Right now, we're dealing with a fendered-tube bass amp, it's The Bassman 135, sitting on top of an Ampeg speaker cabinet. When you're dealing with tube amps, it's important to realize that there are certain things you need to do before you can actually get into it and take off. Especially when you're not dealing with a combo. A combo is an amp that has the head and speaker together, built into it. This is actually, you know, what you call a piggy-back, it's a head on top of its own separate speaker cabinet.
Before you plug in, or before you even turn on the head, it's important that that head is seeing the correct matching impedance. If it says 4-Ohm, it needs to see a 4-Ohm or greater load from the speaker. That's all plainly written on the back of the amp and on the back of the cabinet. Always remember that the head needs to be equal to or less than the load that's shown on the back of the speaker cabinet. So, if the speaker cabinet is, say, 16-Ohm, then you can put a 4-Ohm head on it, an 8-Ohm head or a 16-Ohm head. If a speaker cabinet is 4-Ohm, you can only put a 4-Ohm head on it. If you put an 8-Ohm head, or 16-Ohm head, you will do catastrophic damage to the amp. No bueno.
So, there are two switches on these amps, generally. There's an "on" switch, and a "standby" switch. When you're in standby mode, you will not hear any sound coming out of the amp.
The amp is on, but we're on standby. That, you know, gives you a chance to warm up the tubes, and get the amps settled, which is always a good idea. You usually tell people if you're in a gigging situation to ensure that you have given the amp the proper warm-up time. Have that be the first thing you do is plug the head into the speaker cabinet, with the speaker cable, not a guitar cable, or an instrument cable, very different things. Turn the amp on and leave it on standby while you set up your effects or band gets ready or whatever. So, by the time you flip it off standby, you should be in the clear of not doing any damage. And, when you're done playing, the first thing that you should do is put the amp back into standby mode, then pack up the rest of your stuff, and have powering down the amp and disassembling be the last thing you do just to ensure the proper cool-down time because just shutting the amp off is also, is also as bad as just firing it on.
You have four inputs but two channels. This bass side is dedicated to these controls, and these controls are dedicated to the normal channel. A bright switch which does, as it says, it brightens up the sound. Volume control, treble, for your high amp, middle for your mid-range and bass for your low-end. The thing about this amp is that it has a master volume control. So, you can turn the pre-amp volume up and get more of a dirty sound, control your overall volume with your master volume, so you can be gritty at a lower volume. Or, if you want to just max it out, you can do that too. So, those are your controls.