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  1. #1

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    I assume changing out tubes and speakers is safe (and I've done both) but I've never seen it in writing: what is safe for regular people to touch and not touch for amp maintenance?

    I've seen the Rob Robinette page but there's a lot of info there. I just need to know: tubes, speakers... OK right? I don't have to discharge an unplugged amp to change that stuff, correct?

    Sincerely,
    A regular person

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  3. #2

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    For tubes and speakers: "Unplug the amp from the wall!"

    Anything "inside" the amp will require more knowledge or an actual tech! I don't touch that stuff!

  4. #3

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    Capacitors hold an electrical charge. That's what they're designed to do. Depending on the capacitor, discharging one through your fingers can be painful. They don't hold a charge forever, though, and begin to self-discharge when power is removed. Don't touch the caps soon after unplugging, and you should have no problems. To be pedantic, you can touch the caps, but not the leads connecting them to the circuit. Mostly, it's best not to touch any bare wires at all until several minutes after the amp is unplugged. But no matter what, if you don't know what you're doing, unplug the amp. I've worked on all sorts of devices, mostly tube stuff, while they were on and running, but I had some idea of what I was doing, or I wouldn't have been working in the repair shop. You don't sound as if you have a thorough knowledge of circuits, though, so I definitely advise unplugging the amp. Did I mention that you should unplug the amp?

  5. #4

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    Many modern amps have a resistor designed to discharge capacitors, but most vintage designs don't, and capacitors can hold their charge for days. A charge that can in theory kill you. But they are usually out of reach and covered.

    Tubes and speakers are safe to change, as long as the amp is unplugged. Make sure tubes are not still hot though!

  6. #5

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    Quote Originally Posted by tomems
    I assume changing out tubes and speakers is safe (and I've done both) but I've never seen it in writing: what is safe for regular people to touch and not touch for amp maintenance?
    Tube and speaker changes are safe to change.

    Note that if you have a pre-1970’s amp with a two prong plug it should be replaced with a grounded cord. Otherwise, a single failure in the chassis could put voltage to your guitar strings. Grounding the chassis prevents that.

  7. #6

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    I always wondered, can you discharge the amp by playing after turning it off until it goes quiet?

    My guess is that the guitar signals would activate the stored charge to flow, but the tube heaters may not be powered by the capitors so the tubes can stop functioning before the capacitors are emptied. Is that right?

  8. #7

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    Quote Originally Posted by Tal_175
    I always wondered, can you discharge the amp by playing after turning it off until it goes quiet?

    My guess is that the guitar signals would activate the stored charge to flow, but the tube heaters may not be powered by the capitors so the tubes can stop functioning before the capacitors are emptied. Is that right?
    I think that’s true, but I wouldn’t count on it. It’s easy to check voltages on the big electrolytics before touching anything, so why take a chance?

  9. #8

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    The caps in the power supply will maintain their charge once the amps off, yes. In order for them to discharge while you played (with the amp off) they would need to see variations in voltage In the circuit they supply but they won’t cause the amp has no power. The very small voltage/current coming from the pickups won’t be enough.

    Caps are kind of like expansion tanks. They hold their charge but if the voltage drops in the circuit they’re part of they will discharge to bring the voltage back to “normal”. In a tube power supply, they smooth out the AC ripple left in the DC after rectification, and smooth out the variations in the amp circuit power as the amp works on feeding the speaker.

    remember pro technician training: one hand always behind your back or in a pocket when dealing with voltage or current that can get you. I’ve seen people say the low current in a tube amp won’t kill. That’s really not true, if bridged from one hand to the other across your chest, and it gets your heart at the right blip. Byes! (I have a permanent shoulder tic from a 850Vt RF radio amplifier power supply cap.)

    Heres some reading: https://www.illinoiscapacitor.com/pd.../filtering.pdf

  10. #9

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    This just made me think of Les Paul and just exactly what he may have been doing when he had that ' come to Jesus' moment...: )

  11. #10

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    My “Come to Jesus” moment was with one of these beasts, with about 500 volts on top of the tube.

