This Marshall Vintage Modern 2266 50 Watt Head features 50 Watts RMS, 4 ECC83 pre-amp valves, 2 KT66 power-amp valves, and a footswitch to select "dynamic range". Read below for more on this dynamic head unit.
From the Marshall Website:
"The 2266 50 Watt head is an all-valve single channel amplifier with a choice of two "dynamic ranges" selectable by footswitch. The low range equates to the performance you would expect from a stock vintage Marshall amplifier in terms of tone and available gain. The High range adds an extra preamp valve into the signal path, facilitating those classic hard rock tones of the seventies. Add to this, the ability to dynamically interface with your instruments' Volume and Tone controls and the experience translates into a truly expressive and organic feel in performance.
Two frequency-selective pre-amp Volumes(Gains) - Body and Detail - facilitate greater flexibility of tonal shaping for individual gutiars and styles while the power amplifier is heavily based on the first Marshall amplifiers to be produced, with two KT66 output valves yeilding that substantial fat and smooth tone. A Mid boost switch on the front panel fattens the tone even more while a traditional Marshall tone control circuit enables fine tuning of your sound."
