G07 focus after tube swap - fail?

Tubular Gearhead

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I think I already know the answer to this one, and I am probably out of luck, but I wanted to just throw this out there and see if anyone else has any ideas.

After doing a complete rebuild of a G07 chassis, I figured I would take out the heavily burt tube (Crystal Castles burn), and put in one from a donor TV. As luck would have it, I found a 19" TV with a yoke impedance of 53 ohms and 2.3 ohms- and amazingly enough, the yoke conector was almost the same as the funky one on a G07 (but only four pin, so I had to break it apart). The swap went very well and the tube is bright and perfectly converged, however, I have the focus knob turned all the way to the right and it is just not enough- it is still blurry.

From the schematic, it looks like there is no easy way to increase the focus voltage other than adding on a satelite transformer or something.

So I guess this "perfect" donor tube maybe is not so perfect after all...

Any ideas?
 
I think it is that tube too, sorry. Save it for a 4900. Maybe it will work better for that. These tubes are electro static focus and need to be in a certain range for each chassis. The range is integrated into the flyback so I don't think modifing the chassis is an option.
 
Is your B+ set properly? I have always needed to adjust the B+ after a cap kit and flyback replacement on a G07.

Yes, I played around with the B+, just to try to determine that it was a shortage of focus voltage that was my problem. After I was done, I reset the voltage back to 120V. As I bumped the voltage up a bit, the focus gets better, but still not enough, and I don't want to be in a situation where overvoltage settting is needed to get the swap to work anyway.

I have also adjusted the color drives, cutoffs, and brightness- and as you would expect, as each is turned down (decreasing the electrons that need to be corrected by the focus plate voltage) the focus gets a little better.

I guess I will save this tube for another swap (4900) or something. Kinda sucks, as it seemed almost too good to be true for a G07 (I guess it is).

Thanks guys!
 
i would not rule out the tube just yet.

look inside the key way on the tube and make sure the focus pin is not bent over.

another thing you could try is swap the neck socket as the contacts could have been enlarged and not making good contact.

Peace
Buffett
 
i would not rule out the tube just yet.

look inside the key way on the tube and make sure the focus pin is not bent over.

another thing you could try is swap the neck socket as the contacts could have been enlarged and not making good contact.

Peace
Buffett

+1 on that. I had one once that I could not focus. Turned out to be a bad neck socket.
 
Well, I am pretty sure it is not a contact issue as I can turn the focus knob back and forth and go from incredibly out of focus to just almost in focus. The knob seems to have very good range- just not the right range... :(

I will go ahead and check the pins anyway.

+1 on that. I had one once that I could not focus. Turned out to be a bad neck socket.
 
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