Cossor OM series valves, were these made by Mazda? - UK Vintage Radio Repair and Restoration Discussion Forum

FERNSEH · 15th Apr 2017, 11:58 am

Those octal based Cossor OM series valves do seem to have a Mazda look about them, the question is were these valves actually made by Ediswan-Mazda?
The examples I've chosen to start the discussion are the OM10 and the Mazda TH41.

DFWB.

Silicon · 15th Apr 2017, 12:11 pm

I was pondering that question last night when I discovered that the heater in a Mullard EF39 in my Eddystone 640 was not glowing. It may have been caused by an invisible corrosion of the valve base pins.

The Mazda OM6 is apparently a direct equivalent.

Has anyone compared the two valves in a valve characteristics meter?

Boater Sam · 15th Apr 2017, 12:12 pm

A good question.
The shape is similar but on a Mazda the screening coating overlaps the base, but not on a Cossor.
Obviously the base is different, Mazda octal and international octal and also the Mazda top cap is larger.
Where was the Cossor valve factory?

Leon Crampin · 15th Apr 2017, 12:18 pm

These valves were all made by Mullard and most carry the give away factory code on the base. The OM10 is an ECH33/5 with grey metallising. Mazda valves of this vintage have MO bases and 4V heaters with a large top cap connection.

Does "OM " stand for octal mains? I bought some OM5C (EF37A) devices at audiophool defeating prices.

Leon.

tri-comp · 17th Apr 2017, 2:45 pm

Quote:

Originally Posted by Leon Crampin

I bought some OM5C (EF37A) devices at audiophool defeating prices.
Leon.

I have the Cossor OM5 which is a close equivalent of the EF36, i.e. NOT the low-noise, low-microphony variant.
Now, my question is if the OM5C actually IS the exact equivalent of EF37A with all it's improvements over EF36 ?
I would imagine the price on the OM5C should be a lot lower than that of the EF37A.

I checked the NOS Cossor OM5 in my B&K 667 valve emission-tester and it measureres EXACTLY like a NOS Mullard EF37A that I have in stock.
The EF37A's I have were bought from Watford Valves many years ago before prices ran wild. Too bad I didn't buy more at the time.....

Leon Crampin · 17th Apr 2017, 9:58 pm

From the Mullard data I have here, the EF36, 37 and 37A all have the same electrical characteristics. I can deduce from the data that the EF37 was a development of the 36 for low microphony, and the 37A was a further development to give low hum - achieved with a spiral wound heater as in the later AF amplifier devices such as the EF86.

Mullard give the equivalents as follows:

EF36 = OM5
EF37 = replaced by EF37A
EF37A = OM5A, OM5B

I can find no reference anywhere to the OM5C but it's obviously a later development and has identical characteristics to the EF37A.

There's one final possibility. Mullard did produce an electrometer amplifier based on the EF37A coded Mxxxx. I'll try to look this up. It was clearly the same device, probably selected for very low grid current which was characterised in the data. It would then be a fair assumption that the Cossor device would be coded as the OM5C.

Any comments of course are welcome.

Leon.

Leon Crampin · 17th Apr 2017, 10:02 pm

Found it - it's the ME1400.

http://www.r-type.org/exhib/aad0185.htm

Leon.

FERNSEH · 19th Apr 2017, 4:54 pm

Two Cossor OM6 (EF39) valves and a Mazda TH41. The bulb of the OM6 on the left is of identical shape and dimensions of those of the Mazda TH41.
The other OM6 is slightly shorter but still has that Mazda look about it. Also, the style of the print in the Cossor valve looks very Mazda.

DFWB.

Cobaltblue · 19th Apr 2017, 5:06 pm

It depends a lot on when the valves were made.

Originally Cossor made its own valves in house.

1943 The company moves its valve and CRT business into a new wholly owned subsidiary Electronic Tubes Ltd (ETEL) based at High Wycombe.

1949 EMI purchases ordinary (voting) shares in ETEL, and takes management control. Cossor retains an investment in ETEL, purchasing its valve requirements from EMI and from MOV, which was jointly owned by EMI and GEC.

1956 Cossor disposes of its holding in ETEL sometime after 1956, and withdraws from valve and CRT manufacture.

1958 Cossor sells its radio and television business to Philips

Cheers

Mike T

Heatercathodeshort · 30th Apr 2017, 10:47 am

I have just discovered this 'Cossor' OM6. It looks like a Marconi or even an original Cossor bulb. The BVA certainly worked in mysterious ways. Regards, John.

FERNSEH · 30th Apr 2017, 3:35 pm

Hi John,
that's an odd looking thing. Could it be a Tungsram valve? The valves designed by Tungsram in Hungary always looked a bit different.

DFWB.

