[morzh]

Larry,


So it was then changed at some point.

Originally the tube was 6T5. Unlike the others it has concentric indicator, not the sector type.
Electrically and pin-out-wise it is exact same as 6U5, and this is why 6U5 (which is likely what you have) typically is the replacement.
However, 6U5 became also pretty expensive (likely for this very reason) and some folks (myself included) use 6E5, which is cheaper, also pin-compatible and available from many manufacturers of the past, and its octal version 6E5S (Soviet) is widely sold around, often from Eastern Europe.
It has different sensitivity and so requires changing a resistor or two.

I need to get a new belt for mine. I put Adams manufacturing (since retired and the business was transferred) neoprene belt in, and for a few years it worked, but since froze. Neoprene belts require constant exercise.