A "can I service my own amp?" fact thread

[WhippingPost]

I didn't see it brought up, but I've seen it in the past:

Chopsticks are your friend. Order some Chinese, get chopsticks, and use those to poke around in the amp without putting your fingers in harms' way.

 

[LPV]

I didn't see it brought up, but I've seen it in the past:

Chopsticks are your friend. Order some Chinese, get chopsticks, and use those to poke around in the amp without putting your fingers in harms' way.

Yes! Excellent! Every now and then when I'm in Thai Express I grab another pair of amp tools.

 

[johan.b]

Left hand in your pocket, no watch or bracelett, long sleeves...
elbow touching ht supply feels like someone is breaking you arm with a baseball bat. I know...
if unsertain, swallow your pride and ask someone. No one knows everything...
j

 

[martin H]

A couple of hand me down tricks:

1- pretend you only have one arm. When checking voltages or anything else when voltage may be present, put one hand behind your back. With voltage - NEVER place one hand on the chassis while the other is in a working position. If you accidentally touch something while your other hand is on the chassis - the shortest path to ground is straight across your heart. Very bad.

.

+1 on this. Excellent advice. I was taught the same technique when I worked for the phone company many years ago. I was also taught that, even if you are TOTALLY SURE that everything is powered down and discharged, it's still a good idea to touch a chassis or component with the back of your finger first.

If something has gone very wrong and the component is live, your finger muscles will naturally tense and pull away from the component. If you do it the other way the finger may tense and grab the live source you are touching.

 

[Marshall & Moonshine]

Death from this shock is a risk, but not a surety, by any means. It's a DC voltage of about 400vdc applied across an average resistance of dry human skin being in the 50k-100k range, give or take.
My electrical instructor (ex-Master Chief Navy Electrician) said it takes 0.01A across the heart for 1 second to kill you.
You'll likely learn a lesson you won't forget, but I don't think death is the odds-on favorite.
Bear in mind that that's Ohm's Law and Navy instruction, not ol' M&M's usual kooky stuff.
That having been said....
Drain the caps, and always check it for dead immediately before touching anything. If you're doing work on a live circuit, don't touch anything without using your meter to ground, first.
If you get the zappy stuff on you, you'll feel like a fool, once it stops hurting.

 

[kevinpaul]

The one hand in the pocket rule is very important. Never put two hands in your amp, you will complete the the path of the electric path right through your heart. Know what you are looking for and get out. Tube bias or tube change are easy jobs that you can do and save some money. The big caps that should be changed as a part of servicing you amp is not hard. Read up on it first. Always work with one hand until you discharged the amp to make it safe to work on.

 

[LPV]

If you're doing work on a live circuit, don't touch anything without using your meter to ground, first.
If you get the zappy stuff on you, you'll feel like a fool, once it stops hurting.

Working on a live amp is whole other can of worms.

A little trick I use to adjust Marshall type internal bias pots in absence of a plastic screwdriver is take a rubber handled screwdriver and electrical tape spirally with a couple of layers all the way from the handle (including the bottom of the handle) to the very tip so only a small 1/8" of the metal is exposed. This will help avoid accidental contact.

 

[Soul Tramp]

I got zapped twice last night. As M&M says, it bites but I survived to tell the tale.

I try to be careful, but get careless in my haste. It's easy to do when prototyping and experimenting with circuits. I'll have an amp connected to an o-scope and will be watching the affect of various changes. Doing so, I'm constantly turning the amp on & off to make adjustments. I hate to say it but I often solder on an amp that's still plugged in.

One time while doing this I dropped my scope probe across the A/C primaries and fried the scope. That was an expensive mistake.

It would be impossible for me to work on amps while sitting on one hand. I spend countless hours inside live amps with scope and DVM probes. You just have to be careful.

 

[Gary]

Working on a live amp is whole other can of worms.

A little trick I use to adjust Marshall type internal bias pots in absence of a plastic screwdriver is take a rubber handled screwdriver and electrical tape spirally with a couple of layers all the way from the handle (including the bottom of the handle) to the very tip so only a small 1/8" of the metal is exposed. This will help avoid accidental contact.

I do something similar. I put shrink tubing on the metal screwdriver shaft and shrink it down.

Also, never use a pencil to poke around inside a hot tube amp chassis. The graphite in the pencil will conduct at high voltage.

 

[LPV]

I got zapped twice last night.

Glad you're still with us!

 

[johan.b]

I got zapped twice last night. As M&M says, it bites but I survived to tell the tale.
.

Asking a tech if he ever got zapped is like asking a diver about peeing in the wetsuit....some say they do, others lie about it...
sometimes it's friday afternoon. You're just gonna flip that chassis over, slide it into the headbox and write the invoice, then it's time for beers and bbq.....and the side of your pinky tells you, in not so many words, that you forgot to unplugg the power cord...
j