tube confusion

snipelfritz · Post by **snipelfritz** » Wed May 30, 2012 2:27 pm

So giving my new vintage amp a good run over, I realize how much louder the lead channel is and how the clean channel seems like it was much louder a day or two ago. So I check the preamp tubes and sure enough the 1st has gone microphonic. The diagram inside the amp labels it a 7025.

The tube itself says 7025 along with ECC83 and 12AX7. I have an extra ecc83 and two 12ax7s and I'm sure at least one is good. Can they be interchangeable or am I just better off getting a new tube (or maybe just a full set?

Psyre · Post by **Psyre** » Wed May 30, 2012 2:35 pm

One of my bassman's tubes came to me microphonic so I just went ahead and got a whole new set, that way I knew exactly how old/ how much use they had on them, and boxed what was in it back up to keep as my spares (minus the microphonic)

snipelfritz · Post by **snipelfritz** » Wed May 30, 2012 2:39 pm

Psyre wrote:One of my bassman's tubes came to me microphonic so I just went ahead and got a whole new set, that way I knew exactly how old/ how much use they had on them, and boxed what was in it back up to keep as my spares (minus the microphonic)

That's what I did with my vox which is why I have the extras but can't remember which was good. I figure I'll change the whole thing soon but I need some cash first. This thing has 3x7025 2x12Ax7 and 2x6L6. Woof. But for an amp priced at $300 with some lenient trades you can't complain about a little investment. It sounds incredible otherwise.

Chankgeez · Post by **Chankgeez** » Wed May 30, 2012 2:43 pm

I think for the most part those tubes are interchangeable.

Amp builders may've used a specific tube for the characteristics it produces. So, your amp may not end up sounding the same as with a 7025. Usually if it's spec'd with a certain tube variant, it's for a good technical reason.

When you can afford it, I'd replace all the preamp tubes.

univalve · Post by **univalve** » Wed May 30, 2012 2:53 pm

7025 is a high grade military version of the 12ax7/ECC83. They are all interchangeable.

snipelfritz · Post by **snipelfritz** » Wed May 30, 2012 3:43 pm

Yeah, popped in the least used ECC83 (a JJ) and it sounds fantastic and loud again.

D.o.S. · Post by **D.o.S.** » Wed May 30, 2012 4:02 pm

univalve wrote:7025 is a high grade military version of the 12ax7/ECC83. They are all interchangeable.

new05002 · Post by **new05002** » Wed May 30, 2012 4:41 pm

any modern production 12ax7 is fine, unless you wanna actually get a NOS pretube

metalmariachi · Post by **metalmariachi** » Wed May 30, 2012 7:18 pm

yup 7025=low noise 12AX7
ECC83= Brit for 12AX7

MM

Gone Fission · Post by **Gone Fission** » Wed May 30, 2012 9:44 pm

For New Old Stock, there's a chance that a 7025 was selected for low noise, but more likely than not it was out of the same line as tubes that got labeled 12AX7. ECC83 is just the European designation for a tube of the same spec as a 12AX7. For current production, it's unlikely that the designation means much in itself. If the current production model has any particular designation on the end of the usual 12AX7 or a variant of ECC-83 it might have some special-ish quality or may be marketing hype.

excane · Post by **excane** » Wed May 30, 2012 10:00 pm

All is correct above.

Just be careful not to mix up an ECC82 with an ECC83. The 82 is used as the inverter in a lot of amps.

Gone Fission · Post by **Gone Fission** » Wed May 30, 2012 10:25 pm

Generally speaking, mixing up 12au7, 12ay7, 12at7, and 12ax7 (and other renumberings of these) ain't gonna blow nothin' up. They're on the same pin layout, same heater requirements, similar current draw, and can often be treated as different gains of the same tube. Might not be an optimal swap in all cases, but it's not like to kill a transformer or make a tube die a glowing red death like swapping KT-88 for 6V6 or vice versa could. The places to be careful in considering swaps and Google-verify the soundness are phase-inverter stages and reverb drivers.

univalve · Post by **univalve** » Thu May 31, 2012 6:14 am

Probably this explains the different a bit:
Gain factor in % in comparision to a 12AX7 (=100%). The whole system is looked at as you would use it in the V1 slot.

100: 12AX7, 7025, ECC83
70: 5751
60: 12AZ7, 6201, 12AT7, ECC81, 12DW7
47: 5965
44: 6072, 12AY7
41: 12AV7
21: 5963
20: 5814, ECC82, 12AU7
16.5: 12BH7

I tried almost all in the first slot of some of my amps. Below 12AY7 (which is e.g. the Fender Tweed Deluxe vintage correct setup) it is not that good anymore to my ears.

dubkitty · Post by **dubkitty** » Thu May 31, 2012 7:49 pm

i was just reading up on this last night, oddly enough. from what i read the 7025 was the mil-spec "low noise" version of the AX7, and as such Fender used to specify it for their preamp stages. even in the 70s it was commonplace for regular AX7s to dep for 7025s; most of the old preamp tubes in my Twin Reverb were AX7s despite being specced as 7025s.

excane · Post by **excane** » Thu May 31, 2012 7:52 pm

dubkitty wrote:i was just reading up on this last night, oddly enough. from what i read the 7025 was the mil-spec "low noise" version of the AX7, and as such Fender used to specify it for their preamp stages. even in the 70s it was commonplace for regular AX7s to dep for 7025s; most of the old preamp tubes in my Twin Reverb were AX7s despite being specced as 7025s.

Yep.... my Showman has Dumont 7025s on the recommendation of several outstanding amp peeps that told me to use 'em. Sounds fantastic.

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