Common features of our 40 watt reverb amps:

• 2 channels independent EQ’s
  
• Dual power scale master volume (each channel has its own wattage control)
  
• Tube driven parallel effects loop
  
• Footswitchable gain boost for both channels
  
• Fat control. Feedback attenuation. Controls gain and body of power amp.
  
• 4 tube power amp with 3 modes:
  
  • Mode 1: 20 watts from dissimilar tube operation of a 6V6 and a EL84.
  • Mode 2: 30 watts from a pair of EL 34’s.
  • Mode 3: All 4 tubes operating.

• Ultra Linear / Pentode works on all 3 modes
  
• Unique 6SN7 driver tube circuit in power amp
  
• Reverb amps use a 6SN7 tube to drive the reverb circuit
  

  ***More info on the Fat and Power Scale functions

Stephenson Amplification 40 Watt Amplifier Operation:

Front Panel:

Clean channel:
Gain - preamp level control for channel A
Treble - high frequency control for channel A
Bass - low frequency control for channel A

Distortion channel:
Gain - controls amount of preamp distortion for channel B
Level - controls channel B’s preamp signal output to power amp
Treble - high frequency control for channel B
Bass - low frequency control for channel B
Mid - midrange frequency control for channel B

Fat:
Feedback attenuation – controls the amount of negative feedback employed in the power amp. Negative feedback is a common guitar amplifier method to control the tightness and gain of the power amp. Too much negative feedback can cause a thin, constricted sound, and too little can cause a bloated sound. With the Fat set to minimum, a great deal of negative feedback is employed, which keeps the power amp tight with less body and gain. With the Fat set to maximum, the power amp is running "open loop" (no negative feedback), for maximum gain, body and wattage from the power amp.

Power Scale Ch.A and Ch.B
Power Scaling (PS) is the world’s best and most transparent master volume. PS varies the amount of wattage the power amp produces by proportionally varying the voltages applied to the power tubes. With the PS set to minimum, the wattage output is only a fraction of a watt, and with the PS set to maximum, the power amp produces full wattage. Power tube life is greatly extended with the PS on settings less than maximum. Each channel has its own PS control and is automatically activated with the footswitch channel button.

Rear Panel:

ON/OFF Power switch:
Turns power On or Off

Ultra Linear / Pentode:
This switch selects what mode the power tubes are running in:

• Ultra Linear is a 50’s hi-fi deal that requires a custom output transformer with an extra set of taps that run the power tube screen grids at near the same potential as the plates. Ultra Linear has a smooth, warm sound, and the lower internal resistance of the power tube allows the Fat control to be set higher.
  
• Pentode is the classic guitar amp method of power tube operation. Pentode produces more wattage and generally more grind. This mode prefers the Fat control to be dialed back to keep the bottom tight.

Dual Power Tube Select

V6 / 34 / Quad:

• V6 : This setting activates two of the 4 power tubes, the tubes activated are the 6V6 and the EL84. This dissimilar power tube combination produces 20 watts power output.
  
• 34: This setting activates the pair of El34’s for 30 watts power output.
  
• Quad: This setting activates all four power tubes for 40 watts power output.

Footswitch:
This 5 pin jack is where the footswitch is connected to the amp.

Speaker impedance selector:
Use this selector as a tone control. The output transformer is more than twice over-rated, so there is no harm in running the selector set to the wrong impedance.
*** Do not change the impedance while the amp is being played.

Speaker jacks:
These two ¼ inch jacks are wired in parallel.

Reverb:
Each channel has its own reverb control. The reverb is footswitch activated.

FX Loop:
The loop is a tube-buffered parallel type with a transformer-isolated phase-reversible send. Some effects processors and effects pedals reverse the signal's phase, so use the phase switch to put the effects signal back in phase with the amp. The loop can also be used as a solo boost. Plug a short ¼ inch cable between the send and receive jacks, and adjust the send and return levels for desired amount of boost. The volume boost can now be activated by using the footswitch's EFX button.

Footswitch Operation:

Chan.:
This button controls which channel is activated. When the LED is on, the distortion channel is activated. When the LED is off, the clean channel is activated.

Gain:
This button boosts the gain in the preamp. The amount of gain is internally set and non adjustable. When the LED is on, the gain boost is active. The gain boost works on both channels.

Reverb:
This button activates the tube driven spring reverb.

EFX:
This button activates the parallel effects loop. When the LED is on, the loop is activated

Tips for use:

Channel A Getting a clean sound:

• Channel footswitch LED off.
  
• The Gain, Treble and Bass controls are now active.
  
• The fullest clean sounds are achieved by having the amp's Gain set fairly high (about 5), and the guitar's volume rolled down.
  
• Having the guitar's volume rolled back and the amp turned up has the benefit of not overloading the preamp, keeping the signal cleaner.
  
• For the loudest clean wattage, turn the channel A Power Scale to max.

Channel B Getting a distortion sound:

• Channel footswitch LED on.
  
• The Gain, Level, Treble, Bass, Midrange are now active.
  
• The Gain knob controls the amount of preamp distortion generated. Settings of 5 and higher have the most body.
  
• The Level knob controls the preamp volume sent to the power amp.
  
• Set the Level in conjunction with the Power Scale. The higher the Power Scale, the higher the Level can be set. In other words, if the Power Scale is set low, then the Level needs to be set low as well, or excessive distortion is generated.

Using the V6-34-Quad:

This switch selects what power tubes are active.

• The V6 position activates the 6V6 and the EL84 power tubes. This mode produces 20 watts.
  
• The 34 position activates the pair of EL34s for 30 watts. This mode is the familiar guitar amp push/pull class A.
  
• Quad position activates all 4 power tubes for 40 watts. This mode has the fullest sound tonally from all the even-order harmonics generated from the mismatched tube combination. When in the Quad position, experiment with the different tonalities of the different speaker impedance settings. Using an 8 ohm cabinet and setting the speaker selector to 16 ohms will produce more mids and highs.

Using the Pentode/Ultra Linear:
This switch can be used with any of the power tube modes (V6/34/Quad).

• The Pentode position produces the most wattage and is the more familiar guitar amp sound. The Pentode position works the power tubes the hardest, especially the 6V6 tube.
  
• The Ultra Linear position is warmer sounding, and is easier on the power tubes. Expect longer power tube life when in Ultra Linear mode of operation.

Using Power Scale:
The Power Scale control is the amp's master volume. It controls the wattage output. Stephenson Amplification amps are designed to run reliably at full wattage settings; however, much longer tube life can be expected by having the Power Scale set below maximum.