"Cook" 10BP4 Sencore CR70

[baursam]

Hi Folks

I just came into possession of a couple 10BP4's, that test in the red on my Sen core CR70. TO COOK a tube slowly, would I

1. Increase the filament voltage from 6.3 to say 8 at bias of 52
2. Strangely enough, if I adjust the cutoff, while I have it at say 7, it immediately pushes it into the green, which I don't think is accurate. Is there a position the cutoff should remain at while completing this process.

I know there is no set rules to this but wanted to get some feedback on the various methods people use with a Sencore CR70

Thanks

Ross

[miniman82]

I don't trust the filament supply in my CR-70 anymore, so if I cook a tube I use the universal clips and a variac. I'll let a tube sit at 8v for about 20 minutes and if it hasn't made progress I go ahead and put it through a cleaning cycle. If that fails, it's rejuvenation time. When that doesn't work, it's dead.

[baursam]

Thanks Miniman for taking the time to reply. A little surprised only one reply, as I would have thought many people have tried this in the past and have their own special way of doing this. Just was looking for input on ways people have done this. I'll continue to look on the internet.

[Kevin Kuehn]

Since you're able to adjust it into the good range with 7 volts on the filament, I would not be messing around risking a rejuvenation. As miniman suggested, those CR-70's can have flaky filament supplies. I'd try putting your volt meter directly across the filament pins on the tube under test and see if you're actually getting 6.3v with the tester loaded. The real test is getting that CRT into a restored TV chassis. As long as it produces a good watchable picture, that's what really counts.

[miniman82]

Found the same condition in my Eico tube tester recently. Most tubes it gives a pretty good test, like the common octals and all the 7 and 9 pin miniatures. But I recently installed a 9 pin and 12 pin compactron socket so I can test some late model tubes, and apparently a few have some pretty high filament demands. Like the 6LB6, it dragged the whole thing down to the point where the voltage adjust knob was nearly maxed out. Normally that wouldn't be a problem but because the emission indication circuit and filament power comes from the same transformer, it was giving me erroneous indications. You're supposed to adjust it to a mark called 'line' when testing, but these large sweep tubes draw so much current that when doing it that way I only had like 5.5 volts on the filament. Fix will be a small aux transformer that only runs the indication circuit, leaving the filament transformer to do its thing. I also may put in an actual filament volt meter, so I can be sure it's actually putting the correct voltage to the tube under test. That should give more stable and repeatable testing.

[Kevin Kuehn]

The CR-70 version I have utilizes a goofy pulse width modulated filament supply. I suppose in theory it's suppose to keep the voltage regulated, regardless of load, but mine was acting up and running all over the place. Not the funnest thing to trouble shoot, considering the construction of those units.