balanced triodes?

[rabies]

What do balanced triodes mean? Do I need them?
Dual triode preamp tubes like the 12AX7 really have two separate tubes inside one glass envelope. When the plate current draw of each triode is the same(as evaluated by our VTV testers), we refer to that as having balanced triodes. These may or may not also have the same gain on each triode but are still considered balanced. Chances are that these are not required for your particular circuit. What we have observed after testing 1000's of preamp tubes using the Vacuum Tube Valley dual triode characterizer is that tubes with balanced triodes seem to be more consistent with a standard specification tube as to gain and low noise and microphonics.

http://dougstubes.com/faq.html#g1

who uses balanced triodes??

 

[dodger916]

As Doug's site mentions, balanced triodes means each triode in a preamp tube puts out the same current. There are many here who believe balanced triodes are more important in hi-fi amps, but for guitar amps where tolerances aren't as critical, a balanced triode isn't necessary. The idea of a balanced triode is probably most important in the phase inverter as it's dual output is fed to the power section. It kinda makes sense for each triode to put out the same (or very close) current to the power tubes. However, the tolerances reason mentioned above could undermine the necessity of a balanced triode P.I.

By the way, I have a Mullard 12AT7/CV4024 with balanced triodes (from Doug's) in the PI of my C+. I haven't swapped the PI in my other amps, so I don't know how balanced they are.

 

[94Tremoverb]

There is no position in any guitar amp where a balanced dual triode is of any practical use, including the phase inverter - because the standard PI *circuit* in almost all guitar amps is inherently unbalanced anyway, and becomes even more so once the amp distorts. This is yet another piece of mystique wrongly imported from hi-fi practice without understanding why it doesn't matter in a musical instrument amp - and might even in many cases (though not this one) actually make things *worse*. Hi-fi - where the goal is to reproduce the original input signal with as little coloration as possible, and where distortion is never anything except to be eliminated - is totally different even from bass amplification, let alone a guitar amp where distortion - even on a clean sound, you want harmonic distortion - is the whole point of using tubes.

Some people report that balanced triodes do sound better in the PI, but if so that's because - if Doug's results are typical, which they may well be - it just means that both halves are closer to the correct design spec and most likely indicates the tube is simply better quality.

 

[dodger916]

There is no position in any guitar amp where a balanced dual triode is of any practical use, including the phase inverter - because the standard PI *circuit* in almost all guitar amps is inherently unbalanced anyway, and becomes even more so once the amp distorts. This is yet another piece of mystique wrongly imported from hi-fi practice without understanding why it doesn't matter in a musical instrument amp - and might even in many cases (though not this one) actually make things *worse*. Hi-fi - where the goal is to reproduce the original input signal with as little coloration as possible, and where distortion is never anything except to be eliminated - is totally different even from bass amplification, let alone a guitar amp where distortion - even on a clean sound, you want harmonic distortion - is the whole point of using tubes.

Some people report that balanced triodes do sound better in the PI, but if so that's because - if Doug's results are typical, which they may well be - it just means that both halves are closer to the correct design spec and most likely indicates the tube is simply better quality.

I was hoping you'd chime in. You are always a great source of knowledge and info, 94Tremoverb!