3NP4 testing?

[earlyfilm]

Originally Posted by miniman82

Guys, I have a supposedly NIB 3NP4 projection tube I got from that estate in Richmond but I don't know how to test it. I have a CR-70, is there a way to get a meaningful result from that, or am I stuck trying it in an actual Norelco system?

First, you will need jumpers, as it has an odd ball base.

If you need base diagram it is here:

https://frank.pocnet.net/sheets31.html

I'd start by testing it as a 5TP4 which most older CRT testers handled.

In fact, when the 15GP22 first came out, RCA said if the shop did not yet have a color CRT tester use the settings for the 5TP4 for each color and test one color at a time.

I'd like to know your results, as I have two unknown 3NP4's and a NOS 5TP4.

James

Edit: It was just pointed out to me that the above is probably inaccurate, as the only Anode on the 3NP4 is the inside glass coating, while the 5TP4 used both that and a traditional grid anode. Although voltages are similar, the operating method of the two tubes are different. I have no idea of idea the condition of my two 3NP4's.