Help me diagnose before taking to tech?

It's a Genz Benz Black Pearl, which is basically an AC30/BadCat type. When I first turn it on, it's fine. But very quickly... sometimes within a minute, I hear a static-y sound, like if you were to rub a mic against your shirt, or something. Then the sound stops, and the amp has less gain & volume... not ALOT less, just enough to piss me off. lol I have changed every tube but the rectifier (I have read rec's either work or they don't, but they don't cause noises... it's an NOS 5AR4), I have also cleaned all the jacks & sockets. The noise happens whether a cord is plugged in or not, and the gain & MV controls have no effect on the noise whatsoever. I know it's probably a cracked solder joint or a component heating up and changing value or something, but I was hoping to at least get an idea of where to tell the tech to zero in on... I'm not going to try to fix it myself.

don't want to discourage you, but good luck with that hunt. I don't find a schematic online - so not much hope of real help without that.

In general the problem you describe sounds like a cold solder joint or perhaps a plate resistor failing.

Take it to an G/B authorized service center.

Sorry for your trouble.

CBG

Yeah, no schematic. Altho, the amp is discontinued now... I wonder if GB would be willing to send me a schem?

Only 3 authorized SC's around here, none close... closest maybe 45min away... oh well...

With all my research, what you suggest is also what I came up with. The problem has been happening for about a year, slowly going from "occasionally" to "somtimes" to "half the time" to "most of the time"..... at this point, it's like 90% of the time. If the amp has been on TODAY, it's still doing it. If the amp sits overnight, for the first 60 seconds it sounds GREAT, then the static, then the slight loss in gain & volume... like I turned the preamp down 25% and the MV down about "1" on the knob.

I looked for cracked solder joints, but honestly, I don't know what the heel I'm looking for. And I know they can be hidden under the PCB.

You probably will not see a cracked joint, you could try poking them with a wooden dowel or something non conductive (assuming you will not electrocute yourself). A bad capacitor can cause crackling also, You could have a carbon path across a tube socket. As you can see it can be all kind of things. I had two traces on a board too close to each other and the voltage would cause a spark when the current jumped across the gap. That was an easy one to find, you look at the board and the flashes were pretty hard to miss.

OH YEAH.. I meant to wait until after dark & check for arcing. Thanks for the reminder.

The only components that look at all "suspicious" are 2 resistors. The blue one (which is one of the many resistors right next to the power tube sockets) looks scratched... maybe that's all it is, don't know if this could be the "start" of something?

The beige one, which is right between the 2 large caps on the right side of the board, appears to have a burned spot on it... it's either a burned spot or it's old flux... but the inside of this amp is immaculate, I wouldn't think it'd be flux. I'm not touching anything lol. Anyway, in-between those 2 big caps, was thinking maybe this is a "hot spot" and the resistor could be starting to go?

http://i28.photobucket.com/albums/c218/ruger9two/Amp1.jpg
http://i28.photobucket.com/albums/c218/ruger9two/Amp2.jpg
http://i28.photobucket.com/albums/c218/ruger9two/Amp3.jpg

Well, You could take the brute force approach, and simply take your soldering iron and remelt and reflow all the joints with a touch of fresh solder.

You could also just replace that 470k resistor R131. That's probably just a bleeder resistor though...but now that I think of it... I SUPPOSE if it was shorting LOW, why then it would drag down the power supply and drop the B+, which might explain the "loss of gain" thing.

Should be easy to see. Turn it on. Put a meter on the B+ at the filter cap...listen for the noise and watch the voltage drop...or not.

CBG

My MM died on me, bought a new one last night. Going to lift and measure R131 after work... I have a 470K to replace it with, but it's only a 1/2W. I read online that 1/2W is usually fine in an amp, but the one I have is smaller than the one in the amp, so it's rated for less power... if heat IS an issue, wouldn't getting one rated for MORE power be better? Just don't want to go to the trouble of replacing a resistor... only to have to replace it again soon.

Any way to know what wattage the current R131 is?


I have 2 470K types here...

Xicon 470k carbon comp 5% 1/2W

Radio Shack 470k 5% 1/2W (composition unknown... just standard RS resistors)

Get you some 'freeze spray'....I can't recall what the formal name is. IT is used to cool components down to analyze if there is heat sensitivity problems going on. Fire the amp up. When it commences to exhibit the problem, spray different components one at a time to see if cooling a certain component down will eliminate the problem. IF so, there's your problem. I suppose a voltage check at various points might help to find the problem. Chopstick for the physical 'stress test'.

Your thread header reads ''Help me diagnose before taking to tech?" So, you are foregoing the tech? Warning necessary....Danger. Danger..deadly voltages are present even with the amp unplugged.

