Ampeg B-15nf blowing fuses

[beans-on-toast]

Here is an explanation of what drying out of the fluid in an electrolytic capacitor does.

Sencore tech note:
Invalid Link Removed

As these capacitors age and loose the moisture, their internal resistance increases. This causes even more intenal heat. Worst case, the liquid expands and the capacitor fails. A sign that the cap should be replaced is bulging or worse, leaking fluid. Sometimes there is a rubber seal on the end of the cap. This acts as a pressure valve, preventing the cap from exploding. Sometimes this stopper dries out and cracks which hastens the drying out of the cap. Caps that don't have a rubber seal are designed to open in other ways such as a weak point in the case when the cap fails.

FP type capacitors are built like tanks. The metal tube does not bulge. They are well sealed. They are called dry electrolytics but they are still wet inside. You can see the vent hole in the middle of the one below. The modern products do not have this. Although they can leak, there is usually no visible signs of failure. Their health has to be measured electrically by examining the power supply voltages and testing the cap itself.

Below is a tech note from Nichicon. Part 2 is interesting in that they discuss failure modes of electrolytic capacitors.

https://www.nmr.mgh.harvard.edu/~reese/electrolytics/tec1.pdf

https://www.nmr.mgh.harvard.edu/~reese/electrolytics/tec2.pdf

 

[Lo-E]

A current limiter is you best friend here.

Start with no tubes in the amp. Then add rectifier. Then power tubes. Then preamp tubes. One step at a time, slowly, methodically.... don't try to fix a short if you don't know where the short is yet. Don't replace parts until you know they're broken.

Yes, the "Texas shotgun approach" of just replacing every part might get your amp working- MIGHT - but it will only be through luck if it does. That's no substitute for real troubleshooting.

 

[Coolhandjjl]

A current limiter is you best friend here.

After you solve the problem, that is.
I added a CL-90 to my Dynaco ST35 (1960 vintage power amp)

 

[Coolhandjjl]

The fuse in the amp is supposed to be rated AGC 3A 250V. Try the right fuse first.

Note that the spec'd fuse is a slow-blow fuse as well.

 

[agedhorse]

If you guys are calling PTC inrush current limiting thermistors "current limiters", you are missing the entire point. Generally, tube amps (especially smaller ones) won't benefit from them.

I think Lo-E has it right.

 

[beans-on-toast]

Note that the spec'd fuse is a slow-blow fuse as well.

In this case it is a regular fast blow.

 

[basscapes]

May I suggest that you actually identify the actual fault before assuming a solution. I think you will find the repair attempt more successful. Constantly replacing fuses and trying is a good way to increase the amount of damage.

If you can't troubleshoot and identify the cause, I would suggest a qualified service tech.

Total agreement!

As you've mentioned in the past (and I concur!), Tube amps (or ANY electronics) are no place for anyone to play around with inside or out, without the proper training AND experience!

 

[dan1952]

I have found the B15 to be an amp that should go to a qualified tech. Ampeg made a lot of small changes to these amps over the years, and a tech who works on them all the time will do a lot better than the OP can even hope to do. I'm an okay mechanic, and if you bring me a Chevy 235 6-in-line motor, I'l work on it for you today. On the other hand, if you bring me a 2017 Chevy V8 with a turbo, fuel injection, computer modules, and a bunch of parts that I can't even name, it's going to go to someone who is qualified to work on it. A man's got to know his limitations. Oh, by the way, THE FUSE IS NOT THE PROBLEM!!!!!

 

[agedhorse]

I have found the B15 to be an amp that should go to a qualified tech. Ampeg made a lot of small changes to these amps over the years, and a tech who works on them all the time will do a lot better than the OP can even hope to do. I'm an okay mechanic, and if you bring me a Chevy 235 6-in-line motor, I'l work on it for you today. On the other hand, if you bring me a 2017 Chevy V8 with a turbo, fuel injection, computer modules, and a bunch of parts that I can't even name, it's going to go to someone who is qualified to work on it. A man's got to know his limitations. Oh, by the way, THE FUSE IS NOT THE PROBLEM!!!!!

How about my GMC 228 w/ a Zenith?

 

[BassmanPaul]

like some people replace underwear.

I'll have you know that when I replace my underwear it is always necessary!!

 

[beans-on-toast]

Good recording studios have maintenance schedules in place. They go to great measures to ensure that equipment does not break down. As such, routine maintence is performed, in some cases parts are replaced based on the schedule.

In the case of a capacitor, manufactures provide an expected life based on a formula that includes product life specs, maximum operating temperature, ambient temperature, operating voltage, rated ripple current, applied ripple current, etc. Nichicon has a handy capacitor life calculator: NICHICON CORPORATION | Product & Technology.

Their engineers help in providing more refined estimates. A manufacturer will perform product tests and provide maintence schedules to end users based on desired requirements. Things still happen, that's why a suggested list of spares is provided. Mixing consoles are an example of where this is done. Broadcast tends to go even further and have complete redundancy so that they don't miss a beat.

