Help with Mullard EL34 ID

[tooold]

I have a couple of EL34's that are theoretically Mullards. One's shorter than the other, and has a different internal structure. Before I put them in my SA-212, I thought I'd run a few photos past you guys to see if one or both is fake, or there was some different form factor. I've tried to sort this out on various Mullard ID sites, but I'm not getting it.

First one is the taller one, worn printing, broken off locating pin. Codes read X f 4, then below that B(?) 6 D 1. Embarrassingly enough, I have no idea what the circular wire at the top of the internal structure is called, but this tube has a single large circular element, the other has two smaller elements.

Second tube is a little shorter, better printing. Codes read X f 2, B 5 C 1. Any help you can throw my way would be great.

Here are some photos:

[img:800:600]http://i115.photobucket.com/albums/n308 ... 020209.jpg[/img]

[img:800:600]http://i115.photobucket.com/albums/n308 ... 020213.jpg[/img]

[img:800:600]http://i115.photobucket.com/albums/n308 ... 020212.jpg[/img]

[img:600:800]http://i115.photobucket.com/albums/n308 ... 020219.jpg[/img]

[img:600:800]http://i115.photobucket.com/albums/n308 ... 020220.jpg[/img]

[Cliff Schecht]

XF2 and XF4 are different generations of EL34 made by Mullard. The XF2 is the earlier one. IME both sound relatively close to each other (I have quite a few of both types) and so if they match up decently, I'm sure they'll sound great in whatever you put them in.

[tooold]

XF2 and XF4 are different generations of EL34 made by Mullard. The XF2 is the earlier one. IME both sound relatively close to each other (I have quite a few of both types) and so if they match up decently, I'm sure they'll sound great in whatever you put them in.

Cliff, thanks for that. Great news, obviously... I was prepared for the worst!

[Cliff Schecht]

Glad I could help. These really are some TOUGH tubes, all of mine are pulls from high voltage power supplies (EL34's were the regulation elements!) and all of them test strong and work in whatever amp I put them in. I absolutely love them in my Express and they sound killer in Marshall's. I'm building a 100W 2203 pretty much around a quad of XF2's and a couple of transformers I have.

[tooold]

I bought these used off ebay a few years back. I biased them up in a Marshall 1987 I restored a while back, and they were pretty far off relative to each other, so I used some Siemens in that. Now, these were going to go in a 50 watt Hiwatt that I just put a bias pot in, but I think I might save them for an AC50 I'm restoring, as that has individual bias pots per output tube.

I'll try them in the Hiwatt first, though - one of the opinions floating around on the surface of the 'net is that unmatched power tubes can sound really good, so I thought I might try to form my own opinion...

Any thoughts on the matched/unmatched power tube idea?

Thanks again for the help.

[Structo]

Install two bias pots so you can balance them at idle.

But they may spread apart as you turn up.

The round metal thing at the top of the tube is called a "Getter" it is used to flash the remaining gas out of the tube.

[David Root]

I have an Xf1 and an Xf2 in my Marshall 2204, both well used and they sound great.

If they are matched within 4 or 5mA at idle you're OK in a Marshall IMO, in a Hiwatt circuit I would want to be a little closer than that. I'd also want the bias pot in the Hiwatt as the original design runs the EL34s so hot they won't last, tough though they are. They were a lot cheaper back then!

[rdjones]

I'll try them in the Hiwatt first, though - one of the opinions floating around on the surface of the 'net is that unmatched power tubes can sound really good, so I thought I might try to form my own opinion...

Any thoughts on the matched/unmatched power tube idea?

Leo never tried to "match" output tubes, that was a later CBS revision to be able to use mis-matched tubes and get away with lower residual hum.

Individual bias pots to adjust an unbalanced pair of outputs is just another type of imbalance.
True tube matching involves selecting a pair that are matched to each other in three ways, transconductance, idle current and emission (maximum current).
Dual bias pots adjusted for identical idle currents will still be imbalanced at full output if the tubes are not close in transconductance or in a similar state of "life" (emission).

reddog

[Cantplay]

This is the Mullard decoder:

http://www.audiotubes.com/mullcode.htm

John

[tooold]

Thanks for the replies and info!