8bp4 tube test on 7vt5a2 motorola.

[fumplet]

I bought a motorola 9t1 and decided to test the tube on my 7vt5a2 set. Picture was super dim with lights off and brightness all the way up. I have a feeling I did something wrong.
I slid both tvs real close to each other and disconnected the 7vt5a2 tube socket and connected it to the 8bp4 still mounted in the 9t1 wood case. did it need the grounding strap to function correctly or was that just for noise shielding?

[dieseljeep]

Originally Posted by fumplet

I bought a motorola 9t1 and decided to test the tube on my 7vt5a2 set. Picture was super dim with lights off and brightness all the way up. I have a feeling I did something wrong.
I slid both tvs real close to each other and disconnected the 7vt5a2 tube socket and connected it to the 8bp4 still mounted in the 9t1 wood case. did it need the grounding strap to function correctly or was that just for noise shielding?

It should work that way! There is no aqaudag coating on the CRT.
Being a electrostatic deflection CRT, makes it easy to test this way.
BTW, how's the brightness on the 9Ti set. if OK, the 7JP4 is probably weak!

[fumplet]

7jp4 tube that is in my 7vt5a2 suitcase set works and has plenty of brightness. The 8bp4 was super dim. So I bought another 8bp4 thinking mine was bad as well as I was testing the 8bp4 wrong . (had the crt type set to video instead of scope) Now both tubes test with plenty of emissions. So Im confused as to whats up. Brightness or anything on the 9t1 set hasnt been tested because the ballast has issues. Seems all the wire crimps inside the ballast that hold the nichrome wire are slightly green and they do not ohm out to specs. One selenium rectifier was replaced and the other is still in circuit so not sure if the tube has to be tested using the 9t1 chassis or not.

[jr_tech]

Are both 8BP4s dim when plugged into the suitcase set?

jr

[fumplet]

checking now. Ok original 8bp4 lights up now with living room lights on. Purchased tube lights up even better. Both showed very good emissions test on cr 70. Going to place tube in same exact spot on floor and turn lights on to see if results are same or better.

[kvflyer]

Electrostatic CRTs can test good but appear dim when operating. I think that part of the problem is that the phosphorus becomes contaminated and therefore dim. I have a few that test good but are dim.

[bandersen]

Yes, they really can't be tested properly in any tester. I've tested dozens in the past using a Sencore CR-70. Just about all had very good emissions, but brightness varied considerably.

[kvflyer]

Originally Posted by bandersen

Yes, they really can't be tested properly in any tester. I've tested dozens in the past using a Sencore CR-70. Just about all had very good emissions, but brightness varied considerably.

I too have a Sencore CR-70 and agree exactly with what Bob has said.

[fumplet]

wow I didnt know that phosphorous could get contaminated, or maybe aged?
Is it also true one can tell the life of these electrostatic tubes by how dark the filament cover is inside?

[kvflyer]

The CRT tester will identify a dead tube. But the only real test is to have a working set and to substitute the CRT into that set. With the 7JP4, it is rather easy because most of the time, all that you have to do is unplug the CRT in the working set, swing around the socket and plug in the CRT you want to test. Since they are electrostatically scanned, no yoke, focus coil, ion trap etc. to have to deal with.

[fumplet]

so the real question is do 7jp4's and 8bp4's go to sleep like other tubes can that sat for 20/30 years? Picture gets brighter as it wakes up? Coulda swore that when I first plugged it into my working ts18 chassis, it was super dim even with lights off.

[Zenith26kc20]

Electrostatic tubes suffer from ion burn over the entire face. There is no ion trap nor are they aluminized. As the phosphor degrades over time the electron gun can still be good but the phosphor will get dimmer from ion bombardment. My 8jp4 is bright and clear. The set it came from probably failed early on. Some of my 7jp4 tubes have to be watched in the dark.

[kvflyer]

Originally Posted by Zenith26kc20

Electrostatic tubes suffer from ion burn over the entire face. There is no ion trap nor are they aluminized. As the phosphor degrades over time the electron gun can still be good but the phosphor will get dimmer from ion bombardment. My 8jp4 is bright and clear. The set it came from probably failed early on. Some of my 7jp4 tubes have to be watched in the dark.

As they say, "What he said ^^^". Totally my observation as well.

[fumplet]

Trying to recreate bandersons diode ballast with the 2 diodes, 47 ohm, 22 ohm, and cl 90 thermistor. I was under the impression that this would be a plug and play ballast yet my 9t1 chassis has no connection to pin 8 of the ballast tube socket. I believe one end of the cl 90 is in pin 8 or am I wrong? Do I need to run the power to pin 8?

[bandersen]

Pin 6. Nothing connects to pin 8.