[Penthode]

This evening was the moment of truth: initial test of the 15GP22

I have a BK467 and a Sencore CR-70 CRT testers. I chose the CR-70 as it has the universal leads and the BK-467 hasn't the 20 pin CRT socket connector.

The 15GP22 appeared to light properly. It also looks as if the original 15GP22 socket was damaged and the previous keeper made an epoxy mold to fix it. Seems a satifactory fix and it is translucent which allows the filament glow to pass.

As I indicated earlier, I could not see any trace of white around the getter which offered hope the tube still had a vacuum. My initial setup to test did not allow me to set cutoff on the 15GP22. I decided to try testing a known good 10BP4 with the same negative result. I searched back on this forum to find any information and one post revealed adjusting the the cutoff, the G2 voltage should swing between 20 and 400 volts. I have not been able to find a schematic or any service data on the CR-70 and so took the CR-70 apart to find what was the matter. It appears one of the connectors was loose and reseating it got it working. I was able to test the 10BP4 now with success.

Back to the 15GP22, I set up the Sencore on first the RED gun, then Green and finally Blue. I was able to swing the cutoff adjustment for the needle in the box. Importantly the Cutoff adjustment swing was smooth from minimum to about mid scale deflection without any sudden jumps. I have read sudden jumps adjusting cutoff may imply ionization due to gas. Testing emission, the needle reached a respectible good on RED, GREEN and BLUE as depicted below. It looks like I may be lucky.

The pictures below depict:
1) RED Cutoff
2) RED Emission
3) GREEN Emission
4) BLUE Emission
5) Tube neck glow

So the chassis restore is next. I have read a lot on this forum about the 15GP22 and the use of Vacseal or its equivalent. This poor tube appears to have suffered in storage over the years and would appreciate opinions on the tube preservation.