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Faulty tube?

Posted: October 9th, 2018, 9:49 am
by kopo
Hi,


So I recently got back my recapped ms9 chassis from Grant and today I found some time to hook them up to the 2 A68KJU96X Toshiba tubes. One tube was behaving normal but the other one I couldn' t seem to correct.
Photo on 09-10-2018 at 10.46.jpg
Is it broken?



thanks

Re: Faulty tube?

Posted: October 9th, 2018, 9:58 am
by PrincessPrinPrin
The vertical yoke is bad. There are two windings in parallel and one is open.

Re: Faulty tube?

Posted: October 9th, 2018, 10:11 am
by kopo
I'll check the wiring on the yoke.

thanks

Re: Faulty tube?

Posted: October 9th, 2018, 10:33 am
by PrincessPrinPrin
Check the resistance at the points shown on the good tube. If on the bad tube the resistance is doubled, the yoke is bad and would need to be replaced.
ms9yoke.jpg

Re: Faulty tube?

Posted: October 9th, 2018, 10:37 am
by geotrig
outside of it being **** !!!! its a great effect

Re: Faulty tube?

Posted: October 9th, 2018, 11:37 am
by kopo
Hi again,
43419373_299371230660514_5017645816144199680_n.jpg
I got this measurement on the faulty yoke. I don' t know if I did it right, the numbers kept flickering on and off and the measurement kept going between -100 and -200 . I did the same measurement with the same chassis on the good tube and got no numbers at all.

I can see that the wires are not in one piece and have been cut and reconnected. Maybe I should do it again properly?

Are these yokes available still?


cheers guys!

Re: Faulty tube?

Posted: October 9th, 2018, 12:08 pm
by PrincessPrinPrin
200K is too high. Set it to 200 and touch the meter leads together. You want to read very close to 0. Then try again on the yokes. The monitors must be off of course. Make sure the leads are touching metal/solder and not the crusty flux. Clean the soldering with alcohol if necessary.

Re: Faulty tube?

Posted: October 10th, 2018, 8:15 am
by kopo
OK,

I did as instructed and the good tube reads 6.5 and the bad one 12.6. So the yoke is probably broken.

What are my options here? I guess I should look for a yoke with the same measurements as the ms9 one?

best regards, kopo

Re: Faulty tube?

Posted: October 10th, 2018, 8:58 am
by PrincessPrinPrin
Look closely at the two tabs: is one of the enamel copper wires (coming from the windings around the yoke, not the insulated wires that go to the chassis) loose? There's two on each tab. If all four look well soldered on, look at the four groups of wires around the yoke for any point that looks burned/charred. If everything looks OK the coil must be open in some point that cannot be reached (under the ferrite core) and the yoke or the whole tube must be replaced. You cannot normally buy the yoke and even if you had one it takes skill to get good geometry, purity and convergence so replacing the whole tube is the way to go, if you can find one.

Re: Faulty tube?

Posted: October 10th, 2018, 10:26 am
by kopo
Hi again,

found it

Image

Anything that can be done?


cheers! and thanks for helping!

Re: Faulty tube?

Posted: October 10th, 2018, 12:14 pm
by mufunyo
PrincessPrinPrin wrote:
October 10th, 2018, 8:58 am
You cannot normally buy the yoke
I should still have one or two MS2930 yokes, but the resistance on those are wrong for MS9, correct?

Re: Faulty tube?

Posted: October 10th, 2018, 12:33 pm
by Asure
kopo wrote:
October 10th, 2018, 10:26 am
Hi again,

found it

Image

Anything that can be done?


cheers! and thanks for helping!
I have no idea if you can solder this together without altering the yoke's impedance, paging @gunblade and @mkl :)

Edit: Removed bad tips..

Re: Faulty tube?

