21" RCA B&W from 1955

[radiotvnut]

A friend gave me this 21" RCA table model B&W set that is housed in a metal cabinet and the CRT, a 21AMP4A, appears to have an intermittent K-G1 short that won't blow out (it's a shame because the emission tests "good").

Actually, I had a melt-down because the 4 CRT testers that I have easy access to all appear to have issues. The first tester I used was a mid '70s RCA and it showed a hard K-G1 short, and "remove shorts" did nothing. In fact, it appeared that this aspect of the tester was dead (before now, I've never used the "rejuvenate" or "remove shorts" function of this tester).

The second tester I tried was a B&K 466 with a flaky meter. I could align the pointer with the screw on the meter Lense, turn the tester on to set the heater voltage, and then the meter pointer would land in the incorrect place when I turned off the tester. Finally, I got the meter to behave, but who knows how long that will last. That tester also showed the same K-G1 short and the instructions say to let the tube cool for 5-10 minutes, before attempting to remove a short. That did nothing and I determined that the short only exists when the tube is hot. So, I quickly hit the "remove shorts" button before the heater cooled and it flashed in the neck, but it didn't remove the short. The short seems to be intermittent when tapping on the neck, but it does not go away for any length of time.

The third tester that I tried was a B&K 465. It indicated no short (possibly a fault with the tester) and I could not properly set cut-off with that tester (meter stays about mid-scale, no matter the knob setting).

The last tester that I tried was a Sencore CR70 and the last time I used that one, it would not register emission, but would rejuvenate a tube. Today, the heater would not light and I suspect the problem is with the adapter cable.

One day, I need to sit down and go through all of these old CRT testers. The ones that can easily be fixed will stay in service and the "dogs" will get thrown out. However, today was not the day for that because as mad as I was (all I need to do is test a CRT, something that should take 5 minutes, and got four freakin' CRT testers that all appear to have issues....I just want something that works when I need it to work), I would have smashed all 4 of them and then regretted it later.

Anyway, I'm going to check with a friend to see if he has a 21AMP4A tube, or a substitute. If he doesn't, I'm probably going to scrap the set because buying a tube plus the high shipping cost probably would not be worth it.