30W hybrid amplifier 02

The preamplifier and inverter of the amplifier are served by two three- to five-pole transistors 6F2. The pin distribution is shown in Figure 2.9, and the electrical parameters
are shown in Table 2-3. This tube is quite famous, its strength and resolution are higher than 6GH8. Two 6F2 transistors are partially
connected into a single-ended parallel push-pull SRPP (Shunt Regulated Push Pull) circuit to achieve large dynamics, small distortion and low output
impedance. Due to the limitation of "internal force" in the amplifier , the SRPP circuit cannot directly drive the power amplifier . This machine uses the
pentode part of 6F2 to connect into a common cathode differential inverter circuit (often called "long tail inverter
") to supplement the insufficient "internal force" of SRPP. In order to correct and
compensate for the "long tail" cathode Due to the influence of the common resistor, the loads R6 and R7 have different
resistance values ​​(see circuit schematic diagram 2-10). The purpose is to
balance the gains of the upper and lower inverter tubes. The operating point of the SRPP circuit is set in
the linear section of the triode output characteristic (J ≈ 3 mA), and the "long tail" circuit's
I, o ≈ 2.5 mA.