Amp Safety

[Clearspider]

I'm not one to find out firsthand of the ACTUAL consequences of mistakenly working on a live amp, but...
Has anyone actually known or heard of anyone that was hurt, maimed, killed even by working on an amp that was not properly bled. I don't mean to diminish the importance of correct procedures, however I just want to know if the threat is real or implied in direct relationship to the possibility of such outcomes.

[teleamp]

The danger is very real, some may get zapped and be OK, but its kinda like Russian roullette, you never know which zap will be your last.

It is very easy to properly drain the caps. Much better to be safe than dead.


Mike

[waveman]

I'm sure there are some old TV repairmen that can tell you some stories, but don't freakin' risk it. That is the #1 thing they taught us when was in high school electronic vocational class. Those caps hold some dangerous amounts of electricity

[WaltC]

It's real. Trust me <G>. If you'd like stories I'll share a few but sufice it to say that it can cause long term muscle pain, loss of use of a hand or arm for varying time periods and even cardiac arrest in some cases (especially for those who insist on working with *both* hands on the amp at the same time).

One of the most significant issues with tube amps is the difference between AC and DC current. AC will knock you across the room, cause your muscles to spasm closed and open, but DC has the tendency to cause muscles to contract and stay, which can easily make you hold on to whatever is shocking the s**t out of you until the source of the current is gone.

Which is why I only work on the B+ rail with a shorting resistor to ground connected *while* I work to prevent shock and keep the caps from recharging themselves even without being powered up (which they *will* do to one degree or another).

The danger is definitely not Old Wives Tale stuff, but real and present.

FWIW

[John Phillips]

It's real... trust me too.

I learnt it the hard way with one of the first tube amps I ever worked on (50W Marshall, one of the dangerous ones with no divider resistors on the filter caps). Up until then I was fairly experienced working on solid-state electronics, and thought that if something was turned off and unplugged from the wall, it was safe (which it is, more or less, with solid-state since the voltages in the power supply are quite low - it's only the AC supply you need to worry about).

Wrong. Unexpectedly and very painfully so.

I checked the voltage on the thing that did it - a resistor on the board which is directly connected to one of the caps, if I remember - and was horrified to find over 200V there after some of it had already discharged itself through my arm. Took me a while to work out why...

I've had several other shocks since then too (as most if not all techs have) - I wouldn't say it's absolutely unavoidable, but if you work on enough amps it probably will happen - there's no way of avoiding working on live amps for many jobs. I'm still alive and not suffering any long-term effects, because they've all been minor 'contact' shocks, not anything involving major current for any length of time. Simple good working practices - especially to never hold the chassis with one hand while poking about inside with anything in the other hand - will reduce the risk, but it's still best to be as careful as you can be. It really hurts, anyway.

[Fuchsaudio]

Let us remember my experience with 6550's in an Engl: One power tube was installed incorrectly (due to a broken keyway), and when I reached in to remove it (since it wasn't lighting), was sent on my a$$ by about 500-Volts. This happened while working ABOVE a live chassis, with no "exposed" high voltages. Absolutely no reflection on the Engl, but it shows you a) someone experienced still can get zapped and b) there's no way to know everything is " completely safe", in some cases.

[dbx]

...would wearing latex/leather gloves and using insulated tools help? I know it would block some of the feeling in your fingers ;) but would that give some protection from shock?

[brad347]

...would wearing latex/leather gloves and using insulated tools help? I know it would block some of the feeling in your fingers ;) but would that give some protection from shock?

I once asked this question. Apparently the answer is "no."

You can still get shocked.

[nateG.]

I did something similar when I was 14 and stupid. Actually I'm not much older, so I guess I'm still stupid. Anyway, I had a little Marshall solid state combo with a reverb pan inside the chassis. (It was about 6 inches long, with no shielded cables, inside a chassis!!) Since reverb crashes sound cool, I decided to take the chassis out, and flick the reverb springs while playing guitar. Stupidest thing I ever did. I slipped and took 120 volts, and let me tell you, it sucked. Ever since then I've been super anal about checking for stored voltage, and attaching my own bleeder resistor to keep it from recharging. I don't want to think about getting hit with 500+ volts.

[brad347]

i guess i've been really, really lucky.

The only time I've ever gotten shocked was from the stored voltage in a little Vibro Champ that had been off for a couple of days that I didn't discharge the caps (stupid...) because I was "just gonna do one little thing."

Ha. It wasn't too bad... but it was only a champ and had been off for awhile.

I've been more careful since then but I've also been inside a few amps and fortunately, nothing bad yet...

[Clearspider]

My first amp was a Gorilla. I reached in the back for something I don't remember. My finger touched something and started vibrating but it stuck to the thing for a couple seconds. When I realized what was happening I took my finger out of the thing. Weird. I called it the Vibe-rilla after that.

[trdlasvegas]

I got zapped last year from one of those 400 Watt +700 Volt new Hiwatt's. It made me jump back about 4 feet and burned a small mark on the tip of my finger. I've been shocked quite a few times but that's the first time I ever saw a burn mark on my skin.

I always use whatever resistor I find lying on the bench to discharge the B+, but I'm think maybe I should make a actual discharge resistor with a florescent orange clip lead. This way when it's clipped in you know the amp is safe, and due to the color you can't forget to remove it before powering it up.

-Tony

[rockon1]

...would wearing latex/leather gloves and using insulated tools help? I know it would block some of the feeling in your fingers ;) but would that give some protection from shock?


One would think they would help somewhat at least?:confused:

[John Phillips]

Yes, they do help to some degree - but the problem is that they then can make you less careful, and they're NOT guaranteed to protect you at the sort of voltages inside a typical tube amp. You must NOT rely on them as a substitute for knowing what you're doing and good working practices.

I do wear gloves often - actually because I'm allergic to some of the chemicals typically used in older amps - but I try not to become complacent about the electrical dangers.

Actually, the biggest benefit is that you're much less likely to burn yourself on your soldering iron :).