BTH type CG1-C CV425 GEX44 subminiature germanium point-contact diode, mil packed since 1952
We normally expect the CV numbering system to apply to valves but a small number from the CV4xx range applied to the quaintly quoted "crystal valve" - in actuality a germanium point contact diode.
The first of this series was the CV425 is a subminiature germanium point-contact diode, equivalent to the BTH type CG1-C and these are what we have on offer today. Interestingly, these very early semiconductors were all hand made and sealed at a BTH facility. They present in individually sealed LDPE sealed bags and you can see from an example packing card that they were made/packed during 1952 - wherever have they been for the past 65 years!!!!!!!! These are just the thing for your crystal set construction project as they look suitably quirky and old.
Now, little bit of history about the British Thomson-Houston Company Limited (BTH). BTH was a very long established enterprise being formed initially in 1896 with funding from GE in the USA. However, in 1926, BTH became one of several UK electrical companies to fall under the umbrella of a holding company called Associated Electrical Industries (AEI) which went on to become a conglomerate of many smaller UK industrials.
Transistors and other semiconductors were a relatively minor part of BTH/AEI's product line, initially manufactured in Rugby but later at the Lincoln semiconductor plant. The BTH company is acclaimed for having built the world's first prototype jet engine for Sir Frank Whittle in 1937, The change of name from BTH to AEI occurred just after the company started manufacturing germanium transistors, and so both sets of initials can be found on early devices. As is the way in British industry, the AEI name was extinguished in 1967 following a takeover by the GEC company.