12ax7 -VS- 12au7

24kilo · Post by **24kilo** » Sat 04/22/06 2:33 pm

There both Preamp and I know the 12ax7 has a little more gain but what else is there. I see some amps use one or the other and some amp use both. Can someone enilghten me?

jimipage · Post by **jimipage** » Sat 04/22/06 2:48 pm

For any technical info your best bet is to consult a tube chart. As for any practical info, I can tell you that I've used them in my Chandler preamp and my old Tube Driver pedal with good results. They definitely sounded warmer and smoother in those particular units than 12ax7's ever did. Obviously not a "high gain" tube, but useful nonetheless. I think it's a good idea to keep one or two around for experimentation or for when you're feeling fickle about your tone (and what guitarist doesn't ever get into that mood?

)

bigsbybender · Post by **bigsbybender** » Sat 04/22/06 3:20 pm

Sometimes the 12AU7 has too little gain to be useful for anything. I've used them from time to time in Phase Inverters or Cathode Followers but I don't recommend it as a V1. That said.... the pin out is correct so it doesn't hurt to try.

J.

Post by **zaphod_phil** » Sat 04/22/06 4:37 pm

12AU7s are really driver tubes or for use as small power tubes. Although they get used in preamps, IMO they're not too well suited to preamp use. And to use 12AU7s (or even 12AT7s) at their correct operating point, you really need to change bias resistor values - you can't just swap them into a circuit meant for 12AX7s. They're very different animals. If someone wants lower gain, a 5751 is a better replacement for a 12AX7.

Post by **Plexi** » Sat 04/22/06 9:13 pm

the 12AX7 has..Plate Dissipation ..................... 1.2 W

the 12AT7 And 12AU7 have ..Plate Dissipation...................... 2.75 W

Richie

sub · Post by **sub** » Mon 04/24/06 7:51 pm

I tried 12AU7 (ECC82) in my Vox AC50 on V1......

hmmmm very dead sound.... i put back 12AX7

.

cool gain info:

http://www.thetubestore.com/gainfactor.html

timg · Post by **timg** » Wed 04/26/06 3:41 am

It really depends in what position you put them. Swapping tubes in the phase inverter will have hardly any effect.

In e.g. a blues junior, swapping the V1 tube will have the greatest effect on distortion and headroom.

Check out http://home.comcast.net./~machrone/bjr/bjtubes.htm for the effects of swapping preamp tubes.

Dynaflow_Donnie · Post by **Dynaflow_Donnie** » Wed 04/26/06 11:13 am

I had talked to Bill (bilm) about getting a tweed pro like sound with a blues jr using a 15" speaker, he suggested his tone mods but also said I might try a 12DW7 in V1. I guess its a dissimilar triode. Its like 1/2 12ax7 and 1/2 12au7. I never got around to it, I'll probably just build a tweed pro down the road. But thought I'd mention the tube.

Regards,

Dyna

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12ax7 -VS- 12au7

12ax7 -VS- 12au7