Cossor rectifier valve identification?

[Techman]

This valve was in the recent 'lot' of valves I acquired and there were a few that I thought I was going to have to ask for help identifying due to numbers being rubbed off, but after careful use of light and magnifying glass (and the Valve Museum) I've pretty much sussed them all out except this one, other than it's a Cossor, although I still haven't looked at them all, but I think I've so far found all the 'exciting' ones...

[Marconi_MPT4]

In 1935 two listed, 506BU 250-0-250V 60mA with 4V 1A filament, or perhaps 460BU rated at 500-0-500V 120mA with a 4V 2.5A filament.

Rich

[wave solder]

A Cossor 412BU as a guess

[Techman]

Thanks chaps - the cold resistance of the filament did measure as an expected 4 volt one would.

[Techman]

Looking at the online pictures of the suggested valves, I'm thinking that it's exactly like the 412BU. Interestingly, it says in the writeup that it's just the makers name on the top of the glass and that the type designation would be on a paper label on the side - this would account for why I was only able to decipher the word Cossor on the top of the valve globe, as the actual type number was never there in the first place. Looks like I can now get the felt tip pen and mark the type number low down on the side of the valve glass for future identification.

[Hartley118]

I sympathise, having just solved a similar mystery on an anonymous Cossor 42OT 4-volt heater B7 base output beam tetrode which had been substituted for the original Ever Ready A70C output pentode in my Pye T10 at some point in its life since 1936.

Cossor's practice of printing the valve type number on a paper label doesn't serve our hobby well - time's ever-rolling stream tends to have long since swept them away, particularly on hot mains radio valves.

Still, it keeps our grey cells working towards the solution, often by a process of elimination. Thank goodness for online data which often features photos of the candidate valves in question. I've found an interesting and useful reference book is "British Radio Valves - The Classic Years:1926-1946" by Keith R Thrower. It's available online at
https://nvhrbiblio.nl/biblio/boek/Th...01926-1946.pdf

As well as being a useful source of information, it's a tour de force telling an interesting series of historical stories about valve development.

Martin

[Techman]

Originally Posted by Hartley118

Cossor's practice of printing the valve type number on a paper label doesn't serve our hobby well. Still, it keeps our grey cells working towards the solution, often by a process of elimination. Thank goodness for online data which often features photos of the candidate valves in question. I've found an interesting and useful reference book is "British Radio Valves - The Classic Years:1926-1946" by Keith R Thrower. It's available online.

I agree.

In one of the online Valve Museum pictures it points out a small remaining piece of the said paper label that can still be seen stuck to the glass. I'd already got that Keith Thrower book downloaded and was looking at examples in it when first trying to identify this particular valve - definitely a recommended download.