Power amp distortion: actually just the phase inverter?

[TheMagicEight]

I've heard time to time that the phase inverter starts to go well before the power tubes would, and that most of what I know as "power amp distortion" is simply the result of this happening. I'm wondering because to my ears, my Ecstasy at a high volume - but not creating power amp distortion, because it's clear on the clean channel - on the blue channel sounds really similar to this "power amp distortion" on all the classic rock recordings.

So without further adieu, I want to ask if the old non MV Marshalls and other amps are actually distorting in the power section, or if it's the phase inverter and sounds as good as it does because they're loud as f**k?

 

[glpg80]

the voltages before the phase inverter are very small, in reference to the power amplifier section of your amplifier.

for one, if you distorted the phase inverter by any means, it would NOT sound pleasant. the phase inverter stage does exactly what the name implies, and that is to act as a standalone amplification stage that is clean and stable that provides two outputs that are 90* out of phase with one another to designate the proper use of class A/B amplification that tube amplifiers normally run.

the only way you could fuckup a phase inverter, is to cause internal clipping with improper design, wrongful biasing of the stages, or signal injecting before the tube in a manner that causes it to overload.

the preamp of your amplifier will have a set impedance load because of all of the stages before the PI. if you even try to distort it by putting 4 clean boost pedals in the front of the amplifier, you are only going to distort the preceding gain stages in the input of the amplifier back first.

so simply put, no. you are hearing power amp compression. if anything, depending on the tubes that you run, you may be experiencing voltage sag from the power transformer itself which makes it easier to play, because some tubes have such a large headroom before they compress and distort that it carries back into how well the amplifier was designed.

theres also alot that deals with how the cathode follower stages compress and distort, but they do so in a way that is good or pleasant to our ears. not many people know of this, i know mike fortin does. so in the matter of marshall versus other boutique amplifier models, marshall sound great because they are built with simplicity in mind.

 

[TheMagicEight]

Awesome! Thanks for the well a thought out and understandable response; very happy to have learned that!

 

[glpg80]

Awesome! Thanks for the well a thought out and understandable response; very happy to have learned that!

no problem

 

[TheMagicEight]

Now that I'm thinking of it...does that mean the phase inverter is one of the least stressed tubes? In other words, is a tube in this position likely to last longer than one in a gain stage?

 

[glpg80]

Now that I'm thinking of it...does that mean the phase inverter is one of the least stressed tubes? In other words, is a tube in this position likely to last longer than one in a gain stage?

for guitar and audio amplifiers anyway. it comes down to impedance loads with tubes.

 

[just42dave]

What are you running in your xtc right now homie???
Ive noticed my tastes for the Winged C is not like it used to be..
I bought a set of the 6l6 for my renegade and really do not like them so I ve yet to put the el34s in the renegade as well...I remember my xtc having that certain xtc tone when it had the jjs and Tad el34s in it..seems to have lost something with the almighty winged c's


Preamp tubes are a whole nother story...Tons of switching Chinese still sound best to me contrary to all my nos bull crap/

 

[TheMagicEight]

What are you running in your xtc right now homie???
Ive noticed my tastes for the Winged C is not like it used to be..
I bought a set of the 6l6 for my renegade and really do not like them so I ve yet to put the el34s in the renegade as well...I remember my xtc having that certain xtc tone when it had the jjs and Tad el34s in it..seems to have lost something with the almighty winged c's


Preamp tubes are a whole nother story...Tons of switching Chinese still sound best to me contrary to all my nos bull crap/

Haha, sad story actually. I'm running an old-as-dirt set of =C= EL34s. I started using them after I had my previous set of JJ E34Ls blow a tube, and they actually came from a Marshall JCM900 that I bought used last June. The guy I bought it from said the Marshall sat for 2 years because he hardly ever used them amp - that the guy before him installed the tubes - but the problem is that the Marshall had a sticker saying "Use only 5881 tubes". I know this would probably wear them out more slowly, but I think they were abused quite a bit before I got 'em. My point is they're old and beat to shit.

Even still though, they sound incredible to my ears! I have a new set of JJ E34Ls to use as a backup for when the =C=s finally do go, but until then, the =C=s have a top end that I just can't get away from.

Preamp tubes seem to be a similar story on my end, with a couple of exceptions. First, I don't care for Chinese in every spot. Love that LPS! Second, I have a NOS Tesla and in the phase inverter, it opens the amp up to a new dimension! Most of the preamp tube swapping I've done recently was for nothing though; in the end all I needed to do to get where I wanted was to rethink the controls and how I was setting it up.