dead AD15?!?

Ian Caruth · Post by **Ian Caruth** » Mon Dec 01, 2003 8:31 pm

My much-loved AD15 has appeared to die on me! My amp won't turn on; it's plugged in, but when I flip the power switch, the jewel doesn't light up. No sound comes from the speakers. Looking through the back, it looks like the GZ34 rectifier glows a little bit, but the other tubes don't detectably glow.

Could there be a fuse blown? How would I replace that? Might the tubes be bad? I email [email protected] eight days ago but I haven't heard back from them. Has anyone had a similar problem? Did they have similarly frustrating experiences with Orange's product support?

grgurich · Post by **grgurich** » Wed Dec 10, 2003 2:24 pm

Sooner, I am an electronics novice. Would you please explain how there can be voltage inside an amp after it's unplugged? Seriously. Thanks.

JG

Post by **bclaire** » Wed Dec 10, 2003 10:26 pm

You won't die from the electrical shock but when every muscle in your body stiffens and throws you across the room, you might get injured on what you land on...

Keep one hand behind your back and don't touch anything attached to big round metal cans... if you're just reattaching a connector you should be fine- I pull amps apart all of the time and I've never (knock on wood/ touch wood) gotten a shock... Billy

tluxtele · Post by **tluxtele** » Sat Jan 24, 2004 5:03 pm

boy. i hate to be someone who comes in a just disagrees but i think there is some very bad advice in this thread. out of your wall socket (assuming you live in the u.s.) you have 120v. as a kid i stuck a hair barret in a socket and was thrown accross the run, hand turned black, passed out, and shook for about 10-15min. i servived but do i want to do it again? no. do i want to tell someone that they can do it and not die? no. have peopled died from doing what i did? yes. you can die from the voltage stored in the caps. that's what caps do is store voltage. you have 120v coming out of your wall but you can have up to 400v stored in your amp. do you want to take that chance? there is a very safe way to drain the voltage if you're going to work on an amp. get a wire that has insulated alligator clips on each end. get a 10k - 250k 5w resistor. cut the wire in half. solder the resistor leads to the ends of the wire. your wire should now go
insulated alligator clip - wire - 5w resistor - wire - insulated alligator clip
attach one alligator clip the plate of the first gain stage (that would be pin 1 of the 1st 12ax7) while being careful not to have the other alligator clip touching you. after the first one is secure on the plate, attach the other alligator clip to the chassis. go drink a soda or eat a sandwitch or something for a few minutes. come back and check it with a meter. you should have no (or very little) voltage stored in the caps. the amp is now safe to work on. but, if you don't know what you're doing, it's better to take it to someone that does.

clean as a whistle

Post by **bclaire** » Wed Feb 04, 2004 6:54 pm

If you are careful and avoid the filter caps and their connecting wires you will be fine. I have worked on basic troubleshooting of amps for over 25 years and have NEVER been shocked. I am very careful but a loose spade connector isn't going to hurt anyone as long as you don't go touching other stuff...

fiveightandten · Post by **fiveightandten** » Mon Feb 09, 2004 4:53 am

Just to interject a bit more safety advice in here...

If you're working on a PCB amp with charged filter caps, you can't ever assume than what you're touching will be safe.

The AD30 has all the tube sockets mounted on the board. You can catch a jolt from touching anything that's connected to the filter caps, voltage divider resistors, plate resistors, pins 1 and 6 on the pre-tubes, pin 7 and 9 on the power tubes, the HT fuse, or the output transformer secondary junctions. That's a LOT of traces to stay away from on the PCB.

Let the amp sit for an hour or so before you open it up. And if you have to touch anything, do so with insulated plyers. If you need to use your hands, and you have any reason to believe you may get hurt, take a screwdriver and drain the can caps (positive end), hold it there for 30 seconds or so. You may see a spark, it'll make you jump. This is a crude but effective method of draining them.

Not trying to scare anyone, or make it out to be a bigger deal than it is. But when I see people doubting that amps can hold a charge, I figured it's best for one more person to re-iterate safety advice.

-Nick

fiveightandten · Post by **fiveightandten** » Mon Feb 09, 2004 5:06 am

<BLOCKQUOTE id=quote><font size=1 face="Verdana, Arial, Helvetica" id=quote>quote:<hr height=1 noshade id=quote>
Sooner, I am an electronics novice. Would you please explain how there can be voltage inside an amp after it's unplugged? Seriously. Thanks.

JG
<hr height=1 noshade id=quote></BLOCKQUOTE id=quote></font id=quote><font face="Verdana, Arial, Helvetica" size=2 id=quote>

Short story:
Some caps hold electricity in them after the amp is turned off.

Long story:
You plug your amp into the wall and get AC voltage from it. Your power transformer makes that small voltage (120V in the US) much larger...say 400, 500, even 600V in some amps. There's a problem though. Tubes run off of DC, not AC. So we have a part of the amp called a rectifier. This is a device that changes AC into DC, so the tubes can operate.

A rectifier isn't a perfect electronic device, and the DC it creates isn't perfect either. It's impure, and it fluctuates. We put capacitors in the power supply of an amp to deal with these issues.

The big caps are called electrolytic filter caps. They are there to cure the volage fluctations in the amp. If the voltage spikes, they absorb the extra electricity, to even things out. If it drops, they let out electricity. Again, to even things out.

The problem here is, electrolytics can't just magically make that extra stored voltage go away when the amp is turned off. Most amps have "bleeder resistors" that let the voltage bleed off into the chassis over time. But there's always a risk of having a cap drain that excess voltage into you when you're working on an amp. This is why you need to drain them and eliminate that possibility.

As an aside...some old Ampegs have SCARY high voltages, and amps like the SVT will "find" voltage even after you drain the caps. I don't know where it comes from. But I know more than one tech who has worked on an SVT, drained the caps completely, and come back to work on it the next morning to find that they had a bit of a charge in them again.

At any rate...I hope that clears things up and gives you the reasons behind all this, without being too confusing.

-Nick

Post by **bclaire** » Mon Feb 09, 2004 12:38 pm

Caps have "memory." You can discharge them but after a period of time, the charge will return.

SVT's do have high voltages but they won't kill you- like I said earlier, it's every muscle in your body stiffening and throwing you across the room and what you land on, that'll hurt you.

dead AD15?!?

Who is online