The need for a simple tube preamplifier was realized with this project.
It started with a PT that has similar specifications used in the Bottlehead Foreplay preamp kits.
A FWBR into a typical CRCRCRCR filter provides low ripple B+ for the signal circuit. The UF4007 diodes are snubbed and the on/off switch is bypassed by a .1uF /250VAC rated line cap to mitigate any unpleasant power on disturbances with my subwoofer.
The signal circuit is simple : cathode biased , resistor loaded 12SN7 twin triodes cap coupled to the RCA outputs. There are a single set of RCA inputs for line level devices. A dual 100k ohm pot provides a means of attenuating the input signals.
Output Z is about 8k ohms. The phase inverts 180 degrees on the output of this preamp.
I might revisit the idea of a simple 12SN7 tube preamp using a choke load and higher B+.
This circuit originally used an IRF510 Mosfet as a source follower as seen on www.diyaudioproject.com .
I have also tried a linear PS with this circuit that puts out about 34VDC.
PT 90-0-90 > 5U4G FWR > 320mH > 44uF > 2H > 1100uF / 200K bleeder .
Subjectively, the circuit seems to sounds better at higher B+ voltage than the original schematic calls for when using the MJE340 follower.
DT 667 12/11/2019