tube swap help!

[Beretta]

ok im starting a new thread.
my old thread i was really bouncing around so i figured it would be better to start fresh.
http://forum.arcadecontrols.com/index.php?topic=96827.0

i've got a couple 19inch monitors, both have nasty burnin.
i had'nt been able to find 19inch tv's for a swap.. i kept coming across 20inch.
yesterday i spotted a zenith star command [ss1915w2] (1991) for 7 bucks in a junk store.. it worked so i bought it.

i already looked up the tube.. it looks to be compatible CR-23 pin out on the neck board,.
the tube in question is a zenith G-A48ACB02X

i checked the yoke and it measured
10.5 vert / 3.7 horz

the two monitors (they both currently work and powerup)

WG: 4901 = 37.0 (vert) / 3.0 (horz)
EH: g07 = 54.0 (vert) / 2.4 (horz)

so the zenith TV's yoke has a lot less resistance in it's vert windings, and a touch more in it's horz.

so here's the questions.

how close must the yokes be in order to avoid swapping?
.. would it be possible to simply add resistors to the vert winding?
... the horz is higher then the monitors, is the horz winding as important as the vert? if so is there a way around this?

i really really do not wanna have to swap the yokes and deal with convergence, so if i can avoid changing yokes that would be great.

i'll have more questions but i wanted to try and keep it short.

[SirPeale]

Sorry...you just wasted seven bucks.  Well, maybe if you use the chassis for parts, you can use something out of it.

1) the 20" tube won't work without a LOT of modifying the frame.

2) both yokes on the monitors are high impedance, and the readings on the TV yoke is low impedance.  Totally non-compatible.

[Beretta]

no you misread the tube IS 19inch i even verified it by tube type number.

resistor wont work?

can't i swap the yoke then?


P.S btw are you saying all else equal a chasis originally on a 19 would work on a 20inch tube?
cause i've had several 20incher's it's the 19inch that took be forever to find.

[MonMotha]

The yoke inductance is what matters more than resistance, but since many people don't have a meter that can measure inductance, resistance is often used as an approximator to get a feel for if it's a high or low impedance yoke.

You MAY be able to swap the yoke.  It's a fair bit of work, and you are likely to have purity and convergence issues, but you can try it as long as the yoke isn't bonded on either tube.

[Beretta]

ah i see, so about how close do they need to be for a swap to work without changing yokes.. just for reference.

i'll probably try a yoke swap then cause it took me months to find a 19inch tube to start with (i kept running into 20inchers) i do not like my odd's of trying to find another that is an exact match.

[Kevin Mullins]

so about how close do they need to be for a swap to work without changing yokes.. just for reference.

An Ohm or two at most.

[Beretta]

so about how close do they need to be for a swap to work without changing yokes.. just for reference.

An Ohm or two at most.

does that apply for both vertical and horz?
seems like the biggest variations are on the vert.

[MonMotha]

I'd usually say +/- 10-15%, which is going to be an ohm or two in most cases.  Tolerance will vary by what boardset you're hooking it up to.  If necessary, you can tag a low value, high power resistor onto both sides of the yoke (equal value on both sides) to fudge it a little, but don't get carried away with this, and you may then not be able to get proper geometry.  The further off it is, the more likely you are to have geometry problems, and you'll stress the output stage leading to quicker (or immediate) failure (blown vert IC or HOT).

[lilshawn]

I'd usually say +/- 10-15%, which is going to be an ohm or two in most cases.  Tolerance will vary by what boardset you're hooking it up to.  If necessary, you can tag a low value, high power resistor onto both sides of the yoke (equal value on both sides) to fudge it a little, but don't get carried away with this, and you may then not be able to get proper geometry.  The further off it is, the more likely you are to have geometry problems, and you'll stress the output stage leading to quicker (or immediate) failure (blown vert IC or HOT).

agree 100%... or just go ahead and swap the yoke and set up the convergence again... it really is easier that it looks / sounds.

[Beretta]

thanks guys, disappointed to hear i'll have to swap the yoke but i'll give it a shot.

Now that it's settled.. i figure if im going to swap the tube it's a good time to recap the board.
should i do the tube swap BEFORE or AFTER capping the board?

also since these monitors are from the early 80's would it be a good idea to preemptively change the flyback?, or does the old saying if it ain't broke dont fix it ring true?

lastly anyone have a preference as to which monitor i should pick to do the swap on?
the electrohome or the WG?

[SirPeale]

Sorry mate...I misread.  Yes, that tube should work fine for your swap.  You'll have to swap the yokes.  Sorry, no way around it.

G07 - DEFINITELY change the flyback.  They're failing left and right (30 years of hard use will do that).

4900 - So far they've been okay, luckily they're available now.  They weren't for years.

[Zebidee]

Yeah, doing a yoke swap is definitely an option. I did a swap recently and posted about it here. The trick is to be patient! Getting purity & convergence right is a pain, and will never be 100% perfect, but you can get it pretty close.

Unless you have a monitor frame of the right size, keep the tube in the front part of the old TV case until you have the purity/convergence right, because it'll be easier to fiddle around in the back. If you don't have a portable power supply with a JAMMA harness, you can set it up next to your cab and run the power/video signals out of it that way.

If you can hook up a windows Mame PC, you can run the free Nokia Ntest program (use your favourite search engine) to get a good set of test patterns/screens for purity/convergence.

[lilshawn]

the wells gardner site has a good explanation of how to do the convergence in the "k7500 service manual".

it's not the same monitor, but it's going to be similar setup.

HINT: it's on page 5 -> http://www.wellsgardner.com/pdf/Service/K7500.pdf