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previous: jaysg [QUOTE]I think Albert King used Aco... -- 10/8/2004 8:44 PM View Thread

Re: Tube distortion with SS devices

10/8/2004 10:08 PM
Re: Tube distortion with SS devices
Here's a few things that Mr. Sulzer hasn't figured out yet.  
I post #1 there's a little graph of Eg vs Ep. I used an X-Y scope to view this. What you find is that as soon as you go up in frequency around 1 to 2 kHz, an "eye" opens up because of the finite frequency response of a 12AX7 with 100K plate load. Then, because guitar amps for the most part don't have regulated power supplies, the whole thing scrunches down when the power supply sags which couples to the next stage and increases the "rectifier effect" and shifts the operating point of that stage. Also the gain goes down a little causing the compression effect.  
In post #6 Mr. Sulzer states that a cathode follower has a low output impedance. This is true for small signals but when a large signal comes through the tube cuts off on negative excursions and for a while you just have the 100K pulling down on the tone stack.  
When you get to the phase inverter, Marshalls do something that most other amps don't. I call it the "Marshall Wave". When clipping first occurs, the waveform is pretty symetrical. As drive increases, the duty cycle changes and shifts to about 60-40% much like the red wave in the figure of post #12. If drive is increased further, the top part of the wave squares up nicely but the bottom part starts to collapse after the initial transition. The only other amp I recall doing this was a Duncan Convertable, and it did it with variable power !  
Then there is the behavior of a speaker when driven by the discontinuous output impedance of the tube power amplifier.  
In post #8 Mr. Sulzer states that he has never built a tube guitar amp. I should have guessed that. I hope to see him on this forum someday seeking advise on a 5E3.