Matching sections for phase inverter (12AU7) tubes in an MC240

[Pio1980]

If i was doing my own amp, I'd prefer everything in the balanced portions of the amp was parity matched, including the output tubes. The front end class 'A' input 12AX7 matching isn't critical in the Mac stereo chassis, and as only one section is used in the monoblock amps, a non-issue for section matching.

 

[thevinoman]

This has been a very good, informative thread today.

 

[jlovda]

I have never owned to a tube amp or heard one in ten years. The interesting thing about this thread is that everything revolves around the numbers that pop up on a tube tester. How does the unit sound if not matched? If it a matter of unequal gain or some type of distortion? Sorry, just had to ask.

 

[Pio1980]

I have never owned to a tube amp or heard one in ten years. The interesting thing about this thread is that everything revolves around the numbers that pop up on a tube tester. How does the unit sound if not matched? If it a matter of unequal gain or some type of distortion? Sorry, just had to ask.

Depends on which tubes in what amp, but generally results in phase imbalance distortion to varying degree with a mismatched splitter or balanced amp driver stage. Mismatched output tubes can do similar, and give asymmetric clipping at full power. Mac unity coupled amps like the MC 240 may comp to some extent, the MA230 integrated's power section isn't unity coupled and would behave as any other similar tube amp.

 

[c_dk]

Actually other than checking for shorts and is the heater working I am speaking of testing in the actual unit....on a test bench where it can be properly stressed and the distortions seen on a scope and measured by a distortion analyser.

To use a speaker anology for a old school speaker designer....

Imagine if the glue let loose at the 0 point of a cone drivers motion.....at that zero point it would not nessesarily want to go in or out but would "flop" around, eventually catching up with the voice coil.....with a slam? Then get pulled back, flop around and then get driven back into the driver.....to slam again?

When you see notch distortion on a scope you will often see two "loops" emanating from the 0 or crossover point between the + and - of the wave form......that is the "slop".