Old (presumed Dud) CRTs discovered - value?
 

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

Re: Old (presumed Dud) CRTs discovered - value?
 

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.

Re: Old (presumed Dud) CRTs discovered - value?
 

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

Re: Old (presumed Dud) CRTs discovered - value?
 

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.

Re: Old (presumed Dud) CRTs discovered - value?
 

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.

Re: Old (presumed Dud) CRTs discovered - value?
 

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!

Re: Old (presumed Dud) CRTs discovered - value?
 

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?
:beer:
Mark

Re: Old (presumed Dud) CRTs discovered - value?
 

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

Re: Old (presumed Dud) CRTs discovered - value?
 

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.

Re: Old (presumed Dud) CRTs discovered - value?
 

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.

Re: Old (presumed Dud) CRTs discovered - value?
 

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

Re: Old (presumed Dud) CRTs discovered - value?
 

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.

Re: Old (presumed Dud) CRTs discovered - value?
 

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.

Re: Old (presumed Dud) CRTs discovered - value?
 

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 ;D

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....
:beer:
Mark

Re: Old (presumed Dud) CRTs discovered - value?
 

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...

Re: Old (presumed Dud) CRTs discovered - value?
 

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

Re: Old (presumed Dud) CRTs discovered - value?
 

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

Re: Old (presumed Dud) CRTs discovered - value?
 

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.

Re: Old (presumed Dud) CRTs discovered - value?
 

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

Re: Old (presumed Dud) CRTs discovered - value?
 

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.

Re: Old (presumed Dud) CRTs discovered - value?
 

Can I just say well done for saving these pieces; even down to the bunting, mannequins and misc. there will be a use. Glad to say it all seems rather steampunk-proof, particularly given the nanny state's nervousness about old CRT's.

Should anyone ever visit RAF Elvington (Yorks) I would be interested in their opinion on the mannequins and dioramas in the control tower (which I assume are still there..) Saying more would be giving the game away.

Dave

Re: Old (presumed Dud) CRTs discovered - value?
 

Just a quick update from my friend who has removed all the CRTs from the shop.

In addition to the CRM92 we have already seen, he has discovered three more CRM92, two CRM121 and one CRT with a broken neck and no identifying labels.

I'm hoping to get a look at them next week and a colleague at work who plays with vintage TVs may be able to lend me a CRT tester. I better check it can test these Triodes, I gather that not all testers can.

Regards,

SR

Re: Old (presumed Dud) CRTs discovered - value?
 

You are correct, most CRT testers cannot be used on a CRM92. I use either my Avo or Taylor valve testers to check these types.
A simple lead was made up from an octal valve base to connect to the tester to crocodile clips to the CRT pins, the results are quite accurate on the tubes I have tested so far.

If I remember correctly, an external PSU was used to supply the CRT heater.
It should draw 1.4 amps @2v.
:beer:
Mark

Re: Old (presumed Dud) CRTs discovered - value?
 

Just to mark my interest in one of the CRM92 if there's some life in it. This will be going into a Murphy v136 or my EKCO TS88.

One point of caution would be to take care of the tube base especially if it is loose.
Also to protect the tube from damage by storing it in a suitable box.

I read somewhere where a tube had imploded sending glass all over workshop damaging other tubes close by.

Mark.

Re: Old (presumed Dud) CRTs discovered - value?
 

I'll keep the forum updated. I hope to be collecting the remainder of this stash in the coming week then will see if I am able to test in any way. I like "space_charged's" test method but I can't lay my hands on an EHT supply.

Some test results would allow us to suggest a price and start a Parts Offered thread. The main purpose of this thread was to established that there is some interest, which there now is, so these CRTs shouldn't end up down the tip.

'radiomarktv' I'm happy to earmark one CRM92 for you if the Mods and fellow forum members are happy to allow this. I think further expressions of interest should wait until we've decided a price and put these up on the appropriate section.

I've seen a post here on a CRM92 that imploded in storage. I am treating this with a little more respect now. If testing, will probably go for croc clips rather than trying to wiggle an octal valve base on the end.

Regards,

SR.

Re: Old (presumed Dud) CRTs discovered - value?
 

