So your amp was once a Marshall, or a Fender, or a Mesa, or an Ampeg. But right now, you’re standing on this stage, in front of a lot of people, who want to be amused. And your amp (whatever it is, in this situation, it’s going to be a ‘Bastard’,) doesn’t work. What next? A variety of entertaining ideas spring to mind.
1) You are dismembered in nasty ways by an audience who finds a load of folks on a stage not doing anything at all, disappointing.
2) Thoughts of hammers, axes and (admittedly a little extreme) chainsaws, mincing your nice amp into a sackful of bits the size of an oxo cube, rush unbidden through your steaming brain.
3) Possibly worse than those improbable alternatives, you reach for a screwdriver.
4) In order of prospective danger, figuring out where you might stick that screwdriver ranks high on the list of ‘Dont’s’
So might we find some useful alternative to panicking like a headless chicken? Shouting at the drummer is usually a good start; just to ease the tension, you understand. After that, here’s few things that might at least feel positive.
Let’s concentrate on the amp. Concentrating on anything at all at least alleviates the ‘Black Hole’ syndrome. That’s where you wish that one would turn up and spirit you away to another galaxy.
Does it light up? No? Is it switched on? Don’t pull your hair out; it happens.
Is the wall socket switched on? Is the multi-block plugged in? Is the IEC socket (the kettle plug) fully plugged in? That’s an easy one to miss.
The IEC mains inlet in the amp might be fused. If so it will have a little slot-in plastic section moulded into the IEC socket. You can get to this without opening anything.
UNPLUG IT!!!!!!!!!!! Then you get a small screwdriver (I’ve done it with a fork, a toothpick, a cocktail stick) and lift the slot-in section out. Inside there is usually two fuses. One at the bottom which is the operative one, and the one nearest the surface plastic that is a spare. They’re usually glass, 20mm things, and if it’s blown you’ll see that the wire inside is either broken or non-existent. Then you take that one out, and put the other in that slot. Hey presto! Done!
No? Oh dear. Check the fuse in the plug. You can’t see whether these are blown or not, so it’s either swop it, or put a meter on the ohms scale, and check it reads zero. Failing that showing anything, borrow somebody’s lead.
Beyond that, you’re struggling. There may be two more fuses in the back of the amp, usually of the same (20mm) type that we found in the mains socket but installed in screw-in fittings, usually not far from the IEC socket. Either of these blown could be due to a surge at switch on, or you could have big problems. If you have spare give it a go.
On switching on valve amps:- Always use mains first and then standby after. Give it as long as practical to warm up before switching on the standby. Otherwise surges can occur as the bias voltage builds up. This is especially true with solid state rectifier design. Leave it as long as you can before you move a valve amp that is hot. The elements within the valves distort slightly when hot, and can give you faults (particularly heater-grid-cathode shorts which are very bad news on power valves, and unpleasant on preamp valves).
What if everything seems ok but it just doesn’t sound? Is there anything from the speaker if you wind the master volume up? No? Have a look at the spade connectors on the back of the speakers. Make sure the amp is off, if they’ve drifted loose slot them on again and check they’re a tight fit. If all looks ok, concentrate on the front of the amp, as there’s nothing more you can do at the back.
A lot of modern amps have a relay that switches off the input stages of the amp. This (I think) is because modern amps tend to be noisy because of the high gain stages, and by effectively disabling the input stage it makes the amp tick over at the same sort of noise levels as an old Fender Twin. Which were deathly quiet. How does that help?
Well, if the switching at the back of the input sockets is bad, you’re amp won’t work. Blast some switch cleaner in there (if you have any) and then shove the jack in and out. If no switch cleaner, do the jack thing anyway. DON’T USE WD40. It has a sticky oil base that although fine on electrical things, is not good on electronics.
Still nothing? Use the same trick on FX loop send/returns. You could also try a patch lead in them, instead of your pedal system. A bad lead/ dud pedal could easily be the cause.
What about buzzes? Loud hum/buzz can be as bad as your amp not working at all. Check the daft things like instrument leads. Is it affected by control settings? Spring line reverbs can make nasty noises. If you turn the reverb down and it goes away, get to the phono leads that plug into the amp and pull them out then plug them back in. Contact cleaner also, if you have any. You can’t always get to the amp outs to the reverb, they’re sometimes hard wired. But you can get to the reverb tray which is often screwed to the inside of the amp cab (Marshall, Mesa, etc) or in a black plastic case in the bottom of the amp. Same thing as the other phonos. Otherwise just switch it off.
Last of all, and this is a bit extreme; a very loud buzz that won’t go away if you turn all the controls off can be a soft output valve (red plate is the modern version of the terminology). Have a quick look in the back for a glowing red valve (that’s one of the power valves. Big; EL34 or 6L6 or 5881; or maybe EL84 or 6V6 if it’s a Vox or a nice little Ampeg. Anyway, if there is a soft output valve in there, it will be GLOWING. SWITCH IT OFF.
There’s not much you can do. But if you have a hundred watt amp (ish) you’ll have four in the back. If you take out the two inner valves (or the two outers, depending on where the red valve is) you’ll have a fifty watt amp, that works; rather than a hundred watt one that doesn’t. This won’t bother your amp, but it’s best to get it sorted out at your earliest opportunity.
You can’t do that trick with an old AC30. The biasing arrangement is quite different.
One other possibility on the buzz/hum thing is a heater/cathode short on a preamp valve. Unless you have somebody pretty familiar with taking the back off an amp, it’s probably best left alone. If you have a spare ECC83?
Check if the hum can be turned off at the master volume. If yes, the fault is in the first stages of the amp. The preamp valves are usually furthest away from the power valves. So progressively swop those for the good ECC83 you have.
Watch how you replace them. They’re a nine pin base with a locating gap. The gap is usually marked in some way on the chassis of the amp (might be a little tag or a v-shaped nick). Make sure any screening cans go back over the valve.
If the master volume doesn’t affect the hum, the fault could be on the phase-splitter. This will be the nearest small valve to the output valves. It’s usually an ECC83 (12AX7) but it might be an ECC82 (12AU7) or even ECC81 (12AT7). Either way, your ECC83 won’t hurt anything in there, but you might find a difference in overall gain and it might distort. All this you might just get away with by adjusting the master.
Sounds like a lot of messing about, but the first bits you could do in less than ten minutes, and the whole lot in maybe a half hour.
If all else fails there’s always the rear exit. Time for tea.