"Matisse" preamp - 12AX7 12AT7

Depending on how the gain stage is setup, you could replace the 12AX7 with a 5751. The 5751 usually has 30% less gain, depending on how the tube is used in the circuit.

12AY7 reduce further to 50%. 12AU7 reduce to 80%. Though personally I have never substituted any of these for my AX7's.

okay - ace. presumably I could run it with 4 matched 12AT7 instead, too. is there any danger to the circuit/power supply by running a non-specified tube? so many forums say yes, and and equal amount say no!

I have always been told and/or read, that you should never sub an AU for an AT, or an AX for an AU, or AX for an AT, or any of the above combinations. Some preamps, like the Lector ZOE, let you use whatever tube you want, but this is usually not the case.

The 5751 is a DIRECT replacement for the 12AX7, just less gain, again, depending on the circuit.

Maybe ask your question over here also:

http://www.audioasylum.com/cgi/etv.mpl?forum=tubes

Are you sure it's the pre and not your source? I've seen this when someone has a high gain piece plugged into a low gain input (ie mixing up mc & mm or cd into phono)?

hmm could be the source, but how do I test? I have only one source, one pre and one power amp...

An easy and inexpensive way is to put in a fixed value attenuator at the amp input. You can buy them or have a techie do it for you. Cheap commercial ones are made by Rothwell. I believe you can get different values. Cost about $60. They are fairly transparent. Worked for me when I needed to do that. BTW, you may also be able to use them between your source and pre-amp if you underlying problem is too much gain from your source.

There is absolutely NO danger in swopping the tubes you have mentioned. You will not damage anything, and 9 times out of 10 it will run OK, and give you the gain lowereing you desire.

But it may not sound as good as it would if the stage had been designed to take the tube you use - but it won't harm anything - and may work perfectly!

Of the tubes that you can sustitute, the 12AU7 has by far the lowest gain.

Just don't try fitting something that uses different pin connections - or uses far more heater current than the ones it was designed for.

Regards, Allen (Vacuum State)

wow... ...Allen just completed the thread. Hell, I'm ordering some replacements for my gear now. LOL. Thank you Master Wright. Heck, I'm going to go listen to my JLTI right now. :)~

Okay that is good news, thanks guys. I will try it with a spare set of 12AT7 tubes (ie 4 12AT7 tubes) and let you know how it goes.

Okay well, to report back, I tried it and it did not really change much at all!!
I rolled in a few other sets of tubes to see if any differences could be noticed, and slightly less gain was apparent on the following combination;
Brimar CV4004, GE JAN 12AT7WC
This also sounds great (except for the first time I turned it on there was good deal of buzzing whilst turning the volume dial on low levels - although it went away after a while, any idea what could cause this?).

I will now head down the in-line attenuator path I think....

why not go to the 12au7's?

don't have any : (
simple as that - I'd probably rather try the attenuator than hedge my bets on a new tube after so much experimentation to get the correct sound and then perhaps not even get the correct reduction in gain!

Feel free to talk me out of it though ; )