This is a totally unique Pentode Tube based Bandpass Filter Pedal designed by Eric Barbour of Metasonix. It's designed to replicate the filter circuit in his famed Assblaster KV-100 and the R-54 Module. The circuit is based around a pair of 5U8A (stock) tubes but can be switched with a pair of  6U8A's and the equivalents. I've included the stock tubes, a pair of 6U8As, a 6GH8 which I bought accidentally (compatible but not paired), and a set of Tung Sol 5U8A tubes (installed). There is a significant sound different between these tubes as the plate voltage is different. I find the 6U8a's good for music where noise is not a problem, but the 5U8's are very useful for most applications.The pedal is marketed as perhaps the most unique wah or filter pedal for guitar, but it is my impression that this pedal is superior on bass or baritone guitar. With a typical 0-5 volt expression pedal plugged in the highest note that can be swept is the high E on the 1st string. I have confirmed that if you plug a -5/+5v expression pedal into a CV offset device like the CP-251 or CoPilot BroadBand that it is possible to extend the range of the expression pedal's sweep up to the high B or C at the 19th and 20th frets. This is because the pedal is designed with a sweep from 0-10v like most synth devices and unlike most guitar pedals. The pedal can also act as a self resonating noise generator, and has that growly vocal quality the KV-100 does when used as an auto-wah or with an expressionpedal.. It does say "Stop Sucking Monkey C*#k" and the box does say "F*#k You!" but I'm not putting that out there, so the image was altered w/ Microsoft Paint. It's all original mint condition and has not been altered like the pictures. When it lights up it has really cool red LEDs.Free Shipping via USPS Priority Large Box.