21" Philco Predicta CRT mystery.

[Electronic M]

So way back before the Corona beer virus plandemic I bought a cheap Predicta Continental at Radiofest.

The CRT heater barely lit at 2.68V and tested weak, and at 6.3V the heater was a pinch bright but it tested strong.
So when I got home I pulled the shroud and looked for a part number on the CRT and couldn't find it. If the heater wasn't already set to 6.3V (the continental has a transformer and is similar to the 17" chassis) I made sure it was and ran it on 6.3V a while, then stored it when I got my first tandem.
I dug it out the other day to do some parts swapping with a few other 21" Predictas I plan to sell. When I powered it up I had no brightness control and very little video in a BRIGHT retrace laiden raster. Testing the CRT at 6.3V revealed shorts both HK and G1. At 2.68V it tests weak but no shorts.

So the only 2 CRTs I know of that fit a 21" predicta are 2.68V 600mA and 6.3V 600mA.

Not knowing which this CRT was I decided to figure it out ex-spearmintaly. I hooked my DMM in current mode in series with my CRT tester and dialed around the voltage while watching the current. At 2.68V it draws 450mA and the heater barely lights, at 600mA the input voltage is somewhere between 4 and 4.7V and heater brightness is normal, and at 6.3V the heater is at 710mA and a bit bright...

Has anyone heard of a ~4.7V 600mA heater in a 21" predicta before? What do you think this unlabeled CRT/heater combo is?

That 4.7V heater voltage seems to be about it's happy place... Emission is healthy there, and shorts seem to be mostly gone (though G1 still tries to creep up). There is no easy way to give it 4.7V in the transformer powered Continental...So I'm thinking about swapping this CRT into one of my 600mA series heater predicta tandems. If this is a 600mA heater tube it should automatically get the right heater voltage in a series string set.

[old_coot88]

Even tho Ohm's law says it'll work, I would jumper the heater into the series chassis with clip leads before swapping the CRT, just to verify things.

Or what about a dropping resistor to get the 6.3 down to 4.7V

[AlekZ]

Could you please take a picture of the electron gun of this picture tube? I am interested in the diameter of the pipe and the construction of the gun.

[Electronic M]

You're lucky you didn't wait any longer. I installed the back cover on the headshell I transferred that CRT to a few minutes ago.

The only diameter I can measure is neck glass and it is identical to a 21EAP4 as is the rest of the envelope.
Below are the best pictures I can take.