Using a conventional, three stage, single ended, power amplifier circuit. This circuit has been re-engineered with many unconventional features. The first stage, 12AU7, offers a usable signal level for the next stage, the driver stage. This driver tube, a 12AT7 and the output tube, an EL-34, pure pentode, are coupled in a loop, similar to negative feedback (NFB). This loop is referred to as a “summing loop” and is not NFB, it does not lower the power like NFB and will not add global compression and phase shift.
The operational characteristics of the 12AT7 and EL-34 balance out or see each other in comparison, as the same tubes, in exactly the same operation, but opposite with the 12AT7 being a medium Mu triode and the first half of the EL-34 pentode. The, cathode, control grid, and screen, operate as a triode plate offering an exact signal cadence, in opposition, so signals at both grids and plates have no comparative change in amplitude and current draw. This is measurable and this action will not allow any part of the low frequency of the signal to modify the mid and high frequencies, which would result in Intermodulation Distortion (IMD). ISO-LINEAR, so named, is what this balancing and nulling, in opposition, is called.
The special wound output transformer allows these two series triodes (the EL-34 pentode) to add the power of the lower triode to the upper triode and the sum will provide about 11 watts of power. The result is extremely clean power up to about 7 watts with no compression of the original signal. IMD is kept to lower than 1.5% to 3 watts and will rise to 10% at about 7 watts, then clip at 11 watts. In most conventional amplifiers with no NFB, IMD will rise to over 30% at the respective 7 watts.