Today's Mystery Guest (RCA CTC-4)

[Phil Nelson]

Testing the CRT with my Sencore CR-70 doesn't have me dancing, so far. I measure .7 ohms between pins 1 and 14, so the heaters are not completely open.

Before connecting the universal adapter to the CRT, I set the heater voltage to 6.3. When I connect the UA clips to the pins and turn on the tester, the voltage drops to around 3 volts and the CR-70 makes a high whining noise. If I disconnect a heater pin, the noise goes away and the voltage goes back to normal.

The CRT passes the H-K shorts and G1 shorts test, but the needle doesn't move at all for cutoff test or emission test. This is the same for all three guns.

Suspecting operator error, I double-checked the manual and looked at an old photo of my tester connected to the 21CYP22 in my CTC-7. With exactly the same settings, the tester worked normally and checked the emission, etc., for each gun in that tube. I even hauled the tester out to check a B/W tube, and the tester works normally.

Not sure what is going on here. For an old B/W tube, I'd just let it sit on the tester for a while, to see if it wakes up under normal or slightly elevated filament voltage. I don't see any glowing inside the base, but the base is getting warm.

Phil Nelson