15th Apr 2017, 11:58 am	#1
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Cossor OM series valves, were these made by Mazda? Those octal based Cossor OM series valves do seem to have a Mazda look about them, the question is were these valves actually made by Ediswan-Mazda? The examples I've chosen to start the discussion are the OM10 and the Mazda TH41. DFWB. Attached Thumbnails

15th Apr 2017, 12:11 pm	#2
Silicon Nonode Join Date: Jun 2007 Location: Coulsdon, London, UK. Posts: 2,163	Re: Cossor OM series valves, were these made by Mazda? I was pondering that question last night when I discovered that the heater in a Mullard EF39 in my Eddystone 640 was not glowing. It may have been caused by an invisible corrosion of the valve base pins. The Mazda OM6 is apparently a direct equivalent. Has anyone compared the two valves in a valve characteristics meter?

15th Apr 2017, 12:12 pm	#3
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Cossor OM series valves, were these made by Mazda? A good question. The shape is similar but on a Mazda the screening coating overlaps the base, but not on a Cossor. Obviously the base is different, Mazda octal and international octal and also the Mazda top cap is larger. Where was the Cossor valve factory?

15th Apr 2017, 12:18 pm	#4
Leon Crampin Octode Join Date: Nov 2005 Location: Surrey, UK. Posts: 1,870	Re: Cossor OM series valves, were these made by Mazda? These valves were all made by Mullard and most carry the give away factory code on the base. The OM10 is an ECH33/5 with grey metallising. Mazda valves of this vintage have MO bases and 4V heaters with a large top cap connection. Does "OM " stand for octal mains? I bought some OM5C (EF37A) devices at audiophool defeating prices. Leon.

17th Apr 2017, 9:58 pm	#6
Leon Crampin Octode Join Date: Nov 2005 Location: Surrey, UK. Posts: 1,870	Re: Cossor OM series valves, were these made by Mazda? From the Mullard data I have here, the EF36, 37 and 37A all have the same electrical characteristics. I can deduce from the data that the EF37 was a development of the 36 for low microphony, and the 37A was a further development to give low hum - achieved with a spiral wound heater as in the later AF amplifier devices such as the EF86. Mullard give the equivalents as follows: EF36 = OM5 EF37 = replaced by EF37A EF37A = OM5A, OM5B I can find no reference anywhere to the OM5C but it's obviously a later development and has identical characteristics to the EF37A. There's one final possibility. Mullard did produce an electrometer amplifier based on the EF37A coded Mxxxx. I'll try to look this up. It was clearly the same device, probably selected for very low grid current which was characterised in the data. It would then be a fair assumption that the Cossor device would be coded as the OM5C. Any comments of course are welcome. Leon.

17th Apr 2017, 10:02 pm	#7
Leon Crampin Octode Join Date: Nov 2005 Location: Surrey, UK. Posts: 1,870	Re: Cossor OM series valves, were these made by Mazda? Found it - it's the ME1400. http://www.r-type.org/exhib/aad0185.htm Leon. Last edited by Leon Crampin; 17th Apr 2017 at 10:19 pm.

19th Apr 2017, 4:54 pm	#8
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Cossor OM series valves, were these made by Mazda? Two Cossor OM6 (EF39) valves and a Mazda TH41. The bulb of the OM6 on the left is of identical shape and dimensions of those of the Mazda TH41. The other OM6 is slightly shorter but still has that Mazda look about it. Also, the style of the print in the Cossor valve looks very Mazda. DFWB. Attached Thumbnails

19th Apr 2017, 5:06 pm	#9
Cobaltblue Moderator Join Date: Dec 2010 Location: Exeter, Devon and Poole, Dorset UK. Posts: 6,864	Re: Cossor OM series valves, were these made by Mazda? It depends a lot on when the valves were made. Originally Cossor made its own valves in house. 1943 The company moves its valve and CRT business into a new wholly owned subsidiary Electronic Tubes Ltd (ETEL) based at High Wycombe. 1949 EMI purchases ordinary (voting) shares in ETEL, and takes management control. Cossor retains an investment in ETEL, purchasing its valve requirements from EMI and from MOV, which was jointly owned by EMI and GEC. 1956 Cossor disposes of its holding in ETEL sometime after 1956, and withdraws from valve and CRT manufacture. 1958 Cossor sells its radio and television business to Philips Cheers Mike T __________________ Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk

30th Apr 2017, 10:47 am	#10
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Cossor OM series valves, were these made by Mazda? I have just discovered this 'Cossor' OM6. It looks like a Marconi or even an original Cossor bulb. The BVA certainly worked in mysterious ways. Regards, John. Attached Thumbnails

30th Apr 2017, 3:35 pm	#11
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Cossor OM series valves, were these made by Mazda? Hi John, that's an odd looking thing. Could it be a Tungsram valve? The valves designed by Tungsram in Hungary always looked a bit different. DFWB.