Ampeg B15-N Capacitor ID

[Brennan]

For what it's worth, I am a diehard DIY guy and trained as an electronics tech. I think it's worth the money to get an amp tech to diagnose/repair that amp.
I would probably install a new grounded power cord ahead of time and have it ready for the tech to connect inside the amp.

Yea, I was thinking of going that route. Good advice

 

[Brennan]

I am all for the right to repair, but if one does not have the tools or skills then they should not attempt.
Nothing is worse for a repair person than fixing what the customer already took apart or further broke so a proper diagnoses in its original (pre attempted) state could not have been found.

Got to puzzle what they done before the diagnosis of the original problem is can be done.

Then the sadness of the person that attempted when it does not work or makes a bigger problem when more goes boom when the part was replaced but not the reason why, now there are five burned up items inside and the bill will be more than one will be willing to spend.

This is more than a solder iron repair. It needs to be hooked up to an oscilloscope, a multi meter, and a variac, then take measurements and understand them. Not knowing you were talking about a resistor leads us to believe these tools and skill are not their.
Nothing wrong with that.

Are you also able to clean up or repair that burnt trace successfully?

Part swaps in amps do not usually have the same results as a home improvement repair. There are underlining causes to the one you do see.

Just general cleaning and removing the bad AC cable. Years of gunk. I’m more concerned with the circuit board potentially being compromised.

 

[Boundary Effect]

I would not worry about the circuit board being compromised. Those old boards are easy to work on, not like the light and small traced stuff of today. A good tech can figure out how things should be and craft a fix where the board is burnt if need be. The guys are right though, there is something significant that has failed elsewhere in the amp. That resistor smoking was a result of some other failure. And no, a crappy extension cord is very unlikely going to be the cause of an amplifier's internal failure.

 

[Brennan]

Ok, if there are two 22k resistors, they are RC filter elements for the B+ supply feeding the PI or preamp. When these resistors fail, it’s either because of a load fault, wiring fault or a failure of one of the caps in the RC filter network.

Thanks, could a ac surge cause that?

 

[Thebiggestjerk]

Do you know how to work with capacitors? If not STOP! First, Read up on discharging capacitors.

 

[MVE]

View attachment 4809973 I should have said highly problematic and dangerous ac situation. See photo. Look, 90% I’ll probably have to take it in but everyone here has taken a shot at trying to fix it themselves first. If we had to take in every piece of gear that we’ve modded or repaired we’d all be broke…by spending all our money in gear…in an endless quest of getting more gear…and better gear… I think I just had a breakthrough

You can certainly repair it yourself, if you have a variac, scope w/ an octopus, good meter, dummy load, cap discharger, tone generator… and the right schematic for that model.

Seriously, old amps that have not been turned on in a while should always be brought up slow on a Variac to limit the chance that one failed component would cause damage to other components. (If something if starting to give off a tiny little bit of smoke at 10 volts, you can bet it would be melted or on fire at a 120.)

 

[iiipopes]

I think that's a resistor, not a capacitor. The area under the burnt resistor needs to be inspected for further damage to the traces.
I also see a cut wire near it and have no idea where it's supposed to go.
I'd find a capable tech and let him give it a full inspection. I think such a well respected amp deserves good treatment.

Indeed. That amp took a big hit, whether voltage spike, tube short, lightning, something. Don't plug it in until you've had a qualified tech check it out.

 

[agedhorse]

Thanks, could a ac surge cause that?

No.

You can certainly repair it yourself, if you have a variac, scope w/ an octopus, good meter, dummy load, cap discharger, tone generator… and the right schematic for that model.

Seriously, old amps that have not been turned on in a while should always be brought up slow on a Variac to limit the chance that one failed component would cause damage to other components. (If something if starting to give off a tiny little bit of smoke at 10 volts, you can bet it would be melted or on fire at a 120.)

What’s an octopus?

When using a Variac, always monitor the current to PREVENT additional damage.

