Eroica Phoenix70 power amp
Price unknown (around the mid 1960 s?)
Commentary
Separate amplifier Phoenix70 power amplifier.
6CA7 is adopted for the output tube, and three connections are made to lower the output impedance. In addition, strong NF is applied, and the damping factor is set to 40.
Since 6CA7 is a Hi-gm output tube, there are problems such as parasitic vibration, but stable operation is realized by circuit design and layout and wiring technology.
The 6CA7 has a fixed bias circuit.
The transformer uses a directional cold-rolled copper plate (cold roll) specially ordered by tamura Manufacturing.
This transformer has a third winding dedicated to NFB (patented by tamura Manufacturing Co., Ltd.), so it can operate stably even under the worst load condition.
The phase inversion circuit adopts the cathode coupling type with the best balance.
The basic circuit is the same as the EW-50, EW-50S, and Infinite-55. However, since the output stage is 6CA7 connected to three, 12BH7 is used for the phase inversion circuit, and the cathode and follower are directly connected drive types.
This eliminates the clipping distortion and prevents the coupling capacitor from being charged even if the grid current flows through 6CA7.
Model Rating
| Type | Power amplifier |
| Undistorted maximum continuous output | 27W+27W |
| Output impedance | 4 Ω, 8 Ω, 16 Ω |
| Distortion factor | H. D. 0.1% (at 50 Hz, 10W) |
| Signal-to-noise ratio | -110dB or less (IHFM) |
| Damping factor | 40 or more |
| Frequency characteristic | 11 Hz ~ 60 kHz + 0 -0.5 dB at 10W |
| Input sensitivity (at maximum output) | 1.2V |
| Vacuum tube used | 6CA7 : 4 pieces 12AT7 : 1 Piece 12AU7 : 2 Pieces 12BH7 : 2 pieces |