At your risk.
Take all safety precautions.
Any voltage or current can be dangerous.
After a (somewhere around 2000) suggestion in a phonecall, by Allen Wright author of the Tube Preamp Cookbook (found at Papassotiriou bookstore in Athens) to use more involved circuits for pro audio it had been decided while reading the book to build such a preamplifier.
It has Sowter transformers 4935f for input.
2 Nuvistor 7586 electron tubes per channel on Penta bases supported inside the 1U chassis with nuts soldered on base and bolts in such a way that they look like UFOs from the electronic game Space Invaders.
Output transformers are Belclere EM 20014 ZH5951 with a brilliant white Bel logo.
PSU is a ground connection to chassis, fuse, toroidal transformer made by Giatras, 6X4 rectifier, low voltage electron tube voltage stabilizer possibly after the 2 possibly Fraco electrolytic capacitors and then 4 Vitamin Q Spraque big can capacitors.
Output impedance of preamps is 600Ω and can be finely adjusted by varying the heater voltage.
Input inductance of Sowter transformers is 9.8H.
The output transformers are wired as 1:1 and inductance is 7H or 8H on the other channel transformer possibly due to manufacturing variation?
(Transformers had been measured while in circuit which may not be a good idea.)
How does it sound.
It has not been powered up for years. At that time Pleiades (R,L) filters had not been made. It is remembered it sounded alright, but without gentle slope high pass filters it should had sounded bass heavy as all flat frequency response amplifiers connected to flat frequency response microphones.
Pleiades (R,L) filters consist of just an inductor in series with a resistor and the total in parallel with mic's output or voice coil if it is a moving coil microphone.
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