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if i am just removing power tubes and replacing fuses that have blown, turning it on to see if the fuses blow again without the power tubes to troubleshoot rectifier tube, to see whether it power tube or rectifier, then i will not be exposed to the area that could possibly have the high voltage store charge in the caps/plates right? i have a 2008 vox ac30cch reissue so it brand new equipment. thank you for any help. im trying to save money here and replace the tube myself.
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If you don't take out the chassis then the only way you could get a HT shock is poking something metal into the tube pin holes. So steer clear of that course of action and you'll be fine! -
Oh the AC30cc - well yes you will have opened it up far enough to have some HT on display, you will need to avoid all the circuitry areas, but leave it on the wooden tray thing and don't touch anything apart from the chassis top, ie where the tubes plug in. Btw the wooden tray has four screws underneath that hold it in.Comment
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im not at the amp im at work so i cant look at it but if i remember correctly when the back panel is pulled the circuitry is right there so i think i have to go through that to get to the tubes. im by no means an electrician but there is metal all over the place on this thing. ive posted on so many sites and i get so many varying answers. how do i make sure the high voltage is discharged? leave standby on even with it unplugged for a while and it will drain to safe levels, heard that one. also use some kind of jumper cable ground to chassis and resistor on other end touch the caps, heard that one. then i gotta check it with a multimeter which the one i got the probes dont clamp so id be using 2 hands. so i dunno if this is possible for me, but im tryin to save money too. i appreciate your help. i wish there was a walk through for this that said exactly what to do for this particular amp. i know people change their own tubes all the time with no problem but there is so much voltage that could be lurking around in there i dont see how more people arent injured by this. how can i drain/safely discharge the high voltage before working on it? or am i not even gonna be near that pulling tubes?Comment
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To be honest I am concerned that your knowledge level is not high enough for your safety here. All the things you have heard are true to an extent, but it isn't within anyone's knowledge to say whether or not the caps have discharged after any given period of time without checking the voltage on them, and that means knowing where it is. The problem with the AC30cc is that you have to take off the back panel and expose the preamp circuitry, which has HT at a number of points, before you can get the chassis out and get at the tubes.Comment
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Just leave the Amp off over night with the AC plug pulled and the HV is surely drained (bleeder resistors on the caps). Regarding the blowing fuse: I would recommend to pull all tubes and then check if the fuse blews again, if yes something in your power supply is smoked => get it to a Tech. If not seat one tube after another and test with power on , as soon as the fuse popps you got the bad one....I can fix everything, where is the duct tape?Comment
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I wasn't aware that the AC30cc had bleeder resistors on the caps. Does it?Comment
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Could you point them out on this schematic?
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so the bleeder resistors help drain the high voltage to safe levels everywhere in the amp circuitry so i can work on it my beginner electrician self?Comment
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I don't see any bleeder resistors in there, that was my point, I don't know what the guy was referring to but there is nothing in there that's meant to discharge the caps. You cannot rely on there being no voltage left after any given period of time. And every time you turn it on they charge right up again, so what were you supposed to do, discharge it every night and add one tube a day? Yes it probably will discharge overnight but also it might well not!
Look, it's not that hard not to get electrocuted so long as you can tell the difference between a circuit board, wires, components etc, and the other side of the amp chassis where the tubes stick out. Don't touch any of the printed circuit boards, wires, components etc. Just the tubes. Then you can't get a shock. Burned fingers maybe, but that won't kill you.
I will give you the step by step guide you asked for. Your widow may wish to note my last paragraph
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If you take all the screws out of the top back panel and lift it off you will see a lot of the stuff you shouldn't touch in there. If you go underneath the wooden shelf that the amp chassis sits on, same side as the speakers, you will find two screws either side, right hard up against the sides of the cab. Unscrew them once you are sure you're not confusing them with the six other screws that hold the amp chassis to the shelf. Don't push up too hard on the screws once they are loosened or you will pop out the claw nuts, just go carefully with them. Once they are out you will be able to pull the chassis towards you using the wooden shelf, like a drawer. Don't unplug anything from under it, you probably will be able to get at the tubes without doing so, but be careful not to strain anything trying. Pull it out gently. Not too far or it will drop on the floor and scare the bejesus out of you. Then you will see the tubes. The four tall thin ones are the power tubes, and the fattest one the rectifier. These are your suspects. Take them all out and try them one at a time, turning the amp off at the wall whenever you touch it, and on again to see if the fuse pops. It will be ok to add them one at a time, just don't leave the amp on too long each time after you see the fuse doesn't pop, as it just strains the power tubes a wee bit until all four are in there, it will run as hot as hell with just one tube in, not so bad as you add more, just leave it on for long enough to see the amp warms up and you can hear the extra hum you get when not all the tubes are in, then off at the wall again and add another tube.
You seem to lack confidence. If the above still leaves you feeling at all unsure then don't go there, take it to a tech instead. This will ensure that you stay unshocked, and that you don't make the problem more expensive whilst trying to do it cheaply.Last edited by Alex R; 12-22-2010, 07:45 PM.Comment
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yeh i appreciate your knowledge and help man, ive decided to take it to my amp tech this time and have him show me what he does with this particular amp, then i can change the tubes form now on. i really appreciate your help.Comment
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Cool, let us know how it goes.Comment
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