7jp4 testing

[timmy]

Ok, I know the cr70 tests electrostatic tubes but what is missing from other testers to test these tubes, is it a specific voltage used to test. If it's voltage then can this voltage be applied to the terminals that require it to be tested ,And where or what terminals would this voltage have to be on to even think about this working. Any modification might help.

[Kevin Kuehn]

I think it's mostly because of the unique base/socket arangement. The CR70 has a universal(test clips) adapter. Otherwise I assume it tests like most other electrostatic CRT's.

[timmy]

Well problem is I don't have a cr70 tester.

[Kevin Kuehn]

I hear they can test strong on the CR 70 and still have a dim picture - something about the phosphor getting weak, I think. So ultimately you'll need to plug one into a working TV to get the whole picture.

[pendulum]

Yeah, the cr70 really is just good for seeing if the tube is holding vacuum, if it is shorted, and fixing shorts. They almost always test very good. Really the only true test is putting it in a working tv.

[bandersen]

Yes, they do use different voltages than magnetically deflected CRTs. The CR70 has a mode switch specifically for electrostatic 'scope' CRTs. You'd need to compare the datasheet for a 7JP4 to something like a 10BP4 to figure out the exact differences.

Originally Posted by pendulum

Yeah, the cr70 really is just good for seeing if the tube is holding vacuum, if it is shorted, and fixing shorts. They almost always test very good. Really the only true test is putting it in a working tv.

I agree. I've tested 20 or so 7JP4s and all had very good emissions on the CR70, but definitely vary in brightness when actually used.

[timmy]

Aside from the heater voltage what voltages should I compare to from the 7jp4 and 10bp4 tubes listed on the data sheet.

[timmy]

Where would the differences take place , on one of the grids of the 7jp4 ? If there is a 500 volt difference between the 2 then I was thinking of putting together a power suppy to apply this voltage to where ever this voltage is needed to be able to test. Even if I was able to test a good one and then a bad one I could use that comparison and get an idea of what a true one is as well as maybe remove shorts if any. Shorts in the gun could have an affect on its operation so being able to test and or remove a short may help. Does anyone know what PIN numbers on the 7jp4 are used to test the tube? I know 1 and 14 are the heater. There are 6 shielded wires that carry hv for the vert, horiz other then those there are 2 for the heater and 2 others, yellow and brown heater and red and orange are left. There must be a way to modify a tester to do this even if it does not lift the meter into the good zone, but rather have a baseline between a known good tube and a known bad tube.

[bandersen]

The CR70 setup chart for the 7JP4 shows

K -> pin 2 (7JP4 cathode)
G1 -> pin 3 (7JP4 grid)
G2 -> pin 9 (7JP4 A2)

G1 requires -72 to -168 for cutoff. I think that's where you'll need to add voltage since a typical magnetic picture tube only needs -27 to -63 volts for G1.

[dieseljeep]

Originally Posted by bandersen

The CR70 setup chart for the 7JP4 shows

K -> pin 2 (7JP4 cathode)
G1 -> pin 3 (7JP4 grid)
G2 -> pin 9 (7JP4 A2)

G1 requires -72 to -168 for cutoff. I think that's where you'll need to add voltage since a typical magnetic picture tube only needs -27 to -63 volts for G1.

I bought one of those old, early-to-mid 50's Precision CRT testers, just for the purpose of testing 7JP4's. Just a tester, not a rejuvenator!

[timmy]

Would the negative voltage on g1 be the negative side of the power source to get the neg 72, 168 v . Not sure just how to do that because positive,and the neg is a return. If the negative voltage is on pin 3 where does the positive go. If I can get the negative in place where it belongs then I guess it's safe to say I would use the 10bp4 setup on the bk440 tester.

[bandersen]

The cathode is the return or ground. Positive goes to pin 9.

[timmy]

Looking at the bk tester schematic there is a 145v lead , maybe I can place a switch in between that and send that to pin 9 if that circuit with that voltage is not used during bw testing .