It is to dampen microphonics caused by physical vibration. Usually used
on the detector tube.

-Bill


xcalibur wrote:
Recently acquired a vintage 1927 A****er-Kent Model 33 TRF radio.
It has six identical CX301A tubes with one exception: Tube#4, which I
believe to be the final tube of the TRF section (input to the two AF
tubes),
has a heavy chrome cap over the top of it. This cap is supported by a
couple felt pads between the cap and the top of the tube. There appears
to be no provision to ground this to the chassis (and use as a shield).
Was/is there a function of this cap, or was it just a cosmetic thing ?
Did all the tubes originaly have these caps ?

PS: Why does the name "A****er" appear with stars between it ?
(Word Police: Please fix the censor pgm to allow the A-K name, there's
nothing vulgar about it.)