guitarmanjt Posted May 28, 2011 Share Posted May 28, 2011 I play a Blackstar HT-5H 5-Watt amplifier. It uses one 12AX7 preamp tube and 1 12BH7 power amp tube. It is self-biasing. The first time I replaced the tubes, I did it myself with no problems. However, I have read that tube amps can store electricity somewhere in them, which can possibly be realeased when replacing the tubes, and that wouldn't end well. Do I have anything to worry about when replacing these tubes? Link to comment Share on other sites More sharing options...
Tman5293 Posted May 28, 2011 Share Posted May 28, 2011 Nope. You should be able to just yank em' out. You'll be fine. Just make sure you grab the tubes on the glass part with a paper towel or cloth of some sort. Link to comment Share on other sites More sharing options...
stein Posted May 28, 2011 Share Posted May 28, 2011 It is like plugging into a wall socket: of corse it is safe, but if you happen to do something to touch both prongs, you could technically get zapped. The basic rule is this: the amp CAN store as much electricity in it as it is able to draw from the wall. So, even if you shut it off and unplug it, you could get zapped if you take it apart and go touching things inside that would get you zapped. An amp can also draw current from the wall when it is plugged in even when it is off. Simple rule: you turn off the amp and unplug it to protect the amp from damage. To protect you, you treat the amp as live and plugged in and on regardless of if it is plugged into the wall. Like a gun, if you are sure to never point a gun at anyone, it won't ever shoot someone if you make a mistake and it happens to be loaded. So, changing tubes yourself is fine. A tip: when you first fire up the amp with the new tubes, check to make sure the PLATES of the tubes are not glowing red. Then, regardless of where it is biased or if it needs it, you will not be destroying the tubes, and thus safe for your tubes. Link to comment Share on other sites More sharing options...
2lambchops Posted May 28, 2011 Share Posted May 28, 2011 electricity is stored in the capasitors (the big ones)smaller ones are coupling caps. remember turn off the amp and unplug it.never never mess with it while it is on. you can damage the amp and kill yourself probably at the same time. if you don't have electrical knowledge take it to a tech or learn the knowledge yourself. whatever, just be safe that is the most important thing. Link to comment Share on other sites More sharing options...
guitarmanjt Posted May 28, 2011 Author Share Posted May 28, 2011 @stein: The plates are the two vertical parallel structures right? Link to comment Share on other sites More sharing options...
flyingarmadillo Posted May 28, 2011 Share Posted May 28, 2011 electricity is stored in the capasitors (the big ones)smaller ones are coupling caps. remember turn off the amp and unplug it.never never mess with it while it is on. you can damage the amp and kill yourself probably at the same time. if you don't have electrical knowledge take it to a tech or learn the knowledge yourself. whatever, just be safe that is the most important thing. This is correct and the capacitors are the only place the electricity is stored in an amp. One easy way to make sure they're discharged is to unplug the amp, ground all the prongs on the plug together (copper wire, pennys, aluminum foil...), then turn the switch to the "on" position and leave it sit for about 1/2 hour. It should be safe to work on then. One other rule is never reach in with two hands. Put one hand behind your back, then use the other to remove the tubes. Try not to get fingerprints on the tubes - if they're running hot, fingerprints can create hotspots that make them burn out sooner. Link to comment Share on other sites More sharing options...
guitarmanjt Posted May 28, 2011 Author Share Posted May 28, 2011 So wrap both electrical prongs and the ground prong to tin foil while the amp is unplugged? Link to comment Share on other sites More sharing options...
stein Posted May 28, 2011 Share Posted May 28, 2011 @stein: The plates are the two vertical parallel structures right? Yup. Link to comment Share on other sites More sharing options...
Riverside Posted May 28, 2011 Share Posted May 28, 2011 So wrap both electrical prongs and the ground prong to tin foil while the amp is unplugged? That is nonsense. The caps all live on the other side of the power transformer, and are therefore isolated from the plug. If you want to drain the charge, play a chord and then shut the amp off - as the sound bleeds away, so will (more than likely) the charges stored in caps. If you don't know enough about electricity to keep yourself safe, don't go poking around inside your amp. You're not likely to be zapped by stored charge in a cap while changing the tubes, just so long as you're not touching a combination of pins and/or ground. Link to comment Share on other sites More sharing options...
