phase inverter

[jlctele56]

If I change my phase inverter 12AT7 to a 12AX7....will I have to rebias my amp? and also what are the pros and cons of doing so? I know that with my 12AT7 thats in there, I have a twin modded for 4 6V6's......I have two JJ 6V6's middle that are bias'd @ 26mA and the outer two are EH 6V6's bias'd @ 23mA that I was told with my 426 plate volts, this was a little less than max for each brand in my amp....(1mA)less......If I move that 12AT7 will it mess up my bias? the way that they fell at each tubes max bias.....it sounds awesome BTW.....thanks, Jerry

[PRNDL]

Changing the PI tube won't affect the bias of the power tubes.
You'll get a little more gain with a 12AX7, but (in some amps) it dramatically changes the tone.
Most people like to change the preamp tubes, which has more of an effect on gain and distortion.

You have to try and see in order to find out how the tone changes.

[JohnnyCrash]

The PI will push the power tubes a little harder.

You'll notice a difference in sound, but it'll be more apparent when you really crank her up.

More gain. You won't need to rebias.

[jlctele56]

Thanks guys, I'll let you know how it does at the gig this weekend.....Jerry

[JohnnyCrash]

A Twin modded for 6V6's... that's very interesting.

How's it normally sound?

I take it, thats why you're looking to bump up that PI... get more power tube sauce goin' on :)

Very cool.

[jlctele56]

my amp tech is a 6V6 freak......he modded my first channel to his gibson tweed type clone sound......and hooked up the reverb to this channel, and also a vol pull..mid boost....I love this channel, I use it all the time....but being a twin, wanted it to hit the sweet spot, at a little lower vol....!haha.. we put in a supper bassman OT we got from David Allen..45 watt, with 4 ohm load for my two 8ohm webbers that I love....anyway it sounds totally awesome.. but still can't turn it up past 3 at band practice......just started messin with preamp tubes.....I put a 12AY7 in V1 for that channel...I could turn it up to 4 to achieve the same vol...but it was a little quieter and fatter? so I tried a 12AU7 in there...this was a big drop in volume........I could turn it up to 5 and 6 to achieve the same vol....but again it was quieter and even fatter? is it ok to do this? will it hurt anything? I think I'll stay with the 12AY7 though.......thanks, Jerry sorry so long! just pumped at the tone.......