So I have an Ampeg 50h Reverbrocket halfstack (my first tube amp) and last night I finally had an issue with it. I should first mention that we were having problems with breakers popping in our practice space in case that has something to do with it.
Anyway, I was playing like usual and I hit the channel switch. When I did the amp just stopped making noise. I first bypassed all of my pedals and plugged my guitar directly into the amp. I was able to hear my guitar very faintly but when switching channels the sound did not change. Then I tried powering the amp down and back up, this didn't help. I even tried plugging it into another socket without any luck.
I'm guessing there is a tube or a fuse out, I hope. The two large tubes that glow (the power tubes?) seem to be working, at least by looking at them, of course I know almost nothing about these things. Any ideas?
I can provide pictures of the back of the amp if needed.
The problem could be any number of things. It's really hard to say in a situation like this. However, I would bet the fuse is good, since generally when they go out, the amp will no longer turn on. About the only user serviceable part of any tube amp outside of the fuse are the tubes. So if you have some extra tubes lying around, you could switch your tubes and see if everything comes back. If you don't have any tubes lying around, I might pick up a couple of preamp tubes and swap them out to test them. Preamp tubes are cheap enough and simple to swap out. If that doesn't fix anything, then I'd take it to a tech. It may be a power tube, in which case you'd want a tech to replace them so he/she could properly bias them when he/she installs them, or it may be something else. And if it's something else, then that could take a very long time, cost a good bit of money, and put your personal safety at risk if you don't know what you're doing. So you'd be better off on all points by taking it to someone who does.
You might want to double check with by looking at the preamp tubes that are already inside it, but from what research I've done, it appears as though it just uses 12ax7 preamp tubes. So really any 12ax7 or equivalent should work fine. They are the most common type and should be easy to find.
You could also switch out the larger 6L6's, and they would work without re-biasing them, but if you don't re-bias them and they wound up running "hot" you could significantly shorten their lifespan. However, if you're just going to run them for a few minutes to test things out, it shouldn't hurt anything. Besides, it only takes a good tech a few minutes and a few dollars to bias an amp.
Thanks for all the help man, I ended up getting some tubes from Guitar Center (Mesa 12ax7). The amp sales guy told me he thought it sounded like the fuse. He said it could still turn on with a blown fuse. So I think I'm going to pick up a fuse too, but I'm not sure what kind it takes. I emailed Ampeg's support dept. and they're going to send me a schematic (which i'm not good at reading). The product manual for that model doesn't tell me anything about the fuse, so hopefully I'll figure it out. I'd much rather try replacing that before screwing around with the tubes.
Oh ya one more thing, how likely am I too shock and kill myself changing those tubes? The guy at GC said to just turn it off with the standby on for a while and then unplug it in order to drain the filter cap, but I've read that there are different ways to accomplish this for different types of amps. I'm kinda in the dark on that part, but i certainly don't want to die doing something as insignificant as this.
Last edited by VozDef; 6th February 2013 at 06:24 PM..
The fuse should be easy to check. You can just pull it out and look at it. They're glass tubes with a little metal filament that connects the two metallic ends. If the filament in between them is broken, i.e. it doesn't make a connection between the two ends, then it's blown. Otherwise it should be good. Usually near the fuse will be some kind of indication of what kind it is. Most amps use slow blow fuses, which basically means they take a second or so to blow, because some amps will blow a fast blow fuse when you turn them on, even if nothing is wrong. Some amps don't require the slow blow fuse. At any rate, the rating should also be on the metal part of the fuse itself. They'll say something like 3A, which means 3 amps. Still, if the power tubes light up, then I'd still think the fuse is good. But it's an easy problem to spot with the naked eye, and a cheap and easy fix, if that is the problem.
I don't know about the Guitar Center guy. I've worked at a GC before, and I have to say, some people know what they're talking about, and others there don't. But they all seem to be confident in whatever they say, regardless of what they actually know. At any rate, his method for draining the filter caps isn't a good one. At least not one I'd trust with my life. But I wouldn't worry about that. You won't get shocked replacing tubes. The only time I'd worry about getting shocked by the filter caps is if you had the actual chassis open and were touching the circuit. With the tubes themselves, you just be touching the glass while installing them, and glass is an insulator that won't conduct current, so you'll be safe. Even those large transformers on the outside of the amp are safe to touch, though back when I didn't know much about circuits, I was pretty afraid of them.
It still sounds to me most likely to be a tube problem, but you never know. After swapping out the preamp tubes, if that doesn't work, then my money would be on the power tubes, which are probably the most likely problem. They have the shortest lifespan of all the tubes. But like I said, you'll want to have them biased, so I'd take it to a tech and just ask him/her to fix the problem, whatever it is. A good tech should be able to fix it without too much trouble.
Thanks again for the info. I'm familiar with what a fuse is from working on cars and other things, i just don't know what type (like you said 3a, etc). Is there any kind of standard? Really, I just don't want to drive out there, check the fuse, find out its bad and have to drive back another 20 miles to Radio Shack. I was hoping to stop there after working and pickup a fuse (I'm an impatient a$$hole). I suppose I could buy an assortment.
The power tubes definitely glow and appear to be working as they always have, but of course there's a good chance I wouldnt notice something. I agree with you on the knowledge of GC reps. There are a lot of guys there i've heard say things that I know are incorrect, but I don't know much about tube amps. The guy I talked to was in his late 40's so I figured he would know, but it's hard to tell. Thanks again for the info, i feel better about changing those tubes now.
Last edited by VozDef; 6th February 2013 at 08:33 PM..
It looks like it uses a 100 Volt T2A fuse. Which means you'll want a slow blow 2 amp fuse that's rated at at least 100 volts. You may have trouble finding 100 volt fuses, but a 250V fuse should be easier to find, and will work just as well. As long as the voltage rating is equal to or higher than the original, it will be fine. It's the amperage rating that you want to get exact.
Well, I changed the preamp tubes. The good news is that it was really easy, the bad news is it didnt fix the problem. There's a somewhat large circular plastic cap on the back of the unit where i thought the fuse might be but it's not. So, I have no idea where the fuse is and Im a bit wary of taking my amp apart too much. It looks liked I might just end up taking it somewhere. Thanks for all your help, I appreciate it.
No problem. Sorry it didn't work out. It probably is a power tube, but like I said before, who knows? A tech would, I guess. The good news is preamp tubes will last for decades if you store them away in a safe and dry place, and the ones you are using will wear out eventually, so it's not really money lost. Just money displaced.
If you had an issue where the channel switching did not change the sound and that it was low in level - as I understood you stating -there is an IC that they use to make the switching, and I would be willing to bet that that's the culprit. It is usually an opamp arrangement to minimize pop noises during channel switching, if this goes, you'll get weak or no signal feeding the rest of the amp. Peaveys used to be notorious for that , Crate/Ampeg use very similar designs.
That makes sense, Moonbaby. Right now I get a very low signal that cam barely be heard through the speakers. I dont really understand some of the terminology your using though. It doesnt sound like something I can fix.