Angry E-mail
Class A Advertising

important to the listener. If an amplifier is good sounding and reliable, who but the status monger cares if it is Class A or Class AB? Second, do remember that all manufactures fluff their ads, only some do so egregiously.
   But really, my guess is that you already own such an amplifier and that you are irked by the disrespect being paid to it. If my guess is right and you do own such an amplifier, then you are in luck, as you can test the amplifier yourself, assuming you are technically trained to deal with lethal voltages, and determine the truth for yourself.
   At the plate of each 6AS7 triode, you will probably find a 1 ohm resistor. If the resistor is not there, one will have to be wired in place on only one triode. (This resistor will make an insignificant difference to the total performance of the amplifier, as its value is effectively reduced by the number of triodes being used in the output stage and then further by the mu of the tube plus 1.) Hook up an 8 ohm dummy load to the output of the amplifier and attach a sine wave generator to the input. Now, hook up a hand held oscilloscope across the 1 ohm resistor, which will allow for safe and accurate measuring of the current through this resistor. If a hand held oscilloscope is not available, then a high quality transformer (actually, a cheap isolation transformer can be used if the sine wave is limited to no more than say 200 hertz) can be used to couple the signal to a bench top oscilloscope. The sine wave generator's output is increased until the full output is achieved.   

   First of all, I expected more flaming e-mail over September's article on the Circular/Balanced amplifier and TRUE Class A operation. Only a one e-mail wanted to talk math and current and voltage and resistance; and this writer agreed entirely with the article's conclusions. Several e-mails express hot emotion, but nothing mathematical was voiced. The message was that since many believe half an amp of idle current is all that is needed for 60 watts of RMS Class A output, why rock the boat.
    Why indeed? Because I believe audio could use a few less sacred cows and clothes-less kings. So what follows is a general purpose answer to angry e-mail.

ONE company makes and advertises an amplifier as you describe; therefore, why do you not mention that company by name so that their attorneys can assemble many of jurors from the OJ Simpson trail to enforce what they say is Class A and what is not Class A.

   Well the best way to find out who is advertising what, is to do a search on the web; use keys words such as + "60 watts" + "6AS7" + "OTL." You will find at least TWO manufactures making such claims. )And since the issue seems to be Math vs. PR, it would not hurt to point out that TWO does not equal ONE.)

Why do you not tell me the name of the offending amplifier and I will make a point of not buying it?
    First of all, I thought the whole point of high quality audio was the sound. "Class A operation" is important to the music lover only to the degree that it has some bearing on the sound and is not in itself otherwise at all

Test of a Circular / Balanced amplifier's range of Class A operation by monitoring the current flow through the output devices.


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