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BCM
Durkin Tactical Franklin Armory
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11/2/2022 4:30:06 PM
Posted: 4/26/2022 6:32:42 PM EST
Hey, I've got a question about a pretty weird Photonis tube. It's 18mm inverting, but has a third terminal on the side (for manual gain I believe). Applying 3V to the two outer +/- terminals seems to do nothing, but the tube is in pristine condition. So here's the question: is this tube:
a) Completely bonkered, loss of vacuum or similar
b) Has a bad PSU and needs repotting
c) Needs the third pin connected in some way? Maybe a resistor?
d) Something else entirely
Some people have suggesting this is a wiring issue possibly lowing the gain to unnoticeable amounts, and maybe would be fixed by bridging the egac pin to ground with a resistor. Any advice would be greatly appreciated.

Ascii art of tube pinout for reference (Side view, fiber output on right hand side)

      -------------------
      |         [  +  ]   |
      |         [   ?  ]   |
      |         [   -  ]   |
      -------------------
missing
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