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Hatsune Mike

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Just a heads up: I wouldn't run the MS-293x tube without a neck board without some serious caution. Pin 4 - often unused on tubes of this shape and age - presents the full ~28kV through a large resistor:

IMG_7233.JPG


When I say large, I mean that it's so high resistance that it is immeasurable with my meter.

This resistor has two taps partway down that allow the tube to create a few extra grids using a division of the 28kV voltage, without requiring another voltage from the chassis. I expect these are part of why the Blast tube has such exceptional focus when it is in good condition.

Anyway, it's highly current limited, but the result of this is that you should still be weary that when left floating there exists the full HV potential at pin 4, which is not shrouded like the focus pin. Consequently, using an MS8 or MS9 chassis on this tube will result in some arcing between pin 4 and the grounded or negative pin 5, which is audible.

I also fear that this more complex and high-tech electron gun design may be responsible for HV arcing to the glass or outside of the neck (to the yoke?) which could help explain some damage underneath the yoke that we've seen.
 

mR_CaESaR

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It's not. It's just annoying.

Thanks. I had hoped this would be the case.

Just a heads up: I wouldn't run the MS-293x tube without a neck board without some serious caution. Pin 4 - often unused on tubes of this shape and age - presents the full ~28kV through a large resistor:

Thanks for the heads up, it's definitely not something I wouldn't be planning on doing.
 

mR_CaESaR

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I worked up the courage to finally look into the buzz with the arrival of some convergence strips..

Taking out the convergence rings and yoke was WAY more nerve racking than the first time I discharged a monitor. I was worried about necking the tube.

It took me a good 30 mins to get out, the rings felt so fragile and it just wouldn't budge!

I eventually got it out and as soon as I took the yoke out, all this stuff came off

HY4856l.jpg


Pretty much new that was the cause of the "buzz"

After putting back everything, the buzz was mostly gone - still a little buzz, but nowhere near as loud.

I started mucking around with the convergence strips and you can see the difference.

Before convergence strips

View: https://youtube.com/shorts/xkKmZ_YuRtM?feature=share


After

View: https://youtube.com/shorts/RzY8RUkIULg?feature=share


Only problem I have now is I seem to have introduced "wavy" corners and I have no idea how or why they've been introduced. It can't be "caps" as I don't recall this previously and this chassis has been serviced back in October with very minimal use. They seem more prominent on the right side versus the left side, but it's definitely there.

View: https://youtu.be/q1o4dS3Ab-Y


I'll have to take the yoke out again and suss it out.

Would loose windings cause this?

If you look at the bottom there's probably a couple of loose copper.


qHKTYg5.jpg


Any suggestions would be great! TIA
 
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