Re: Vector Monitor HV power...

Hi, Clay!
Sounds like a natural evolution on my idea. I beleive though that you
willfind that unless you can get the HV up to the 19KV range that you
will not get a sharp image. You need the 19KV to accelerate the elctron
beam so it can be bright and sharp.
Still this is the right direction. The GO7 flybacks are quite cheap
right now, and if the supply was modified so that one would get a
voltage doubler to raise the relative B+ to areound 120VDC then chances
are this would work. Who has the time to do this???
(Not I)
John :-#)#
Clay Cowgill wrote:
>
> Over the holiday weekend I had plenty of time to play with "stuff"... One
> of the things I did was finally force myself to understand how the HV
> supply of monitors works (and to design a "new" one as a test).
>
> I concentrated on the Wells Gardner HV design and the GO-7 power section
> (since those two use the same CRT). It looks to me as though the only
> reason we're using "custom" HV transformers at all is that they're
> insistant on using the differential +-25V DC power supply. The only big
> difference from most of the "raster" type power supplies (other than not
> being triggered off the Horizontal retrace speed) is that the transformer
> that triggers the Horizontal Output Transistor sits with one leg at chassis
> ground on a Raster where as the Wells Gardner/Atari monitor designs hold
> one leg at -DC rail. (I assume that having the +-DC supplies were just an
> artifact of the deflection system, so rather than bring 120VAC out to the
> HV cage they just used the DC supplies already available.)
>
> It looks to me that the "special" windings of the vector HV transformers
> really only increase the turns ratio to make up for the 50-60V peak to peak
> output of the HOT instead of a ~120V P-P on a Raster. (So in theory, if
> you replaced an amplifone HV unit with a GO-7 HV transformer-- wired up so
> everything matches correctly-- you'd get about 50% of the HV you'd want. I
> run my Wells Gardners at about 16KV-- I wonder if you couldn't just turn up
> the "HV adjust" a bunch and get somewhere close to 16KV for a usable
> display... :-)
>
> Now that I "get it" it looks really easy to make a HV power supply for an
> Amplifone or Wells Gardner Vector monitor. All you do is take 120VAC and
> run it through the DC rectification front end (like a GO-7) that gives you
> about 120DC. Instead of all the horizontal retrace stuff and whatnot you
> trigger a couple transistors off of a 555-timer circuit like the Wells
> Gardner uses. The transistors kick a little trigger transformer (the Wells
> Gardner/Amplifone used step-down transformers to pick up more current) that
> triggers the HOT which applies the potential of the +120VDC rail to the HV
> transformer. Screen and grid voltages just come off a resistor divider
> network. That's all there is to it.
>
> Basically you could make a replacement HV supply using parts from a GO-7
> with no problems-- and you wouldn't need to worry about keeping the
> deflection yoke and the rest of the "raster" crap attached to the chassis.
> I bet the whole thing would cost less than half of a new Amplifone
> transformer...
>
> -Clay
>
> Clayton N. Cowgill Engineering Manager
> _______________________________________________________________________
> /\ Diamond Multimedia Systems, Inc. clay@supra.com
> \/ Communications Division http://www.supra.com/

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