The Lazy J 20. Please read the product description which is from the Lazy J website:
 
"This amp is a 2 channel, hand build, point to point wired amp, which delivers ca. 18 Watts into a 12”, 8 Ohm, Celestion Alnico Blue Speaker. The cabinet is built from finger jointed pine and covered with hand aged, lacquered tweed. The 2 channels are marked Normal and Bright with a Volume control for each one. The Tone control affects both channels equally. Looking at the 4 inputs from the back of the amp, the 2 on the right are for the Normal Channel and the 2 on the left are for the Bright Channel. Both inputs labeled 1 are higher gain than the ones labeled 2. The interesting thing is that the both Volume controls are interactive. The Volume of the Channel you’re not plugged into has an effect on the tone/tightness of the Channel you are plugged into. In other words, if your guitar is plugged into the Bright Channel, the Normal Channel Volume affects the way the Bright Channel responds. This is subtle, but definitely audible. With the Bright Volume turned up to any given setting, and the Normal Volume off, you hear the sound of the Bright Channel alone…by turning the Normal Channel up about halfway, you hear an increase in low mids. By turning the Normal Volume up to 10, the bottom end will tighten up…from 10 – 12 the sound will get choked, compressed and become quieter. This can be used to get interesting tonal variations from the amp.
The amp is set up with a GZ34 rectifier and a pair of 6L6s in the power amp, and uses two 12AX7s. However, for a different feel and character, the amp will take a 5Y3 rectifier and a pair of 6V6s without the need of re-biasing.
An optional feature that can be added to the amp in place of the Ground Switch, is a Variable Attenuation Control (VAC), which allows the user to dial seamlessly from full output down to ca. 5 Watts while retaining the amps character all the way along.
Upon request, a Lazy J Reverb module can be added to the amp. It is a tube driven reverb circuit with a full size reverb tank, adding another dimension to the amp. The reverb circuitry and controls are housed in a small enclosure that is mounted to the inside of the cabinet, on the right hand side, looking at the amp from the back. The controls, Reverb Volume and Reverb Tone, are easily accessible. The module is supplied with a Cut Off footswitch. Variable Attenuation Control (VAC)
This circuit allows the user to reduce the Output of the amp in an even sweep from Full Power down to less than 5 Watts. However, this is not a Master Volume. This circuit retains the amps tone and response while reducing its Output Volume.
In other words, you turn your amp up to get the tone you want… which might make it too loud for certain situations. Now you can turn the amp down with the VAC to exactly the level you need…while retaining all the character and response of your sound. This circuit is an optional feature on the Lazy J 20. However, it can be retro-fitted to most amps under 40 Watts"