The TB-303 generally used the 2SA733ap, which is a transistor with a gain of about 300-350. Unfortunately the 2SA733ap is no longer being manufactured, so LadyAda used the 2SA733p, which for the most part is a drop in replacement. However, in applications where the transistor gain is important, like shaping the Square in the VoltageControlledOscillator, or converting the voltage to current for the VoltageControlledFilter the gain is very important.

The 2SA733p has a transistor gain of about 270-310, so if you perform a TransistorBetaTest on your 2SA733p transistors, then you can have a much closer clone. Some x0xb0xers have found that buying a batch of 100 or so from Mouser can yield some good transistors. Of corse, pretty soon we will all be swimming in batches of 97 733s, so we should figure out just WhatTheHellToDoWithTheOtherTransistors. Another option is to try and find 2SA733ap transistors in older VCRs.

There is also a 2SA733k that is available, that has a gain from 300-600 (!). Lots of people have them on order, but no results are in of their testing.