7JP4 Adapter - Videokarma.org TV - Video

Chris K · #1 11-12-2022, 11:06 AM

I'm confused (again!). I have a 7JP4 CRT that needs a special adapter to test it due to it being an electrostatic tube. Yes I can test it in a working chassis or I could buy a Precision CR-30 tester but I don't have access to either. There's a strange item I can buy listed as an adapter socket for the B&K tester I have (465). The socket is called a B&K Precision CR-30 socket. I looked up Precision CR-30 and it's an instrument so...is this socket meant to adapt the B&K testers to test tubes like the 7JP4?..It's NOS sealed in the box so the seller won't destroy the seal so I can see it visually. Does anyone know what's up with this? If the socket IS an adapter for tubes like 7JP4 testing on a B&K, will the base match the 465's connecter to my 465 instrument? I guess B&K went from a pin and socket connecter at some point to something much smaller.

Tim · #2 11-12-2022, 12:04 PM

First hit on Google. No, it is not for 7JP4.
https://elektrotanya.com/bk-precisio.../download.html

Tube TV · #3 11-12-2022, 12:18 PM

Damn they're charging a premium for it too. You could still buy a whole CRT tester for that price.

Did you see this pinout chart?
https://elektrotanya.com/bk-precisio.../download.html

Here's a better copy in PDF

http://www.arcade-museum.com/manuals...RT_Adapter.pdf

It seems to be more for color CRT's by the looks of those tube numbers on the second page.

Chris K · #4 11-12-2022, 01:04 PM

It has the wrong base plug too. Oh well.

Electronic M · #5 11-12-2022, 03:17 PM

If you want to test an electrostatic tube the best way is on a working chassis. The next best way is a Sencore...The CR-70 and CR-7000 support electrostatic tubes (I think the CR-31 does too). B&K testers of the color era don't support electrostatic tubes.
Third place is one of the late 40s testers that support 7JP4s.

Only the working chassis will show you if phosphor light conversion efficiency is good enough for a bright picture....Collectors with working testers have reported VERY POOR Correlation between emissions and image brightness. Which is why I just pull a restored VT-71 chassis whenever I want to check a 7/8JP4...Now I have a TV37 for those tubes too.

bandersen · #6 11-12-2022, 06:28 PM

Exactly. This 7JP4 has excellent emissions and cutoff in a Sencore CR70, but produces an unwatchable, ghostly picture.

Kirk · #7 11-13-2022, 07:17 PM

That adapter is for a late model color crt. For electrostatic tubes- I too use a VT-71 chassis for this purpose to test an unknown tube. I have found no other reliable way to be sure.

kvflyer · #8 11-14-2022, 12:05 PM

Quote:

Originally Posted by Kirk

That adapter is for a late model color crt. For electrostatic tubes- I too use a VT-71 chassis for this purpose to test an unknown tube. I have found no other reliable way to be sure.

And yes, that is the ultimate reliable test. I have a few 7JP4 tubes which have great emission. But ion burn on the screen has one of them dim and another one has a burn about 2 inches in diameter, which is dim. I guess it's just the nature of the beast.

dieseljeep · #9 11-15-2022, 11:10 AM

Quote:

Originally Posted by Kirk

That adapter is for a late model color crt. For electrostatic tubes- I too use a VT-71 chassis for this purpose to test an unknown tube. I have found no other reliable way to be sure.

I picked up a Precision CRT tester from the early 50's, that can test a 7JP4/8BP4 type tube.
Unfortunately, the time I tried to use it, it pinned the needle on the meter! I never checked into it.