British Valve Numbering System?

[Roy Nichols]

Is there a standardized system used for numbering British valves? While working on our recently acquired Alba I've noted from the diagram and data in states specific make and number like "Cossor 7S7". Did different firms use different numbering systems? Is there a specific method to the numbers like US tubes?

According to the Trader date our Alba has the following valves:

Cossor 7S7 - Triode/Heptode
Cossor 7B7 - Variable MU Pentode
Cossor 7C6 - Diode/Triode
Cossor 7C5 - Pentode Output
Cossor 7Y4 - Half-wave rectifier

It says the valves are Loctal bases but they don't look like US Loctals. They have a thick glass bottom and a spring tension retainer. Undoubtedly very familiar to you all but a new experience for me. I've yet to locate a specific tube data book like the US RCA Receiving Tube Manuals which covered most all US consumer tubes by universal RMA numbers.

[paulsherwin]

There were some odd tubes used in the 40s / early 50s and this lineup is one of them. Loctals like this were used reasonably widely in British sets of this period though conventional octals were more common - later, B8A rimlocks and, later still, B9A novals took over.

Most British sets used tubes which use the Pro-Electron coding system developed by Philips/Mullard - first letter is heater voltage or current, second letter is tube type, first number is base, subsequent numbers are model numbers. Some used American types often made by GEC or Brimar, and some used a Mazda private coding system (though there are usually Pro-Electron equivalents for these).

Apart from the base these are normal 6.3V radio tubes found in any American set of the same era. They can be ordered from one of the tube dealers listed elsewhere on this site though they're not especially common these days. That said, I've just had a look on the Colomor website and they seem to have them all in stock at reasonable prices: http://freehost03.websamba.com/colom...asp?typ=Valves

You will find info on these and many other tubes by downloading the TDSL database from the Duncan Amps website - it's free and very useful: http://www.duncanamps.com/tdslpe/

HTH, Paul

[quantum]

Fortunately these loctals had direct electrical equivalents to the more common octal ranges, so, for example, a 7C5 is the direct electrical equivalent of a 6V6 and the 7Y4 to a 6X5. Some UK models could use either the loctal or octal series, or a mixture of both, often because of shortages in supply of tubes caused by post WWII conditions and/or the Korean War firms had to make do with what was available.

[Roy Nichols]

It turns out the tubes are not as described in the diagram/data sheets. The tubes are all Mullard miniture with a little rim around the very bottom and held in by a spring. The tubes are:

EL41 - Power amp
EBC41
EF41
ECH42
EZ42 - Rectifier

I'm guessing there was some production change between the Trader diagram description and our set.

[paulsherwin]

This is a completely standard tube lineup for an early 50s British set. It's possible Alba switched to this lineup during the model's production run. Occasionally you'll find the chassis has been fitted with adaptor plates for the smaller tube base.

The Ex4x series are B8A Rimlock tubes which were never manufactured in the US. They're very, very common in Europe though - they were adopted at the same time US makers were switching to 7 pin miniatures. I think the base was a Philips design, and thanks to the dominant position of Philips/Mullard they were widely adopted by many manufacturers.

EL41 = output pentode
EBC41 = double diode triode (AF amp / detector / AGC)
EF41 = IF amp pentode
ECH42 = frequency changer (triode hexode)
EZ41 = rectifier

All these are still widely available from dealers, and users of this forum will be very familiar with them.

Best regards, Paul