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Old 15th Jul 2019, 11:30 am   #1
Ian - G4JQT
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Default Using old TV tubes

I'm about to select an old Mullard tube for a Bush TV24. I have various MW31.xx of which I think at least one is aluminised.

Is there a preferred method of 'waking them up', assuming vacuum and emission are already reasonable?

I think I've been told just applying 6.3 VAC to the heaters for a day or so does them good, but I'm happy to hear thoughts and suggestions.

I don't have access to a tube tester, although I think I know someone near Kings Lynn who does...

Thanks.

Ian
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Old 15th Jul 2019, 11:47 am   #2
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Default Re: Using old TV tubes

Yes, I'm getting old now but does that lead to cathode poisoning. It may be after years but when tv's used to leave the heaters on to cut the warm up time it was an issue. Obviously 24 hours surely can't cause it but I would research under cathode poisoning on line. One of the Hitachi models had a switch on the side that enable the crt heaters so that you got a picture immediately. Yes, you have probably sussed it, they all went flat. Again it may have been a many years use problem.
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Old 15th Jul 2019, 12:26 pm   #3
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Default Re: Using old TV tubes

I've heard of letting them "cook" around 8 volts (assuming 6.3v heater) for 20minutes is supposed to wake them up a bit, but assuming a vaguely watchable picture from the get-go I'd personally prefer to just run the set and let it wake up of it's own accord. Especially a mono set, as there's not the question of guns coming up at differing rates to mess with the setup.
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Old 15th Jul 2019, 6:33 pm   #4
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Default Re: Using old TV tubes

I'm with Dan on this one, just get the set running. It's amazing sometimes just how much a tube comes up whilst you are fixing all the other things that need fixing. After a number of hours, if the picture is not of entertainment value then consider bopping it if you are absolutely sure it is the CRT and not some cruddy 'orrible 'unts capacitor hidden somewhere.

TTFN,
Jon
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Old 15th Jul 2019, 6:50 pm   #5
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Default Re: Using old TV tubes

From the top of my head.
MW31-16. 12" non aluminised. 6.3v .3amp heater. Ion trap magnet required.

MW31-18 12" non aluminised 6.3v .3amp heater. Liable to have ion burn due to no ion trap.

MW31-74 12" non aluminised 6.3v .3mp heater. [The last conventional Mullard 12" tube.] Filter grey glass screen. Ion trap required. A nice tube.

MW31-7 12" non aluminised 6.3v .6amp heater. Not suitable for series operation but could be used in TV24 with a heater transformer and a socket change [Loctal] A super tube, never seen a bad one

Just run them for a while with a picture as Dan and Jon suggest. Nothing more required.

Mullard did not market a narrow angle aluminised tube for domestic use. They did produce monitor tubes such as the MW31-20 but they never turn up. They all give excellent pictures. Hope you find a good one. John.
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Old 15th Jul 2019, 7:31 pm   #6
Ian - G4JQT
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Default Re: Using old TV tubes

Thanks for all the helpful info guys.

I've got a rewound LOPT from Mike Barker and also an aluminised tube from a TV24A which has a bright picture.

Hope to start work tomorrow on replacing both tube and transformer on my rebuilt TV24. Maybe I'll keep you posted...?
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Old 16th Jul 2019, 8:10 am   #7
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Default Re: Using old TV tubes

Interesting. It must be a Mazda CRM124 or a non standard regun. Any possibility of a picture? The TV24A employs a Mullard non aluminised tube, probably a MW31-16.
The Mazda tube will work well in place of the 12" Mullard's. It is a tetrode with a 12.6v .3amp heater for series operation. It was most commonly encountered in the Murphy V230 12" portable [1954] John.
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Old 16th Jul 2019, 9:15 am   #8
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Default Re: Using old TV tubes

It's good that someone is rebuilding a TV24.
They often get dismantled as a parts supply for the cheaper, plastic-cased TV22.
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Old 16th Jul 2019, 11:27 am   #9
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Default Re: Using old TV tubes

I have in the past tested tubes by powering up the heater and applying an electric fence exciter to the final anode.
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Old 16th Jul 2019, 12:27 pm   #10
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Default Re: Using old TV tubes

I suspect that Mullard must have made a number of "for replacement purposes" round CRT's at a time when aluminised production was the norm.

I also have a metallised Mullard MW31-74 which I bought new and fitted to my parents' TV24C in the early sixties.
It's still in there, definiteley isn't a regun, and has a normal bent ion trap gun which is characteristically Mullard in construction.

I've always thought it was an oddball.

The label is a Mullard yellow "Radiant Screen" one, and the aluminisation is clearly visible around the anode cavity which has a clip in adaptor which came with the tube to permit its use with the set's original final anode connector.
As you would expect. the picture is not visible when looking along the neck at the back of the screen phosphor as it is with unmetallized crt's.

