amp repair gurus, I need your help

[bungalowbill]

Re: amp repair gurus, I need your help

I'm starting to get aggravated........as soon as I touched the PCB it started popping. If you touch the chassis it pops and is steady popping all the time. i wonder if it is a main ground or something.

[Scott_F]

Re: amp repair gurus, I need your help

David Allen showed me a quick and easy way to discharge the capacitors that i have seen alot of people refute on the internet, but i figure, if anybody would really know, David Allen would.

elaborate for the masses please...

[Scott_F]

Re: amp repair gurus, I need your help

I'm starting to get aggravated........as soon as I touched the PCB it started popping. If you touch the chassis it pops and is steady popping all the time. i wonder if it is a main ground or something.

definitely sounds like a ground somewhere. Not knowing the inside of your amp, check where wires come off the board and go to ground. There might be several. Check any wire that goes to the chassis ground anywhere.

Are you using the wooden dowel?

[JB_From_Hell]

Re: amp repair gurus, I need your help

BTW Scott, what does the arm behind your back do????

Keeps you from grabbing a + an - at the same time and zapping yourself.

[Jeff Seal]

Re: amp repair gurus, I need your help

Unfortunately, I've been shocked more times than I would care to admit.

Capacitors remain charged for a very long time, unless there is some type of drain on them. How long you might ask?? It's now 11:00 am and I'm going to charge up a 15000uf/100v cap to about 18v, we'll check on it later in the day.

The biggest concern with tube amps, is basically they're ability to store quite a bit of power at a pretty high voltage. 480v is not uncommon (MusicMan's are at 700v), for operating HV. Defibrillators are used to shock the heart back into a normal rhythm and operate at anywhere from 200 to 1700v. As a side note, defibrillators only work on people with irregular heart patterns, not dead people like you always see on TV. They simply work by charging up capacitors and then discharging them into your body, the only difference between this and most tube amps is the ability to plug a guitar into one of them. Learning how to properly deal with HV is important, be smart...but still be wary!

Which brings us to a much more likely hazardous scenario, have you ever seen musicians onstage that touch a mic with the back of their hand and wonder why? (or better yet why this is a good idea!) If you're playing live and going to check a mic, always touch the mic with the back of your hand first! One of two things is going to happen, either it's going to shock you or it's not. I realize that's pretty obvious, but it happens much more often than you might think. (especially outdoor generator driven gigs!) What happens when you get shocked is your muscles tense and tighten. If you have your hand wrapped firmly around a mic and get zapped, you hand is just going to clamp down harder and make it worse! If you use the back of your hand it will naturally constrict and pull away towards your body. And as long as we are discussing this instead of bungalowbill's amp dilemma...(sorry bro! I don't know how I got this far off track..)
If you do see someone getting shocked, don't even think you can just pull them away. As soon as you lay your hands on them your body is just "joining the team" getting electrocuted. You have to physically "tackle" them away from the offending condition. Minimize contact, but make it forceful..

Ok, that's enough of that.....just words to be wiser by!

Jeff Seal

[bungalowbill]

Re: amp repair gurus, I need your help

definitely sounds like a ground somewhere. Not knowing the inside of your amp, check where wires come off the board and go to ground. There might be several. Check any wire that goes to the chassis ground anywhere.

Are you using the wooden dowel?

The wooden dowel is my weapon of choice right now. i'll check the grounds.

[bungalowbill]

Re: amp repair gurus, I need your help

It is fixed! Thanks to all of you. Scott and Jeff both deserve special thanks for the help and for the concern over getting electrocuted. The culprit was a ground wire that is attached to one of the mounting screws on the OT. Happy camper I am.

To Scott & Jeff & everybody... You all saved me a bunch of $.

[J Moose]

Re: amp repair gurus, I need your help

Which brings us to a much more likely hazardous scenario, have you ever seen musicians onstage that touch a mic with the back of their hand and wonder why? (or better yet why this is a good idea!) If you're playing live and going to check a mic, always touch the mic with the back of your hand first! One of two things is going to happen, either it's going to shock you or it's not. I realize that's pretty obvious, but it happens much more often than you might think. (especially outdoor generator driven gigs!)

I use a different trick when I can.

Turn the guitar amp on & holding the guitar (but NOT the strings) touch the strings to the microphone and you can audibly hear if there's a ground loop or if there's shock potential & the room is dark enough...you might see an arc from the mic to the strings.

WAY safer then using a body part...but if you HAVE to use a body part, the back of the hand or a single finger is pretty safe.

[Scott_F]

Re: amp repair gurus, I need your help

It is fixed! Thanks to all of you.

Chopsticks rule! Everytime I get a chance to scam some chopsticks at a resturant, I grab em!

Hoity Toity places like PF Changs have polymer chopsticks. No splinters! They work great as well.

I first esperienced this popping ground thing when I replaced a 2 prong power cord off my Pro Reverb for a 3 prong. I didn't get the ground soldered in good and that nasty popping noise would occur on certain resonant frequencies. Drove me nuts for a few minutes.

[Jeff Seal]

Re: amp repair gurus, I need your help

...just an update..... you remember that capacitor I charged up Sunday, it's now three days later and guess what??? It's still holding 12.6 v!

fwiw..

JS