This is kind of a cool little item.  It was designed and will ONLY work on pre-1978 Fender amps (blackface, silverface) with reverb (Twin Reverb, Deluxe Reverb, Vibrolux Reverb, etc). I have not tried it on any of the reissue amps.  This is a passive device, it attaches on to the back of the amp where the reverb cables would go, then the reverb pedal.  What it does is make the  reverb section act as an extra gain boost when the slider is to the Boost side (NO REVERB), but reverb works properly when you are to the Reverb side, with a blend possible in between. This was an improvement over the original SuperCube which didn't allow switching back to reverb.  I haven't used this for a long time and don't have one to attach it to but no reason why it shouldn't still work since there is not much to it.  Some wear to the silver sticker but no other problems. Shipping will be $6.50  for priority mail in the CONUS, elsewhere email me for a quote.  I sold one awhile back for around  my asking price, but of course offers will be considered.