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AdrianH 20th May 2021 11:00 am

Help with some old TV tubes.
5 Attachment(s)
I picked up a small quantity of CRTs earlier in the week (details on Golborne), and would like a bit of assistance trying to fathom a few of the tube types as they either have no label or unreadable labels to them.

The 1st is a 17 inch with a partial label on it COSSOR 17?K It has an external aquadag coating 34mm dia next and overall length approx 490mm

Now I have not found data sheets on Cossor CRT's and wonder if these are the same as the Mazda CRM172 so a pointer in the correct direction would be appreciated. I have a Murphy V280 which has a CRM171 CRT fitted and in case that is bad I am wondering if this would be OK to use, I notice the Mazda tubes are 12 Volt heaters, this one I have not powered up.
Attachment 234476
Attachment 234477
Attachment 234478


The next is a 14 inch tube very the same as the MW36-26 in dimensions, requires an ion trap magnet, has some printing in the screen band area that says made in Holland, The gun assembly is different to the MW36-24 and it has what I would describe as the standard later spring clip anode connection of a ring in the glass. Lastly a standard Duodecal 7 pins base.
Attachment 234485
Attachment 234486

AdrianH 20th May 2021 11:15 am

Re: Help with some old TV tubes.
3 Attachment(s)
The last tube I am asking about is a 12 inch round CRT, this has been reworked by Nuvac has a neck diameter of 32mm, overall length around 480mm.
It has quite a grainly looking Phospher in the screen, it is a straight gun assembly, i.e. not an ion trap. It does have a label that I think says Mazda 622 or 122, but again I can find no information on this CRT.
Attachment 234488

Attachment 234489

Attachment 234490

So if anyone can assist with finding data and what TV's these would have been in I would appreciate it.


FERNSEH 20th May 2021 12:24 pm

Re: Help with some old TV tubes.
The Cossor tube was most likely made by Mullard and will be an equivalent of the MW43-69. Possibly Cossor type 172K.
The 12" tube is a Mazda type, possibly a CRM121(A or B) if it has a 2volt heater.


Lloyd 1985 20th May 2021 12:31 pm

Re: Help with some old TV tubes.
The round one could be a CRM-122? I’ve got an Ekco that used such a tube, can’t remember what the heater voltage was, try it on 2V and see how it looks.


Marconi_MPT4 20th May 2021 12:39 pm

Re: Help with some old TV tubes.
Brief data in the Ediswan 1954-55 booklet suggests the Mazda 122 might be a CRM122 which is 12" round screen (possibly not aluminised), triode gun. Designed for series heater configuration and has a Mazda Octal base.

VH = 7.3V @ 0.3A,
Typical operation:
Va = 9kV (10kV max)
Vg for cut off = -71V
Peak modulating voltage = 30V average for a peak of 150uA


AdrianH 20th May 2021 12:43 pm

Re: Help with some old TV tubes.
1 Attachment(s)
Thanks for that I have been googling for a 172K CRT without a lot of success. I have not applied any heater volts as without the information Knowing me i would do damage.

For the round tube after downloading lots and reading through things I have just found on site a download on Mazda tubes and it I think it is as per the label a 122 tube or a CRM122 the it could be this: -
Attachment 234493

CRM122 12 inch round, 57 degrees, trode, non-aluminised, 7.3 V heater 0.3 A

I will have a search on that number to see if I can find more details and base pin out and what TV it was in.


AdrianH 20th May 2021 12:45 pm

Re: Help with some old TV tubes.
I am reading and typing to slow looks like Lloyd and Rich beat me to it.


AdrianH 20th May 2021 12:53 pm

Re: Help with some old TV tubes.
OK just downloaded a 1960 Ediswan book from fransk.pocnet and it lists it there with pin out thanks for the information. I do not know all the names of the companies and how they all merged so this information is of great help.


Marconi_MPT4 20th May 2021 2:39 pm

Re: Help with some old TV tubes.
Brief info on Cossor 172K

Heater = 6.3V @ 0.3A
Final Anode V = 16kV max
Final Anode I = 150uA max
Vg = -60V (cut off)
Deflection angle 70 deg.
H-K Volts max = 150V
Capacitance, g = 8pF, k = 6pF
Ion Trap
B12A base, pin 1 = h, pin 2 = g, pin 7 = a2, pin 10 = a1. pin 11 = k, pin 12 = h
17" Rectangular


FERNSEH 20th May 2021 3:16 pm

Re: Help with some old TV tubes.
I believe the Cossor 171K had a tetrode gun assembly and was similar or equivalent to the likes of the Emitron 17ASP4.
The Mullard Maintenance Manual informs us the the MW43-64 is a direct replacement for the Cossor 172K. Certainly, from 1957/8 all domestic Cossor CRTs were made be Mullard.
The Cossor 173K has the Mullard-Philips pentode gun assembly and was an MW43-69.

AdrianH 20th May 2021 3:17 pm

Re: Help with some old TV tubes.
1 Attachment(s)
Thank you Rich, can you possibly let me know what publication the information is in and I can look for it on line, It may help me stop asking these sort of questions?

