SE DC 2A3 with 12AX7 driver stage

Signal Circuit and LSES PS filter


This circuit was inspired by Jeffery D. Medwin's SE DC 2A3 amplifier design guide circa 2009 version.

Note: AC ripple to finals (A) was 180mVp-p.  

Additional  filtering might be required for quiet circuit operation.

This is strictly an LTSpice schematic showing basic operating points and test data. 

Note : I have not tried to build this circuit . 

Bandwidth Sweep


Bandwidth sweep in LT Spice for the SE DC 2A3 with resistor loaded 12AX7 driver stage.

Harmonic Profile


Harmonic profile of SE DC with 12AX7 driver stage in LTSpice.

Pulse Testing


Dennis Fraker of Serious Stereo often comments on how music is pulsed and not entirely sinusoidal in composition. 

The late Bernard Salabert of Phy-Ph loudspeakers commented that 70% of music is non-sinusoidal.

I examine the how fast the voltage at the output of the amp settles after a pulsed test tone in LTSpice.

Note : I am no LTSpice expert and the test results are probably generic but still interesting to observe.

If anyone has some additional information on pulse testing tube amplifiers, please contact me at my deathtube email address that is posted on this website.

Loftin white SE 2A3

Signal Circuit


Loftin White SE directly coupled 2A3 with 6SL7 SRPP driver stage with  SE 3K:8 OPT.

Operating points and basic test data.

Note : no power supply filter shown on schematic, only idealized DC supply in LTSpice

Bandwidth Sweep


Bandwidth sweep from 1Hz to 100KHz at output.

Harmonic Profile


Harmonic profile of LW SE 2A3 : 2nd - 5th order harmonics in LTSpice.

SE DC 2A3 6SN7 choke loaded driver

DHT Finals with Feedback


Signal circuit only. Without feedback, THD @ 1W = 2%

Note : I have not built this circuit, only modeled in LTSpice with generic OPT and DC supply.