    Fortunately those type of tube connectors are only needed for radio frequencies.

  12. #11

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    KirkP
    BC-459?
    Nothing like discharging a 850vt cap in an RF transmitter power supply to spark up your day.
    Once was enough (AN/ARC 4)
    dave
    KC2XU

  13. #12

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    This thread reminds me of when I had a student who was a great kid who wanted to be an electrician, and he used to help me out by fixing amps that went down in the music dept.
    He was working on an old PV in my office, when all of a sudden it made a sound like it just blew up, and there was flash of light.
    The kid looked like he was in a daze. I asked him, "Are you alright?!"
    He said he lost all feeling in his right hand.
    I saw the amp was still plugged in, but not turned on, and I yanked the cord out of the socket.
    I told him never to work on an amp with the amp plugged in. He said the amp wasn't on, but I told him it doesn't matter.
    Thank God, his hand was okay after a few minutes, but that was the last time I let him work on anything again.

  14. #13

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    For anyone who wild like some really excellent training on electronics search the web for NEET. Its the US Navy electronics course. You might skip the radar, but its basic intro, amp, tube, test equipment, and troubleshooting chapters are as good as can be.
    d

  15. #14

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    One thing I've never been tempted enough to do is work on my amps unless it's something simple like changing out a bad cord.
    It's not rocket science but one slip or lapse of judgement and you can be six down and 3 across.
    I'll stick to guitar setups, hard to kill yourself doing those.

  16. #15

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    It's not the voltage that kills you, it's the current. I've been hit by >25,000 volts from discharging a color CRT tube, but there wasn't much current. It hurt, but I survived. I've been bitten by CRTs many times, and it usually hurt because my hand was inside the TV cabinet, and I involuntarily jerked at the shock, and slammed my hand or wrist into something sharp. The worst thing that could happen with a CRT is picking it up, getting shocked, and dropping it. The resulting implosion scattered small glass shards and all sorts of toxic stuff all over the room.

  17. #16

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    A 'regular person' might want an amp tech to do those things. For example, how do you know your tubes are bad? How do you know which one needs to be changed?

    In terms of the speaker a 'regular person' would need to know if it is front mounted, rear mounted, mounted on studs or blind nuts, impedance matching, polarity, wattage and efficiency to do the job. A field-coil speaker can shock you good!

  18. #17

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    Sorta like Covid. You can argue politics but in the end it’s a virus that can kill you.

    Electronics is the same, you can argue all you want, but if you don’t have the training and experience it will do you in.

    25kv at low current can kill, depends on the current path in your body. So let’s not go telling people with no training it’s a safe thing to do. Cause a professional tech would never advise that.

    in the late 50’s we had a Sylvania TV that the tube imploded. After the family went to bed. Lucky for that or we’d been a family full of tiny glass shards.

  19. #18

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    I didn't say that 25KV is safe, necessarily. But it is the current, not the voltage. 110VAC, with the current a household outlet can supply, will certainly kill you. Even less voltage than that can be fatal. It depends on the current delivered. Direct current is as deadly as alternating current, and there was a big argument about that back when electricity was first beginning to be used in homes and businesses. Edison's DC transmission scheme ultimately went bust after being used for executions. The voltage losses over distance had something to do with it, TBF, but both human and animal electrocutions were involved in the current wars. Electricity can certainly kill you, given enough current, whatever the voltage. I'm very careful when handling a car battery. Those can produce enough current, under the right conditions.

  20. #19

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    All true.
    i have always been concerned on guitar forums that people without training and experience don’t get the wrong impression, and then take a careless attitude. Sorry if I was overbearing on that. Just a matter of always stressing the safety basics.

  21. #20

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    A word to the wise: As an unknowing youngster I took my Dad's old steel electric drill into the garage to try something. On my feet in the garage. I received the shock of my life, lasted quite a bit, frozen for a while, lucky to be alive today. Don't fool around with alt cur.

  22. #21

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    Listen to Woody Sound.
    I got the shock of my life in a Photo Studio. I was shooting a beautiful model when I backed up into a steel pole, a camera in hand hooked up to a studio strobe light. Well, we used studio strobes forever but on that day - a loose wire inside a strobe head (who would have ever suspected that?) (you can't see inside them) You get the idea.

