Of course in a world wherein a circlotron amplifier is seen as being a dual, single-ended, class-A-by-necessity design by many audiophilesРІР‚В¦but I won't go on. Just ask a musician and see what he tells you. Why use only one shared cathode resistor? Because it cheaper to implement, with only one bypass capacitor needed, and because far too many believe that using a single common cathode resistor will transform any amplifier into a class-A amplifier, regardless of the resulting idle current.

So, given these results, which topology do you think has found the widest acceptance? The single common cathode resistor is the winner it is immensely popular, much more so than the dual cathode resistors, and Blumlein's circuit is all but forgotten. And using a single common cathode resistor (C) produces the worst results: a mismatch of 7.43mA, or 100%. Using separate cathode resistors (B) yields poorer results: a mismatch of 2.12mA, or 21.5%. As shown in figure (A) below, one tube conducts 10.2mA, while the other conducts 11.07mA, a mismatch of 0.87mA, or 8.5% not too bad, considering the grotesque mismatch in tubes. Ideally, when both output tubes are perfectly matched, the idle current should equal 9.86mA in the Blumlein circuit. (No bypass capacitors were added, as no AC signal was used in the simulation.) I used SPICE and I created a greatly mismatched set of output tubes by using two tubes in parallel, effectively creating a new tube with the same mu, but twice the gm and half the rp. A shootout between the Blumlein garter circuit and two alternatives is needed. How well does it work? Better than you might expect, but with a few caveats. Conversely, if a tube conducts too little, it lowers the bias voltage on its fellow tubeРІР‚в„ўs grid, causing the tube to reduce its conduction. As one tube conducts too much, it raises the bias voltage on its fellow tubeРІР‚в„ўs grid. His circuit, know as the РІР‚Сљgarter circuit,РІР‚Сњ cross feeds a sampling of each output tubeРІР‚в„ўs current conduction via a tap in the cathode resistance to the other tubeРІР‚в„ўs grid.

He realized that a mismatch in idle current would steal performance from a push-pull amplifier, as it would lead to partial magnetizing of the output transformerРІР‚в„ўs core, which reduces its inductance, worsening its low-frequency reproduction, and which limits its maximum output wattage, as the transformer prematurely saturates in one direction. Shown below, Blumlein came up with an auto-bias matching circuit that does not aim to set a specific idle current, but works to keep both output tubes conducting the same idle current a current balancer, in other words. And, no doubt, he would have made many more contributions to amplifier design, both tube and solid-state based. Had he lived another forty years, we would all be better off, as I am sure he would have helped prevent the audio wrong turn known as quadraphonics from having inveigled so many. Tragically, like Mozart, he died when he was still in his thirties. over one hundred patents in audio, TV, and radar. But what a truly humbling experience it is to read of Blumlein's life and contributions to electronics: first of all, he invented stereo, the ultra-linear circuit, the moving-coil microphone.

well, at least one out of three is a genius (unless, of course, you have three children, which would raise the ratio to three out of three), that the cover of the latest Esquire magazine proudly proclaims that this is their yearly genius issue, that extraordinary intellectual and creative power is readily available from Manpower or-via the Web-cheaply available in a score of underdeveloped countries, that enumerable self-help books and audio tapes are ready to release the latent genius in you.

Yes, I know that today everyone is a genius. The tube is a single 6DJ8 and it falls out of class-A operation after 1V of input signal, so we should only look at the first few input volts of the graph to compare the two circuits use in a single-ended amplifier.Р”В«elow is a closeup of the first two volts of input signal.Р”Р„s the graph clearly shows, both circuits work exactly the same up to about 0.6 volts of input signal thereafter, the Broskie circuit performs much better with the remaining class-A range and beyond.Р”Р„lan Dower Blumlein was a genius period. The graph below compares the generic DC servo auto-bias circuit against the Broskie auto-bias circuit. The answer is yes, as SE amplifiers often (almost always is closer to the mark) exhibit a rectification effect, unless a great deal of feedback is applied. One reader asked if the clipping or Broskie auto-bias circuits were suitable for single-ended amplifiers. One reader wanted to see how the Broskie auto-bias circuit could be used with power output tubes above is a more fleshed-out version of the Broskie auto-bias circuit that would work well with a set of power tubes like the 6L6, EРµвЂ¦С“4, KT88 or 2A3-or even a single output tube.

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