Channel 1 is the EF86 Preamp channel - It features two inputs wired in the traditional way that gives them a 6dB gain difference between them. A two-position BASS SHIFT switch is included, with position 1 voiced to the original vintage-correct bass response and position 2 voiced to tighten the bass response and reduce any muddiness during high volume use. The three-position BRILLIANCE SWITCH provides flat response when in the OFF position. Position 1 is a new position voiced like the early AC30 “Treble” amps, while position 2 is the original brilliance circuit, which acts as a dramatic bass cut. The EF86 Mode switch re-configures the EF86 valve from Pentode mode to Triode mode. Triode mode will give a lower gain tone with higher headroom. Pentode mode is the famed original mode and has a very sweet high gain tone with not very much headroom.
Channel 2 is the Top Boost Preamp channel - Like Channel 1, this channel includes two inputs wired with a 6 dB gain difference between them. The Treble and Bass controls are from the 1963 Top Boost circuit and are extremely interactive. Very minor adjustments of these controls can yield dramatic changes in tone color.
And true to VOX form is the Top Cut control, which cuts high from either channel end as it is turned up.
Flexible power - The O/P Switch adds even more flexibility to the AC15. This switch changes the power output valves from Pentode Mode, which is the normal operating mode of the power amplifier, to Triode Mode which halves the power output to 7.5 watts and will alter the tone to be somewhat smoother.
- Info from: http://www.voxshowroom.com/uk/amp/ac30h2l.html