How fudged is my amp?

[MultiScaleMale]

Financially, it's probably not worth repairing. The bench fee to look at it will probably be about what resale value would be, if operable. But since it has sentimental value, I guess that's a different story.

 

[dan1952]

Somebody has messed with it, the Kep-nuts on the output device are missing. What else has been messed with?

Sorry, OP, you can't fool Andy...;-)

 

[Dave TB Killer]

Leave it alone or you'll burn the house down!

Just buy another one. They are cheap and the cost of a used one is probably the same as a repair bill.

 

[byacey]

This came up in another thread, regarding it's worth of a repair.

This is a very simple amp, and any qualified tech should be able to fix this up quickly at a reasonable cost. If it's beneath them and not worth their attention, find another tech who will fix it.

In DC coupled power amp stages, just replacing what you think is the only bad part will often just cook the replacement part again, and possibly do even further damage to the other components too. It has to be properly evaluated through troubleshooting to get it right.

 

[Pilgrim]

Thats a good point, I'd like to get it repaired at some point mostly for sentimental value. It was my first amp, bought by my dad when I was 13. I have other amps, Just hoping its not beyond repair. I have a good local shop I'll take it to soon for an estimate.

That is exactly what makes it worth spending a few extra bucks on. I have the blackface Bassman my parents bought me in 1967. They're gone now, and even though I only use it occasionally, and then for practice, it is NEVER leaving my hands. I'd pay a bunch to fix it if it failed.

 

[Slevage]

You’ll go through a lot of time and $$ changing parts. Bring it to a tech who has trouble shooting skills.

A variac and lightbulb in series with the load is your friend. Don’t know what I’m talking about? Close the amp and find a professional.

 

[Spectre Gunner]

Since it may not be cost effective to have it repaired, why not disconnect or remove the amp section altogether and convert it to a cabinet?

 

[agedhorse]

Sorry, OP, you can't fool Andy...;-)

Yup, identifying such factors has saved my ass on a bunch of repairs before getting too deep into it. As soon as I see something monkeyed with, it means that I now have to check a whole bunch of things that wouldn't need to be looked at, to be sure that nothing else was screwed with that would come back to bite me. When a warranty is offered on a repair, all the T's must be crossed and the i's dotted or it can come back for rework on my dime.

 

[Jim C]

To answer the original question presented in this post:
Your amp is way fudged. Like way beyond dark chocolate fudged.
It needs to be take to a fudged amp repair tech (as you know!)
May not be worth the cost of the repair; only you know that.

 

[vvvmmm]

Since it may not be cost effective to have it repaired, why not disconnect or remove the amp section altogether and convert it to a cabinet?

OT but I did this with a Classic and some decent Celestions, blocked the amp hole with some fabric-wrapped 1"x.
Coupled with my Musicman HD160 it sounds better than any Fender Twin I've ever heard.

 

[kingforaday]

This is really similar to an issue I had with an old Peavey amp I bought. I asked here and got really similar responses… I then tried a music tech forum, and got talked through the process of how to troubleshoot, and ultimately fix it myself. It cost me so little in parts, I had a go at fixing other bits and pieces I had (that weren’t worth paying for repair on). I even bought another similar faulty amp and repaired that too. I’m by no means an expert, but I learned a lot with the help of some very knowledgeable guys.

Yes there are dangers and you have to be careful of course, but that doesn’t necessarily mean “don’t do it, you’ll die” - it just means, be careful. Make sure you’ve learned enough to be confident in what you’re doing, before you start poking around.

How did any of these amp techs get started? They learned stuff.

 

[agedhorse]

This is really similar to an issue I had with an old Peavey amp I bought. I asked here and got really similar responses… I then tried a music tech forum, and got talked through the process of how to troubleshoot, and ultimately fix it myself. It cost me so little in parts, I had a go at fixing other bits and pieces I had (that weren’t worth paying for repair on). I even bought another similar faulty amp and repaired that too. I’m by no means an expert, but I learned a lot with the help of some very knowledgeable guys.

Yes there are dangers and you have to be careful of course, but that doesn’t necessarily mean “don’t do it, you’ll die” - it just means, be careful. Make sure you’ve learned enough to be confident in what you’re doing, before you start poking around.

How did any of these amp techs get started? They learned stuff.

