CurtPalme.com Home Theater Forum

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

Please understand that the Frankenyoke mods are going to benefit those who are initially stuck with the INFERIOR Thomson yokes. They're used in SOME Barcos, Some AmPros, and All Marquees.

Any PJ that has Kanto Denshi yokes (2211 or 22-22 types, among a few others) may be assumed to already have better yokes than Thomsons.

The problem with the Thomson yoke design is that it has a short magnetic field. The longer field of the K-D design gives better beam control over a wider range of beam current settings. They're also a more efficient and precise design, which is likely the reason why they give greater resolution abilities as well.

CJ

lamestlamer · Joined: 08 Mar 2007 Posts: 11 Location: Seattle

Perhaps it would be easier if we could simply rebuild the Thompson yokes into a longer profile. We wouldn't get the advantage of better astig, but we should be able to get the better spot and beam control. Or better yet, someone with Frankenyokes could make a caste then produce some injection molded frames for the rest of us. Maybe we could even experiment with even longer yokes to see if the Frankenyokes can be improved upon.

Joust · Posted: Sat Mar 10, 2007 12:50 am Post subject:

there is a thought. I'd give her a spin. I have some pics of CJs original mod. It would be a lot easier if i could find one to start with.
since supply is awfull low and there is some demand, who would be willing to buy these if I invested the time and effort to build them?

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

That would be well outside the realm of practicality for the hobbyist. I thought about it.

The Thomson yoke design is still fundamentally inferior. it's a cheapest way out solution, while the K-D design is a far more optimally designed yoke. It's a precision instrument.

Putting eight cheap bar magnets in a cage structure is a poor alternative to making precision ground ring magnets with ferrite spacers.

If someone wanted to make something really useful, they'd adapt the K-D design so that it works with Thomson housings and retains the raster shift feature AND has the astig windings.

For 50 grand, I could probably start production in three months. Anyone wanna loan me the money? Very Happy

You don't want a LONGER yoke than the 22-11 design, or the Thomson housing. You just don't have any extra room on the tube neck.

CJ

Joust · Posted: Sat Mar 10, 2007 1:56 am Post subject:

We should be able to reproduce the Kanto Denshi yokes, don't you think?

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

Patent issues notwithstanding, do you have the resources to custom machine and form your own alnico-V ring magnets? And magnetize them to a repeatable specification?

Do you have the resources to produce custom ferrite cores in ring and disc shapes? They're not standard size parts, you know.

Do you have precision coil winding machinery and the custom coils that will be necessary?

Have you even SEEN how the astig coils in a Kanto Denshi yoke are made? Well, to envision it, imagine a cylinder with eight rectangular windows in it, with rounded corners on the windows. These windows are evenly spaced around the cylinder.

Each window is a precision wound coil made of flat ribbon. They're precisely located on the former and have no bobbins of their own.

And you'd have to have custom bobbins made, too.

It would take respectable resources to reproduce them.

It really is out of the realm of the hobbyist.

Yes, subcontractors could make every part, but every part is a custom part and that
would result in costs adding up rapidly.

CJ

Joust · Posted: Sat Mar 10, 2007 3:47 am Post subject:

ah....no

didn't realise there were magnets and ferites in there. THought it was just windings on a bobin.

Joust · Posted: Sat Mar 10, 2007 3:55 am Post subject:

ok i'm an idiot.
I went back to look at your pics of the disasembly of the 22-22. shoulda did that before i shot my mouth off. Neutral

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

Well, it's a nice idea if you can pull it off, but obviously it's a sophisticated design that would take lots of money to duplicate.

CJ

Joust · Posted: Sat Mar 10, 2007 9:36 pm Post subject:

I guess we could find some off teh shelf ferrite rings and bobbins to fit inside. wouldn't be worth while if we cannot use ready made and available parts.

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

I know there are many manufacturers of custom ferrite products and custom magnets, and getting the bobbins made would be easy, with most of the money going to tooling costs.

It might be worth ordering a few catalogs, anyway.

I know that TDK is a major player in the ferrite industry. They might be a good place to start looking for suitable ferrite rings and discs.

Kyocera is also a big ferrite supplier.

CJ

Joust · Posted: Wed Mar 14, 2007 4:12 am Post subject:

These yokes are from a barco 808s. will they work as frankenyokes?

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

I do not know.

I would have to know their inductance values in order to give you some sort of an idea.

Refer to earlier in this topic for the inductance values that are optimal.

Magnetic strength is also an issue but not as much of one as I might have thought.

CJ

Lyckman · Joined: 09 Nov 2006 Posts: 66 Location: Gothenburg, Sweden

It's worth a try.
Measure the windings. As you might know from earlier in this thread the 3203-yokes from barco wont work. If possible, measure the windings..
https://www.curtpalme.com/forum_archived/viewtopic.php@t=2498.html

To determine if the strength of the magnet is sufficient I guess you have to mount it on a tube. You don't have to connect the dynamic focus and stig. Just check if you can get a good static focus.

I have thought about raster centering a lot and decided to try using small "refrigerator magnets" for this. Just attaching them on the focus coil at the right place.. like balancing a wheel. Any thougths from the pros?..

Joust · Posted: Wed Mar 14, 2007 3:59 pm Post subject:

I'm sure that would work.
they used to do that long ago but its a manually labour intensive step and not economical in a factory.
works for us though Smile

Lyckman · Joined: 09 Nov 2006 Posts: 66 Location: Gothenburg, Sweden

So I did some expimenting with this...

First of I tried some small magnets from my kid's refrigerator-letters. They seemed to be to small to do the trick. There was some raster movement (eg ½" on the screen), might work for fine tuning.

Next of I tried to use a magnetinc screwdriver bits. That would create a movement of about 3 inches on screen. After some playing around I noticed that even if I removed the magnet, the raster would not go back to its initial position. No matter if I turned the pj off and on. The new position persisted. I know that you can change the magnetic ability of an object by rubbing it, etc, but I would never thought it would have that huge effect. I mean, compared to the bits, the yoke-magnet is huge.

In your opinion, will this new magnetic alignment persist in the long run?? Eg, can one use this behauvior to tune the 22-22 magnets for long term use?

Joust · Posted: Thu Mar 15, 2007 4:09 pm Post subject:

You probably affected the magnetic properties of the internal magnets.
I would expect you would only want the small movements though this mode of adjustment.
its like those magnets you can get to magnetize your screw driver shafts.
flip it and you can demagnetize them.

try putting the magnetinc screwdriver bits in the opposite polarity

madpoet · Joined: 30 Mar 2006 Posts: 851

Question since I've never seen them... how hard is removing the yokes from a 1292? I've got a lead on some but I don't want to mess up the tubes, they are good tubes. Can I do it with the tubes still in the projector or do they need to be pulled? In know in the Ampro they are held on with a dab of hot glue.

Thanks!

Rdean · Joined: 13 Oct 2006 Posts: 258

I think they should come off without removing the tube.

Once the neck cards (and astig magnets) are removed the coils come off easy. There is only a "hose clamp" screw to be loosened on the focus yoke then it can slip off the neck.

madpoet · Joined: 30 Mar 2006 Posts: 851

Cool, thanks!