2. amps-preamps
  3. 1026351669

Tubes: 12AU7A or 12AX7 or can one mix them?

I just acquired a 55 watt per channel tube power amplifier with eight EL34's (four per channel configured in push-pull) for power tubes. There appears to be five input/driver tubes (lined in a row in the front of the amp) three of which are 12AU7A's and two of which are 12AX7's. My question is how interchangable are these two types of tubes or should I be running 5 of the same type for optimal performance purposes? Any ideas about this would be greatly appreciated. The amp, in case it matters, also has 2 RU4G tubes as rectifiers and one each of the following tubes that round out the tube compliment: one OA3, one GAS7, and one 6SJ7.
ered66
buckingham
333 posts
 
Not a good idea, I accidentally switched the positions for my 12au7 and 12ax7 and I had some MAJOR distortion coming from my 120W monobloc.
ed_sawyer
588 posts
 
5u4G and 5u4GB should be fine to interchange. Those are also interchangable/compatible with some other rectifiers if needed. Agreed, do not swap the Au7s and AX7s - not the same tube in many ways, unpredictable results if you do so. OA3 is a cold cathode voltage regulator tube. (neat colored glow on those. ;> )

-Ed
ered66 OP
4 posts
 
Thanks for the input (especially on the mixing of the 12's), you saved me from making a mistake!
fletchj
91 posts
 
A 12AU7, and a 12AX7, both uses the same filament(heater) voltage, 12.6 volts. Any heater that is designed for a 12AU7, will do just fine, for a 12AX7. Yes, you might get distortion, or a unbalanced gain, but you will not fry a 12AU7, or 12AX7, in a 12.6 volt filament.
More to discover