MID CONTROL: Adjusts mid-range frequencies. HI CONTROL: Shelving control for frequencies of 1500 Hz and up. Changes output volume without noticeably altering the tone. BIAS CONTROL: Quoting from two page owner's manual, 'The bias control actually adjusts the amount of cathode bias voltage of the tube stages, thereby regulating the amount of plate current' MASTER CONTROL: Sets overall output level. CONTOUR CONTROL: Adjusts the amount of low frequencies driven into the tube. Increasing this control beyond 5 gradually adds more harmonic distortion. Setting the drive at 5 or below yields some tube warmth, but with a clean output signal (no distortion). DRIVE CONTROL: Can be thought of as a pre-amp volume control, as it determines how much gain will be provided by the preamp section. This seems to be most useful for guitarists & bassists or keyboard players wanting to switch back & forth between the straight amplifier tone and the tube tone. This can also be controlled using a footswitch (TRS Footswitch not included) plugged into the bypass jack on the back. BYPASS SWITCH: Switches the Blue Tube II in and out of the effects chain. Guitarists can simply boost input levels with an expression pedal for the same effect. The idea is that you can drive the tube hard for a solo using the boost switch for increased volume and distortion, then turn the switch off after the solo to fade back into the mix. The switch is overridden when a footswitch is connected to the boost jack on the back of the unit (TRS Footswitch not included). BOOST SWITCH: Increases the amount of gain to the tube by 10dB.

STACK MASTER: Controls balance of mix of Channels 1 & 2. CHANNEL SWITCH 1 & 2: Selects between Channels 1 or 2. as it can make a subtle but noticeable tonal difference. I highly recommend experimenting with different compatible tube types such as 12AX7 12AU7 12AT7 12AY7 ECC 81, ECC 82, ECC 83, ECC 802 etc. I switched the original 12AX7 tubes (easy task) and replaced them with two vintage tubes - 12AX7 (overdrive Channel 1) and 12AU7 (clean Channel 2). Channel 1 (overdrive), Channel 2 (clean), or Stacked Channels 1 & 2 (both). RT-24 circuit board is identical to the Real Tube RT-922, the only difference being the tube choices. The two preamp tubes make an incredible tonal difference compared to non-tube effects. This dual channel Blue Tube II RT-924 has been stored in a rack case its entire life.

Authentic tube tones for classic blues & rock. A guitarist I play with tried it and loved it.Condition: Virtually mint, excellent cosmetic condition (see photos), functions perfectly (just tested). I used it to warm up a solid-state Leslie and also used it with a vintage Fender Rhodes for a Fender Twin Reverb-like tone using a solid-state amplifier. Great for Guitar, Bass, Pedal Steel or Keyboards. Original owner, always safely stored in enclosed rack case. Rare and hard to find in this quality condition. Design by BK Butler, made by Tube Works, Genz, USA. Simply one of the more sought after vintage tube overdrive instrument preamps made.

Bk butler real tube ii