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In the manual for my amp it says 2 of the tubes are ECC81/12AT7 and 2 are ECC83/12AX7. I was wondering if they are interchangable, and what the tonal difference between ECC and 12A tubes are. Thanks.

If this is your problem, here is the answer. ecc81 and 12at7 are the same tubes, just different names. IIRC the ECC titles are the british names and the 12 titles are american.

ECC and 12A are the same thing. American/European names i'm pretty sure. The two types 12AX7 and 12AT7 should be interchangeable. The 12AX7 should produce more gain than the AT7 though.


Originally Posted by YJM_RocksThe two types 12AX7 and 12AT7 should be interchangeable.

Exactly right -- I've made that swap myself.Originally Posted by YJM_RocksThe 12AX7 should produce more gain than the AT7 though.

Exactly right. The AT7 gives you only 70% as much gain as the AX7.

But my question is: Is there a preamp tube that is somewhere between the AT7 and AX7 gain-wise? Like 80-85% of an AX7?
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[QUOTE

But my question is: Is there a preamp tube that is somewhere between the AT7 and AX7 gain-wise? Like 80-85% of an AX7?
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About the only other option is a 12DW7- you may or may not be able to use this tube depending on how your amp is wired- the 12DW7 is 1/2 12AX7 and half 12AU7.

Just use the correct values for your amp. More than likely, the AT7's aren't part of your preamp's signal path, so it won't matter. They may be a reverb driver or phase inverter.
The AX7's are probably furthest from your power tubes, making them the 1st and 2nd gain stages.


Originally Posted by ZhangliqunBut my question is: Is there a preamp tube that is somewhere between the AT7 and AX7 gain-wise? Like 80-85% of an AX7?

Given the variance in current production tubes, you can probably get a low-gain (out of spec) AX7. The problem would be finding it.


Originally Posted by GearjoneserJust use the correct values for your amp. More than likely, the AT7's aren't part of your preamp's signal path, so it won't matter. They may be a reverb driver or phase inverter.
The AX7's are probably furthest from your power tubes, making them the 1st and 2nd gain stages.

I put some AT7's in my Fender Hotrods so that I could make more precise volume adjustments. With the AX7's, the jump in volume on the master volume from 1.63 to 1.78 or 1.9 to 2.2 is just ridiculous -- such a hair-splitting difference and you either can barely hear it or it's knocking the walls down. This is not a problem at a gig where I'm up around 3 or 4 or more (the taper levels out up there), but for practicing in my apartment, it can be annoying.

My Hotrods still are a little touchy that way but the AT7's did help some. Sure the gain is reduced for the drive channel but I don't look for overdrive from my Hotrods (lousy to begin with), I want them for the killer clean tone so I get my crunch from a Maxon Overdrive Pro stompbox.

I've used ecc83 and 12AX7 and the difference was very noticeable. The ECC's sound more boxier (linear). I prefer the more quot;openquot; sound of 12ax7, or 7025.
And yes the 12AT7 is considerably less gainy.


Originally Posted by TrilogyI've used ecc83 and 12AX7 and the difference was very noticeable. The ECC's sound more boxier (linear). I prefer the more quot;openquot; sound of 12ax7, or 7025.
And yes the 12AT7 is considerably less gainy.

Were they the same brand? The electrical properties of the two tubes are supposed to be the same.


Originally Posted by alecleeWere they the same brand? The electrical properties of the two tubes are supposed to be the same.

Yeah actually they were. Groove Tubes.

Edit;
from : localhost/www.groovetubes.com/tubes_lis...ctGroup_ID=107

So I can just pop 4 AX7's in there, huh?


Originally Posted by Slash2987So I can just pop 4 AX7's in there, huh?

Yes, pre-amp tubes are self-biasing.

try reviewing this article from KCA NOS:
preamp tubes

yes, some tube swaps are OK, but it helps if you know the comparisons, and understand the reason for doing a swap

personally, I usually end up preferring the stock tubes. The one substitution I liked was switching the first 12AX7 in a Bassman reissue for a 12AY7, which is what the original circuit had anyway. The lower gain 12AY7 seems to make that amp a little sweeter.

you will also find more info on tube swapping at guitar amp blueprinting

This is a high gain amp so I think 12AX7's will do for the next time. It's actually part of the power amp, though. 8 5881's and then 4 preamp tubes, maybe it's the phase inverter or something. I relaly don't know.