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Okay, so, my amp kind of gave me a "fuck you" tonight. Silvertone 1484 head. Started crackling and distorting (overmuch) and cutting out, so I plugged my guitar into the other channel and it worked fine for about twenty seconds, then got REALLY distorted and went entirely silent.* Anyone have any idea what causes such things? Do I need to retube? Some of my tubes are original '60s stuff so I might have to anyhow... Any help would be much appreciated.

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*Luckily it was at the end of the last song so I threw down the guitar, grabbed a mic, jumped on something, and screamed the last chorus. Whee.

Could be a fuse.
Sounds a lot like a fuse.
Also, make sure the right fuse was in there to begin with.
The reason I say this is because I had a similar experience, but during the set up of a show.
I was using a MusicMan 50 watt bass head and not a Silvertone, but I doubt that matters since they are both tube heads.
My amp made a really weird tone, then a low volume tone and then nothing.
Replacing a fuse will cost you infinitely less money than replacing a tube, as I'm sure you know.

That could be it. The effect was sort of like this:

DISTORTION
ok quiet now
AAAH DISTORTION
.......

I guess I'm going to have to get it checked out properlike.

see if this helps you:

http://www.geofex.com/ampdbug/ampdebug.htm

I have the Sears Silvertone 1481 model, so we're talking fairly similar models ("fairly similar" = "not exactly the same"). Is your location currently LA or ChiTown? If you pass through Minneapolis on your way to either (though it's pretty out of your way) I can offer you a diagnostic.

Hey, thanks for the offer. I'm in Chi presently, don't think I'm going to be passing up that way on the drive home, though. I think I'm going to try to find a tech in Chicago.

I had that happen to me, but it was the bass' fault. I played for 20 minutes without any problems, then I heard more fuzz than ever, and all of a sudden it got really quiet. I figured out that it wasn't the amp, because my other bass didn't have any problems, or my guitar. The wiring is all fucked up in that bass.

no smoke? if there was no smoke, my guess would be an output tube croaking. you may well just need new output tubes.

No smoke. Hopefully it is just an output tube; one of them is/was still the original Silvertone tube, and I'm sure I've abused it more in the past two months than it had taken in years.

I think Scott's on the right track. Did the lamp/light go off (on the amp--if you took out all the lights in the room, congratulations!)? This would indicate the fuse blowing. What you're describing sounds like an output tube dying; it will often take a screen resistor with it. If you're feeling adventurous, and have spare fuses and tubes, you could:

: take out the output tubes, put in a good fuse, turn it on. If it lights up and nothing smells funny, try...

: putting in new/good output tubes. Let it warm up a bit. Once again, if it doesn't blow the fuse, and nothing smells/smokes, plug your guitar in. If it sounds okay, you're probably fine. If it still sounds low-power/too-distorted/crackly/etc., you may have a blown screen resistor, though this is just the most common problem--there could be other damage. I don't know if you really want to get into that stuff; if not, it would be time to see a tech.

Good luck--those are cool amps.

-Tom