about some one else step up to the plate. There are a lot of time nuts
>there with the 5680A,many for the first time will have a very good
>reference and some of our experts with proper equipment can make a big
>In a message dated 6/28/2014 12:20:12 P.M. Eastern Daylight Time,
>newell+timenuts at n5tnl.com writes:
>At 04:32 AM 6/28/2014, wb6bnq wrote:
>>monitoring process ? In other words have you traced out the
>>connections to see what is driving the pin you think is the temperature
>No. I've only traced back from the ADC input to the voltage divider.
>>The next big question is have you monitored the frequency and its
>>stability, externally, to observe what effects are taking place when
>>you disable this input to the A/D ?
>I have not.
>>That sounds complicated and messy but may be easier than it
>>appears. An appropriate container would be:
>It does sound messy. I don't think I'm willing to dunk one of my units.
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