[Radioroslyn]

Great!  That picture is worth a thousand words!  I don't have that spring in mine and not sure where it went.  Makes a lot more sense now.  I'll see if I have one small enough to work.

On the 75 tube, would the bottom diode be D2 pin?

Thanks!
Mike25

Wasn't trying to be cagey about the diode pin but I couldn't find a tube diagram that was drawn like the one in the schematic. The diode plates where on the right side rather than the left so wasn't sure which diode was which. So it's the one that isn't connected to the IF transformer. Must use a high impedance meter to measure this voltage.

Glad mine had a spring in else these thing would be a great unsolved mystery!!!!! I found it a few months ago when I was working on the 660L. The original one had an open coil so I was scrounging around looking for a replacement. I was a bit puzzled that the coil resistance is much lower than the other styles their about 1.4K. Now that I look at it it may be that it's more efficient. The vane has a small ear that passes pretty close to the coil. Perhaps it doesn't require as much  magnetism because of the close proximity of the vane and since has a spring it doesn't have fight the fixed magnet's magnetism. And of course it's cheaper to make, less time to wind, less copper.