Andy R Posted May 29, 2011 Share Posted May 29, 2011 That is nonsense. The caps all live on the other side of the power transformer, and are therefore isolated from the plug. If you want to drain the charge, play a chord and then shut the amp off - as the sound bleeds away, so will (more than likely) the charges stored in caps. If you don't know enough about electricity to keep yourself safe, don't go poking around inside your amp. You're not likely to be zapped by stored charge in a cap while changing the tubes, just so long as you're not touching a combination of pins and/or ground. Good advice on being careful and understanding what you need to do to be safe. However, I would forget all of the theoretical ways to discharge the caps ( unplug, stand-by on, stand-by off, stand on your head, wait for chord to bleed away ( no offense) , yadda, yadda) and just discharge them properly. There are too many ways an amp could be wired or mis-wired to trust these techniques... Make a cable with Insulated alligator clips on each end and a 100K 5W resistor ( I know over kill but better than being killed) between the leads ( heat shrinked or taped well so the leads aren't exposed.) I ground one end first to the chassis and then connect to the capacitor lead(s). Some do it the opposite way but I like choosing what I'm going to ground to first instead of grounding out on something accidentally after I have clipped the lead to the cap... and of course check with a volt meter to be sure. Any small voltage can be discharged with the continuity tester on a decent meter.... JMHO Andy Link to comment Share on other sites More sharing options...
Versatile Posted May 29, 2011 Share Posted May 29, 2011 with Insulted alligator clips Andy Try to be sensitive....a croc has feelings too.... V Link to comment Share on other sites More sharing options...
Andy R Posted May 29, 2011 Share Posted May 29, 2011 Try to be sensitive....a croc has feelings too.... V Ha! LMAO good catch. Yes so Insulate the gator clips before insulting them or they may bite you! Link to comment Share on other sites More sharing options...
G McBride Posted May 29, 2011 Share Posted May 29, 2011 I always wear a pair of cotton gloves when changing out tubes just to keep my fingerprints and oil off of the tubes. Changing tubes is similar to changing a light bulb. Even if the power is on, as long as you only touch the glass you will not get shocked if the power is on. Having said that, it is smartest to turn the power off when changing anything out electrical. Link to comment Share on other sites More sharing options...
Riverside Posted May 29, 2011 Share Posted May 29, 2011 Good advice on being careful and understanding what you need to do to be safe. However, I would forget all of the theoretical ways to discharge the caps ( unplug, stand-by on, stand-by off, stand on your head, wait for chord to bleed away ( no offense) , yadda, yadda) and just discharge them properly. There are too many ways an amp could be wired or mis-wired to trust these techniques... Make a cable with Insulated alligator clips on each end and a 100K 5W resistor ( I know over kill but better than being killed) between the leads ( heat shrinked or taped well so the leads aren't exposed.) I ground one end first to the chassis and then connect to the capacitor lead(s). Some do it the opposite way but I like choosing what I'm going to ground to first instead of grounding out on something accidentally after I have clipped the lead to the cap... and of course check with a volt meter to be sure. Any small voltage can be discharged with the continuity tester on a decent meter.... JMHO Andy Agreed 100%, but... we're talking to a guy who's afraid of getting shocked while changing a tube. It's not necessary to go through all that (discharging caps) just for changing a tube. Link to comment Share on other sites More sharing options...
duane v Posted May 29, 2011 Share Posted May 29, 2011 I just don't mess with stuff like that ..... My amps goes to tech every two years for tubes Link to comment Share on other sites More sharing options...
