Conventional wisdom says...
The power rating and size of speaker you choose for your amp will depend to some degree on application and price. Practice amps are usually solid state or modeling combo units featuring low power (10-30 watts) and small (8" or 10") speakers, although there are some small tube amps to be found. For rehearsal and playing smaller venues, consider tube and modeling combo amps with power ratings averaging about 50 watts and 12" speakers for fuller sound. For larger venues or for performing loud, expect power to average at 100 watts and up. You can use "twins," or combo amps that have pairs of 12" speakers, but this is where a separate head and speaker cabinets (a "stack") are most effective.
I found a discussion thread on “How many watts do I need to be heard over drums”. Some people said 50 because they tried 15 and it didn’t cut it. Other people said 15 was plenty in their experience.
Personally, I don’t think I’ve ever gotten the volume on my 15 W solid-state combo even to 12 o’clock. Even when playing with a drummer.
Ironically, if you’re going for overdriven tube-amp tones, you’re actually better off with less wattage because it’s then easier to overdrive the circuits. If you have to turn it down because it’s too loud for the venue, you won’t saturate the power-amp section and won’t get the best overdrive tone that the amp can give. Clean tones require more wattage to ensure you can get the volume you need without distortion.
Slightly less-conventional wisdom says to get one amp for all venues. For venues too small to have a sound system, it’ll be enough. For venues with a sound system, run it through that system. (Whether mic’d or DI.) Though that still leaves the question of how powerful that amp needs to be. The less-conventional wisdom seems to say about 30 W tube or 50 W solid-state. I’m not so sure that’s not still overkill. 100 W seems clearly overkill in any case.
Even without any justification for a full Marshall stack, that still leaves room for gear envy. Check out the Peavey JSX Mini Colossal.
- 5 W combo amp
- 8 inch speaker
- Built-in power attentuator (to get cranked tube tones at quiet volumes)
- Effects loop
- An XLR output (for connecting to a PA or recording console)
- Speaker outputs so you can drive a cabinet full of 10 or 12 inch speakers
The next question: How many speakers?