Ct-100

[jr_tech]

Originally Posted by Tom Albrecht

Anyone have any idea why I'm seeing the screen voltage behavior I mention above (red is stronger at low screen voltage, not higher)? I wonder if the higher screen voltage is throwing off the purity? Wouldn't really seem to make sense that it is actually lowering the emission...

Is the spot size from the red gun larger under these conditions? I'm guessing that with lower g2, much of the beam current is being generated from a larger area of the cathode surrounding the very center, which is likely fairly well depleted by now.

just a WAG,
jr

[Tom Albrecht]

I think you're on the right track. Now that I've modified the screen control circuitry so that the adjustment range of the screen controls is at a little lower voltage, as I go from the lowest screen voltage to about 1/3 the way up, red brightness increases. Beyond about 1/3 up, the red brigthness decreases, and near the top of the range, I think the entire picture (all guns) is defocusing a little. This might be consistent with additional current dragging down the voltage on either the first or second anode, without additional beam current actually making it to the screen (it's hitting elements within the gun).

I don't think I'm seeing a bigger spot size on the red. Picture is pretty sharp overall. Don't know if that's consistent with the idea that the center of the cathode may be worn out, but I'll simply report what I see.

[etype2]

Really looking nice. I think if you took some closeup shots in the dark the images would look spectacular.

[Electronic M]

Nice work!

[dtvmcdonald]

I just had an idea. I improved my 7JP4 with the grid-cathode short remover
of my Sencore. Maybe my 15GP22 arcs are not caused by gas ... I never saw
a purple glow. I'm going to try that short remover on every single pair of
electrodes in the gun, including ones between different guns (excluding
heater-cathode). It can't hurt. I'll first check it with a 2kV supply set to
current limit at say 50uA. That should catch gas.

[Tom Albrecht]

Sure sounds like it's worth trying. If we can stave off the death of one more 15GP22, that would be very nice. Let us know how it goes!