You never replied to one of my question. I will ask again. Is that C40 a tantalum. Post the picture if u don't know. This will help others.
Enjoy
Gajanan Phadte
Enjoy
Gajanan Phadte
Gajanan Phadte
I don't have a way of testing caps other than to ohm them for a short. I just happened to have two .47uf 50v caps on hand so I replaced C40 and instant WONDERFUL!!!
No more buzzing, the outputs are running about 87 degrees after about 15 minutes of playing on all three channels. And it sounds wonderful! Did I mention that yet? lol Of course I still have the 4.6k resistors at R95 and 96. Is that going to be a problem? I ask because I really like the sound of the amp like this. It seems like it has a fuller sound. Although that could very well be because this amp has always sounds WAY better than my other amp. Maybe I should put the 2.2k resistors back in and see what it sounds like. Hmmm
Anyway I ohmed the old cap and its shorted. So I guess its no wonder the outputs were running hot.
Hopefully this is the end of problems with this amp for a while.
Of course I wish to thank Gajanan for his advice here because it led me to the immediate solution. But I wish to thank all of you for your tireless help. Sorry this went so long. I didn't give up though and I have learned so much from you guys and all the research I have had to do. Thank you thank you thank you! You guys are wonderful!
BR
Time for a beer!
Just an update: Its been 5 weeks since we found the problem with the amp. I gotta tell you all, this amp plays better than it did when it was new. Running the bias colder has made a tremendous difference in the tone and playability. It has always sounded like it was on the edge of quitting on me or something. It has at times overheated on me in summer months. Now there is no more crackling, popping etc. It sounds solid, smooth, powerful and best of all Good!
Since correcting the amp I have rewired my guitar and corrected a problem I didn't know I created when I wired it several years ago. I even added a mod to keep the fidelity when I roll the volume off as well.
This amp sounds so good these days I have given up on my idea of purchasing a tube amp (for now).
This whole experience has been very rewarding in that it forced me to spend a lot of time learning about amp electronics, I learned to be much better at soldering etc. and it caused me to learn to get better sound from my Spider Jam which I pretty much hated before. And this has carried over to my Fender amp. And most of all, I got to meet some pretty neat people on this forum. Just want to say thanks for all the help and for sticking through my mistakes, stupid quiestions and learning curve. I know I would have given up without you guys.
Jeff
Since correcting the amp I have rewired my guitar and corrected a problem I didn't know I created when I wired it several years ago. I even added a mod to keep the fidelity when I roll the volume off as well.
This amp sounds so good these days I have given up on my idea of purchasing a tube amp (for now).
This whole experience has been very rewarding in that it forced me to spend a lot of time learning about amp electronics, I learned to be much better at soldering etc. and it caused me to learn to get better sound from my Spider Jam which I pretty much hated before. And this has carried over to my Fender amp. And most of all, I got to meet some pretty neat people on this forum. Just want to say thanks for all the help and for sticking through my mistakes, stupid quiestions and learning curve. I know I would have given up without you guys.
Jeff
I used to just take the bias setting recommended for any amps I had.
It was only when I designed my own amp did I give the bias setting any more thought.
I have read lots of threads where people prefer high bias currents.
I found myself that it was surprising how little bias current I needed to get rid of crossover distortion. I found I could get away with as little as 5mA.
I found out later that Peavey are quite famous for using low bias currents too.
It was only when I designed my own amp did I give the bias setting any more thought.
I have read lots of threads where people prefer high bias currents.
I found myself that it was surprising how little bias current I needed to get rid of crossover distortion. I found I could get away with as little as 5mA.
I found out later that Peavey are quite famous for using low bias currents too.
Well I know lowering the bias sure made a difference with my amp because I changed it back to stock and did not like it at all. I wonder how much difference changing the opamps made? I changed them all to RC4558's I guess the next time I open the amp I can try some different ones to see what happens.
I've followed this long thread and learned a lot about this amp. I had a similar problem with 39V DC at the speakers when ever anything was plugged into the inputs only. I first replaced the 4 transistors on the heat sink as that is usually the problem however they all tested good off the board. I found R144 had actually went open causing the DC voltage. Now all is well.
Great thread.
I'm happy to delve into a tube amp but the SS stuff makes me apprehensive. Less so after just reading all 270 posts here.
I think it would be worth making this thread a sticky for SS newbies (and not so newbies)?
