[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.
Bert Kehren
In a message dated 7/3/2014 9:37:27 P.M. Eastern Daylight Time,  
not.again at btinternet.com writes:

Hi  Bert,

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 
work, how   
>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 
>Bert Kehren
>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 
>input ?
>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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