Re: New Vector monitor project progress : Yoke issues

Multiple windings in parallel is really no different than one heavier
winding. But if you go the parallel route you may want to stick to
something like quadrafiler wire so that all wires are the exact same
length and couple into the core in exactly the same way. Otherwise
you're going to get some really nasty effects like keystoning or
excessively high drive currents due to parts of windings trying to
fight each other.

The way to make a deflection board that doesn't self destruct and
still has high drawing speed it to use a stacked output arrangement
where there is one set of transistors running from a fairly low
voltage that can hold the beam in any given position with low
dissipation and another set running from a higher voltage for
high speed movements. The G08 is an example of what happens
when you try doing both with only one set of transistors.

Another possibility is to use FETs. Biasing can be a royal bitch,
though. I had a circuit that used both bipolars and FETs in a
cascode (or is it cascade, I can never get those right) arrangement
where the FET dissipated most of the power and the bipolars
didn't have to see excessive voltages. Looked like a winner for
a G08 replacement board, but I sold off my games and have no
money for development.

Zonn wrote:

> On Thu, 14 Oct 1999 17:11:27 -0400, you wrote:
>
> >The magnetic field is proportional to the current (in the yoke), and thus
> >more windings in parallel is better because:
> >
> >1.) the voltage does not have to be pushed too high due to higher impedance
> >and
> >2.) Less heating in the coils.
> >
> >I'm mostly looking for a technical dicsussion on this.
> >Thanks for the comments,
>
> Ok, technically, you are still going to have a problem with the speed
> of your trace. You still have multiple coils acting similar to
> capacitors (for completely different reasons) in their ability to
> store a charge.
>
> By placing them in parallel you have lowered the voltages needed to
> quickly slew to different positions on the screen, but on the other
> hand you have proportionally raised the currents needed to do the
> same. (Ohm's law). If adding paralleled coils were a "win win"
> situation, this surely would have been done by the original designers
> saving themselves much grief. Instead, the higher speed monitors all
> had less windings on their yokes, leading to higher stresses on the
> drive electronics. Placing additional, paralleled coils, will only
> increase these stresses. You will need higher current driving
> transistors.
>
> Previous searches for replacement transistors have shown that there
> are not many around with the higher drive currents you will need. You
> will probably have to place lower powered transistors in parallel to
> get the instantaneous currents you will need for high speed
> deflections.
>
> This will also put a higher strain on your low voltage power supplies.
> The internal resistance of the supplies will also need to be lowered
> to deal with the instantaneous current spikes needed. Chances are
> very good you will also need to double up on pass transistors there.
>
> Everything's doable, but costs do add up.
>
> I was serious about buying these. $250 is a deal! That's only $50
> bucks above the price of a raster monitor. I'm not even sure you
> could get a deflection board for that. I *know* you couldn't get a
> new HV transformer! Hell, it be worth buying your kit just to rip out
> the HV sections of my current monitors and use yours!
>
> You can keep this at a technical level if you want, but you need to
> consider costs very carefully before quoting prices, and there are
> people on this list who have experience in putting together kits, and
> all the costs involved. The multi-kits and the LV2000 come
> immediately to mind.
>
> Clay sold his original Tempest multikits for $75 (special pre-order
> deals), I believe they're like $99 now. These are very simple (read:
> all digital/no analog -- I don't want to start a flame war here! ;^)
> designs with parts that are lower in price than what you will be
> needing. From as much as I can tell, he's not planning on retiring by
> selling these things, my guess is that when you add up the labor
> costs, he's barely breaking even. (If I ever find out otherwise I can
> guarantee you Clay's going to have some mighty strong competition!
> ;^)
>
> -Zonn
Received on Fri Oct 15 03:18:32 1999