Lovett Amps are completely hand built tube amps, made right here in Long Island NY, USA, using the best components available. Each amp has it's own unique twist on the vintage circuit it is based upon. In this case the "5E3 Tweed Deluxe" The Boomer features a unique 3 position gain switch on the underside of the control plate. (easily accessible from the back of the amp, shown in pic 8) this allows the amp to breakup in three different ways.  Position 1: Tightest lows, added headroom, least gain.  Position 2: Moderate gain, less preamp tube distortion more output tube distortion  Position 3: Standard 5e3 circuit, highest gain, Tweed-style breakup. 
From Lovett Amps:
BOOMER

"Boomer is based on the popular 5E3 circuit. This amp has 12 watts, it has a normal and bright channel with individual volume control and a shared tone control. At higher volumes, this amp produces great breakup that has been the corner stone sound of rock and roll for decades. This amp is equipped with Mercury Magnetic’s transformers, Sozo capacitors, and F&T electrolytic’s."

Output: 12 Watts

Circuit: 5E3

Class Type: AB- All Tube

Bias Type: Cathode

Tubes: 5Y3-Rectifier, (2) 6v6 Power, (1) 12AX7 Preamp (1) 12AY7 Preamp

Speaker: 12” Jensen C12Q 35 Watts

Dimensions: (H) 18” x (W) 22” x (D) 10 1/2”.