Andy R Posted May 29, 2011 Share Posted May 29, 2011 Agreed 100%, but... we're talking to a guy who's afraid of getting shocked while changing a tube. It's not necessary to go through all that (discharging caps) just for changing a tube. Yeah was thinking the same thing ( and wasn't ragging on your comment) but was too lazy to see if by chance his tubes might have to be accessed by removing or exposing the chassis which then would be a better safe than sorry situation. Also since others read these posts who knows what someone will take as gospel and apply what is said for one situation to a totally different one. I have seen so many arguments over the best way to discharge caps Using the standby etc... that I just say Screw it and make damn sure they are discharged the right way.... IMHO if you are not prepared to discharge a cap properly as you said stay the hell out of it and take it to someone who does. Andy Link to comment Share on other sites More sharing options...
tazzboy Posted May 29, 2011 Share Posted May 29, 2011 If they are EL84 Driven power tubes then you don't need to bias them Link to comment Share on other sites More sharing options...
Andy R Posted May 29, 2011 Share Posted May 29, 2011 If they are EL84 Driven power tubes then you don't need to bias them With much respect Tazzboy, Not to be a know it all, bickering turd but this is not a true statement. The Type of tube on it's own doesn't determined if it needs to be biased it is the amp design and how they have configured the output section of the amplifier to use the tube. All tubes require some form of biasing even Preamp tubes etc... though they are usually biased by the design of the circuit it is in A.K.A as cathode biased. Not arguing that his particular amp may not need to be biased though... Again, respectfully Andy Link to comment Share on other sites More sharing options...
stein Posted May 29, 2011 Share Posted May 29, 2011 I just want to say that everyone is a little right in some way, but just a little wrong can be taken wrong. And a big plus for ANDY for getting down to business and telling us how to do it right and clarifying. My 2 cents: A summery: If you do not touch any internal components, you won't get shocked. If replacing a tube and it sounds good, (of the same type) if it isn't glowing on the plates, you are good to go, regardless of how it is biased. Link to comment Share on other sites More sharing options...
jaxson50 Posted May 29, 2011 Share Posted May 29, 2011 Does anybody else remember when every drug store and department store had a tube testing machine? Shows you just how much things have changed...You just pulled out the tubes out of the TV, radio or amp, took them to the store and checked them yourself, replacements were sold right there. Link to comment Share on other sites More sharing options...
craigh Posted May 30, 2011 Share Posted May 30, 2011 Does anybody else remember when every drug store and department store had a tube testing machine? Shows you just how much things have changed...You just pulled out the tubes out of the TV, radio or amp, took them to the store and checked them yourself, replacements were sold right there. You just pulled the tubes out & got them tested. Didn't bother wearing special gloves etc. Craig Link to comment Share on other sites More sharing options...
milod Posted May 30, 2011 Share Posted May 30, 2011 Jax... I think few folks remember those days. I kept more than a few old radios running in the 1950s and a horrid aged tube type PA system operating the spring of '63 thanks to tube testers and just plain "cleaning the contacts" on tubes. Well, watching for loose wires, too. <grin> Nowadays? Yuh toss out the old if it ain't working, it seems. m Link to comment Share on other sites More sharing options...
dem00n Posted May 30, 2011 Share Posted May 30, 2011 Man, this thread now makes me scared when i have to change my tubes on my amp. Link to comment Share on other sites More sharing options...
Riverside Posted May 30, 2011 Share Posted May 30, 2011 Does anybody else remember when every drug store and department store had a tube testing machine? Shows you just how much things have changed...You just pulled out the tubes out of the TV, radio or amp, took them to the store and checked them yourself, replacements were sold right there. Yep, and there was no such thing as a "matched" set. Link to comment Share on other sites More sharing options...
Andy R Posted May 30, 2011 Share Posted May 30, 2011 Yep, and there was no such thing as a "matched" set. I remember one at our local drug Store back when people were still using tube televisions. Wonder where those all ended up???? Funny you mentioned the matched sets since that is partially the reason for adjusting the Bias to begin with to average the idle settings of tubes that aren't exactly matched... I would much rather work on tube amps than old CRT televisions any day. Used to do board level repair on WYSE 60 dumb terminals and was always getting the piss shocked out of me. Couldn't imagine working on one of the old behemoth tube color televisions... Link to comment Share on other sites More sharing options...
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