10BP4 without Ion Trap?

Originally posted by jshorva65
10BP4A used the same gun as 10BP4. The only difference was a faceplate of gray filter glass instead of clear. The 10BP4C and 10BP4D (clear and gray filter respectively) versions were the ones with aluminized screens. Aluminized-screen tubes are easily identifiable by the aluminum coating being visible particularly near the front of the "funnel" at the junction of the faceplate just ahead of the front border of the outer "dag" coating and near the anode connector where the tube was masked to keep the outer "dag" away from the HV terminal. If you see a silvery coating through the glass in these areas, the tube is probably equipped with an aluminized screen (example, 10FP4).

1. The 10BP4 and 10BP4-A require a double field ion trap.

2. The 10BP4-C and 10BP4-D require a SINGLE FIELD ion trap, even though they are aluminized.

3. There is no telling what a rebuilder might have done, but if straight guns were used for rebuilding, they most likely would have been used on the C and D versions, since these already had aluminized screens. Rebuilders usually do not replace the phosphor screen, so the A and B versions should have been rebuilt with bent guns requiring an ion trap (unless the screen was replaced, but this would make it a C or D version).