FET power amplifier with output transformer 01

This article introduces the production of a field effect tube power amplifier with an output transformer. Its tone is very close to
the effect of a tube power amplifier. This circuit is introduced for the reference of audio enthusiasts.
    Technical indicators of the power amplifier:
    rated output power: 50w (load 8n);
    frequency response: 4 0Hz ~ 25Hz flat curve;
    harmonic distortion: 0.5‰ (measured at 1kHz);
    signal-to-noise ratio: 90d13;
    input sensitivity: 800n1V o
    The power amplifier is composed of a dual differential amplifier pre-stage and a field effect tube power amplifier stage with an output transformer. The design concept is based on the principle of "simplicity first".     As can be seen from Figure 7-15, a pair of NPN transistors Vl.v2 constitute the first stage differential amplifier. In addition, a pair of PNP transistors Vl.v2. Mutodes V3 and V4 constitute the second stage differential amplifier. Two pairs of transistors with different conductivity types improve the utilization of the power supply voltage, and have different temperature characteristics, which significantly improves the stability of the entire machine. The resistors R5 and R6 in the figure provide bidirectional AC negative feedback for this circuit, and the circuit is fully complementary and symmetrical, so the DC stability of this circuit is very good, while the distortion is reduced and the amplitude is very wide. The polarities of the collectors of the front-end output terminals V3 and V4 in the circuit are exactly opposite, providing two signal sources with opposite waveforms     for the complementary push-pull power amplifier stage.