[R-390] Black Tube Shields, IERC

[Jon Schlegel]

Tisha,

Great post.  It sounds like your dab of flat black paint was key in 
getting the measurement consistency needed to use the optical 
pyrometer.  I'd be interested to hear more detail if decrypting your 
notes wasn't too much of a task.  Thanks for the info.

Regards,
Jon Schlegel, WA3MVM



At 12:09 PM 4/17/2009 -0500, Tisha Hayes wrote:
>A few years ago I went through the process of measuring envelope
>temperatures on a wide range of tubes in a SP-600 with different tube
>shields. It did turn out that the black IERC tube shields did make a
>difference in envelope temperature.
>
>Generally speaking I was seeing 20-60 degrees F difference across the range
>of shields. I had tested with the following;
>
>Factory default, silver cam-lock tube shields with the loading spring to
>keep the tube down it the socket
>
>No shield at all, just using ambient air and radiative cooling from the
>tubes.
>
>IERC tube shields
>
>IERC tube shields with a dab of thermally conductive paste applied to the
>finger-stock grippies inside of the IERC shield (to improve thermal
>conduction between the envelope and the shield).
>
>I had strictly controlled air-flow and room temperature and would let the
>radio stabilize for an entire day before making measurements. This was also
>in a room where I was not moving around in so there was a bare minimum of
>air movement. Room temperature was at 70 F. I measured temperature with an
>optical pyrometer and had put a dab of flat black paint on the top of the
>tube (so I could get consistent temperature readings without gluing
>thermocouples everywhere).
>
>By far the worst was the silver tube shields. If anything these kept the
>heat on the envelope with some temperatures well above 250 F
>
>When I used the IERC's I could get the temperatures in the 150 to 160 range.
>If I used the thermal paste it would knock the temperature down another 5-10
>F on average.
>
>Interestingly the chassis temperature went up when using the IERC shields
>due to the mechanical connection at the base of the IERC shield and the
>radiative cooling off of the shields. If you have a concern about capacitor/
>resistor aging this may offset your worries about tube temperatures.
>
>In every instance, the use of a small computer-fan to move air across the
>chassis really helped out in lowering the temperature of the tubes and the
>chassis. This does not need to be a gigantic fan.
>
>If someone was really interested I could drege up my notes and put them into
>a human-readable format. At the time I was doing my little experiment to
>justify the cost of the IERC shields. (I did end up finding IERC shields for
>every tube operated device I have)
>
>--
>Ms. Tisha Hayes
>
>----------------
>"I will not recant the truth. I am corn, not chaff; I will not be blown away
>with the wind or burst by the flail. I will survive both."
>-Walter Milne, 1558
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