In an ideal world we should all be so lucky to have this level of maintenance. Some artists require that their techs be proactive when it comes to maintenance to avoid potential issues. Some parts are changed whether or not they need to be.

Some musicians like to do their own maintenance. Changing some parts gives them confidence that their gear will make to through the tour or season. Sometimes they want to ensure that an amp's performance will be consistent and optimal for a recording session. Nothing wrong with that.

Being taken advantage of by a tech is something else.

 

[agedhorse]

Replacing parts that do not need to be replaced is a feel good exercise.

Scheduled maintenance is carefully calculated so there's real value and minimum exposure of the equipment to damage in the process. I see equipment that has had "proactive replacement" of parts that is now unreliable because the replacemet of parts caused damage to the PCBs, or wiring harnesses, or whatever.

My experienced guess is that probably 85% of all parts replaced are perfectly good for many more years of service.

 

[beans-on-toast]

Replacing parts that do not need to be replaced is a feel good exercise.

Scheduled maintenance is carefully calculated so there's real value and minimum exposure of the equipment to damage in the process. I see equipment that has had "proactive replacement" of parts that is now unreliable because the replacemet of parts caused damage to the PCBs, or wiring harnesses, or whatever.

My experienced guess is that probably 85% of all parts replaced are perfectly good for many more years of service.

For high end equipment in the broadcast and recording area, procedures are detailed. Service manuals specify the required diagnostic equipment and tools such as for soldering and desoldering. Training courses are offered. Other industries follow suit. I worked in the bio-medical area at one time. The procedures and regulations were over the top, they had to be.

I've seen my share of butchered amps as well. At the same time, there are very good people out there. Some of the better ones are engineers who like to keep their hand out in the field by doing tech work. Finding good people to maintain their equipment is often a challenge for many players.

 

[agedhorse]

For high end equipment in the broadcast and recording area, procedures are detailed. Service manuals specify the required diagnostic equipment and tools such as for soldering and desoldering. Training courses are offered. Other industries follow suit. I worked in the bio-medical area at one time. The procedures and regulations were over the top, they had to be.

I've seen my share of butchered amps as well. At the same time, there are very good people out there. Some of the better ones are engineers who like to keep their hand out in the field by doing tech work. Finding good people to maintain their equipment is often a challenge for many players.

I'm just commenting based on what I see come in from the field... sometimes by service techs who might want to look for another line of work that's more in line with their skill set.

 

[beans-on-toast]

Automobile dealerships like to push scheduled maintenance.

I tell them to stick it.

 

[agedhorse]

Automobile dealerships like to push scheduled maintenance.

I tell them to stick it.

Of course, you need to verify everything a dealer suggests, many times the recommendations are based on sound data but sometimes things get stretched... a bit thin

When it's based on the combined knowledge of elapsed time and mileage, PLUS large sample size experience with failure data, it makes some sense. In MI amps, it's often based on irrational metrics, like internet voodoo, mythology, spirits and medicine man dances, therefore I don't trust these recommendations nearly as much.

In the aviation business, everything is well documented, well engineered, failure modes and fatigue data verified and many millions of flight hours logged with data from this to arrive at service intervals. It's regimented, it's 100% fact based, there's independent oversight, resulting in practical real world reliability results. My riding partner is an FAA certified inspector for air frame & power plant, he's been doing this a very long time, he 100% follows the book because the book is always right... the book is not based on voodoo, or internet mythology, it's based on science and engineering.

 

[BadExample]

In the aviation business, everything is well documented, well engineered, failure modes and fatigue data verified and many millions of flight hours logged with data from this to arrive at service intervals. It's regimented, it's 100% fact based, there's independent oversight, resulting in practical real world reliability results. My riding partner is an FAA certified inspector for air frame & power plant, he's been doing this a very long time, he 100% follows the book because the book is always right... the book is not based on voodoo, or internet mythology, it's based on science and engineering.

Ask bro. @Al Kraft about NAVAIR vs. civilian tool control. Or don't if you ever want to fly commercial again

 

[agedhorse]

Ask bro. @Al Kraft about NAVAIR vs. civilian tool control. Or don't if you ever want to fly commercial again

But there are process in place to insure that the gaps are well covered. My college roommate has been flying commercial passenger jets (737's and such) for several decades, he's more worried about having to unplug the lav

 

[Al Kraft]

Ask bro. @Al Kraft about NAVAIR vs. civilian tool control. Or don't if you ever want to fly commercial again

Funny you mention that. Early in my career I headed up a group that included the folks who managed the NAVAIR tool control program. Between FOD walk-downs, tool control and serious QA I think we had more flight line personnel going down aircraft inlets than we did anything else. We also prevented folks from using the wrong tools for the job and potentially damaging aircraft components or contributing to maintenance induced failures.

Now as far as aircraft parts and external stores staying on the aircraft during flight back in those days, our TFOA reporting didn't look nearly as stellar. Bottom line - you might have been safer flying in an aircraft than standing under one that was in flight.

 

[dan1952]

How about my GMC 228 w/ a Zenith?

once I get all that varnish off the Zenith, we oughta be able to get the 228 running.