Tube Phono Pre-amp

Have you ever wanted a tube phono pre-amp? Or the ability to have inputs for magnetic and ceramic pick-ups, for hi-fi sound, and the convenience of an automatic changer? And used a simple circuit and minimum of tubes? Well, I was, until I found this circuit. Based off an old Stromberg-Carlson design from the golden age of hi-fi, this circuit has been an interesting one to tinker with.

It is presented here without a power or filament supply circuit schematic. My tinkering has been to incorporate this into an already existing amp, and use its power supply for the B+, and some sort of DC current supply for the filaments. You may want to do likewise, so the slate is clean. The schematic shown is for one channel. Thus, you will need two 7025 tubes for stereo. The circuit features RIAA equalization, and uses an inverse feedback loop between the two stages.

Click on the schematic for a larger view.

List of Parts

Resistor ID Value Function, Notes
R1 100K 1/2W 5% Ceramic load
R2 2.2M 1/2W 5% Signal coupling
R3 100K 1/2W 5% Grid leak
R4 6800 1/2W 5% Cathode
R5 120K 1/2W 5% Feedback coupling
R6 140K 1/2W 5% Tone comp
R7 100K 1/2W 5% Plate load
R8 354K 1/2W 5% Tone comp
R9 140K 1/2W 5% Tone comp
R10 1M 1/2W 5% Grid leak
R11 3300 1/2W 5% Cathode
R12 100K 1/2W 5% Plate load
R13 100K 1/2W 5% Output


Capacitor ID Value Function, Notes
C1 10mmF 500V Tone comp, silvered mica
C2 50mF 50V Cathode, electrolytic
C3 .0047mF 630V Coupling, metalized polyester
C4 10000mmF 500V Tone comp, silvered mica
C5 470mmF 500V Feedback, silvered mica
C6 10000mmF 500V Tone comp, silvered mica
C7 10000mmF 500V Tone comp, silvered mica
C8 3300mmF 500V Feedback, silvered mica
C9 .047mF 630V Output coupling, metalized polyester


Shielding of audio leads and dress of all component leads is very important to prevent hum in this circuit. If using AC for tube heaters, use twisted pair for heater wiring and keep wires as close to chassis as possible. Do not run AC heater supply with one wire grounded to chassis.

A single, common ground point is recommended.


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