BK Butler Blue Tube Works RT-904 (12AX7 Tube Preamp) Overdrive Distortion Drive Bass & Guitar

BK Butler RT-904, Blue Tube, Tube Works, Tube Instrument Preamp, Vintage Rack

Made in USA

Tested and sounding fantastic

Condition:   Near mint excellent cosmetic condition. This is previously owned but well taken care off expect very light wear/scratches.

Awesome tones and classic blues & rock tube sounds.  This Blue Tube RT-904 has been stored in a rack case, therefore it has no tiny rubber feet, I may find some around the work bench and add them. 

No box.  No manual, but online manual link below in the description.  Simply one of the most desired Overdrive Boost preamps ever made. Rare and hard to find in this quality condition. The 12AX7 preamp tube makes an incredible tonal difference compared to non-tube effects.

BOOST SWITCH: Increases the amount of gain to the tube by 10dB. The switch is overridden when a footswitch is connected to the boost jack on the back of the unit. 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. This feature seems intended for guitarists as I simply boost my input level via the expression pedal for the same effect.

BYPASS SWITCH: Switches the Blue Tube in and out of the effects chain. This can also be controlled using  a footswitch plugged into the bypass jack on the unit back.  Again, this seems to be more useful for guitarists as well as bassists.

DRIVE CONTROL:  Can be thought of as a pre-amp volume control, it determines how much gain is provided  by the pre-amp section. Setting the drive at 5 or below yields some tube warmth but with a clean output signal (no distortion). Increasing this control beyond 5 gradually adds more harmonic distortion.

CONTOUR CONTROL: Adjusts the amount of low frequencies driven into the tube.

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. Changes output volume without noticably altering the tone.

HI CONTROL: Shelving control for frequencies of 1500 Hz and up.

MID CONTROL: Adjusts mid-range frequencies. Center is 500-600 Hz.

LOW CONTROL: Shelving control for frequencies from 100 Hz down.

Manual


Thanks to Chris Mann for his YouTube video

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