The Hot-Rod Plexi pedal is inspired by vintage amps of the same nickname. While those hulking stacks are known to sound best at ear-bleed levels, this pedal can painlessly transform your existing amp without pulling a muscle or mandatory rig cranking. With the Hot-Rod Plexi, you can completely change the personality of a clean amp or use it as an instant mod to a dirty amp.

In Stock mode, it’s as if you have the signal path from the input jack to the speaker jack (without the speaker emulation) of a stock ‘68 Plexi. Hot engages an extra “12AX7” pre-amp gain stage. With its own level control, Hot can kick in up to 28dB of pre-amp boost --a pretty insane amount of gain.

http://www.tech21nyc.com/products/effects/plexi.html