Tubes in General: Position and Selection

[bradtfw]

I have been wanting to experiment with tubes a bit more, but that means spending a bit of money. Before I go and do something silly like that I'd like to get a handle on a few of the basics.

I plan on doing some experimenting with my Remedy to increase the headroom a bit and smooth out the high-end.

I have found that Hiwatt chose to use a ECC81/12AT7 in the phase inverter. What effect does using a 12AT7 in the PI position have in comparison to a ECC83/12AX7? Does using a lower-gain tube in the PI offer more headroom, or just prevent the output section from overdriving since the input is weaker?

While I'm on the subject of PI tubes... Dr. Z often uses the Sovtek LPS in the PI section. Do long plate tubes, like the ECC802also commonly offer more headroom when used in the PI section?

More questions to come, I don't want to be too greedy on the first post.

Thanks.

[Deleted]

I found 12at7s to be lifeless. It will give you more headroom but the feel will be gone. I use 12at7s in some of my mic pres they work nicely in that application. My favorite thus far have been 5751s. I now use two NOS 5751s Five Star in my Mazerati. 12ax7 being full power the others our lesser than. I'm sure there is a tube chart out there explaining the differences.

[bradtfw]

Interesting. The Hiwatt circuit was likely designed around the 12AT7/ECC81 PI from inception.

With an amp that was designed around the 12AX7/ECC83 I suspect it could change it in a less-desirable way.

Any specific experiences with a 12AT7,5751, or ECC803 in the PI position?

[Deleted]

The Mazerati stock comes with a 12ax7 and 5751. I tried a 12at7 in place of the 5751 and I did not like it. I also tried two 12ax7 in V1 a V2 it was overkill IMHO. The only 12ax7 I have liked of late is made by Mullard. I don't know if they make a 12at7??? I might be confusing the thread a bit. I would try it 12ax7s are readily avaliable.