BetterOffShred wrote:Typically circuits are designed to use a certain gain range of transistor, in either NPN or PNP. Some circuits are far more sensitive to this range, and will either sound like ass, or not work without a pretty exact gain.. most circuits are not like this and you can probably coax good shit out of a few substitutions.
So that being said you can look up the gain range of the specified transistor and see what else you have in that range etc.
Since we started talking about Devi circuits I'll bring them up again.. the Torns Peaker sounds so much better with some substitutions IMO. I think mine only has a single MPSA18 left .. the others are subbed.
So to answer the original question, both. There are certainly "try these instead" lists people have made.. but they are just based off gain ranges typically. Mind the pinout too, your component tester should help that
I think this is all very good advice. I want to speak on the devi thing. she was using transistors with a Hfe 5000 (MPSA18) and piggybacking two transistors together to lower the gain. sometimes she would put a transistor in backwards sharing a socket with another transistor that was not backwards. death by audio had a pedal that was using reverse gain only found in some transistors. all of the transistors were intentionally installed backwards after they tracked down a bag or rare transistors that were tested to have gain in reverse. some of my early pedals had transistors installed backwards but they worked fine because of the reverse gain. or maybe the previous gain stages were driving the last attenuator stage hmmm?
swapping germanium transistors for other germanium transistors is pretty good practice. swapping silicon NPN for other silicon NPN is not always useful. it depends on the circuit. I think there are two things happening here. some people swap germanium out for other germanium of a similar gain to get different sounds. but swapping silicon for other silicon of similar gain will rarely change the sound. that is why you swap out a 2N3904 to a 2N5088. this will increase the gain. then you swap to a MPSA18 to increase the gain again (or to just try darlington transistors compared to BJT). there are an infinite number of part numbers for 2N3904 replacements of similar gain. I have tried a LOT of them from mouser, tayda etc...they are %100 compatible (they sound exactly the same).
swapping transistors is probably more useful if you understand the purpose of every component in a guitar pedal. if you understand how to change some resistors to make the higher gain transistor work in that circuit then you will be able to compare apples to apples as far as possible differences in sound between transistors. if there are no differences in gain, then the differences you hear are all related to some other property or some other interaction. this is usually explained by differences in linearity and to a lesser extent, leakage, and noise.