Re: New Vector monitor project progress : Yoke issues

***SEE COMMENTS BELOW ON THIS, THANKS

----- Original Message -----
From: Zonn <zonn@zonn.com>
To: <vectorlist@lists.cc.utexas.edu>
Sent: Thursday, October 14, 1999 6:24 PM
Subject: Re: New Vector monitor project progress : Yoke issues

> 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.

*** The speed of the trace is completely governed by the magnetic
characteristics of the core materials, not the number of coils on the core.
Think of a 200 turn inductor as 200 turns or 100 turns x 2 or 50 turns x 4.
As long as the current in each turn is the same, the magnetic behaviour is
identical.

>
> 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).

* yes, 8 windings instead of 1 would mean 8 times more current and 1/8
voltage required.

> If adding paralleled coils were a "win win"
> situation, this surely would have been done by the original designers
> saving themselves much grief.

*** Roughly speaking two thin wires = one thick wire. The original
designers wouldn't wind a bunch of small wires in parallel for some tiny
performance difference... Have you ever heard of Litz wire? It is a bunch
of small wires that are used in high performance magnetic transformers,
etc... For high frequency magnetics, Litz is superior. Skin depth is the i
ssue in high performance designs. This is a little off the point, but not
too much. All high performance transformers we make use multi conductor
wire. (When I say high performance transformer, I'm talking about a high
frequency ~ 20 kHz + at high power levels )

***Now, I'm not saying you need a bunch of parallel windings. I'm trying to
get out of re-winding cores. That's all, and technically, my approach is
just as good as re-winding.

 Instead, the higher speed monitors all
> had less windings on their yokes, leading to higher stresses on the
> drive electronics.

*** Understood, but It really isn't that much different than the horizontal
drive in a standard monitor.

Placing additional, paralleled coils, will only
> increase these stresses. You will need higher current driving
> transistors.

*** No. All that matters is the inductance, and that the wire isn't so thin
that it burns up or requires extra drive to overcome the resistance.
Paralleling the coils decreases the net current required in each coil in
order to get the same number of AMP-Turns. Don't forget, I'm just doing
this so I don't have to build a 400V power supply to drive the vertical
axis, or get someone else's un-matched yoke.

> 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.
>
*** We should look at the 25" monitors. They should have devices that will
do the job just fine.

> 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.

*** If I use a modern switching supply, the capacatance won't be nearly as
big a factor.

> 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!

*** Well, I'm thinking more like $250 for the kit that you add to a monitor.

> 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.

*** Yeah, I know. Clay has really cool stuff, and I need to get an order in
with him now that you mentioned it. To my credit, I have designed dozens of
high performance analog, digital and power related boards for use in some
very exotic equipment. I can design cheap when I want to.

> 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!
> ;^)

*** I think Clay did it for his own edification, and the satisfaction of
accomplishment. He's probably making a little off each kit, but volume
can't be very high. I like the Pals he uses here and there. That's smart,
so somebody can't just copy his work easily.

*** Thanks for the comments and discussion, keeps me sharp, and on
track... -James

> -Zonn
>
>
Received on Thu Oct 14 18:53:06 1999