amp repair gurus, I need your help

[bungalowbill]

I changed the speaker in my Crate V-32 Palomino Thursday and played it for a couple of hours with no problem. I fired her up today and after about a minute or so I started to get an intermitten popping sound. I thought it was the speaker so I hooked her up to another speaker....same thing, after the amp gets good and warm there is intermitten popping noises. I then checked the preamp tubes by cranking the amp and lightly tapping them with a pencil eraser and none were microphonic. I'm now suspecting the power tubes, they are the original Groove tubes (EL84's) that came with the amp. Any suggestions? ScottF, Jeff Seal,.....anyone.......HELP....I'm about to pull the rest of my hair out.

 

[J Moose]

Re: amp repair gurus, I need your help

Power tubes can & will "go" whenever they feel like it! LOL All tubes will make some noise, bad tubes will make LOTS of noise.

'Popping' sounds to me like a cap or PSU/regulator issue rather then tubes...but it might be tubes.

Is the amp doing the rice crispie thing while it's idling? Ie; no guitar plugged in but off standby? Or does it not even matter?

 

[75lespaul]

Re: amp repair gurus, I need your help

My U45-B did the same thing and it was one of the preamp tubes.

 

[bungalowbill]

Re: amp repair gurus, I need your help

Power tubes can & will "go" whenever they feel like it! LOL All tubes will make some noise, bad tubes will make LOTS of noise.

'Popping' sounds to me like a cap or PSU/regulator issue rather then tubes...but it might be tubes.

Is the amp doing the rice crispie thing while it's idling? Ie; no guitar plugged in but off standby? Or does it not even matter?

Thanks for your response..........
Yeah, it does it idlling without the guitar plugged in with the standby off. I hope it isn't a cap or something difficult to find.

 

[Scott_F]

Re: amp repair gurus, I need your help

Only happens when it starts getting warm? solder joint. open it up, turn it on and probe with a wooden chop stick. Keep one arm behind your back in case you shock yourself. Take off all your jewelry, watch, rings, etc before you start doing this. Just start to probe and after it gets warm and starts acting up, you'll eventually tap the offending joint and it'll become obvious.

if you're not comfortable, take it to a tech.

 

[theodie]

Re: amp repair gurus, I need your help

This isnt the first time Crate has had a big problem with solder joints when the amp gets warm!!! Probally wont be the last!

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

 

[bungalowbill]

Re: amp repair gurus, I need your help

Only happens when it starts getting warm? solder joint. open it up, turn it on and probe with a wooden chop stick. Keep one arm behind your back in case you shock yourself. Take off all your jewelry, watch, rings, etc before you start doing this. Just start to probe and after it gets warm and starts acting up, you'll eventually tap the offending joint and it'll become obvious.

if you're not comfortable, take it to a tech.

I can do that, no problem. Thanks Scott. And to theodie, thanks for not suggesting a kick to the johhson.

 

[joelap]

Re: amp repair gurus, I need your help

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

to stop the current from going through your chest instead of down your leg, and to stop you from grabbing onto something and having the current once again go through your chest. Cardiac arrest is a b*tch and a half.

 

[kmcguitars]

Re: amp repair gurus, I need your help

I had a similar problem w/t my HRD. I could visible see orange burnt rings around the solder pads to R78 & R79 (470 ohm 5 watts) Soon as I touched the soldering Iron to the resistor, The trace curled up and evaporated.:yell: Took a lot of jumper wires to put it back together.:smack: I Imagine Crate uses the same cheesy flimsy PCB material as Fender. (Nothing wrong with PCB's as long as they are made properly IMO) Good luck finding your gremlin.
BTW, Next time this HRD PCB gives me grief... Into the trash it goes, And will be replaced with 59' tweed Bassman P2P Circuit!!:banana:

 

[Jeff Seal]

Re: amp repair gurus, I need your help

BB, most Crate's suffer from the afore-mentioned problems, usually it's easily repaired and the amp will be better than new (given the way they're made, this is actually feasible!) They're not poorly designed, just poorly made....trust me it could be worse, you could have gotten a new Marshall.

Any tech worth a flip, should resolder almost all the high wear components....jacks, pots etc.

The whole hand behind the back thing is another story and one I'm rather reluctant to discuss. Keep in mind this, you really shouldn't be poking around inside an amp unless you have some clue.

JS

 

[bungalowbill]

Re: amp repair gurus, I need your help

BB, most Crate's suffer from the afore-mentioned problems, usually it's easily repaired and the amp will be better than new (given the way they're made, this is actually feasible!) They're not poorly designed, just poorly made....trust me it could be worse, you could have gotten a new Marshall.

Any tech worth a flip, should resolder almost all the high wear components....jacks, pots etc.

The whole hand behind the back thing is another story and one I'm rather reluctant to discuss. Keep in mind this, you really shouldn't be poking around inside an amp unless you have some clue.

JS

Thanks Jeff.
I know how to discharge the caps if need be. I will be careful and use a long piece of dowel rod to poke around.

 

[Scott_F]

Re: amp repair gurus, I need your help

BB, most Crate's suffer from the afore-mentioned problems, usually it's easily repaired and the amp will be better than new (given the way they're made, this is actually feasible!) They're not poorly designed, just poorly made....trust me it could be worse, you could have gotten a new Marshall.

Any tech worth a flip, should resolder almost all the high wear components....jacks, pots etc.

The whole hand behind the back thing is another story and one I'm rather reluctant to discuss. Keep in mind this, you really shouldn't be poking around inside an amp unless you have some clue.

JS

Jeff, how many times have you been shocked? You've been doing this for a while now. The hand behind the back thing sounds like a good ounce of prevention. (although I don't follow it too closely)

In my experience (limited as it may be), those filter caps tend to discharge rather quickly. I always check them with a meter and there's never much there. (now we'll have ever tom **** and harry opening up their amps!)

Could it be that the discharged filtercaps thing is just a tale that techs have used to keep the uninitiated out of their amps?

:banana: :dance: :smack: :laugh2: :chairfall

 

[joelap]

Re: amp repair gurus, I need your help

^ Seems plausable sometimes Scott. On the Hoffman boards, one guy said it is possible to discharge the filter caps simply by putting a jumper from pin 1 of Valve 1 to ground. Another thing some people do in general is try to keep information to themselves, so when someone new to the game posts a stupid question, "if you dont know the answer to that you shouldnt be messing with amps" yet I'm sure at some point in time they didnt know the answer to it either!

 

[Scott_F]

Re: amp repair gurus, I need your help

It's just I've always been so freaking paranoid about the voltages and when an amp is turned on, you better be respectful. But when the amp has been off for a few minutes, the caps seem to drain out pretty quickly on their own. Just my observations on the amps that I'm messing with.

 

[flank]

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.

 

[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.:blackeye:

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