Old (presumed Dud) CRTs discovered - value?

[Stuart R]

A friend is clearing through the dark corners of his family-run shop. Years ago, before they acquired the premises, it used to be part of a larger department store. They've found mannequins, coronation bunting and some boxed CRTs from the 'Radio department'. My friend is keen to know if the CRTs are worth anything and would like them to end up in the hands of people who could make use of them. One has been brought to me to take a look at, but I'm not an early TV expert, so we'd both be grateful for your opinions.

It's a Mazda CRM/92. Boxed, but the serial numbers don't match and sadly box is also labelled "Dud". Reading-up on these tubes, they didn't have a good reputation for reliability and failed early, so I would imagine this is one of many dead ones saved from a tube swap. I've also read that the glass is extremely thin, so am handling with extreme care.

The tube neck has some uneven steps in it. Is this a result of re-gunning, or just how they were assembled? It only carries Mazda and Edison-Swan labels, nothing suggesting re-manufacture. There is also some discolouration at the tube base. It looks more silvery than white under normal daylight, but very white under camera flash. Has it gone to air?

I have no facilities to test, other than heater continuity. There are 4 or 5 similar CRTs waiting in the shop, I'm told one has the neck missing and one is a larger one. The pessimist in me says they'll all be duds, but can't be sure until I see the rest.

In order to answer my friend's enquiry, on a scale of 'dud' to 'new-old-stock', is there any value in old CRTs of this vintage?

Thanks in anticipation,

SR

[Lloyd 1985]

That looks like a dud to me I've got a larger CRM122 that looks like that and it only produces a very dim picture with lousy focus. Having said that though, I'm sure one of the Mullard's fitted to one of my TV22's has a slightly dodgy looking getter and that produces a fantastic picture! Definitely worth having a look at the others, if they are OK then I'm sure several people on here could make use of them, no idea on actual value though.

Oh, and the step in the neck is normal for these Mazda's!

Regards,
Lloyd.

[bobsterkent]

Speaking as someone who does things in a museum, the mannequins and other stuff might also be very useful

[Dave Moll]

What a shame. It certainly looks like the vacuum has gone walkabout from that CRM92. In working order it would have been quite sought-after, but not so sure in that condition.

[stevehertz]

Was used in 9" Ekco sets for one. Worth keeping as with the rarity of spare tubes they can be rebuilt, but it is a very specialist procedure. Value of that one (if faulty), very little, for display purposes only - fiver? If working, hard to say, on the day maybe up to £50.

[Sideband]

Definitely looks like it's gone down to air with that white getter. Most of these Mazda's were called 'airbags' and with good reason!

[mark pirate]

I agree, even if the getter did look healthy, it would probably be zero emission!
Looking at the neck, I would say it was probably a regunned tube.
These CRT's were notorious for loss of emission after only two or three years of use, I have two sets fitted with CRM92's, both of which only show a weak picture in the dark

It would be interesting to see if the others have any life left, and what types they are.
If they are all duff, I wonder why they were kept all these years?

Mark

[high_vacuum_house]

At least the tube is intact and has a good screen.

Could be used to cosmetically restore a television set should the original tube's neck had been snapped off and the phosphor coating blown off.

I think one set it could have been fitted is the Ekco TMB272 portable receiver.

Christopher Capener

[Heatercathodeshort]

I have a number of CRM92 tubes just sitting around with the birds and rabbits that have taken up residence under my workshop. They just seem to multiply like their close friends.

The glass 'ridge' often mistaken for a regun glass weld is normal and forms the mounting point for the internal glass 'spark trap'.

This enables the tube to operate above 5kv the maximum EHT permissible with the earlier CRM92. Typical EHT for the CRM92 is between 5-7kv max.

The bulb shape is similar to the tetrode tube employed as Chris has mentioned but there the similarity ends.

The CRM92 is a triode with a 2v 1.4A heater. It is also fitted with the Mazda Octal base and is not aluminised.

The CRM93 [TMB272] has a 12.6v .3A heater, tetrode gun similar to the CRM124 CRM141 series, aluminised with an ion trap. It also has a long life. Due to this it would be very difficult to fit this in a TMB.

I have never seen a rebuilt CRM92. I guess these early 9" receivers would have been completely obsolete by the time the tube rebuilding process had been perfected.

Regards, John.

[radiomarktv]

As many have said the tube looks like it's gone to air. If the serial numbers don't match its possible a set has had its tube replaced with new and the dud tube placed in the box.

Not worth much in this condition although someone may have a use for display only or a set without a tube.

I would loved to have it but it will only add to the ever increasing collection of dud CRM92's in the collection.

Keep us posted with the other tubes.

