HP9836C colour alignment (grey scale tracking)

[Philip Belben]

Gordon JC Pearce MM3YEQ wrote:
> Tony Duell wrote:
> 
>> I am wondering about measuring the average beam current when 
>> displaying the level 15 raster of each primary colour and making sure 
>> it's reasonable. Beam current is near enough the final anode current, 
>> so measuring that would do. But that would mean having a microammeter 
>> floating at 25kV wrt earth. What fun...
> 
> I haven't seen the circuit, but I'm guessing you'll find some handy 
> resistor around the cathode to sample the voltage across.  Obviously 
> this will be somewhat high due to the grid currents, but my gut feeling 
> is that they won't be significant compared to the anode current.

I would be reluctant to float a delicate instrument at several kV. 
Can't this damage the instrument through corona discharge around some of 
the internal components?

Philip.