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

[TinCanAlley]

Which connections are my cathodes and G1s? I know which are the G2s (the higher voltages of 400 - 600V), but the ones I've been thinking are the G1s might not be. Take a look at the for the CRT schematic and the circuits feeding it. Are those in order of cathode, G1, G2 and focus? Do they represent the actual configuration inside the neck of the CRT? If so, then the G1s should be the 36.4V?

If that's correct, then how exactly does the cutoff work? Is the G1 supposed to be a fixed voltage? If not, what makes it change? If those are the G1s in my setup, then I see no way for the voltage to change. They get their voltage from a step down of the 240V Boost and in that circuit there's nothing but the 2404V boost, two resistors, a capacitor and a spark gap. From there it goes directly to the CRT socket.

And if the G1s are the 36.4V leads, that makes the video output transistors the feeds for the cathodes?

If color of wires helps, there are three white wires with stripes (a red, green and blue), three yellow wires with stripes (a red, green and blue) and a red wire, green wire and a blue wire. I know the whites/stripes are the G2s, browns are the heater leads and the black is the focus.

I guess I'm still a little too new to all this. I thought I had this correct, but if I don't, I've been doing things wrong and looking at the wrong things.

[jr_tech]

Yes, it appears that the G1s are tied to a fixed voltage and the cathodes are driven by the 3 color video signals. The only controls that you have for cutoff are the G2 pots. Did you ever test the crt? were the cutoff voltages ok?

jr

[TinCanAlley]

Originally Posted by jr_tech

Yes, it appears that the G1s are tied to a fixed voltage and the cathodes are driven by the 3 color video signals. The only controls that you have for cutoff are the G2 pots. Did you ever test the crt? were the cutoff voltages ok?

jr

Yes, I used a B&K 467 and the CRT tested good on all tests.

See my other post (the one with 5 pages). 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).

[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?

[Electronic M]

I could be wrong, but I think the monochrome signal modulates the g1 elements in this set. I have that chassis and a hybrid chassis from 71'. I don't have the schematic for that, but the one for my hybrid has monochrome video to the g1s and the color difference signals to the cathodes.

Most good setup switches dim the electron guns because if the service man forgets to turn the brightness down the service line will be too bright and burn a horizontal line into the phosphors. I'd try increasing the brightness until the other guns start to light.

[DaveWM]

not this one, the mixing is done in the video drive transistors, the emitters get the luma, the bases get the chroma, the collectors drive the CRT cathodes.

[old_tv_nut]

Originally Posted by Electronic M

the one for my hybrid has monochrome video to the g1s and the color difference signals to the cathodes.

If this is true, it's the first time I've heard of a design like this. Tube sets for years (and I thought hybrids also) put color difference on G1s and mono on cathodes. Then CRTs got unitized guns (common G1 for all three colors), and the color had to be matrixed into three cathode drives (R,G,B).

Edit: besides, TCA's schematic clearly shows fixed voltage on the G1s.

[zeno]

Originally Posted by old_tv_nut

If this is true, it's the first time I've heard of a design like this. Tube sets for years (and I thought hybrids also) put color difference on G1s and mono on cathodes. Then CRTs got unitized guns (common G1 for all three colors), and the color had to be matrixed into three cathode drives (R,G,B).

Edit: besides, TCA's schematic clearly shows fixed voltage on the G1s.

I think it started on Zeniths in A or B line, 19-25". I think
the 14 & 16" used a triple triode & I dont remember where it was
mixed. Cant remember what others used it, been to long.
Maybe I will look at a few Sams tomorrow to refresh.

73 Zeno

[old_tv_nut]

Originally Posted by zeno

I think it started on Zeniths in A or B line, 19-25". I think
the 14 & 16" used a triple triode & I dont remember where it was
mixed. Cant remember what others used it, been to long.
Maybe I will look at a few Sams tomorrow to refresh.

73 Zeno

thanks - will be interested