Ultron 3S4 tubes

[airdronian]

Hello lads - wanted to poll the members here to see if anyone might assist with an ID of the manufacturer of some Ultron tubes I have.

As I understand it, Ultron is a rebrander of tubes.  I bought 4 pair off the big auction site for a good price.  These came out of Germany, and I think it's safe to say the box is German.  But the tubes ?  Here's some photos that I hope offer enough detail to provide some clues.

I guess that is what could be called a "D" getter, there is lettering present of "HCFX", and on the base there is what looks like a "C" or a "U".  Hard to tell.

I've just started using a pair.  Fairly warm sounding, not as much depth as my Mullards, and pretty low microphonics compared with the stock tubes.  Not bad.

Any guesses would be welcomed.

[mcandmar]

I dont know what those are, they aren't Philips, Siemens, or Telefunkens so i would guess they are US made.  Possibly Sylvania?

[Paul Birkeland]

I would suspect they are French.  I'd have to dig into my stash to see if I could procure an identical set.

[airdronian]

If you do find something like them that would be great.  I'd tried searching to no avail.  There's no etching like an RCA or GE might have.

The labels are all in good shape but fragile, the boxes somewhat delicate, and they were sure stinky/musty when I first got them.