>   OK, I think I've just about nailed the biasing for my DG7-32 CRT, but the
> Intensity control doesn't seem to have much of an effect on the brightness of
> the trace.
>   If I set it all the way to one end of its travel, I get an unfocussed
> 5mm-ish ragged elliptical spot on the screen that seems to fade (brightest at
> the bottom left of the ellipse, darker towards the top right). At about
> 25%-100% position the brightness does vary but not by any perceptible amount.
> There is no setting where the spot will extinguish completely.
>
> Here's a schematic of the resistor chain as it is now:
>
>              100k    120k        68k      220k    680k
> -500V <<<---/\/\/---/\/\/---*---/\/\/----/\/\/---/\/\/----------------> 0V
>               ^             |              ^
>               |             |              |
>               |             |              |
>               |             |              |
>           Vg1 (inten)   Vk (cathode)   Vg3 (focus)
>        -522V to -465V     -396V        -366V to -276V
>
> Anode (Vg2,g4) voltage: +243V
>
> At one point I had a 47k pot between +240 and GND, with the wiper connected
> to the CRT anode as a primitive "astigmatism" control. This has since been
> removed because I thought it served no useful purpose. The anode is wired
> straight to the +240 supply.
>
> The voltage ranges were taken relative to 0V and were measured with the CRT
> connected. They all appear to be within range of the figures in the CRT
> datasheet...
> The only thing I can think of is that it might be related to Vg3. The
> datasheet says:
>  Limiting Values (design center values)
>  ======================================
>   Vg3: Max 200V (note 4)
>   Note 4: For calculation of the grid 3 potentiometer a grid 3 current of
>           min. -15uA and max. +10uA must be taken into account.
>   Note 5: Negative grid No.1 voltage for visual extinction of the focused
>           spot.
>
>  Max Circuit Values
>  ==================
>   RD: Max 5 M[ohms]
>   Rg1: Max 0.5M[ohms]
>
> Now based on my calculations, there should be 0.4mA available for that.
> Here's what I did:
>   G3 section: 68k + 220k + 680k = 968k
>   Ig3 = 400V / 968000 Ohms = 0.413 mA
>
> Can any CRT experts who might be lurking here please tell me what I'm doing
> wrong?
>
> Thanks.