The signal at the reproducing head should be a very bright signal 6dB per octave rising with frequency.
The playback preamplifier just have a very high gain at low frequencies and low gain at high frequencies.
This is usually done by a frequency selective negative feedback circuit using resistance, capacitance.
For the example on the EMI BTR2 tape recorder the head is connected to an input transformer by a balanced connection. Exactly how moving coil microphones are connected.
The signal is connected to the control grid of a high voltage gain pentode EF37A.
A 0.01 capacitor is connected to the anode.
A 150KΩ resistor is connected in series to the capacitor and its other end to grid. This as explained in the service manual provided the basis -6dB per octave high cut.
Similar feedback ideas from the second electron tube to the first's cathode can be seen on Ferrograph series 6.
Also such feedback circuits are used on RIAA, record playback preamplifiers.
Would it be possible to connect 3 low gain battery powered EF183, anodes operating with 6-12V as on Pleiades V series and feeding from the anode of the last tube to the grid of the first?
Also JFETs could be used.
References:
EMI BTR2 manual
Ferrograph series 6 manual
VTL vacuum tube logic handbook
Tube preamp cookbook - Allen Wright
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