CurtPalme.com Home Theater Forum

[Curt Palme]

So I finally got a bunch of tubes on the bench, and am playing with the Sencore 7000.

First up, a VDC rebuilt NEC XG green that had a very obvious H-K short. It showed a short on the tester, then I went into zapping mode. It would not clear the short. So I went into rejuvenation mode, and bumped up the filament voltage.. which burned out the tube. Now my test set has no green instead of a way too bright green, but I could still see the image.

Not a good start.

Next up, I started playing with some low emission Marquee MEC tubes. I have one question:

If I can't set the cutoff on the tester, the bars never go into the gray area, in fact I get no bars at all, I'm assuming the tube has really low emission, right?

So I zapped the one tube, and now I have emission, but still no cutoff reading, even when the cutoff controls is maxed out.

I don't have a projector set up yet to put these tubes back into, but I plan on doing that shortly, that way I can blast the tube while it's in the set, and see what kind of progress I make.

Lastly, I have some Sony tubes out of a BG808s. One was sent to me by a forum member, and I can't get any emission out of it. I swapped in a 9" tube that I know was good, and got emission, so now I'll go put the bad tube in, and I'll try zapping it.

[Curt Palme]

So I finally got a bunch of tubes on the bench, and am playing with the Sencore 7000.

First up, a VDC rebuilt NEC XG green that had a very obvious H-K short. It showed a short on the tester, then I went into zapping mode. It would not clear the short. So I went into rejuvenation mode, and bumped up the filament voltage.. which burned out the tube. Now my test set has no green instead of a way too bright green, but I could still see the image.

Not a good start.

Next up, I started playing with some low emission Marquee MEC tubes. I have one question:

If I can't set the cutoff on the tester, the bars never go into the gray area, in fact I get no bars at all, I'm assuming the tube has really low emission, right?

So I zapped the one tube, and now I have emission, but still no cutoff reading, even when the cutoff controls is maxed out.

I don't have a projector set up yet to put these tubes back into, but I plan on doing that shortly, that way I can blast the tube while it's in the set, and see what kind of progress I make.

Lastly, I have some Sony tubes out of a BG808s. One was sent to me by a forum member, and I can't get any emission out of it. I swapped in a 9" tube that I know was good, and got emission, so now I'll go put the bad tube in, and I'll try zapping it.

[macgyver655]

The shorted tube may not of been contamination. It may be a warped plate. Not uncommon if the gap is narrow.

[macgyver655]

As far as the cutoff reading.....have you tried a known good tube of the same. Sometimes projector tubes react differently then regular ones.

[Tom.W]

The CR 7000 is not designed to clear an HK short as the filament will usually burn out first. It's risky at best and more so if you kick up the filament voltage !

See page 5 of this pdf http://repairfaq.cis.upenn.edu/sam/reppic/sencrt.pdf

[Curt Palme]

Yep, I found that out.

I put a zero emission tube into a Marquee and blasted it a few times. No go, the tube is toast.

While I really like this Sencore, I need to see this beastie rejuvenate a front projection tube for it to prove its worth.

[Curt Palme]

Yep, I found that out.

I put a zero emission tube into a Marquee and blasted it a few times. No go, the tube is toast.

While I really like this Sencore, I need to see this beastie rejuvenate a front projection tube for it to prove its worth.

[stefuel]

Is someone there playing with you or are you playing with yourself
Heywood has the older version of that and it's worked on 10 of 12 tubes I've hooked up to it.
I'll tell you what. If I was doing calibrations on crt projectors for a living, I would have one of these and every tube would be tested prior to calibration. It makes a big difference in the final outcome.

[Curt Palme]

Yep, I just need to find the right tube(s) to get to work on it. I didn't think it would bring completely dead tubes to life, and I was right. What I need is a Marquee set with a G2 setting in the high 70s, and I wanna see if I can bring it down into the 60s.

[Curt Palme]

Yep, I just need to find the right tube(s) to get to work on it. I didn't think it would bring completely dead tubes to life, and I was right. What I need is a Marquee set with a G2 setting in the high 70s, and I wanna see if I can bring it down into the 60s.

[tse]

Try reading the actual voltages that the tester is applying to the tube. Like if G-1 is 0V (reference the DVM ground there), K is +50V, G-2 is +800V, and heater at 6.3V I would expect the tube to be showing emissions. On the other hand if K is +180V, G-2 is +300V, and heater is 5V I would expect no emissions.

Scott

[Curt Palme]

More playing with the Sencore today.

I got a set in that I sold 3 years ago, that's run 14 hours a day in a pub. 0ver 10K hours on the tubes, that were used to start.

Funny enough, the green is worn, the R and B are pretty good, but both the R and B lost emission due to the high hours. Filament was a bit elevated, not enough to cause damage. Blue tube was almost dead, red tube not far behind, green had a G2 of 68.

I checked emission on the Sencore, and got 1 LED bar to light above the standby/power one on the red. Zapped the red, and it didn't increase much, but when I put the neck board back on, I got much better emission. Onto the blue tube, that was the worst. Zapped it, got good emission, G2 was 68 instead of 100. NOw the green was low compared to the R and B. Zapped it, and got emission back.

The only thing I don't quite get is that I can't get the cutoff to read anything but zero when I test the tubes, and the emission reading doesn't seem anything close to what it should be. The rejuvenation process seems to work well though.

[Curt Palme]

More playing with the Sencore today.

I got a set in that I sold 3 years ago, that's run 14 hours a day in a pub. 0ver 10K hours on the tubes, that were used to start.

Funny enough, the green is worn, the R and B are pretty good, but both the R and B lost emission due to the high hours. Filament was a bit elevated, not enough to cause damage. Blue tube was almost dead, red tube not far behind, green had a G2 of 68.

I checked emission on the Sencore, and got 1 LED bar to light above the standby/power one on the red. Zapped the red, and it didn't increase much, but when I put the neck board back on, I got much better emission. Onto the blue tube, that was the worst. Zapped it, got good emission, G2 was 68 instead of 100. NOw the green was low compared to the R and B. Zapped it, and got emission back.

The only thing I don't quite get is that I can't get the cutoff to read anything but zero when I test the tubes, and the emission reading doesn't seem anything close to what it should be. The rejuvenation process seems to work well though.

[tse]

So the tester is not telling the truth. Check the voltages that are being applied. If I remember right I played with one of these testers a while back and had to make slight adjustments to their suggested settings to get realistic readings. Or there could be something wrong with your tester.

Scott

[Curt Palme]

Could be. I'll ask Sencore for the schematic. This is the one that I bought off eBay, but seriously, it looked like it was never used, very little wear if any on the sockets.

Still, if your tester reads the projection tubes as it does 'normal' direct view CRTs, that's something to go on. I'll put a new blue tube on the tester as well, to see how it reads.

BTW, after 1/2 hour, the red tube died again, but the blue is nice and strong still. I'm leaving it off overnight, and will fire it back up in the AM to see what happens.

[Curt Palme]

Could be. I'll ask Sencore for the schematic. This is the one that I bought off eBay, but seriously, it looked like it was never used, very little wear if any on the sockets.

Still, if your tester reads the projection tubes as it does 'normal' direct view CRTs, that's something to go on. I'll put a new blue tube on the tester as well, to see how it reads.

BTW, after 1/2 hour, the red tube died again, but the blue is nice and strong still. I'm leaving it off overnight, and will fire it back up in the AM to see what happens.