Hmmmm... This Mullard seems a little fishy! EL-34 content

[Matt D]

I picked up a pair of lightly used "Mullard" xf-1, large base EL-34s at a local electronics surplus shop VERY inexpensively, and I have my doubts that they are the real deal. They do sound fine in my AX84 build. The most obvious thing that makes me suspicious is that the silkscreening doesn't rub off easily even when scraped with a fingernail. Also, something about the fonts doesn't look right.

The interior construction where the base meets the bottom plate of the tube is identical to a known xf-2 Mullard, and the plates are welded. However, the known xf-2 has 5 welds per side while the suspicious xf-1 only has 4. The suspect tube also has the proper hole in the center guide. Also, the two halo getters overlapping each other seems unusual. My picture taking is limited to a phone-camera but if anyone can confirm my suspicions based on these pictures I'd appreciate it. I think I might have some re-branded teslas.

There are codes that say:
xf-1
BBG
1022-907
178

Any ideas? Thanks

[Structo]

Hi Matt,

If you don't get an answer here, you might try over at The Gear Page.

There are several tube aficionados over there that should know.

[rooster]

I say real but your pics do suck like you say..

[Cantplay]

Do you have xf1 etch codes on the glass?

I thought all xf1 were metal base.

John

[Matt D]

Thanks for the replies guys. I found an article in an old Vacuum Tube Valley magazine where there is a quick mention of the fact that Tesla made some xf-1 knock-offs with a wide base and everything. I've also seen pictures of Teslas with the same kind of overlapping halo getters. Who knows? Anyway, they sound good and they were cheap!