 

[SamanthaCay]

No.


What’s an octopus?

When using a Variac, always monitor the current to PREVENT additional damage.

An octopus is an eight legged sea creature, no idea where that comes in when fixing amps though, inspiration perhaps.

Op resistors burn when there is too much load placed on them, ie something between the resistor and ground not the resistor and a positive charge.

Bottom line is you need a competent tech with the proper tools for this. It's not a matter of swapping parts that might be suspect or that someone on the internet recommends, it's a matter of having the skills and tools to properly diagnose what is needed.

 

[Old Garage-Bander]

Thanks, could a ac surge cause that?

If it were large enough, and long enough.

If you weren't there when the surge happened then there is no point in asking. Is it likely that the typical AC power surge could have done this? NO. For a "surge" to do this kind of damage to your amp, pretty much a lot of other equipment in a lot of other homes or business would have been damaged too.

If your next questions are about a direct lightning strikes, solar mass ejections or large EMP's, then stop. Whatever unlikely external factors you can come up with that you wonder may have caused this does not matter at this point. What matters is getting it fixed by someone who knows what they are doing.

No one here can diagnose what's wrong with your amp in a forum. Everyone has done their best to give you all the free advice you need. Take what you saved on that advice, add that to the money you haven't spent yet chasing guesses, and get it to a qualified tech.

Don't even bother with the AC cord. There are right and wrong ways to do that as well. If you get it wrong, then you'll have to pay the tech twice. Once to undo it, and again to redo it properly.

 

[Paul New]

I agree, another component, probably a cap, failed and caused this, but resistors can and do fail all on their own. There are more than a couple of failure modes. Seen it many times.

 

[MVE]

No.


What’s an octopus?

When using a Variac, always monitor the current to PREVENT additional damage.

AKA, curve trace component tester.

And watching for smoke is an easy way to monitor current.

Here is a QSL article about octopuses… (yes that is the correct pluralization of the singular.)

https://www.qsl.net/kd7rem/pdf/octopus.pdf

 

[Lo-E]

An octopus is an eight legged sea creature, no idea where that comes in when fixing amps though, inspiration perhaps.

They’re extremely intelligent and those that use vintage amplifiers (rocktopi) are very capable of repairing their own gear due to their high intellect and their ability to hold a lot of tools at once. That’s why they’re handy to have around for doing amp repairs. I’m here to help….

OP, it might seem like everybody’s ganging up on you when they tell you not to try this yourself but it’s really not meant maliciously. Tube amps operate with internal DC voltages that are very high. Hundreds of volts. If you’re not sure - really, really sure - what you’re doing in there the amp can kill you. No fooling.

What’s worse is that the banks of capacitors in these amps can store those hundreds of volts for several days in some cases. That means you can unplug the amp (to make it “safe”) and it can STILL kill you! Seriously; be very careful.

I’m a big fan of DIY. I’ve been working on my own tube amps for 25 years or more but I also studied electrical engineering and I started with simpler, less dangerous things. If you want to learn to work on your own tube amps I totally recommend it but don’t start here. Work your way up. A pedal, a kit…. Something to get your feet wet without putting yourself (and possibly your new vintage amp) in great danger.

 

[agedhorse]

I agree, another component, probably a cap, failed and caused this, but resistors can and do fail all on their own. There are more than a couple of failure modes. Seen it many times.

Resistors do not fail on their own burned like that.

The failure of resistors is very uncommon and almost always mechanical in nature. On our products, we see a resistor failure less than 1 in 1 million, all axial resistors are tested on our auto-insertion equipment before being inserted into the PCB during manufacture. Since there are only 5 or 6 axial resistor manufacturers of these types of resistors representing ~95% of resistors manufactured, and we use 4 of them, our results will be the same as everybody else’s.

I do see resistors fail because the designer didn’t do their calculations right, or simply screwed up, but that’s not a resistor failure, it’s a design failure.