Old post from Darius:
https://www.vintage-radio.net/forum/...ead.php?t=5505

Jac

Re: Old (presumed Dud) CRTs discovered - value?
 

I had a bit of company on my way back from car club last night.

Sadly two haven't been stored that well and the only non-Mazda CRT is a necked Cossor. It's been like that for a while and the model number label is too faded to read. The second pip on the bulb has been snapped too. I imagine this one is only good for the tip, but it does have an interesting looking base connector with 4 flat sockets. I could save that if that's of any use.

Only armed with my Maplin analogue multimeter, I've established that all the Mazda heaters are intact and cannot detect any shorts (on Hi Z ranges) between other base connections.

None of the serial numbers match those on the boxes and all boxes are marked with a cross, 'U/S' or 'No Good'.

Interesting to see two different box designs; some CRTs are face down on a pad of corrugated cardboard whilst others are face up suspended by the cone in a cardboard cradle. One box includes an Edison Swan guarantee card whilst another box was a nice surprise.....

The pictures that follow do not include the first CRM92 shown on this thread a couple of weeks ago.

SR

Re: Old (presumed Dud) CRTs discovered - value?
 

So here's the first CRM92A, serial number 42128

Re: Old (presumed Dud) CRTs discovered - value?
 

Another CRM92A, serial number Z50718.

Re: Old (presumed Dud) CRTs discovered - value?
 

Final CRM92A, serial number Z37560.

This seems to have a few blemishes in the phosphor in the form of small black dots. They definitely can't be felt on the tube face.

Re: Old (presumed Dud) CRTs discovered - value?
 

Then carefully, pulled out a CRM121A, serial number 13869/5.

This seems to have a single 'bubble' visible on the face.

Re: Old (presumed Dud) CRTs discovered - value?
 

Hi Stuart,
Could you hold on to the Cossor tube remains and not bin it, for interest I would like to see it.
As for the remainder it looks like they may never work but still should be kept if they are all dud.
Mark.

Re: Old (presumed Dud) CRTs discovered - value?
 

Then the last, another CRM121A, serial number 10117.

This one has a small blemish in the screen too, centre of frame in the last photo.

Re: Old (presumed Dud) CRTs discovered - value?
 

My HMV 1807 has a large bubble on the face and always thought this should of been rejected from manufacture. The tube does give a great picture, its a shame the 1807 had such a bad reputation for HMV.
Mark.

Re: Old (presumed Dud) CRTs discovered - value?
 

So that's all the CRTs done. The unboxed Mazda was actually lurking in this box, which somebody may also like to save (radio not included).

https://www.radiomuseum.org/r/master..._d120d_12.html

One CRM121A box was marked with £18.3s.2d. Would that have been the price, or just someone's random jottings on a a box that was close to hand?

Mark, I can certainly keep the remains of the Cossor and hand them over for inspection at NVCF, I won't want to be taking them home again! I know that you're also interested in one, maybe more of the Mazdas.

I'm not sure now if I can make any headway with further testing before NVCF. TV isn't my speciality.

Probably time to decide on a price and start an Offered post soon.

Regards,

SR

Re: Old (presumed Dud) CRTs discovered - value?
 

Seems probable. The nearest comparable reference to hand here is Ferranti's 1956 guide to valve and tube replacement, where 12" tubes are priced, inclusive of purchase tax, at £17.5s.4d or £18.6s.11d according to type. (Pre-tax prices were £12 and £12.15s. respectively).

Paul

Re: Old (presumed Dud) CRTs discovered - value?
 

The CRM92s look very much vacuumless, but I'm not absolutely sure about the (more desirable) CRM121s. Is it still available for £18-3s-2d (£18.16)? ;)

Re: Old (presumed Dud) CRTs discovered - value?
 

Probably a 10" 108K [post war]

A very good tube and used slightly modified under the EMI label in some 1807 receivers. It was given the EMI number 3/20. John.

Re: Old (presumed Dud) CRTs discovered - value?
 

Thanks for all your thoughts and comments so far.

I have had a few other PMs from interested parties so to keep everything fair and open, I hope that freya and Catkins won't object if I mention that here. After a discussion with my friend, I think it's time to offer these up for sale.

Keep your eyes peeled in the Offered section.