Matched triodes on the phase inverter

[highroller]

Is there any advantage of using a matched triodes tube (two halves of the tube with equal electrical performance characteristics) in the V5 phase inverter position of a Mark amp ?

My Mark IV use a 12AX7 in that position. Some says that using un-matched triodes would produce a harsh sounds.

Any comments on that ?

Thanks

 

[Rich M]

I think that is a load of crap. Save your money and let the anal audiophiles spend their $$$ on the matched ones.

 

[hoople]

The advantage is more money in the pocket of your tube supplier.

Everything else in the power amp would have to be "balanced" as well to make a difference. This means precision components, perfectly matched power tubes, AND (least likely to happen) equal number of turns and same length of wire for each half of the OT primary.

Bottom line: save your money. In fact, you can use microphonic tubes in the PI. Last time I checked, Lord Valve sold microphonic 12AX7s for $5.

 

[fatboy135]

I think that get a correct balance between triodes on the phase inverter is essential to get a great tone

 

[Monsta-Tone]

Almost all amp Phase Inverter circuits are imballanced on purpose.

1 Triode has a 100k input resistor, the other has an 82k input resistor. This is done to create a bit of unballanced signal.

If the PI were too ballanced, your tone would be somewhat sterile. I think some of the Fender/CBS Ultra Linear amps had ballanced PI circuits.



It's not a MacIntosh, it's a Mesa.


I have a Ballanced PI tube that I got from EuroTubes as an experiment. I think that it makes my amp "Sing" less than with a normal, unballanced High Gain PI Tube.

For what it's worth:
When I got my High-Gain Preamp set from Eurotubes, almost all of the 12AX7's were within 2 digits on their rating. Bob wrote their ratings on the boxes, but I don't know if this is the Transconductance, or the Gain characteristics of the tube.



I don't buy it. I don't buy NOS tubes either, although I have a set of GE's and RCA's in my Blackfaced Pro Reverb because that is what it came with. I got it DOA for free from a friend. It had these fine tubes in it when he gave it to me. I think they sound incredible, but not incredible enough to warrant their prices from NOS vendors.

 

[fatboy135]

Almost all amp Phase Inverter circuits are imballanced on purpose.

1 Triode has a 100k input resistor, the other has an 82k input resistor. This is done to create a bit of unballanced signal.

If the PI were too ballanced, your tone would be somewhat sterile. I think some of the Fender/CBS Ultra Linear amps had ballanced PI circuits.



It's not a MacIntosh, it's a Mesa.

I´m totally agree, the unbalanced purpose produces a similar fx like asymetrical pedal fx, the becomes on odd harmonics that makes a more rough and agressive tone. Even some amps have an internal relay to swap the signal path for extra tone, but......
If you like the colour sounding amps you will be very happy with asymetrical clipping ( in fx pedals it is done just with different diodes per phase ). If you want the harsh saturation just look for the odd harmonics that are done by the asymetrical. I really like this kind of saturation, but in the other hand you will never had a perfect clean.
Mesa clean´s are so great, but you can hear a bit of harsh harmonics, so.... In my point of view if you like the colour sounding matter the cleans of mesa will be the best, and if you are a purist of high ended class A amps, maybe mesa will sound with a bit of harsh.
The sterile sound that monsta saids I think that reason is that in symetrical phases there is not odd harmonics done, but in asymetrical phases odd harmonics are created getting more harmonics and richness over your spectral. Remember that harmonics are artificial, they don´t becomes on the original signal, they are usually called THD ( total harmonic distortion ) and for audio purist this is a matter to avoid.
In conclusion: Theory are theory, opinions are opinios, but the only judge for this matter is your ears, so get a balanced and unbalanced tube, and enjoy it

 

[fatboy135]

sorry I was mistaken, I was thinking on diodes rectification, and square signals.
on asymetrical phases even and odds harmonics are produced. on pedal fx asymetrical clipping only odd harmonics, so the mesa are not are rough are some pedal fx with the diode rectification. But you still have some extra harmonics components ( THD )