KV9200 Issues

[Alex KL-1]

You may use the 400V trimmers in theory, if you can make a voltage divider. Is possible since you have found that the ideal voltage are between a interval, so the initial 200V can be at the resistive divider, and the pot at top (like most focus dividers). Of course, a real higher voltage device is safer.

[vol.2]

Originally Posted by Alex KL-1

You may use the 400V trimmers in theory, if you can make a voltage divider. Is possible since you have found that the ideal voltage are between a interval, so the initial 200V can be at the resistive divider, and the pot at top (like most focus dividers). Of course, a real higher voltage device is safer.

Thanks! I figured as much. I was looking at the available devices and I think I'm going to buy the 500V pot. It's about $20, and I can reuse it in the future. I will tweak the pot until I find the right spot and then put a fixed voltage divider at the correct values and leave it.

That way I can take it out and use it again. Also, there isn't really a good spot to put such a device when it's closed, so it's better if I just put some 1 watt resistors in it's place.

I thinking about now how I would wire that in. Should I put in between the 500V source and ground? Seems like I should just use the F1 spot for the far side of the pot because it's zero volts.

[Alex KL-1]

Yes, you can connect one end to F1.
From your link, it seems to be a 2k pot. Too low value; will load too much the 530V supply.
You can choose a pot >1M ohm, since the focus grid almost don't drain current.
In fact, I use a 12M pot I found in a local electronic store when optimizing focus.

[vol.2]

Originally Posted by Alex KL-1

Yes, you can connect one end to F1.
From your link, it seems to be a 2k pot. Too low value; will load too much the 530V supply.
You can choose a pot >1M ohm, since the focus grid almost don't drain current.
In fact, I use a 12M pot I found in a local electronic store when optimizing focus.

Thanks Alex,

I looked on Mouser and Digikey, but the highest thing I can find in stock is a 1Mohm pot. It's a 2W bournes unit: https://www.mouser.com/ProductDetail...76JZfFDA%3D%3D

There's others in stock, but they all seem pretty similar.

Do you think 1M would be fine?

[Alex KL-1]

Seems to be perfectly fine.

[vol.2]

So I finally got the 1 MEG pot to try fine tuning the Focus Voltage.

I hooked up the Focus (F0) to the wiper, and then I hooked up one end of the pot to the F2 terminal (500V), and the other end to F1 (Ground).

To my surprise, the focus looks the clearest when it's all the way at 500V, but it looks better with the pot hooked up this way than it does with the Focus (F0) hooked up directly to F2

I'm assuming here that this is because I have essentially have a 1 Meg resistor hooked up between the 500V source for the Screen pot and GND

This seems to have the effect of lowering the overall brightness quite a bit (meaning I then have to turn up the Screen to compensate), but it then gives me a lot more headroom for the Picture control, and I can turn up the Contrast (Picture) more before the whites start to bloom.

Is there some reason not to just hook up a 1 Meg resistore between the 500V source and ground at this point?

Thanks

[Alex KL-1]

The potmeter was there for factory adjustments to compensate for CRT variations, but it seems that you got a CRT with optimum focus voltage just right with the supply value, so is not really necessary if is working well at the moment. The issue will be only in the future, if CRT changes a little, then will not have how to readjust it.
That said, probably the CRT stands with the current value for years.