用2A3自制20W推挽输出胆机
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This section introduces one example using R core audio interstage and output transformer: 2A3 push-pull 20W monaural power amplifier. Maximum output of this amplifier is 20W that is quite enough for family use. The main features are excellent performances (low distortion, wide bandwidth, high output, and low noise level) that are difficult to be achieved by the single-ended amplifier, and good sound quality straightforward that is particularly characterized by interstage transformer coupled circuit.
Rated performance of 2A3 push-pull 20W monaural power amplifier
Maximum output
20W
Frequency bandwidth (1W)
10Hz to 55KHz +0,-3db
Damping factor
3.8
Distortion factor (1KHz)
1W : 0.055%, 10W : 0.6.%, 20W : 3.2%
Residual noise level
0.1mV (without weighting network)
Sovtek 2A3
For this amplifier, we used 2A3 made by Sovtek, Russia. Different to popular 2A3 made by RCA or in China that have two electrode units in parallel connection, Sovtek 2A3 has a single electrode very similar to 300B. Overall dimensions are also one size larger than ordinary 2A3.
The published rating is the same as ordinary 2A3, but in a practical sense, it seems to have an extra power handling capacity. The quadruple that we used this time are well matched and have no irregular faint noises that are heard occasionally with 2A3 made in China.
Main rated characteristics of the tube are as follows.
Plate dissipation
15W
MU
4.2
Mutual conductance
5250uS
Plate resistance
800ohms
Maximum plate voltage
300V
Filament voltage
2.5V
Filament current
2.5A