phase inverter question

rockabilly daniel · Post by **rockabilly daniel** » Fri Oct 22, 2004 3:55 pm

Ok, this is a general question that stems from a question about my 68 fender bandmaster head. I read somewhere that you can switch in a 12ax7 for the 12at7 driver tube to get a little more gain out of the power section, I believe I read this in the tube amp book. I was talking to a local fender tech about it though and he said that it wouldn't sound as good because the circuit is designed around the 12at7. So my question is, does it matter what type of driver tube you use? Will a 12ax7 sound good in place of the 12at7 in the fender? Could you switch the driver tube in a marshall to clean up the sound a little? Any help appreciated as I am a newbie to all this.

rjgtr · Post by **rjgtr** » Fri Oct 22, 2004 4:16 pm

The answer is Yes. The 12at7 will give a Marshall more clean headroom and less gain and a 12ax7 will give the Fender more gain and less headroom. Won't hurt a thing.

Flames1950 · Post by **Flames1950** » Fri Oct 22, 2004 10:00 pm

I've swapped 12AX7's into my Bassman and Bandmaster heads, it sounds and works just fine. It isn't the SAME sound to be sure, but it will give you more grunt, doesn't sound bad in any way, just different.

flemingmras · Post by **flemingmras** » Sat Oct 23, 2004 5:12 am

Yes, the 12A series of tubes are basically the same exact tube, but with differing gain factors, the 12AX7 having the highest gain factor(100).

And so what if the driver circuit was designed around the 12AT7!? Electrically any 12A series tube will work in any position in the amp. And whether or not it sounds good is all up to the player.

Jon