By the way, here is a variation on the circuit :

An ultra-linear  single-ended amplifier that uses
a push-pull output transformer in a para-feed arrangement. (Thanks Al M.)

A simple single-ended amplifier that uses the DCR of the primary of
the output transformer as part of a self-biasing setup.

Subject: Lead Polarization
   Your theory as to why applying a polarizing voltage to a wire should alter its sound seems very plausible, and I wonder if it would be worth trying this on speaker cables. That a polarizing voltage affects a capacitor seems perfectly understandable, as dielectrics do have a hysteresis problem. The problem with the wire is that your explanation relies on a flow of current, and if the commercial gadget is wired as you show it, no current will flow in the cable. Could another explanation be that the two conducting paths in the cable are attracted to, or repelled from each other according to the voltage level of the signal, and applying a relatively high permanent voltage swamps this
effect?
  Thanks for a very interesting magazine.
Richard

  You are right. As drawn, no current would flow from the battery. I briefly looked inside one of the black boxes years ago and I cannot quite remember how many resistors were used.
   Nonetheless, a small idle current is what is needed. This current would have to be greater than the largest expected current draw through the cable, based on signal voltage leaving the preamp and the input

  The advantage this topology holds over the previous one is that it requires no electrolytic capacitor to bypass the cathode resistor. A secondary advantage is the certain confusion it would provoke.

[Lest any reader imagine that I am amazingly responsive, I must admit that I received this next e-mail after having begun this month's article on ultra-linear operation.] 

Subject: Ultra-Linear
  I love your webzine.  Thanks to you, there is finally a resource on the web for people who want to really know about tube amps.
  I wanted to ask you to write an article about ultra-linear operation.  It perplexes me.  What is the proper ratio of screen load impedance to plate load impedance?  Is it the same for every tube?  Do you have to run the screen and plate at the same voltage?  What effect does a difference between plate and screen voltage have on performance?  Is it possible to use ultra-linear in a line stage?  Thanks a lot.
Todd N

  I think you find both the reprint of the Audio Engineering article and my article on ultra-linear operation perfectly timed for your request.  Expect more along these lines. Here is an additional schematic to ponder:

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