Most GOOD tech learn by taking classes, learning some electronics theory and then worked under somebody who understood troubleshooting and safety.

Some got their skills studying and working in military service, trade schools and VA programs also.

 

[byacey]

Yup, identifying such factors has saved my ass on a bunch of repairs before getting too deep into it. As soon as I see something monkeyed with, it means that I now have to check a whole bunch of things that wouldn't need to be looked at, to be sure that nothing else was screwed with that would come back to bite me. When a warranty is offered on a repair, all the T's must be crossed and the i's dotted or it can come back for rework on my dime.

Absolutely. Unfortunately, when something goes wrong, all fingers point to the last guy that worked on it, regardless if the fault was pre-existing from previous work, or not.

 

[dbase]

Replace the burnt resister with a copper penny and call me in the morning

 

[byacey]

Most GOOD tech learn by taking classes, learning some electronics theory and then worked under somebody who understood troubleshooting and safety.

That's how the apprenticeship system works in Canada. You get a job in the trade, and work under a licensed journeyman learning the trade. Included in this yearly, is a 2 month period in the classroom learning theory and lab work. After four years, if you pass all your exams, you get a completion of apprenticeship certificate, and a journeyman's accreditation allowing you to work in the trade.

Further, a journeyman can write additional exams and get inter-provincial red seal certification allowing one to work in all provinces, and is recognized throughout most of the U.S. as well, from what I understand.

 

[A9X]

barfhorse, if it's a sentimental repair, get it done. If I were approached to do it, it's probably be an hours work, and about $10 in parts, especially if you weren't in a hurry and I could simply bundle to parts order into a larger order and save shipping etc. I'd replace both of the TO3 outputs and the emitter resistors as a minimum, and probably the drivers especially if they were a cheap common device like BD139/140s, just to be sure.

I can't believe I'm the first one to mention this but, in guitar amps anyway one needs to be careful poking around inside an opened up amp.

If you open any electronic/electrical component and don't know what you're doing, there is the risk you'll get hurt. So, don't do it if you don't know.
Not having a go at you B&C, just emphasising the point as someone who's qualified, and has done thousands of repairs over the years.

Leave it alone or you'll burn the house down!

Hyperbolic and unlikely. You're far more likely to get dead from shock. See above.

 

[wmhill]

 

[agedhorse]

barfhorse, if it's a sentimental repair, get it done. If I were approached to do it, it's probably be an hours work, and about $10 in parts, especially if you weren't in a hurry and I could simply bundle to parts order into a larger order and save shipping etc. I'd replace both of the TO3 outputs and the emitter resistors as a minimum, and probably the drivers especially if they were a cheap common device like BD139/140s, just to be sure.

Why in the world would you replace parts without knowing the cause of the fault?

I see a lot of damage and unbelievably stupid mistakes and poor judgement from exactly this.

If you don’t know how to troubleshoot an amp, don’t tell others how to do so.

The very first step to troubleshooting is to first understand how the circuit is supposed to work. THEN, you determine what is not functioning as it should and replace the parts that are responsible for the malfunction.

This does not include replacing parts “just because”. In fact this is often the cause of additional NEW problems.

 

[A9X]

If you don’t know how to troubleshoot an amp, don’t tell others how to do so.

Thanks, but I have lots of quals in electronics from Uni and other sources and have worked in linear electronics (plus broadcast, radio, transmitters, test and measurement incl designing the gear) most of my working life. I've been designing, building, repairing and modifying amps for decades, so if I want a lecture from you about it, I'll ask.

And check your reading comprehension skills: I didn't tell anyone else how to do it, I said what I'd do, but I didn't detail the process, so don't assume you know how I do things. In the thousands of amps I've repaired, I never got one back that was due to me making a mistake or overlooking something.

This does not include replacing parts “just because”. In fact this is often the cause of additional NEW problems.

Same as above; decades of experience, as well as detailed understanding of topologies has give me a good grasp on what causes of faults are, and what has potentially been stressed during the fault.

 

[agedhorse]

I give up.

It should be obvious why I often comment about some of the (lack of) troubleshooting skills that I encounter while supporting under-qualified techs in the field.

In fact, usually the more under-qualified the tech, the better they think they are.

Qualified tech are getting fewer and farther between, this is going to become a big problem for the industry… in fact it already is.