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Old 29th September 2014, 12:01 AM   #1
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Default Questions about found Mullard xf1's

I got a Dynakit St-70 off craigslist. It had a busted rectifier tube and one busted EL34 (cracked at base, cloudy top...). In the course of restoring this amp, I noticed that the EL-34s are marked "XF1" and under that "B0E4" which are apparently some not so common Mullard tubes from around 1960. Some people seem to like these...thoughts? Anything I should know?

I have no idea what condition these are in. I'm planning on taking them to a local vintage amp restoration shop to get them tested, but given my level of expertise and the fact that I only have three working tubes, I'm looking for advice assuming they test well....

1) Is it dangerous to get them tested, even by a reputable tube amp shop?

2) Do I keep them and pray I can magically match a fourth xf1 on the off-chance some come up for sale? I sure can't find many out there...

3) Is it possible to match them to a more common, later model xf2 without doing too much harm in my ST-70? I promise I'm going to use new, 6CA7EH's in the unit first to make sure everything works before blowing these up.

And I guess the final option is to sell them, since if it will be impossible to use them in the ST70 means they're likely worth more to others than to me. I feel like I know just enough about things to be dangerous here, and part of this is just me being excited feeling like "Oh cool, did I hit the DIY jackpot early in this hobby by finding something rare in a cheap craigslist unit???" And maybe they test for crap, but the getters are all good, really sucks that the fourth is cracked at the base.

I've attached two photos to try to show the markings. It's near impossible to photo the markings well, but they all have the same mark of XF1 - B0E4 and the double halo and all that. Sorry for the doctored photos, and I'll try to get a better camera/lighting set up.
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File Type: jpg IMG_1034.JPG (858.3 KB, 99 views)
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Old 29th September 2014, 01:04 AM   #2
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Hi,

Enjoy the amp. As for the tubes is that the same tube twice or two
different tubes? It looks the the glass is cracked in each tube.

You can't use it any more, time to throw it away unless you want
a desk ornament. There is some value in the tubes for a tube collector
for the remaining two or three? Unless you buy same replacement
tubes I'd either sell them or trade for a new quad of tubes. That is
unless you want to start being a tube collector too.

ST70 is a good learner project if you want to start to learn about electronics.
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Old 29th September 2014, 01:32 AM   #3
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Hi,

These Mullard EL34s are well sought after by electric guitar players using VOX AC30, some Marshal and similar amps.

For audio use my favourite were the Tesla EL34 or E34L or the US made 6CA7 (which is not quite the same valve BTW).

Some history:

TC: EL34 6CA7 xf1 xf2 xf3 xf4 tubes from Philips Valvo Mullard - www.tube-classics.de

Mullard EL34 production codes

Scroll down to "Rohren geschichtliches", EL34

Jogis Roehrenbude - Roehrenradios, Roehrenverstaerker und vieles mehr
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Old 29th September 2014, 03:21 AM   #4
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Thank you for the incredibly helpful and quick replies. I haven't been on DIYAudio in a few years after having to put aside the tinkering for grad school, and I'm remembering why I spent so much time here in the first place. Looking forward to learning and sharing more.

edit, @SyncTronX: that's the same tube, was just trying to get the lettering to show up. Yes, it's very unusable.

Last edited by ervington; 29th September 2014 at 03:22 AM. Reason: forgot something
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Old 29th September 2014, 03:53 AM   #5
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Good Stuff fd, nice links.

@ervington, well since you have three if you save up you might find a fourth.
shouldn't be too hard to find another. However, make sure you find someone
to test the other three and make sure they are good, otherwise you'll have
to buy enough to work.

I used to know three or four guys from there who could have tested them.
Two were in Hot Springs...Banjo Dan's, and an old retired guy who had
tubes, manuals, and such at the Antique Mall. The latter was kind enough
to let me check out his basement where it was full of cases of tubes, radios,
and other gear, I bought all I could at $4.00 a pop cash. When I got back
there again, he had passed away. But what a nice old guy with a love for
all this stuff.

There was guitar shop guy John, over by little rock around south west I think
but he closed up shop years ago. There was another guitar shop guy or two
that have passed away too. There is a speaker builder guy on DIY in Hot Springs Village, you might look in the Vender section, he might know someone over in Little Rock...
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