[mikethedruid]

This circuit actually is a circuit that reduces the treble, the higher frequencies from the audio output. The cleanest output would be with NO circuit at all, which would give you the full spectrum of what the amplifier is putting out. The larger the capacity in this circuit, the more the high frequencies will be reduced. This gives the impression of having more bass. With less resistance, the same thing happens. Think RC reactance circuits. You could put a .22mfd condenser directly in with no resistance at all, and it wouldn't harm the radio, it would just clamp off almost all the treble end, and sound like crap. I strongly suggest finishing with the RF and IF alignment work, and getting the radio receiving actual stations well before deciding what condenser to use. Do your evaluation listening to various stations with music and talk both. If your potentiometer is 100K, I would think a 0.1mfd condenser would do the trick pretty well, and not make things too mushy even when full on. It all depends on the speaker and your personal taste.