Re: Vector Monitor HV power...

On Mon, 1 Dec 1997 16:28:30 -0800, Clay Cowgill <clayc@diamondmm.com>
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.

You haven't mentioned regulation. Are you planning on using the same
darlington type regulators already in use by these monitors? They
should work -- assuming the replacement flybacks also have the 180 volt
windings needed to drive the CRT guns (I'm assuming they must), since
this is the voltage used as feedback in the regulation section of these
monitors.

Just wondering.

-Zonn

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Received on Mon Dec 1 16:37:12 1997