Re: Ampliphone HV-other options?!

On Sat, 12 Jun 1999 02:34:05 -0500, Rodger Boots <rlboots@cedar-rapids.net>
wrote:

>You can be connected to the CRT, just unplug the
>neck board.
>
>Resistor? Just where do you think you're going to find
>a resistor that can take that kind of voltage? A HV
>probe would do it, but without the capacitance of a
>CRT present the reading on the probe will be wrong.

Doing a little calculation, it looks like a 10meg ohm resistor would give you a
nice 2ma load (not bad for testing). By doing a little more calculations you'll
find you'll need a 40watt 10meg resistor! (All assuming 20,000v)

Forty 250k 1w resistors in series would do the trick (they'd be running at their
max rating, might want to find some rated at 2w). There would then only be a
500v drop across each one, a little more reasonable.

I'm going to assume that if I use the same components WG used, the HV supply
will be able to handle the load, load testing sound like a pain!

>Be careful what you use for the transistor. The flyback
>pulse at the transistor collector is REAL close to 1,000
>volts! And the resonating capacitors must be able to
>withstand that, too. Without the capacitors that pulse
>will TRY to go to infinity, that's why monitor makers
>are real picky what they use there. It's also why they
>use multiple smaller value capacitors, if one goes open
>the pulse doesn't get too wild.

I assuming by using the same one WG does I'd be safe. Isn't there a very fast
diode (whether internal or external) across the transistor to short this flyback
pulse? While the transistor is on, the voltage drop across it should be quite
low (1v or less), and when off it is (hopefully) protected by the bypass diode.

I need to brush up on resonant circuits, the raster monitors seem to run the HV
in a series resonant mode, while the vector supplies seem to place the tuning
capacitor in parallel with the Flyback. I would think we'd want a parallel mode
and "ring" it with the pulses from the transistor, kinda like a type C RF
amplifier. (I think you'd want parallel, for that, I just don't remember...)

-Zonn
Received on Sat Jun 12 15:39:05 1999