I'm in the US and fixing a vintage German integrated amp which has a crackle static issue I've isolated to a transistor in the preamp section. The transistor is specified in the schematic (below) as a
BC147A (datasheet specs) and the actual part in the amp appears to be a
BC147B (datasheet specs) These are both vintage European parts, not generally available here and now. (I'm trying to avoid navigating international postage during the pandemic on an NOS part.)
I'm not an electrical engineer and frankly don't know a whole lot about transistors outside their basic use in a circuit, but I'm willing to learn. So I'm trying to take the opportunity to understand what guidelines I should follow when trying to source a replacement transistor for a part that I can't source. (I spend a lot of time trying to fix up old audio stuff so this comes up from time to time.)
The very bottom of this web page offers this handy list:
- Use a device with equal or greater breakdown voltage
- Use a device with equal or greater operating current
- Use a device with equal or greater power dissipation
- Use a device with equal or greater gain bandwidth product
- Use a device with equal or lower switching time
- Use a device with equal or lower trigger current
- Use a device with equal or lower reverse current
I'm trying to understand if this set of guidelines makes sense and how important each of these variables might be (or how to determine given the device how important). I'm a dummy on most of this stuff, so my apologies for looking for something more rote, but I'm happy to learn if anyone wants to point me off somewhere that could help contextualize parts for audio circuits
I had someone advise me that RCA used to do a bunch of "universal" replacement transistors, and that in my case their
SK3444 part (datasheet) would be appropriate. It doesn't follow quite all the rules in the list above though, for example the original part seems to have somewhat greater (45V) breakdown voltage collector-to-emitter than the replacement (40V). Not all the above specs seem easily findable for both parts.
Thanks for any insight.