IERC tube shields

[johnsonad]

Let me preface that this is unnecessary.  I did it as an experiment.

I received a few IERC tube shields that fit the 5670 tube and wondered how well they worked.  After the amps warmed up I measured an average of 196F on the 5670 tube using a thermal gun.  After applying the tube shield for five minutes, the shield was removed and measured at the same location on the tube.  The envelope temperature dropped to an average of 155F.  This was repeated a couple of times with similar results.

It does raise a few questions.  Is there a minimal operating temp for a tube?  Does any decrease in temp potentially increase tube life?   

Thanks!

[Doc B.]

Yup, they were reputed to reduce envelope temp by about 15%, and that correlates to about a 15% increase in tube life. I have a crapton of them in boxes in my lab that I have been meaning to put up for sale for years and years.