Critic's Corner

Posted by tomservo (M) on April 12, 2007 at 18:23:23

In Reply to: Re: Tubes' dirty little secret... posted by Charles Hansen on April 10, 2007 at 19:58:20:

Well, it’s a good thing then that being a high voltage device, the currents are exceedingly low and so are the magnetic fields produced internally. A tube like a 6SN7 can produce VERY low distortion with a spectrum that is low order. Hysteresys distortion is a problem in output transformers associated with Tubes however and they are to varying degrees microphonic.
For that the tap test will tell.

Yes they wear out a little bit each time but finding either at a garage sale or attic, the odds of a 20 year old solid state amplifier working are smaller than that of a 30 or 40 year old tube amp working. Plastic transistors are not “air tight” like Pyrex and frit glass, they usually get leaky and fail. Tubes can leak too when the repeated thermal expansion causes micro fractures around the frit and pins.
SS and Tubes are entirely different ways of doing the job, each has totally different strengths and weaknesses from an engineering standpoint.

As for the “memory”, the thermal shift is real, I have no idea if you can hear it.
On the other hand, for a Voltage amplifier the cascade approach already minimizes the collector swing on the onput, making the Voltage between the two transistors larger would further reduce the pdis swing and increased the avg pdis.
Heat them inputs up with static bias
Best,
Tom Danley