A Pleiades V6 without an input transformer and instead of output transformer the voice coils of Sennheiser HD580. See also Pleiades Electra 3 or EF183 power amplifier.
Signal path:
Fame soundtrack CD - Portable Sony CD player line out - 2x Pleiades V6 with EF183, 12V - Sennheiser HD580
Power supply is 12V. One EF183 electron tube per channel. Possibly no cathode underheating. Anode supply 12V. Fuse in series with battery for safety. Same battery powering both heaters in series and anodes through headphone voice coils. So ground of headphones is connected to + battery. Battery in series with suitable fuse.
Pull up bias is by a 1.6MΩ resistor from anode to grid.
Amazing sound. Possibly the best treble that can be heard out of a CD. The headphones seem to be constant current driven as the output impedance of the amp should be around 5KΩ.
How would this amplifier sound directly connected to recording head coils of a reel to reel recorder or a cassette recorder running at 7.5ips? Perhaps decreasing bias so that less current is flowing through the head so that the tape is biased at near mid point of straight part of BH curve. It should be tricky. Both electron tube and recording head should be simultaneously biased at the correct point. Bias of the electron tube will affect both electron tube and tape. This is DC bias for the recording head or tape which should be more noisy. If DC bias proves too noisy or not giving desired max output level from tape then AC can be used. See nearby posts. In the meantime it so much simpler to experiment with DC bias, no components should be needed, just DC coupling of a high output impedance driving the magnetic tape recording heads.
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