I just inquired a tube
 

I just got a 12LP4 to replace in a set, I put it on the tester right after I unpacked it when UPS delivered it. I fired up my Sencore CR70. All tests well except when setting the cut off, at first the needle didn't move, than after a minute or two, the needle budged just a tad when moving the cutoff setting control all the way. In the emissions the needle goes well into the good range as adjusting the cutoff setting... All shorts test great too.. Anyone think the cutoff will be a problem? I didn't do any extended cut off testing, as these old tubes seem to be very brittle..

Sound just like what happens when I test CRTs on my BK 465. It doesn't usually show a cutoff until I set the emissions. Once I set the emissions I go back and set the cutoff.

I would not put too much faith in the results of a CRT tester, esp B&W, try it in the set and see how it looks. What ever you do dont start rejuvinating it with out know for sure that it will not produce a good pic. I have several B&W TV's All but one tested very weak with poor cut off. They are all watchable. Granted the only set that test well does have the best pic of the bunch, but since you cant just go buy a new CRT, it would be good idea to see how it works as is.

Had the same issue and let the tube cook for awhile ( big Dave suggestion) and then ran the test again. If that doesnt do it, try lowering the bias from 56 to 36 and see if the cutoff will adjust into range. Even at a lower bias, the tube worked pretty well for me.

inquire |inˈkwīr; i ng-| (also chiefly Brit. enquire)
verb [ reporting verb ]
ask for information from someone

acquire |əˈkwī(ə)r|
verb [ trans. ]
buy or obtain (an object or asset) for oneself.

The CR70 has different settings for getting a cutoff reading, you may need to go with a different neg bias setting to get it right. If I'm not mistaken, bad cutoff will affect contrast.

I find about half of all old CRTs don't have the right cutoff. I usually have to go to a lower bias voltage range. What I find is that even if I have to go to a lower bias voltage range to adjust the cutoff, if the CRT then tests good for emission, it works very well in a set. No obvious problems with greyscale linearity or anything like that. So I don't worry too much about what the cutoff bias voltage is.

So no need to "inquire" another tube. :)

Don't forget, these Testers are probably 30-40 years old and could need a calibration.

They were supposed to be calibrated every so often.
My B&K 466 has a sticker saying it was last calibrated in 1978!

I'm the one who sold him the tube. I checked it twice on my BK 445. Tested great with good cut off. I tested several other tubes. Good tubes generally have good cut off unless they are on their last legs.
I have checked tester, and, have new electrolytics in it, and, have recently calibrated meter movement.
I don't see the problem with the tube. Heck. The emissions were even beyond 700, heading into new.
I believe this tube has seen very little use.
Bill Cahill

good point about the calibration of the tester, another reason why you should just try it and see how it actually works in the circuit. Same deal with all tube testers, good for testing shorts, but actual in circuit testing is the only real way to see how it works (well if its stone dead then that is diff story, but if it test "weak" then I find it may work fine, could be my tube tester calibration of course). I suspect that tube testers were a good way to sell tubes.

I'm not worried as I was with the last deal with someone whom did a horrible job at packing, and the tube arrived physically damaged.. Plastic cap damaged along with internal damage in the neck. That tube when on the tester had a yellowish glow and a flicker,and not to mention tapping the neck to get the filament to fire up.. So now I have the original tube and a "bad deal" tube, and i don't know what to do with them as they are just taking up space i don't have...

I was thinking it was the tester.. Probably didn't read everything correctly, as mentioned above.. I think I've noticed it misread a few other tubes in the past, seems to be with the roundies.. I don't have the chassis on me, my friend who repairs these old TV's for me has it, I'm just waiting on him to come pick up the tube, to install it.. I'll tell him just to install the tube into the chassis without putting it on his tester... I'm almost 100% sure the tube is fine.. Just wanted some feedback, and thankyou all for the info.. The whole chassis needed recapping along with a couple of resistors etc.

The tube arrived in great condition from Bill and looks to be very well taken care of..

Update: I had my friend install the picture tube into the chassis that I bought from Bill Cahill. I must say the 12LP4 puts off an excellent picture and is in excellent condition. I want to thank you Bill for your efforts and honesty, there was absolutely no problems, packing was well done and he described everything right on. Very well done.. It was a pleasure and will look forward to any other future deals...

Adam...

Thank you. May see pix of it playing?
Bill Cahill

I'll post some pics up when i get the set back next Friday....