So you’ve got a guitar amp, but you want to put a bass guitar through it… hmmm, well in some rare cases it’s ok, but the general rule is that you can’t use a standard electric guitar amplifier for a bass guitar.
Let me clarify what I mean though:
there’s 2 main parts to an amplifier. there’s the actual amplifier, which is an eceltronic device (solid state or tube) and can take a very quiet signal and turn it into a VERY LOUD signal. Then there’s the speaker(s) that actually sound out the signal so you can hear it.
So the actual amplifier part is usually ok, and although a guitar amp probably wont sound great if you’re amplifying a bass, it probably won’t harm the amplifier circuits. Although I still wouldn’t like to run a guitar amp at full power amplifying a bass guitar because the powerful signal of the bass guitar low strings may overload the amp. So take care.
The speakers are a different matter. a standard low E on a 6 string electric guitar vibrates at approx 82Hz (82 times a second). Most guitar speakers are able to output sound well at approx 75-5000Hz so that’s fine. THe speaker will have a watt rating, perhaps something like 50 watts, and will be able to output any sounds between 75 and 5000Hz at up to 50 watts.
You will also find that you could output sounds lower than 75Hz or higher than 5000Hz, but at a greatly reduced power (or watts), and that’s where the issue is. A bass guitar (a standard 4 strings) usually as its low string tunes to E at 40Hz, or for a 5 string, the low B is at 30Hz. So you could maybe use your guitar speaker at really low volume levels to output the bass, but it would sound rubbish, and still possibly damage the speaker.
So the name of the game: You can’t use your guitar amp with a bass guitar.