I have done some testing with a home made CRT tester/checker and the pin out of the CRM122 is as follows: -
Attachment 234502

The base has been changed for a duodecal one, also I have powered up the heater from my power supply with a current limit of 300mA and the heater volts is as near as possible to 6.3 Volts, and with my little tester it is showing as it having a good emission. So I guess a few things were changed in the re-gun?


Lloyd 1985 20th May 2021 4:06 pm

Re: Help with some old TV tubes.
The Mazda CRM122 was used in the Ekco TU-211, very similar set to the T161. That’s the only set I’ve seen one in so far anyway! I’m sure others will know more.

Sounds like they fitted a 6.3V heater in that then, I don’t think it makes a lot of difference in the TV, my TU-211 actually has a Mullard MW-something fitted with a 6.3V heater, the original tube was completely knackered!


AdrianH 20th May 2021 4:12 pm

Re: Help with some old TV tubes.
Thanks DFWB, I have become a bit confused going through data sheets, I tend to use the pocnet site a lot and there is a MW43-69 and a MW43-69Z. The 69 says use the MW43-64 (non metal backed) data sheet for information and the 69Z must be an aluminised screen as it does not have an Ion trap,

I am getting confused by what is meant by metal backed as I see no differences in the glass and I do not think it refers to the aquadag, or does it? I could not see a point in aluminised screens also having an ion trap, so it must refer to something else, is it a metal cone within the glass envelope for the final anode?


Heatercathodeshort 20th May 2021 4:25 pm

Re: Help with some old TV tubes.
The 14" Mullard may be the MW36-44. The Z suffix refers to the later gun fitted to the final production of the Duodecal based tubes. It was in fact the 110 degree gun fitted in the then current tube production [AW47-91 etc]. They were very good tubes. Slight modifications were required, new base connector, maybe alterations to accommodate electrostatic focus etc.

The Mazda tube being a regun is probably a replacement for the .3amp AC/DC tube CRM122 that was fitted with a 7.3v gun. Due to the difficulties of obtaining gun assemblies that matched the heater voltages of the originals it was not uncommon for regunners to fit standard guns with 6.3v heaters in tubes that had odd heater voltages. They were mostly series connected making a volt or two of no importance. In these cases the heater voltage was always marked on the tube. John.
PS Just checked the Nuvac label. Type Mazda 122.

AdrianH 20th May 2021 5:00 pm

Re: Help with some old TV tubes.
Now I am getting confused, the MW36-44 is still down as being magnetic focusing on the data sheet, but I did look at it and wonder if that would also be an alternative to my tube in the 991T, so I have just done a look though some service sheets for the 991T and it says that the MW36-44 was also fitted to this set with the addition of an external wire link between pin 7 and cathode. So a quick dash to my set, take the back off again and check the valve base, low and behold the pins are already wired :)

The only thing is it does not have a top cap anode as indicated in the data, perhaps this is really an addition to the contact on the side? or there could be a simple adaptor?

I love all this information, it just brings more questions.


Maarten 20th May 2021 6:00 pm

Re: Help with some old TV tubes.
Mullard made tubes probably have some small coding near or on the socket. Made in Holland tubes definitely do. Could you have a look for those?

AdrianH 20th May 2021 6:05 pm

Re: Help with some old TV tubes.
Nothing I can see on the CRT necks or otherwise. I know there are marks on Valves but on these nowt.


FERNSEH 20th May 2021 6:57 pm

Re: Help with some old TV tubes.
MW36-24 has a tetrode gun and the MW36-44 has the Philips pentode gun.
All Mullard 17" 70* CRTs including the metal cone MW43-43 have pentode guns.
Looking circuits of early Cossor 17" TVs such as the model 933 of 1953 the CRTs are drawn as having tetrode guns. The 171K and 172K are similar except for the possibility having been sourced from different suppliers. One might have been Electronic Tubes Ltd. ETEL.


Marconi_MPT4 20th May 2021 7:05 pm

Re: Help with some old TV tubes.

Originally Posted by AdrianH (Post 1376255)
Thank you Rich, can you possibly let me know what publication the information is in and I can look for it on line...

Info for the Cossor 172K was obtained from Radio Valve Data, Eighth Ed. in section Television Cathode Ray Tubes page 57. Base diagram number is B12A number 10.

In the meantime I have been turning the place upside down to find the original Cossor Valves and Tubes book c.1956. Success! So far it confirms data in the ILIFFE publication and has a bit more info! Will try to scan later.

Also discovered another Cossor short form data book published in 1959 by which time 172K was obsolete. However information on receivers that used this CRT including 171K, advises it can be replaced with MW43-69 in the following models, 930, 933, 934, 935, 937, 939, 942, and 946.


FERNSEH 20th May 2021 7:35 pm

Re: Help with some old TV tubes.
By 1958 almost all Cossor branded tubes made by Mullard had standard Pro-Electron codes, e.g. MW43-69 and the AW43-80 which was fitted in the model 948.
Circuit diagram of the model 945B shows that the 70* CRT has the pentode gun and therefore is a 173K or MW43-69.


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