Confusion of AC/VP1 valves

[boater sam]

I may be old, short sighted and a little confused sometimes, BUT I am sure that I have 2 Mazda valves both clearly printed "AC/VP1"  one on the correct B7 base, the other has a B4 base!
Now there is no way that 4 base pins and a top cap could be enough connections.
Anyone any ideas?

I had thought that the B4 base could have been fitted and some connections ignored to make up for a non available valve by some clever Charlie but that seems way out.

[AlanBeckett]

Apparently it came in both flavours - http://www.r-type.org/exhib/aag0028.htm
By the way, it's B5 not B4 according to the above.

Alan

[boater sam]

You are correct Alan, my error, it is B5.

I had no details for the B5 version so I made some assumptions and put it on the tester with what I reckoned may be the connections. It was tested and is OK.
So now I have one of each!

I know of the different valve forms such as G and GT and of course the metal ones, but I have never before had exactly the same number but with completely different bases.
Are there any other similar confusions I should be aware of?

[AlanBeckett]

I believe I have come across others in the Valve Museum but I can't remember any exact Numbers.

Alan

[radioman]

According to my 'Radio Valve Data' book, there are quite a few early pentodes in the same boat !
e.g. Mullard VP4 and MOV MSP4 were available with either a B5 or B7 base.
I've seen some valves with a B4 base that even had an extra connection on the side of the base !
Certainly worth watching out for if you need to buy replacements.

Andy