12AT7 instead of 12AX7 in a preamp?

[Ulys]

Beside the fact that the 12AT7 have a lower voltage gain than a 12AX7, is there a significant tone difference?
Let's say that both are from the same brand, and let's say that it's for a tube preamp which have only 1 tube.
Anyone tried it?

 

[devastone]

I've used a JJ 5751 which are the same tube with a gain of 70, it worked great in a high gain preamp (AMT SS-20), the 12AT7 has a gain of 60 and a 12AX7 is 100 for comparison.

 

[Ewizard]

While it will work, the 12AT7 technically has different operational standards. All that means is that while it will turn on and pass audio, it is not optimized when utilizing 12AX7 circuitry. How it will sound? I suppose very similar to a 12AX7 under normal operation. What does it sound like when it is pushed into overdrive? That is completely dependent upon the circuitry surrounding it. Could be great, could be meh? If the circuit is optimized for the 12AT7, I think it would sound pretty much like a quieter 12AX7.

 

[jeremy]

thats basically my experience, sometimes it sounds great, sometimes its meh. worth trying for sure

 

[Mincer]

Yeah, this is something you really have to try in your particular amp with your particular tube set. Sometimes it is just a lower gain/higher headroom, sometimes it really is a change in 'feel' getting more or less compressed.

 

[Blille]

You can. I’ve had more luck with 12AY7 than 12AT7 though.

 

[devastone]

Yeah, I should have been more clear, the 5751 is a ruggedized, lower gain 12AX7, I would go with one of those over the 12AT7. I need to order some more, I cracked the glass on the one I had moving it around too much.

 

[Powdered Toast Man]

One other suggestion I'd have is the JJ ECC83S-MG. The MG stands for "Mid-Gain". It's a lower gain 12AX7 tube with a gain threshold around where a 5751 would be. I put them into my 57 Twin and they really sound great for when you don't want to neuter the preamp section but you want to tame it down some.

I used a 12AT7 in V1 of a Vibro-King for a while. I ended up going back to the 12AX7 because I didn't like what it did to the EQ response of the amp (but that's because that amp's active EQ is driven by the V1 tube). But otherwise it sounded fine.

 

[devastone]

I've wondered about the MGs, sounds like a 5751 to me. In the old days (and my understanding), the 5751 was designed to be a rugged 12A_7 for the military but for the JJs, I kinda wonder if the tubes are built the same then given the different designations depending on where they test. That said, I did like the 5751 much better than the ECC83s in the AMT SS-20 preamp, it seemed clearer.

 

[Powdered Toast Man]

I've wondered about the MGs, sounds like a 5751 to me. In the old days (and my understanding), the 5751 was designed to be a rugged 12A_7 for the military but for the JJs, I kinda wonder if the tubes are built the same then given the different designations depending on where they test. That said, I did like the 5751 much better than the ECC83s in the AMT SS-20 preamp, it seemed clearer.

Structurally, IDK. But the MG sounds good.