Posted: October 10th, 2018, 12:47 pm
by PrincessPrinPrin
In the pic below I put a good yoke for the sake of comparison. If I see correctly, the broken wire in your yoke is "wire 1". Don't try to solder together A and B. Instead you should try to strip and tin the end of A and then solder a loose wire to it and then this wire to the tab with "wire 2". It would be better to use an enamel copper wire. I can send you a bit along with the connectors.
yokes.jpg
How the wire snapped remains unclear. Also, there's something that doesn't look like it should be there. Perhaps a correction magnet that previously was placed where the wire snapped. Perhaps something hit the yoke in that point.
yoke2.jpg

Re: Faulty tube?

Posted: October 10th, 2018, 1:18 pm
by Asure
Mkl: In your pic it would appear the plastic bit with the tabs is a bit further away from the tube, it looks to me as if this plastic fixture is only 4-5mm away in the pic of the 'bad yoke'. It seems the wires for the yoke are also 'caught' inside the area between the fixture and the winding for some reason.

Maybe someone loosened the fixture and tried to slide the yoke the wrong way? Also twisting the yoke itself without loosening the plastic fixture would cause stress on the tabs for fixing the wire ends, causing the break in question.

Also yeah what's that piece of metal/magnet doing there? (well spotted man, i missed that!)

Re: Faulty tube?

Posted: October 10th, 2018, 1:27 pm
by PrincessPrinPrin
Look at the yoke that I used as comparison (it's from an Orion tube but the structure is very similar to that of a Toshiba yoke). It has 4 magnet locations around it. I'm now sure that something sharp hit that magnet and cut the wire that happened to be on top of it. The magnet didn't fell off as it was attracted by the ferrite core. Now the wire needs to be fixed and the magnet glued back in its place.
yokes3.jpg

Re: Faulty tube?

Posted: October 10th, 2018, 4:37 pm
by nem
I don't get it. Why don't you just try to connect A and B together?

Re: Faulty tube?

Posted: October 10th, 2018, 5:03 pm
by PrincessPrinPrin
Because A and B barely touch each other and for a reliable connection you want two wires to overlap a little. Also they're in a very uncomfortable point. If you take A and bend it outwards you can work on it more easily.

Re: Faulty tube?

Posted: October 11th, 2018, 9:32 am
by kopo
mufunyo wrote:
October 10th, 2018, 12:14 MP
PrincessPrinPrin wrote:
October 10th, 2018, 8:58 am
You cannot normally buy the yoke
I should still have one or two MS2930 yokes, but the resistance on those are wrong for MS9, correct?

If this fits and will work, I am definately interested, I am located in Belgium, so closeby.

cheers!

Re: Faulty tube?

Posted: October 11th, 2018, 9:40 am
by kopo
PrincessPrinPrin wrote:
October 10th, 2018, 12:47 MP
If I see correctly, the broken wire in your yoke is "wire 1". Don't try to solder together A and B. Instead you should try to strip and tin the end of A and then solder a loose wire to it and then this wire to the tab with "wire 2". It would be better to use an enamel copper wire. I can send you a bit along with the connectors.

Thanks PrincessPrinPrin, I will wait for the piece of wire you are willing to send to try and solder it back in place. It will be a delicate job. In the meantime I will try to fish out the magnet and glue it back in place. Can I interest you in an original blast city mahjong panel? I was planning on hanging it on the wall but I can send it over no charge as a token of my appreciation.


edit:

found this coil from an old motor between my junk:
43626662_1003359003185201_2412131909212569600_n.jpg
Guess it' s the same wire?


cheers everyone and thanks for helping!

Re: Faulty tube?

Posted: October 11th, 2018, 3:21 pm
by nem
PrincessPrinPrin wrote:
October 10th, 2018, 5:03 MP
Because A and B barely touch each other and for a reliable connection you want two wires to overlap a little. Also they're in a very uncomfortable point. If you take A and bend it outwards you can work on it more easily.
Ahh, I see. I was thinking of overlapping both ends with a second piece of wire. It is a tight spot, I agree.