AKA, curve trace component tester.

And watching for smoke is an easy way to monitor current.

Here is a QSL article about octopuses… (yes that is the correct pluralization of the singular.)

https://www.qsl.net/kd7rem/pdf/octopus.pdf

In my 45 years in electrical engineering, I have never heard the term octopus used.

[edit: it appears that the term octopus is a home brew or DIY name for a DIY type of curve tracer emulator rather than what the industry uses, which is why I never heard it. ]

Hint… if you monitor the current rather than looking for smoke, you can avoid a whole lot of damage.

 

[MVE]

Resistors do not fail on their own burned like that.

The failure of resistors is very uncommon and almost always mechanical in nature. On our products, we see a resistor failure less than 1 in 1 million, all axial resistors are tested on our auto-insertion equipment before being inserted into the PCB during manufacture. Since there are only 5 or 6 axial resistor manufacturers of these types of resistors representing ~95% of resistors manufactured, and we use 4 of them, our results will be the same as everybody else’s.

I do see resistors fail because the designer didn’t do their calculations right, or simply screwed up, but that’s not a resistor failure, it’s a design failure.


In my 45 years in electrical engineering, I have never heard the term octopus used.

[edit: it appears that the term octopus is a home brew or DIY name for a DIY type of curve tracer emulator rather than what the industry uses, which is why I never heard it. ]

Hint… if you monitor the current rather than looking for smoke, you can avoid a whole lot of damage.

Regarding the smoke, yes I agree 100%.

I was only making a joke.

In fact, for anyone who might have an old variac, you can get a digital ammeter on Amazon for about $15 and permanently attach it to that old variac to monitor draw while using it.

 

[Old Garage-Bander]

I agree, another component, probably a cap, failed and caused this, but resistors can and do fail all on their own. There are more than a couple of failure modes. Seen it many times.

Resistors can drift out of tolerance. That is a gradual process that can take decades. Resistors do not spontaneously combust. When the smoke gets out of a resistor, it's because it had help.

 

[S-Bigbottom]

Resistors can drift out of tolerance. That is a gradual process that can take decades. Resistors do not spontaneously combust. When the smoke gets out of a resistor, it's because it had help.

 

[Old Garage-Bander]

 

[Bflat]

Resistors can drift out of tolerance. That is a gradual process that can take decades. Resistors do not spontaneously combust. When the smoke gets out of a resistor, it's because it had help.

Old Garage-Banderyou and agedhorse have got it right. Ive looked at every low impedance path possible for both of the 22k 1/2 watt resistors. so with a single point failure, this can only happen if one of the 20 mfd 500 volt caps shorted. the 22k resistors are voltage dividers. one for both the preamps through 470k and 220k 1/2 watt and the other for the phase inverter through 2 47k resistors 1/2 watt. as agedhorse earlier hinted at. there is 445 v on the first filter cap rated at 40mfd 500vdc then a 1k resistor and another 40mfd 500vdc cap with 425vdc on it tied to the top of both 22k resistors. you can see all of those resistors in the photo provided with at least no catastrophic damage. of course someone could pour a bucket of pennies or dropped a screwdriver in it, etc.
old electrolytics are famous for shorting I would bet if only that were fixed the others would blow soon enough

 

[Canadian APII]

I agree. It looks like a resistor. And without a component layout drawing or some other method to identify that component, the schematic is not very helpful.

That large yellowish/orangish/brownish component at the bottom of the closeup looks like an electrolytic capacitor. And judging by it's apparent age, it could also need replacing, along with other 'lytics in the amp.

There is also a chance that some other component that may visually look OK is bad, and that may have caused your part to burn. Resistors (if that is what your burnt part is) typically do not fail in such a catastrophic fashion all on their own. Something else caused this.

The previous recommendation for finding a qualified technician to repair this classic old beauty, is the best advice you'll get.

No. This schematic is all you need.