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

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Old 20th May 2020, 7:03 pm   #21
19Seventy7
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Default Re: Safe to apply mains?

How would that be set up? I've a few that can be used.

Thanks
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Old 20th May 2020, 7:25 pm   #22
Heatercathodeshort
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Default Re: Safe to apply mains?

The LOPT should be OK. They are very reliable but do suffer from the old saturation problem, loosing width after approx 30 mins use. It is completely curable with the BT302 but don't worry about that yet. Just thought I would give you a bit of reassurance.

The tube label is 7405A A GEC number but it is in fact a Mazda CME1703. GEC ceased making their own tubes around 1958 buying their requirements from MAZDA and having their name in place of Mazda on the familiar rectangular label.

Good luck with it. They are easy to repair or should be..regards, John.
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Old 20th May 2020, 8:07 pm   #23
19Seventy7
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Default Re: Safe to apply mains?

That's definitely reassuring, it does look cracked, is that normal? My G8's one did have a crack in, but I was told it was fine, but again, this is a slightly older set, so better to be safe than sorry.

Thanks for the luck, hopefully i get somewhere with it soon

Thanks
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Old 20th May 2020, 8:18 pm   #24
rambo1152
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Default Re: Safe to apply mains?

Quote:
Originally Posted by 19Seventy7 View Post
How would that (table lamp) be set up? I've a few that can be used.

Thanks
'77
wire it in series with your set, like this:
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Old 20th May 2020, 8:26 pm   #25
19Seventy7
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Default Re: Safe to apply mains?

Quote:
Originally Posted by rambo1152 View Post
Quote:
Originally Posted by 19Seventy7 View Post
How would that (table lamp) be set up? I've a few that can be used.

Thanks
'77
wire it in series with your set, like this:
Thank you, i'll see if i have any suitable bulbs and get to having a go.

Thanks
'77
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Old 20th May 2020, 10:43 pm   #26
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Default Re: Safe to apply mains?

If you search for 'quick CRT test' on the internet you may find the antiqueradios.com web page.

They use a 6V DC power supply to energise the heater.

In addition 6V positive goes directly to the G1 pin.

The 6V negative goes to the cathode via a 1k resistor. A Voltmeter is wired across the resistor to effectively measure the current through the cathode.

They say that a 4V reading can be expected from a good CRT and 1 Volt from a well used tube.

It should work with 12V DC. However the interpretation of the results will be different.
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Old 21st May 2020, 10:51 am   #27
Simon Gittins
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Default Re: Safe to apply mains?

Post 4 of this thread https://www.vintage-radio.net/forum/...ad.php?t=65435
shows another very simple emission test where the heater is powered and an AVO set to measure resistance is connected between cathode and grid.
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Old 21st May 2020, 4:51 pm   #28
19Seventy7
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Default Re: Safe to apply mains?

Thank you.

I'll definitely try those set ups, although it doesn't really matter too much as I wont be using this set as much as a 625 colour set, so it'll be worth it just for the experience and to learn from it.

But as I've said, the set does look relatively low hour, so there's hope.

Thanks
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