Re: 2465B - Weak Readout Intensity

Chuck Harris

Really, the answer is yes.

The new CRT will certainly have different gain for its deflection
plates, its control grid will have a different curve to match.

The geometry plates will be a little different.

Tilt, and Y axis rotation will certainly be different.

And, the transient response is going to be different, because the
vertical deflection plates are really a lumped transmission line.

The manual says full calibration if you replace a major assembly...
the CRT applies.

That stuff said, you might be able to satisfy your own needs by
doing the CRT calibration, and the rotations.

The pots for vertical gain and centering, and Hx1, Hx10, and H-center
could be done without additional test equipment.

Worth a try... most won't notice the transient response... until
they get to the high frequencies.

-Chuck Harris wrote:

The replacement CRT arrived yesterday afternoon, so I promptly sequestered myself out in my unheated shop (in a drafty barn) in 30 degree weather to swap in the new tube. Before I could even think of installing it, I had the very frustrating task of straightening all the bent deflector pins on the neck of the tube, which had been badly bent due to shabby packing for its long trip from Israel. (Who was it on this thread that said something like, every time I order parts from Israel, I've regretted it?) So I spent the first 35 chilly minutes very carefully bending back the bent neck pins. Some of these are fairly stiff and made me cringe as I applied fairly strong mechanical pressure to them to straighten them. I did wear safety glasses and gloves in the event of catastrophic glass failure, all the while praying I would not create a metal-glass leak. Luck was with me, and the only detectable real damage was minor cratering of the glass at the base of the heavier pins.

So with that accomplished, I slid in the new (used replacement) CRT. Some tips on technique are due here which you won't find in the manual, which I had to learn the hard way: Because of the delicate pins on the neck of the tube, "sliding" the tube into the chassis must be done in a thoughtful and deliberate manner or you risk bending one or more of these pins if they contact the sleeve as it is being inserted. Two ways to mitigate this possibility are, 1) turn the scope onto its right side, so that as the tube travels into the sleeve, the inevitable pull of gravity on the neck of the tube will cause the neck to slide along its =side= where there are no pin connectors, or 2) set the chassis onto its back side and lower the tube into the sleeve from the top using your best Milton Bradly "Operation" game skills to avoid letting the neck pins hit the sides. It's helpful to position the chassis on the edge of the bench such that the back of the CRT sleeve is accessible from the the underside so you can support the tube in its final centimeter or so of descent, since your ability to grasp the front of the tube will be lost as it enters the chassis at the top. This second technique has the added advantage that the four corner support wedges sit nicely in place during the descent, which they aren't so happy to do in the first.

Ok, cutting to the chase! With the new tube mounted and all connectors in place, (with more Milton Bradly maneuvers required for the deflector connections), I fired it up. The new CRT came to life with a beautifully bright and clear display that would happily allow the intensity to go all the way up to full brightness.


Chuck Harris nailed it on the first reply on this thread.

Being that my hands were now quite frozen, (remember, I'm doing all this in a 36 degree barn) I decided to leave the rest of the alignment and intensity calibrations for another day.

Speaking of calibrations, one poster noted that after a CRT replacement a full calibration would be necessary. That doesn't seem quite right to me, but this is where my knowledge turns to conjecture. Obviously I will need to conduct all the CRT related adjustments, but my question for the group is, what other post CRT replacement calibrations are truly and absolutely necessary?

- Scott

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