Okay, can't move forward until I clear this up

[jr_tech]

Originally Posted by TinCanAlley

I found that removing the color taps from their connections allowed me to get the setup line. I don't want to adjust the G2s based on this as reconnecting the taps would just throw it off (probably worse than before).

When you pull the taps, the cathode may "float" to some unknown voltage ... adjusting the line for cutoff under these conditions is meaningless.

jr

[zeno]

The schematic shows the elements in order, also physical order.
Hi cathode V=low bright Low Cathode = brite pix.
This is why it gets bright when you pull the taps.
You are putting a high RELATIVE voltage on the G-1
& tons of electrons go towards it.

G1 is fixed, its negative compared to the cathodes.
Make it more neg & brightness goes down. Its a control
grid, make it too neg & you turn off the tube. Make it
to + things get too bright. You can actually melt
some power tubes with a + G-1 voltage.

G-2 is positive related to the K's & G-1 so it pulls the
electrons along, more + means more brightness.
When electrons get there they see the focus at 6KV &
rush along to that & then the 30KV HV.

73 Zeno

[TinCanAlley]

Originally Posted by zeno

The schematic shows the elements in order, also physical order.
Hi cathode V=low bright Low Cathode = brite pix.
This is why it gets bright when you pull the taps.
You are putting a high RELATIVE voltage on the G-1
& tons of electrons go towards it.

G1 is fixed, its negative compared to the cathodes.
Make it more neg & brightness goes down. Its a control
grid, make it too neg & you turn off the tube. Make it
to + things get too bright. You can actually melt
some power tubes with a + G-1 voltage.

G-2 is positive related to the K's & G-1 so it pulls the
electrons along, more + means more brightness.
When electrons get there they see the focus at 6KV &
rush along to that & then the 30KV HV.

73 Zeno

So if a higher cathode voltage makes it darker, then that's why the setup doesn't work. When in setup, the voltage to the cathodes goes up to 188 - 180V from around 143 - 149V. Now all I need to do is figure out why the voltage goes up that high when switching from normal to setup. Anything in the setup circuit stand out as a possible cause of increased voltage?

[DaveWM]

180 is correct for the setup cathode voltage. I show 40v should be at the G1 (12,3,7) per the zenith color service manual pretty close to sams.

You would def want to increase the cathode voltage to avoid burning the CRT when the vert collapes. I don't know why your setup does not produce the lines if you are getting those voltages (180 and 40) unless you just had the G2 turned down. Have you ever checked the HV? should be around 29-30kv

[TinCanAlley]

Originally Posted by DaveWM

180 is correct for the setup cathode voltage. I show 40v should be at the G1 (12,3,7) per the zenith color service manual pretty close to sams.

You would def want to increase the cathode voltage to avoid burning the CRT when the vert collapes. I don't know why your setup does not produce the lines if you are getting those voltages (180 and 40) unless you just had the G2 turned down. Have you ever checked the HV? should be around 29-30kv

Sorry, there was a typo. The voltages go up to between 188 and 190V. Is that still correct?

As for the G1s, they're roughly 33V in normal and 34V in setup. Sams has them at 36.4, so in either setting they're lower than specs.

[DaveWM]

per Zenith 40-180=-140 overall bias

Per yours 33-190=-157 overall bias

extra -17 v neg bias does not seem like it should be too much, but I don't now that for sure.

the 40 or 33v on G1 is a simple voltage divider of a 390k and 75k resistor connected to the 250v source. if the 390k has drifted up that would reduce the G1 bias.

the 190 is a result of the bias and the load on the output transistors. for that I would look at those resistors on the service setup and maybe the 18k collector load resistors on the output transistors (they go to the 250v source).

[TinCanAlley]

Originally Posted by DaveWM

per Zenith 40-180=-140 overall bias

Per yours 33-190=-157 overall bias

extra -17 v neg bias does not seem like it should be too much, but I don't now that for sure.

the 40 or 33v on G1 is a simple voltage divider of a 390k and 75k resistor connected to the 250v source. if the 390k has drifted up that would reduce the G1 bias.

the 190 is a result of the bias and the load on the output transistors. for that I would look at those resistors on the service setup and maybe the 18k collector load resistors on the output transistors (they go to the 250v source).

I have new 18K and 1.8K resistors for the setup. I got them in case I needed to change them. I tried to test them, but they both come up as 1.6K. I'm sure it's because they share a connection. I'll have to life them and test.