>>Another problem is that it seems unlikely
>> that (since sound travels in air) an amplifier could produce a stentorian
>> bang from an arc inside the vacuum.
>I can't comment on the other things you mentioned, Rich (lack of
>but your reasoning seems poor here. The arc you mention has a point
>of origination, and a point of termination. Both of these points are
>are on physical objects inside the tube which are by necessity connected
>mechanically to the outer envelope of the tube.
** the bang is too loud for transmitted sound through the anode stem.
The bang sounds like an air burst to me. I've heard them as loud as a
12ga shotgun blast. 
>Thus the arc doesn't exist
>entirely in a vacuum (pun intended). And BTW, when the bang is due to
>a parasitic oscillation what is the mechanism by which the loud bang is
>generated? External arcing in the tank components?
** The concurrent flash seems to come from the DC side of the blocking
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,