A year or two ago, someone was inquiring if there was such a thing as a 6X5 with a 12V filament. 12X5 does not exist, but the 7 pin miniature 6X4 and12X4 doe as we all know.
I suppose one could pull the old " metal 6V6" trick, which used a 6AQ5 and an octal to 7 pin base adapter, all hidden under the ostensibly "6V6" metal shell. If you had one of these, the 6AQ5 could be removed, and a 12X4 inserted in its place, and a "metal 12X5" would be the result. The pinout might be all screwed up, depends if the internal wiring could be changed or not, or if it is even compatible at all... Yellow_Light_Colorz_PDT_11
There are probable Loctal 12/14V filament rectifiers, I don't have my books and manuals present for quick reference.
Well, it turns out that Bendix had some 6X5 variants:
5852 has a 6.3 V filament,
5838 has a 12.6 V filament, and
5839 has a 26.5 V filament.
Most of these are very difficult to find, one would probably have better luck finding NOS/NIB WE300Bs for $5 each... :o Yellow_Light_Colorz_PDT_04 Yellow_Light_Colorz_PDT_02 Yellow_Light_Colorz_PDT_03 Yellow_Light_Colorz_PDT_05
Can you say "unobtainium"
These are the kind of tube that are likely show up at hamfests and swapmeets for cheap, because the seller doesn't know what the heck they are Yellow_Light_Colorz_PDT_09
/ed B