Which 12AX7 series tubes have the least noise/hum?

[SpinCycl]

I spent some time swapping preamp tubes, and I found that several had much less apparent noise than the others.

I am speaking of zero signal with a hum that is very low, but still some did have quite a bit more effect on hum than the others. The PI position showed this trend most.

[Omar]

Has anyone tried the Groove Tube 12AX7 Mullard reproduction? I'm thinking about putting this in my twreck clone and I'm looking for opinions.

Omar

[SpinCycl]

I like the GT mullard repro.

I use it in the 1st/2nd stage postition on my amps because it has a "bite" to it without being harsh. I typically use 5751 tubes for this, but the mullard clone easily sounds better, and it's much cheaper than NOS 5751's.

Try one, and I think you'll like it, but be sure to try it in different spots. I love it in 1st or 2nd position, but it sucked as a PI.

[Omar]

Thanks for the info on the GT Mullard repro. You mentioned that it didn't sound good in the PI? Have you tried a balanced triode in the PI like Mike at KCA NOS Tubes offers?

Omar

[toddyjoe]

I would think a balanced triode would not make much of a difference in many amps. For instance, Vox amps use dual 100K plate resistors for the phase inverter triodes. This results in an imbalanced phase inverter which will not be corrected by a balanced dual-triode. Other amps like Fender and the TW use an 82K/100K plate resistor setup to try and create a better balance in the phase inverter. However, even the 82K/100K is not a perfectly balanced phase inverter, which is fine if you consider most output transformers and output tubes are not perfectly balanced either. In other words, a balanced triode may change the balance between the two sides of the output, but I do not believe it can ever perfectly balance the two sides in most amps.

Actually, the imbalance in the phase inverter and output section is not necessarily bad. The closer you balance the two sides of the output, the more hum and interference noise gets cancelled out. However, sweet, even-order harmonics get cancelled as well which could sterilize the sound of the amp. On the other hand, the more imbalanced your output section, the more even-order harmonics you will get in a push-pull amp. A good example is the Vox output section. The bad part of imbalance is that you get more hum and noise too. You could say it is a balancing act between undesirable noise and desirable harmonic sweetness.

Sorry for the digression from the topic, but I think some businesses try to take advantage of people and make an extra buck with the "Balanced Triode" marketing. While balanced triodes can change your tone, there is no guarantee it will be for the better.

I still am curious about those GT Mullard clones though.