[R-390] Alternative to IERC tube shields?

[Barry]

> An alternative is to put two of these in series; this also drops the
> RPMnicely, but since you have two fans, you're moving twice as much air and
> not having to put up with the heat from the resistor. 
> 
> -- 
> Mike Andrews, W5EGO

A thermister, a couple of tubes, transformers, and an assortment of other components, and I'll bet someone could design a variable-speed fan that would regulate the temperature within a degree or two.  Maybe it could use another 3TF7 to regulate the filaments on the circuit so that changes in the line voltage would not affect the temperature regulation.

Barry - N4BUQ (duckin' and runnin')