It was boxed, unopened and being sold off cheap because (I was told) it had stood unsold for a long time… mine for a fiver. Oh and it still gives a super picture!

ISTR I also registered the Guarantee, which Mullard accepted, although I don't know where they would have got a replacement from had it been necessary!

Sadly, where the set is stored it is difficult to get at so I can't post a picture at this time.

The original CRT was indeed a MW31-16 which had suffered a neck fracture overnight. The crack was exactly beneath the neck clamp which was undisturbed and had presumably been overtightened for the preceding 10 years or so. On this set the clamp is between the focus assembly and the ion trap.

Pete
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Old 16th Jul 2019, 12:58 pm   #11
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Default Re: Using old TV tubes

Well the TV24C which I thought had an aluminised tube is a Philips MW31-74 and its label looks quite clean so I suspect the set it's in hasn't had it very long. I'm sure the picture was brighter when I first switched it on last year - maybe it was on a dark day!

I have three or four MW31's to check of various flavours...
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Old 16th Jul 2019, 3:21 pm   #12
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Default Re: Using old TV tubes

I'm currently trying to salvage a Brimar C17BM CRT fitted in a Dynatron "Fulmar" TV set, model TV27A.
The set was made in 1952 and was one of the first TV sets made in the UK to employ the 17" rectangular CRT.

The problem with tube is that most of the time the heater fails to light up. Occasionally the heater achieves full brightness and a really bright picture appears on the screen, but that doesn't last long, the heater soon begins to flicker and go out.
We may have to accept that the gun is faulty but there might be a possibility the fault might be in the tube base. The heater pins 1 and 12 have been resoldered but doing that has had no effect at all. Strangely, even when the heater is not lit the base is warm.

Link to the discussion about the set and it's present problems: https://www.radios-tv.co.uk/communit...lmar/paged/10/

DFWB.
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Old 16th Jul 2019, 6:46 pm   #13
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Default Re: Using old TV tubes

Sounds like you have a pair of heavily leaking heater wires from the glass pinch to the Duodecal base. Might be likely they have crossed over and might be insulated with that brown sticky sleeving that has become conductive. What else would warm up the base?

Suggestion. Cut the base with a hacksaw half way along and carefully unsolder the pins for investigation. A replacement base can easily be fitted from a scrap tube.

It is likely to be a simple answer. John.

I think you may be right Pete. There were a number of very late production Mullard tubes that may well have been constructed with aluminising. There was a demand for them to around 1960 particularly with owners of the TV24/TUG24 models. The EHT had to be over 7kv to obtain a good picture.J.

Last edited by Heatercathodeshort; 16th Jul 2019 at 6:52 pm.
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Old 16th Jul 2019, 7:36 pm   #14
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Default Re: Using old TV tubes

Quote:
Originally Posted by Ian - G4JQT View Post
Well the TV24C which I thought had an aluminised tube is a Philips MW31-74 and its label looks quite clean so I suspect the set it's in hasn't had it very long. I'm sure the picture was brighter when I first switched it on last year - maybe it was on a dark day!

I have three or four MW31's to check of various flavours...
There's likely to be a production code (including date code) stamped either on the socket or on the cone of the tube. That might be interesting information for a presumably late example.
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Old 17th Jul 2019, 7:46 am   #15
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Default Re: Using old TV tubes

Quote:
Originally Posted by ekjdm14 View Post
I'd personally prefer to just run the set and let it wake up of it's own accord....
Agreed, this is my normal approach, once I have a set running (reliably) I usually run it for a number of hours with contrast and brightness turned all the way up just to get a bit more current through the cathode.

Cheers
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Old 17th Jul 2019, 9:43 am   #16
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Default Re: Using old TV tubes

I too just let the tube wake up on it's own, normally it gets as good as it is going to get after 10 hours running.

Although I have 3 CRT testers, I find that the readings are a bit low, but the picture itself is fine.

I do use a CRT tester to wake up a tube on a set prior to restoration, just to get an indication of how good it is likely to be.
Usually if the tube is serviceable, the emission rises within an hour on the tester.

Mark
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Old 23rd Jul 2019, 10:36 pm   #17
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Default Re: Using old TV tubes

Quote:
Originally Posted by Heatercathodeshort View Post

Suggestion. Cut the base with a hacksaw half way along and carefully unsolder the pins for investigation. A replacement base can easily be fitted from a scrap tube.
It is likely to be a simple answer. John.
Today as John suggested the the CRT base was removed. The lead out wires are OK so it can be confirmed that the gun is faulty. The replacement tube will be a 17BP4A. This tube has a tetrode gun so provision for the first anode supply voltage will have to be made.

DFWB.
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