Last year I purchased an 18w TMB EF86 amp, in which Nick had installed VVR and PPI master volume.  The amp is just amazing.  I've been particularly surprised by how versatile the EF86 channel is.  Great clean tone, but also tremendous sustain and grit when cranked up-- just a little brighter and better defined than the TMB channel. The VVR works great-- can get all sorts of very natural sounding distortion at any volume.   I have had one issue that I wondered if anyone else has experienced with this amp.  When I've tried to hook it up with another amp to use with a stereo echo or chorus, I get a ground loop hum problem.  I've tried hooking up various combinations of my other amps (including a Ceriatone Overtone HRM), with no hum problem with any of the other combinations.  Nick assures me that the 18w TMB EF86 is properly grounded (and therefore safe!) but wondered what experiences others might have had.