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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old 3rd Sep 2007, 4:18 pm   #1
dominicbeesley
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Default TV24 Metrosil?

I still can't get a picture no matter how I faff with the ion trap.

Is it likely to be the g2 / a1 voltage that is low (at 260V) its about 40V low - is this low enough to warrant replacing the metrosil?

Dom
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Old 3rd Sep 2007, 5:10 pm   #2
yagosaga
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Default Re: TV24 Metrosil?

Quote:
Originally Posted by dominicbeesley View Post
I still can't get a picture no matter how I faff with the ion trap. Is it likely to be the g2 / a1 voltage that is low (at 260V) its about 40V low - is this low enough to warrant replacing the metrosil?
Do you have 40V at g2? - Please keep the Metrosil. You need a high resistance valve voltmeter to measure the exact voltage at g2. And even when you measure 40V, the voltage will have the correct value when you stop measuring.

Do you get high voltage at the anode of the EY51? Do you get arcs when you come with the top of a screwdriver near the anode connection?

Kind regards,
Eckhard
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Old 3rd Sep 2007, 6:26 pm   #3
dominicbeesley
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Default Re: TV24 Metrosil?

Sorry, my original post was maybe not clear.

The published figure for the TV is 300V at g2, I was getting about 260V, which is 40V lower than it should be - but would this be significant to eliminate a picture altogether?

After a bit of poking about at the controls I can get it up to about 290V by fiddling with line hold/width/brightness etc

But still no picture!

I get a spark a little under 1cm long now from the EHT cap. All the other tube voltages seem within reasonable limits with g1 a few volts below the cathode, which is showing the test card from an Aurora beautifully - on my scope but not on the screen!

Gah! I'm about ready to throw the towel in now!

Dom
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Old 3rd Sep 2007, 10:17 pm   #4
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Default Re: TV24 Metrosil?

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Originally Posted by dominicbeesley View Post
The published figure for the TV is 300V at g2, I was getting about 260V, which is 40V lower than it should be - but would this be significant to eliminate a picture altogether?
Please measure the signal at the point metrosil / line output transformer. What do you find?

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Originally Posted by dominicbeesley View Post
I get a spark a little under 1cm long now from the EHT cap.
This is OK. Does the filaments of the EY51 light up?

Did you measure the emission of the CRT?

Try to adjust C28 for a higher line output voltage with maximum width control.

Kind regards,
Eckhard
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Old 3rd Sep 2007, 11:51 pm   #5
murphyv310
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Default Re: TV24 Metrosil?

Hi.
Hi Try shorting the Grid and Cathode of the crt together then set the ion trap you should see a bright raster, if not you may have low EHT or a duff CRT or possibly both.
Trevor
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Old 3rd Sep 2007, 11:58 pm   #6
dominicbeesley
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Default Re: TV24 Metrosil?

Hi all,

Thanks for the replies.

The EY51 lights up lovely and I've tried two of them, this one is NOS.

I've tried shorting cathode to g1 - no luck (though a slightly different noise from the lopt?!)

I'll post a picture of the metrosil waveform tomorrow.

How do I measure emission of the CRT?

How do I measure line output voltage (is this an AC measurement across the line coils?)

Cheers

Dom
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Old 4th Sep 2007, 12:14 am   #7
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Default Re: TV24 Metrosil?

If you've got EHT, don't worry about measuring scan voltage. You can't have EHT without Line Scan. I'll tell you about this some other time, as right now you probably don't want to read stuff like that.

The heaters are lit - oh well it was an idea!

The Cathode-Grid thing sometimes works - Never Mind. Again - an idea.

Tube Emission - don't worry. It's either OK or Low. Rarely does it just go.

Post a scope measurement tomorrow like you said, but I think it's the Ion Trap personally.

Cheers,

Steve P
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Old 4th Sep 2007, 1:13 am   #8
dominicbeesley
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Default Re: TV24 Metrosil?

Thanks to all how have replied to this and other threads!

A few pints, and a bit of serendipity. I was trying out some of the tests on this and the other thread (sorry moderators) when my cats cradle holding the tube in place gave way. Requiring a bit of a "shove" to get it all in place again and I noticed the tube was off centre in the focus collar. A bit more pushing and shoving and the most beautiful Test Card C popped in to almost perfect focus first time no messing with the controls!

The girlfriend thought I'd had a shock as I then proceeded to prance around the house speechless for the next quarter of an hour. When I showed her the picture the only comment was - yes this whistle really is annoying - oh well!

Anyway I'm almost pant wettingly excited and probably won't sleep tonight - once again thanks to everyone for help and encouragement!

And I'll no doubt be back tomorrow with more questions!

Cheers

Dom
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Old 4th Sep 2007, 11:34 am   #9
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Default Re: TV24 Metrosil?

Well done Dom. Now reassemble and use!! Ignore the line whistle or enjoy it - I like it personally.

Pity your girlfriend doesn't agree though. Women are such heathens sometimes....

Cheers,

Steve P
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