Recently finished up this amp-top boost i’ve been working on. Its a simple, single EF86 boost designed to color a bland signal and push an amp. Adds a nice amount of pentode tone coloring, boosting the odd-harmonic content. It wont create any overdrive itself but like a Rangemaster it does an awesome job of smashing the front end of an amp.  This unit uses a proper transformer to achieve high-voltage supply on the tube plates just like in a tube amp.  No skimping on voltage!