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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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13th Jan 2008, 12:10 pm | #1 |
Tetrode
Join Date: May 2005
Location: Norwich
Posts: 87
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Blue-Purple glow from Mullard MW22-14c!!!
Hello to you all and happy new year!!
I have just purchased for my own collection (much to the delight of SWMBO!!) a Pye D18T. After doing the necessaries with caps ,etc, it was time to bring it up on the variac. After a few mins I was rewarded witha healthy line whistle and a cracking (no pun intended) good spark from the anode cap. Sadly, though, there is no picture. All I get is a blue-purple glow inside the tube neck, just up from the heater. I was wondering if I could pick the brains of anyone who maybe able to advise what this could be? I have repaired lots of tvs but the is the first time I've seen this. If nothing else, it will make a cool plasma ball! Any thoughts would be most appreciated. Thanks in advance. Rob. Last edited by Mike Phelan; 3rd Oct 2008 at 4:37 pm. Reason: S&P |
13th Jan 2008, 12:23 pm | #2 |
Heptode
Join Date: Sep 2005
Location: LEEDS.......North of the River Aire.
Posts: 872
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Re: Blue-Purple glow from Mullard MW22-14c!!!
Probably the CRT has gone soft, has got some air inside.
Brunel |
13th Jan 2008, 12:56 pm | #3 |
Dekatron
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,145
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Re: Blue-Purple glow from Mullard MW22-14c!!!
Hello Rob,
As Brunel says the CRT is probably 'soft' a very small amount of air inside. Its odd that you say it is glowing just above the heater. It might be worth checking the CRT base voltages. Its just possible that you have a very high voltage on the control grid due to a short somewhere. Either way it would be curtains for the CRT and its more likely a vacuum fault. Thinking about it, did you have to straighten the pins on the loctal crt base? They are very prone to cracking where the pins pass through the glass base. Regards John. Last edited by Heatercathodeshort; 13th Jan 2008 at 1:02 pm. |
14th Jan 2008, 1:54 pm | #4 |
Tetrode
Join Date: May 2005
Location: Norwich
Posts: 87
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Re: Blue-Purple glow from Mullard MW22-14c!!!
Hi to all again,
Well, I went to the workshop full of high spirits. I tested all the voltages on the tube base, all ok. It was clear though that the tube has gone a little soft, the getter was milky. I tried the above method and was rewarded with a bright silver getter! Power applied, No blue glow, YEAH!! Still no picture, then the heater chain went o/c, yep, you guessed it: the crt heater went o/c. Here are a few picture of the tv, note the after-market draw handles on the side! What a lovely addition! Ps, You can clearly see the getter 'springs' in the pic of the tube base. Last edited by Mike Phelan; 3rd Oct 2008 at 4:41 pm. Reason: Tidying up |
17th Jan 2008, 1:06 am | #5 |
Retired Dormant Member
Join Date: Oct 2007
Location: Leicester, UK.
Posts: 809
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Re: Blue-Purple glow from Mullard MW22-14c!!!
Blue glow is air in the tube without a doubt .. I've seen this before and there is no other explanation (corona discharge) you are lucky it hasn't gone completely and fried the rest of the set. I've had this on modern sets. Is there anyone in the UK who reguns tubes these days? Used to see ads in Television years ago for regunned tubes though can't remember seeing anything about having an existing one regunned.
Wouldn't running the set be potentially dangerous without the usual loading in place? BG |