    Don't ever assume. Don't assume everything is up to snuff. Shit happens. Read up. Take pre-cautions. Expect that something can go wrong. And don't take loose internet advice as gospel - Please.

    Tubes - if they don't shock you (they probably won't) but they can harm the amp if not dealt with properly. What is proper? Read up.

    Speakers - Easier. But unplug the amp, and make sure polarity and connectivity are secured.

    And have a good time learning all this stuff!

  23. #22

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    This is one of those things where following a list of safety practices and procedures is not enough to prevent mishaps, injury, and death. One has to actually understand some things, and there is a wide range of that with a dangerous low information end.

    - Some amps use a built-in bleeder on the power supply caps so they discharge to ground soon after power off, but others don't and hold charge for a long time, so neither may be trusted and must be discharged manually

    - Sometimes people know just enough to be dangerous; like attempting to retention the pin socket connectors during a tube change without knowing that the power supply goes to some of them

    - I bought one of my amps from a fellow who was selling it as broken, as is, because he had attempted to "unscrew" the power tubes and had broken off the pins

  24. #23

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    Quote Originally Posted by jazzkritter
    KirkP
    BC-459?
    Nothing like discharging a 850vt cap in an RF transmitter power supply to spark up your day.
    Once was enough (AN/ARC 4)
    dave
    KC2XU
    I wondered if someone might recognize it. When I was a kid my dad gave me a box of somewhat random electrical parts and an Amateur Radio Handbook, which had an article about converting Navy surplus transmitters for amateur radio use. So I found one at the local surplus store and after building a power supply for it ended up spending a lot of late nights making contacts across the country on CW (Morse Code) in the 40M band. The solar cycle was near its peak, which made long distances pretty easy to reach. I’m still proud that I passed the Advanced Class exam. (Unfortunately I let it lapse for a couple of decades, so I can’t get that back.) I got interested in guitar around the same time, and eventually folk, blues and country rock took over my spare time. I still have fond memories of those days though.
    - Kirk KI7TAY

    (Sorry for taking this off topic folks!)
    Last edited by KirkP; 10-14-2020 at 10:33 PM.

  25. #24
    Im no expert by any means but I really improved the sound of a Peavey Delta Blues by finding some vintage RCA,Mullard, and Telefunken preamp tubes. Amp companies voice some amps for breaking up overdrive at low threshold because some consumers like rockers and blues guys like that sound. Jazz players often want more Headroom whichmeans cleaner sound wo breakup at higher volume. I was well pleased at how around 100$ improved my amp including power tubes. The more knowledgeable members can tell you about V1 etc V2 etc. One thing I wanted to share with people who use 2 channel Fender amps with Reverb I juat learned is to run my AB box into both channels at once and get a fuller sound because the no reverb or vibrato channel has a fuller sound but I am used to Reverb all my life so now I like both channels on at the same time.

  26. #25

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    Quote Originally Posted by steve burchfield
    One thing I wanted to share with people who use 2 channel Fender amps with Reverb I juat learned is to run my AB box into both channels at once and get a fuller sound because the no reverb or vibrato channel has a fuller sound but I am used to Reverb all my life so now I like both channels on at the same time.
    On most (or maybe all) two channel Fender amps with reverb, the two channels are out of phase with each other, so mixing them subtracts the two signals instead of adding. If all the gains and Eq settings were the identical on both channels they’d totally null each other out! It does give you more options for tone sculpting (and complications!), but it doesn’t give you more gain. You didn’t make that claim, but others sometimes do.

  27. #26

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    New solar cycle just starting up.

  28. #27

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    Quote Originally Posted by rabbit
    New solar cycle just starting up.
    Now we’ve just gotta pray a solar flare doesn’t wipe out every semiconductor on earth and put us back in the iron age. ;-)
    https://www.nasa.gov/press-release/s...hat-that-means

  29. #28

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    If it does flare up, our tube amps will still be good to go! Right???? Just kidding.