Thanks, I'll have to find out where to turn in my EE degrees for not thinking about that. I disconnected the other end so I could remove the chassis. The only markings on the tube is a label that says 21EAP4. Is it still inconclusive whether it's 2.34 or 6 volts until I do the current test?

Thanks John, the process you're documenting will be helpful. On your adapter mod, did you just splice the yellow alligator clip cables in to the 2 heater cables or did you replace them? I'm guessing it was splicing so you could still run the CRT tests.

The 21EAP4 is a 2.3V tube. If the tube was 6.3V, it would have a different type number.

In my humble opinion you will not know conclusively until you do a current test. I have seen tubes marked 21EAP4 that turned out to be 6.3V tubes. It's a great feeling when you discover one of these 6.3v tubes that are incorrectly marked because it almost certainly means that someone else passed it up thinking it was dead.

Right, I just cut one of the heater leads and extended each end and attached clips, using the clips to attach the meter leads. That way when I'm done with the current test I can just clip the two ends together. There's probably a better way to do it but this way works for me.

That statement should be true but it's not. I think just through lazyness when the CRTs were rebuilt the markings weren't updated. I've seen that condition on the last three CRT in a row that I tested. Two of the last three CRTs were marked "21SFA" inside... There is no such tube. The current test proved this CRT to be a very good 6.3V tube.

I don't think 21SFA is a valid number, it probably just means a 21" Short Focus Aperture. 21EAP4 is the original 21" Predicta CRT number. I would go by whatever number is glued to the CRT, not the housing.

The last two Predictas I got had 6.3 volt tubes, I found it out through simple trial and error, if it won't light at 2.3 then go up slowly to 6.3 and see if it does, just don't start at 6.3. They also had stickers saying they had been converted to the 6 volt tube but I wasn't taking any chances.

I also question is 2.35 is the correct voltage? I also see some information that says they are 2.68 volts and my B&K has a 2.68 volt mark on the meter but not a 2.35?

Yes, 2.35 is correct for the 21EAP4. 2.68 for the 17DAP4.

The problem with testing that way is that the filaments on those tubes are fairly robust. One could run a 2.3v filament at 6.3V for several hours before it would burn out. One could walk way and think they had a 6.3v CRT because it held up for a few minutes at that voltage only to put it in a set and have it burn out or never work at all. The Current test is fast and definative. I haven't found one Predicta CRT that was marked with the correct voltage. I'm sure they're out there but I haven't found one, Most of the time I can't find any markings on the CRT at all. I usually get some glow on a 6.3v CRT at the 2.3V setting.

That's a good one Eric, 21SFA, "Short Focus Aperture". I thought it was a typo and was intending to say SF21A which it the only 6.3v CRT replacement that my tester shows.

CORRECTION SF21A is 2.3v CRT

Thanks everyone. I understand the tube connection now and have the correct adapters on order. Hopefully by next weekend I will be able to determine the exact type and state of the Holiday tube.

Keep at it and post some pictures of the set up you use and some screen shots of the meter. Good Luck.

OK, I finally got the adapter to test my 21EAP4 with my B&K 465 CRT tester and here are the results: I set it up assuming a 2.34v filament.
No shorts
Emissions = 700/9.2 (not sure which scale I was supposed to be looking at)
Cutoff = 30 ( setup chart says 28 to 72)
Life test: meter went slowly down from 700 to 0 in about 7 seconds. With no experience, what does this tell me? It did hesitate briefly before decaying. Is that a good lifespan left?
The only thing I was not able to do right now was the current test to verify if it is drawing 600 mA at 2.35v as my handheld meter was only rated to 200mA. I have the adapter partially rewired as suggested above, awaiting an order of alligator clips. I there another technique for checking the current?

So based on that, does it look like I have a good tube? Thanks

If you read 700 on emissions with the heater voltage set at 2.3Volts I would say you have a good CRT. I wouldn't put the heater voltage any highter than that. If it was a 6.3 Volt CRT you wouldn't get any emissions at 2.3 volts. You could follow up with the amp test just to confirm but if your getting 700 emissions at 2.3 volts you've probably have a very good CRT.

Awesome. I couldn't do the current test because my multimeter is limited to 200ma and am not sure now whether it was AC or DC, so I ordered a cheapy one that does ACA & DCA up to 10A. But with the good emissions results and all, I will start the restor in earnest. While doing the initial cleaning of the main board while still in the chassis I already found one or 2 components with brokem leads and another tube that was missing (under a metal shield). It's one on the side of the tuner so it doesn't show up in the chassis layout diagram, so I'll have to do a process of elimination with the others already identfied to see what's missing. I'll post a picture of the 21EAP4 emissions reading when I have completed the current test.