Mark.

[Stuart R]

Thanks for your thoughts everyone.

There are plans afoot to visit the shop, I'll see if we could do it soonish, then maybe if anyone wants to take these on, we could arrange something in time for a handover at NVCF.

I hadn't thought of using them as a non-working replacement, but do occasionally see sets in museums with big dark holes in the phosphor, the CRM92 discussed here would at least improve the appearance of such a set.

I wonder if dud CRTs of this era would be more appealing if RACS the tube re-builders were still operating? Although it looks like there is plenty of potential core stock floating around in people's flower beds....

No point guessing on the rest until I've taken a look at them - I'll report back when I've done so. Once we know what we've got and when my friend decides what he wants to do with them, I'll hopefully start an appropriate thread in the Parts Offered section.

Kind Regards,

SR

[stevehertz]

People are saying that this tube was notorious for going soft, yet my experience was different. I had them in a Baird Everyman, Ekco TSC193 and an Ekco TS88 and in all cases they produced nice bright pictures. I also had an Ekco TMB272 (formerly owned by Bud Flanagan) that although I did not get going, I was led to believe that the tube was fine. Of course you have to consider how much use the sets had had, but certainly in the case of the TSC193 it had been someone's 'every day' tele until the late 60s. I have a soft spot (pun not intended) for the Mazda CRM92 tube, probably because of those sets that I restored and gave me so much pleasure, both in restoring them and subsequently watching until 405 ceased.

[Heatercathodeshort]

Of course they are not all bad but a very large number of them are useless now and had a very short life when in service. Compare this with the Mullard product of the same period the MW22-14 series. These are very rarely faulty and give a super bright picture, ion burn permitting after 70 years.

To be fair to Mazda. They were experts at producing excellent screen phosphors and when you get a good Mazda 2v triode, it does produce a very good picture. The 15" CRM152B in my Ekco TC196 is superb but it had very little use from new. John.

[mark pirate]

Of course they are not all bad but a very large number of them are useless now and had a very short life when in service. Compare this with the Mullard product of the same period the MW22-14 series. These are very rarely faulty and give a super bright picture, ion burn permitting after 70 years.

I have yet to find a CRM92 that is not bad, I tend to shy away from any set containing one now, although the later CRM93 seems to be fine.
My Ekco TMB272 has a lovely bright CRT

To be fair to Mazda, I have encountered no less than three Mullard 9" tubes that had gone soft or had O/C heaters.
Mind you, I have nine sets with Mullard 9" tubes which produce great pictures even after being unused for over half a century!
Maybe one day I will find a Mazda with reasonable emission....

Mark

[space_charged]

Originally Posted by mark pirate

I have yet to find a CRM92 that is not bad, I tend to shy away from any set containing one now, although the later CRM93 seems to be fine.
My Ekco TMB272 has a lovely bright CRT

I seem to have found one but devoid of a telly to go round it! I bought a couple of NOS CRTs in their original boxes from eBay. When I when to collect them the seller offered me two more CRTs, both obviously "early" CRTs. Naturally I bought them both, for small tens of pounds. One was gassy, dull glow from the heater and blue glow on application of 1KV. The other the CRM92, correct glow from heater at the correct voltage/current. That implies at once the vacuum is at least 1*10E-04 torr. Application of 1KV produced the attached photos of it.

Now all I need is a set to go with it...

[mark pirate]

The other the CRM92, correct glow from heater at the correct voltage/current. That implies at once the vacuum is at least 1*10E-04 torr. Application of 1KV produced the attached photos of it.

You may have a reasonable tube there, if you don't find a set for it, I have a Baird in desperate need!

Mark

[space_charged]

Originally Posted by Stuart R

I wonder if dud CRTs of this era would be more appealing if RACS the tube re-builders were still operating? Although it looks like there is plenty of potential core stock floating around in people's flower beds....

There is a group in the US who are trying to revive a re-building plant. Last I read they had achieved their first successful rebuild.

http://www.earlytelevision.org/first...t_rebuild.html

[stevehertz]

Philips rebuilt tubes for use in pre and post war sets for the 'Great Optical Illusion' exhibition held at the London Science Museum in around '78. The process is eminently possible, indeed proven but inordinately expensive for the man in the street.

[Lloyd 1985]

I’m keeping my dead tubes just in case they can be re-gunned sometime in the future, or I suddenly become rich and can afford to ship them to the guys in the states so they can do them!

Regards
Lloyd

[stevehertz]

Definitely Lloyd. 'Repairing' them is one thing, remanufacturing them from scratch is another! The other thing is, with todays technology and equipment, one would hope (expect?) the refinished job to be even better than when new.