#1
I use a Marshall JCM800 live (the combo model with 2 x 12 inch speakers) and I don't think it's as loud as it used to be. I had it on full today in a practice room and it was loud, but it should have blown me away. I'm sure I remember it being a lot louder when I got it, but then I've never had it at full volume till today.

Messing around with it on the way home, I noticed that the ohms switch (which can be put on 4, 8 or 16) was only on 8. Both speakers are 16ohms. Would turning it to 16 make it louder? Could it be that the tubes are dying? I thought they usually just died without any warning, but could this be the start?
#3
depends on how the speakers are wired. Find out about that. 2 16 ohm speakers can be wired to be total of 8 or 16 ohms, and the ohmage doesnt do anything to the volume. It HAS TO MATCH! Otherwise some serious damage can occur to your amp. So find out to what ohmage your speakers have been wired to.

And ^+1. Could be tubes. Remember that it can be a power tube even though they were all lit. That doesnt mean its necessarily fine.
#4
The speakers should be wired in parallel. Two 16 Ohm loads in parallel equals 8 Ohms, so the switch is set correctly, so don't worry about that.

It might be the tubes. Is it just quieter or does the volume fluctuate, too? Has the tone changed? Did noise-issues come up that weren't there before? These are typical signs of dying tubes, though they don't guarantee anything 100%, and these symptoms don't always show up, much less all of them.

Ultimately, yeah, it might be the tubes, but take it to a tech to make sure anyway.
#5
Quote by fc89konkari
depends on how the speakers are wired. Find out about that. 2 16 ohm speakers can be wired to be total of 8 or 16 ohms, and the ohmage doesnt do anything to the volume. It HAS TO MATCH! Otherwise some serious damage can occur to your amp. So find out to what ohmage your speakers have been wired to.

And ^+1. Could be tubes. Remember that it can be a power tube even though they were all lit. That doesnt mean its necessarily fine.

Actually, two 16 Ohm loads can be wired to equal either 8 (parallel) or 32 (series) Ohms. Never seen the latter done in guitar equipment, so I'd say we can safely dismiss that possibility.
#6
I've only had the amp a few months and we've been recording the album so we've not done that many gigs with it so I'm not sure if it really is that quiet. I'm just basing it off the fact that the other guitarists line 6 spider 4 75watt thing wasn't much quieter than it at full blast. Made no sense, especially since his only has one speaker. A celestion, but I didn't think it'd be anywhere near as loud.

I have no fluctuations or tone issues. In fact the amp sounds great, I was just expecting it to be unbelievably insane in volume, and it wasn't it was just really really loud. Maybe I'm just overestimating the volume of the amp though. I'd never had it on full before.
#7
Quote by fc89konkari
depends on how the speakers are wired. Find out about that. 2 16 ohm speakers can be wired to be total of 8 or 16 ohms, and the ohmage doesnt do anything to the volume. It HAS TO MATCH! Otherwise some serious damage can occur to your amp. So find out to what ohmage your speakers have been wired to.

And ^+1. Could be tubes. Remember that it can be a power tube even though they were all lit. That doesnt mean its necessarily fine.

It doesnt have to match in all instances. But that is a good rule to follow obviously. I just want to point out that the cab can be rated higher than the head without damage. A 8ohm out put to a 16ohm cab wont hurt anything. (Assuming speaker wattage is sufficient.) Likewise a 4 ohm out to a 8ohm cab..

But not the other way around.

Still its always safe to match.
I wondered why the frisbee was getting bigger, then it hit me.
#9
The amp on full power isn't much louder than the amp on 2.5 - 3, just more saturated and compressed.

Perhaps that's what you're experiencing.
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Feel free to express yours so I can make an informed judgement about how stupid you are.