12AX7 vs 12AX7A? Please help me understand the difference and ....

[joeinid]

please recommend what 12AX7A tubes that you like.

I am still ambivalent as to which McIntosh preamp to get, but will probably end up with the new C22 reissue.

I notice that most, if not all, the McIntosh preamps call for the 12AX7A version. I tried searching for the differences between the 12AX7 and 12AX7A but can't seem to find anything specific enough to understand what's going on with these tubes.

I am not sure, but I get the feeling that the majority of users just use the 12AX7 tube as replacements.

Any help is greatly appreciated. Thank you!

 

[Mamrak1]

12AX7A is a low noise short plate tube.

 

[joeinid]

Excellent, thank you.

I notice there are less 12AX7A brands vs the more popular 12AX7.

12AX7A is a low noise short plate tube.

 

[chuckworkb]

If you have to have a 12AX7A Brent Jesse Tubes has some in stock. Not cheap though. There is a lot of info on tubes he sells on his site.

 

[quartersaw]

If you have to have a 12AX7A Brent Jesse Tubes has some in stock. Not cheap though. There is a lot of info on tubes he sells on his site.

I use 12AX7A's in my Fender guitar amps. (Mostly RCA's) The 7025 is the low noise version of the 12AX7A, and Fender specifies them for the first gain stage. Interestingly, most used 12AX7's that I have come across test out of spec, or close to it on my Hickok TV-10. 12AX7A's seem to be more robust over the long haul, for whatever reason..

 

[joeinid]

Thank you for the replies.

 

[gadget73]

The "A" suffix is usually for controlled warmup. Its important in series string stuff, not important anywhere else.

 

[dewickt]

The "A" suffix is usually for controlled warmup. Its important in series string stuff, not important anywhere else.

Also a much faster warm-up in response to the then new solid state instant-on.

 

[thevinoman]

Have you investigated the benefits of using 5751's in certain spots, rather than 12AX7? If not, then I would recommend you do some research on that.

 

[joeinid]

I have not but will absolutely take a look now that you mentioned it. I’ve seen 5751 tubes talked about but never put it together. Thank you.

 

[x3workshop]

The 5751 has about 70% of the gain of a 12AX7/A.

 

[joeinid]

I always seem to prefer lower gain as rule. So that should be perfect.

 

[gadget73]

Depends where you're talking though. I've tried them in certain phono stages before and it sounded horrible. Other things don't seem bothered by it because it doesn't use anywhere near max gain anyway. No Mac experience though, so I would advise further research on that.

 

[thevinoman]

5751's are not intended for phono stages. Not recommended.

 

[Chubba]

You folks answered that pretty quick,Thanks. I was wondering about phonostages.

 

[joeinid]

Thank you. I am not worried about the phono stage right now but this is great to know.

5751's are not intended for phono stages. Not recommended.

 

[W9TR]

The "A" suffix is usually for controlled warmup. Its important in series string stuff, not important anywhere else.

+1

If I remember correctly McIntosh series stings the filaments in some of their preamps like the 2200. So you shouldn't mix 12AX7's and 12AX7A's without looking at the schematic to see which tubes, if any, are in series.

Tom

 

[joeinid]

I am going to get the C22 new reissue preamp which uses the 12AX7A. Not sure when I'll take delivery, but it shouldn't be too long. I'm looking forward to tube recommendations once I get familiar/comfortable with the sound of it. I am sure it will sound great with my MC303.

 

[welcomdmat]

I look forward to reading more!

 

[joeinid]

I look forward to reading more!

Now that the new MC1.25KW amps have been announced, I'm re-thinking my choice of preamp. I'll need you guys opinions.

Is the C22 new reissue a worthy preamp pairing for the MC1.25KW amps? I think I would prefer a fully balanced SS preamp like the C500P/C1000P, but was hoping for a SS version of the C1100.

Thoughts? What do you guys recommend?