Greetings! Whilst sourcing parts for a Vibro-Champ clone currently under construction, I found myself vexed by the scarcity of options when it comes to the infamous reverse audio pots for the tremolo circuit. Particularly because the amplifier is going inside a wood speaker cabinet with the controls on top, necessitating longer bushings on the potentiometers. Not a big deal for 250K or 1meg audio taper, and I'll even accept a 25K linear if it fits. But that confounded 3meg reverse audio! So anyway, I found this helpful resource that seemed worth sharing. (It's an article titled "The Secret Life of Pots.") The author, R.G.Keen, tells you everything you ever wanted to know about potentiometers but were afraid to ask. About halfway through, he explains different types of tapers, and how to modify them by adding a resistor to the pot, creating a voltage divider. It's a bit technical and there's math but useful for tinkerers such as we.