I know about the deadly voltages. I probably will still take it to a tech, but if the problem is a resistor, I can handle that. I've modded amps before. What is beyond my expertise is troubleshooting the amp from the beginning to track down a problem.

Someone on another forum pointed out its a lead-free PCB. Recommended not using standard solder or even a gun that has ever used regular solder. I'll just take it t the tech. He's 75 miles away, and 3 weeks backlogged, but he's agreed to make an appointment for me to bring it in... and hopefully fix it while I wait, if he has the parts. I've never heard of a tech doing that. I usually get "drop it off, and MAYBE I can get it on the bench in a couple of weeks."

So, I wait. Boooo.

I wouldn't sweat the "lead free" thing too much. "lead free solder" is mostly tin. "lead bearing solder" is about 60-63 percent tin. Lead alloys quickly and easily with tin. That's why they've been used in alloy for about a thousand years to make all kinds of solder (including electronic solder) in the first place. When you melt a "lead free" solder joint and dab a little tin/lead on there, the lead alloys quickly with the original tin/copper/silver mixture that is also at that moment molten. Yes, there is an "alloy transition zone" - at the microscopic level. Yes, in theory the boundary layer transition zone of the alloy is at some point slightly weaker than the tin-only lead-free zone. Yes, if you stand outside long enough a bird will eventually shat upon you and give you a disease.

In reality, the sky will not fall when you mix lead/tin and tin/cu/antimony solder...really. In spite of all the vague warnings you'll find online about how your entire life will come to a screeching halt...it won't. The typical joint working at the level of density of your amp just won't fail. The amount of lead/tin alloy is just way too large to cause micro-fractures. You're not working on surface mount ultraminiature components here. It's a guitar amp, for heaven's sake!

The HORRORS AWAIT ALL WHO TRY LEAD to NO-LEAD BONDING warnings are mostly published by folks trying to sell you all new (expensive) soldering equipment. Curious, that relationship, eh? It's Bad - You need what I have! Let me sell it to you!

Then there are those fear mongers. They also don't have to use it themselves, and can't tell lead solder from a #2 lead pencil. You know the type. They're the ones selling their patented black art sky sticks - mysterious devices intended to prop up the sky and keep it from falling...which they assure you it will do if you don't obey them and buy their sky sticks.

The main issue in repairing non leaded solder joints in the first place is that you have to up the temperature enough to melt the stupid lead free solder areas - which is probably why your G/B amp's component failed!

It probably got too hot during the manufacturing process, thus creating another broken device which you must now repair or (they hope) replace. That, or it has one or more cold solder joints from the da--ed crummy joints that lead free tends to make, as compared to eutectic lead bearing solders.


But I know, I know...we're not supposed to talk about POLITICS on this forum.

CBG

The HORRORS AWAIT ALL WHO TRY LEAD to NO-LEAD BONDING warnings are mostly published by folks trying to sell you all new (expensive) soldering equipment. Curious, that relationship, eh? It's Bad - You need what I have! Let me sell it to you!

Then there are those fear mongers. They also don't have to use it themselves, and can't tell lead solder from a #2 lead pencil. You know the type. They're the ones selling their patented black art sky sticks - mysterious devices intended to prop up the sky and keep it from falling...which they assure you it will do if you don't obey them and buy their sky sticks.

The main issue in repairing non leaded solder joints in the first place is that you have to up the temperature enough to melt the stupid lead free solder areas - which is probably why your G/B amp's component failed!

It probably got too hot during the manufacturing process, thus creating another broken device which you must now repair or (they hope) replace. That, or it has one or more cold solder joints from the da--ed crummy joints that lead free tends to make, as compared to eutectic lead bearing solders.

CBG

the guy who told me that was a tech, on another forum. I know there's no "horror" involved, but he specifically said lead and no-lead solder, when it doesn't properly bond, can cause intermittent connection & noise issues, including static. Static is what I am trying to remedy!

I'm a do-it-yourself guy. But I have no interest in CAUSING any issues, simply meaning, I don't have the experience, and while I'm willing to try almost anything, I don't really know what I'm doing. I've modded amps & pedals, have no problem using a solder gun, I just don't want to cause more trouble than I'm trying to fix.

I hear what your're saying tho. There's alot of that "there's only ONE way to do things"... it's mostly BS. I'm a home improvement contractor, and alot of us think the only RIGHT way to do something is the way THEY do it. BS. There's usually more than one RIGHT way to skin a cat. I just want my amp fixed. It's currently my only tube amp, I love it, I need it. I'd love to take a course in amp repair, just for my own uses.