help sourcing a new arcade monitor chassis

[copados33]

What chassis do I need for this tube, it's a 29".

it reads (M) m68lgl061x

[mgb]

Can't say off the top of my head as there are a few things that come into play but check out Arcadecup.com.
Chad is very helpful and knowledgable.
   He should be able to steer you to the correct chassis board and he very well may have the board for you to purchase.

That tube seems to be possibly common in Panasonic TVs but that's just from some quick googling.

[copados33]

Thanks, I already sent him an email, we'll see if I can fix this.

[lilshawn]

to properly match a chassis to this tube/yoke combination you'll need to get an inductance meter and measure the windings on the yoke.

resistance readings will get you in the right town, but a matched chassis for your yoke will get you TO the ballpark.

willy nilly purchasing a chassis will often result in pictures geometry that can't be adjusted out with the controls. (vertical and horizontal sizes that can't be brought in or out enough... wicked pincushioning. etc.)

SIDESTORY:

I was trying to match up a chassis for a half dozen tubes i had. i thought they where all the same (same branded anyways.) but only one was marked of it's original model (a tri resolution model). After talking with, and on the advice from Rick at Nieman Displays, he suggested i buy an inductance meter and test them. I did, and found out i had 2 different types of yokes on the tubes. one was tri resolution the other was medium resolution.

save myself a couple of hunskies buying chassis for tubes where it wouldn't have worked. Well worth the 30 bucks the meter cost. Ive used it many times since then.

The MasterTech MY6243 or    Vichy VC6243 is a good inexpensive ones well...basically any inductance meter with "6243" is made by the same company anyways... search ebay for "inductance meter 6243" for lots of different manufacturers)

[copados33]

Thank you , I guess I'll have to borrow an inductance meter from a friend then.

[kourampies]

I too have 2 tubes that need chassis. The one is supposed to be a 29" and the other one is a 28" TV. The 29" has 68 on the number, so I guess its considered 27"? I never understood this confusion regarding tube sizes.

I havent taken apart the TV yet, but there is a big chance that the actual tube size is the same.

Anyway, Im planning to measure them sometime soon and get two chassis for them.

I dont even know what or where to buy, other than an ebay seller selling Wei Ya chassis. It seems there isnt much on the market.

I only knew about thee need for measuring resistance from reading some minor tutorials. I dont even know what inductance is.

I have this multimeter thing that can measure capacitance. Is that enough?

After I get my readings and exact tube size, where do you suggest I look for compatible chassis? I'm in europe, so importing anything from outside europe legally isnt an option. Downmarked packages with USPS would probably work.

Thanks!

[copados33]

A simple multimeter wont work, Inductance meters are used to measure windings found on Ac adapters, step down converters, yokes from Crts etc.

[lilshawn]

the number on all tubes is the size in CENTIMETERS. so A68xxxxxx is 68 centimeters or 26.7717 inches (27 rounded) A63xxxxxx is 63 centimeters, which is 25 inches...etc.

inductance is the measurement of a coils resonance. a wire wrapped around an iron core will resonate at a particular fashion. this is measured in HENRYS (or for smaller values millihenries.) it's definition is technically... The induced electromotive force of one volt produced when the current is varied at the rate of one ampere per second.

wrapping a coil of wire around a nail, powering it, and using it to pick up paperclips is a very simple example of inductance. you can also wrap another length of wire around that nail and measure a small voltage being produced when you connect and disconnect the battery even though the 2 coils are seperate. This is how transformers work.

the yoke coil on the tube is "tuned" to a particular frequency that must coincide with the signal put into it. if the signal isn't right, (and it doesn't take much to be off) like i mentioned before, you end up with all kinds of geometry issues. horizontal width issues, Vertical size issues...etc. etc. etc. the difference of a few milihenries is enough to cause all sorts of issues.

we are talking about a stream of particles PERFECTLY timed, flying along at 480,000 inches per second... which is 27,272 miles per hour... to time this signal perfectly to line up perfectly at the beginning of the line scan each time a line is scanned (to have a nice straight square picture) takes some SERIOUS timing.

[MonMotha]

FYI the confusion on sizes is a national convention thing.  Some countries, like the US, specified tube sizes as the size of the imaged/viewable area, which is also what the model number of the tube would indicate (e.g. the 68cm being 27" above).  Other countries, notably Japan, measure the entire glass face of the tube, including the areas where you can't actually draw a picture.  The difference is usually 1-3 inches, depending on the size of the tube.

So, a 27" CRT in the US is a 29" in Japan.

The authoritative way to tell how big a tube is is by the CRT part number.

[kourampies]

the number on all tubes is the size in CENTIMETERS. so A68xxxxxx is 68 centimeters or 26.7717 inches (27 rounded) A63xxxxxx is 63 centimeters, which is 25 inches...etc.

inductance is the measurement of a coils resonance. a wire wrapped around an iron core will resonate at a particular fashion. this is measured in HENRYS (or for smaller values millihenries.) it's definition is technically... The induced electromotive force of one volt produced when the current is varied at the rate of one ampere per second.

wrapping a coil of wire around a nail, powering it, and using it to pick up paperclips is a very simple example of inductance. you can also wrap another length of wire around that nail and measure a small voltage being produced when you connect and disconnect the battery even though the 2 coils are seperate. This is how transformers work.

the yoke coil on the tube is "tuned" to a particular frequency that must coincide with the signal put into it. if the signal isn't right, (and it doesn't take much to be off) like i mentioned before, you end up with all kinds of geometry issues. horizontal width issues, Vertical size issues...etc. etc. etc. the difference of a few milihenries is enough to cause all sorts of issues.

we are talking about a stream of particles PERFECTLY timed, flying along at 480,000 inches per second... which is 27,272 miles per hour... to time this signal perfectly to line up perfectly at the beginning of the line scan each time a line is scanned (to have a nice straight square picture) takes some SERIOUS timing.

But even if I get inductance measurements, how can I know what chassis to buy? I never saw anyone mention inductance before this thread.

[lilshawn]

you get the inductance readings of the horizontal and the vertical and you give it to whomever you are purchasing the chassis from (weiya or whomever) who will match a chassis to it as best they can.

they usually fall into 2 catagories, high impedance >~10uH and low impedance <5uH. middle ground is a crap shoot. usually you get it close enough with some tweaks.

my unknown tubes where 6.25uH and i got a tweaked low impedance chassis for it, i still had some linearity issues, but it was just for a route machine so it wasn't a big deal and something we could live with.

[kourampies]

I will get the inductance multimeter from ebay then... Its only around 10 euros, certainly worth it if its going to help achieve proper geometry. Thanks!