I consider the advice given freely and persistently from Enzo, Juan, & Nigel - & others - is pure gold.
I'm happy to delve into a tube amp but the SS stuff makes me apprehensive. Less so after just reading all 270 posts here.
I think it would be worth making this thread a sticky for SS newbies (and not so newbies)?
I consider the advice given freely and persistently from Enzo, Juan, & Nigel - & others - is pure gold.
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Valve/tube amps are far simpler and cruder - so far easier to repair - the sort of gear you can mend with a hammer and a pair of pliers. Transistor gear is more a tweezers and magnifying glass job, with the ever present danger of a "row of dominoes".
But modern repair agents seem to have little or no clue about valve/tube amps, I get various ones for repair which have been round many shops and couldn't be mended, yet all have simple common faults (but I date back to the latter end of the valve/tube days - they were mentioned ONE DAY at college, and that was when the normal lecturer was off).
And the sad thing is, troubleshooting is troubleshooting. The technologies have specific details, but the approach is still the same: isolate the problem.
I agree with Nigel, tube are much cruder and simpler. Vacuum tubes was a mature technology 50 years ago, there is pretty much a way to make tube amplifiers and everyone did it that way. Detail are the main variations.
SOlid state amps, power amps anyway, are massively fed back on themselves. They are one big loop. That does require attention. And Nigel is right about the row of dominoes. All those transistors connected together, one can blow and take down a bunch more.
But still, when they blow fuses, we look for shorted outputs, then shorted rectifiers, maybe shorted caps... just like a tube amp problem. A signal path problem is still a matter of tracing a signal stage by stage. Voltages may be different but the rule is still the same: no circuit will work right if it doesn;t have good power supply.
As to the 270 posts, keep in mind that we are trying to fix this with the hands of someone else, someone who really doesn't know what he is doing. And we are doing it one voltage reading or one question at a time. That takes a long time and many posts. Something that takes a month to fix this way is probably fixed in under an hour in my shop if it is in front of me. SOmetimes the same point is made by multiple people, if for no other reason than to state the point in various ways so it becomes clearer. The posts add up.
I agree with Nigel, tube are much cruder and simpler. Vacuum tubes was a mature technology 50 years ago, there is pretty much a way to make tube amplifiers and everyone did it that way. Detail are the main variations.
SOlid state amps, power amps anyway, are massively fed back on themselves. They are one big loop. That does require attention. And Nigel is right about the row of dominoes. All those transistors connected together, one can blow and take down a bunch more.
But still, when they blow fuses, we look for shorted outputs, then shorted rectifiers, maybe shorted caps... just like a tube amp problem. A signal path problem is still a matter of tracing a signal stage by stage. Voltages may be different but the rule is still the same: no circuit will work right if it doesn;t have good power supply.
As to the 270 posts, keep in mind that we are trying to fix this with the hands of someone else, someone who really doesn't know what he is doing. And we are doing it one voltage reading or one question at a time. That takes a long time and many posts. Something that takes a month to fix this way is probably fixed in under an hour in my shop if it is in front of me. SOmetimes the same point is made by multiple people, if for no other reason than to state the point in various ways so it becomes clearer. The posts add up.
fender 212 / 2n 4003 transistor
I'm new and realize this is an old post.don't know if you ever solved the fender 212 transistor problem but, a little late with the info maybe but that is a mis-print on the schematic.absolutely 100% for sure.the number on the actual component Q6 and Q7 is 2N4403 which crosses to a ECG 159 PNP audio class preamp transistor
I'm new and realize this is an old post.don't know if you ever solved the fender 212 transistor problem but, a little late with the info maybe but that is a mis-print on the schematic.absolutely 100% for sure.the number on the actual component Q6 and Q7 is 2N4403 which crosses to a ECG 159 PNP audio class preamp transistor
For what good it might do, the source of that noise (crack, pop and fizzle) was,
in my case due to a faulty 2sa1013 Q12 in the schematic.
I replaced Q12 and Q13, 2sc2383 as a precaution.
I firmly believe, one of the best diagnostic tools for finding a noisy discrete
transistor, is a humble can of freeze spray.
in my case due to a faulty 2sa1013 Q12 in the schematic.
I replaced Q12 and Q13, 2sc2383 as a precaution.
I firmly believe, one of the best diagnostic tools for finding a noisy discrete
transistor, is a humble can of freeze spray.
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