i understand it but i will do it my way 😀 i want to mess with it. thanks guys again. from now on i will start by changing sus components and will see how it works .
exaclty there are only 6 caps on board thats easy to fix and 9 resistors those two that i replaced are not included. so if after that it does not work i will replace transistors anyways, thats my plan, after all all that components worth less then regular amp of that power xdd i have guitar amp 40w i paid 80$ so that is my point xd
board is made probably like 30 or 40 years ago it looks like that by the look of the components. but it looks like it is fixed many times before. so thats why i think replacing all components is best thing 😀 btw can someone just confirm small transistors ?
But NO ONE can fix an amplifier without thinking. If you don’t want to think or learn I suggest you just put it away.
Even just replacing every part on the board requires rubbing a few brain cells together and can’t really be done on autopilot.
Hi sg97,
I work professionally doing audio service. I work on items from the 1920's on up to current. You have an excellent reason to repair that amplifier, the only thing you are missing is the knowledge. If you would at least learn something, give it some effort. There is so much to know, you will never be very proficient unless you study and practice. After 45+ years I am still learning, so no one expects you to be an expert. But, at least pick up some knowledge.
Some items I repair, people like yourself have attempted and messed up because they did not think, and refused to learn the basics. Some have destroyed valuable items, some not very valuable. But there is no excuse to destroy anything, it just takes a tiny bit of effort to learn at least a little and do a good job. Sure it's only a few components - but it is how they interact. There are times the simpler circuits are the most difficult to repair.
This amplifier is so valuable to you. First because of its history, secondly because it represents a very good educational opportunity in both electronics and logic (thinking skills). In life, you should grab those learning opportunities when you can. Sure it takes some effort. Tell me one thing that is worth anything that doesn't take a little effort.
You can see the lack of care in previous servicing. Do a good job and that amp may last you a lifetime. Reliability has a great deal to do with workmanship. Knowing you fixed it decades ago and it still works is priceless. I have stuff I built in high school that still works fine. I'm sure most of us do unless we threw them out.
I work professionally doing audio service. I work on items from the 1920's on up to current. You have an excellent reason to repair that amplifier, the only thing you are missing is the knowledge. If you would at least learn something, give it some effort. There is so much to know, you will never be very proficient unless you study and practice. After 45+ years I am still learning, so no one expects you to be an expert. But, at least pick up some knowledge.
Some items I repair, people like yourself have attempted and messed up because they did not think, and refused to learn the basics. Some have destroyed valuable items, some not very valuable. But there is no excuse to destroy anything, it just takes a tiny bit of effort to learn at least a little and do a good job. Sure it's only a few components - but it is how they interact. There are times the simpler circuits are the most difficult to repair.
This amplifier is so valuable to you. First because of its history, secondly because it represents a very good educational opportunity in both electronics and logic (thinking skills). In life, you should grab those learning opportunities when you can. Sure it takes some effort. Tell me one thing that is worth anything that doesn't take a little effort.
You can see the lack of care in previous servicing. Do a good job and that amp may last you a lifetime. Reliability has a great deal to do with workmanship. Knowing you fixed it decades ago and it still works is priceless. I have stuff I built in high school that still works fine. I'm sure most of us do unless we threw them out.
thanks 😀 i appreciate that 😀 of course i will learn and i do and i did learn from you guys, but my point is that replacin all or almost all components will help, because those components are super old and maybe just worn out. first thing that i will replace are transistors who knows if they are 100% working
Do it the way you want, of course. Some time ago I worked in the same way, I just put on parts without knowing exactly how it works. But at some point I got bored with that, and wanted to understand the circuits I was working on. It takes some time and effort, but is much more interesting! I have to say, this is already a bit of a complicated circuit for a total beginner. Start with figuring out how a single stage transistor amplier works, if in the future you want to go that way.
I don't see measurements for my question in post #482 on page 25.
Before measuring, you need to set the output voltage as close as possible to half the supply from +55V. This is approximately +27V. The 2N3055 output transistors must be completely disconnected from the board.
Approximately, for proper operation, there should be at six points:
1) +2V; 2) +28V; 3) +26V; 4) +1.4V; 5) +27V; 6) +1V.
Before measuring, you need to set the output voltage as close as possible to half the supply from +55V. This is approximately +27V. The 2N3055 output transistors must be completely disconnected from the board.
Approximately, for proper operation, there should be at six points:
1) +2V; 2) +28V; 3) +26V; 4) +1.4V; 5) +27V; 6) +1V.
Absolutely. I only do electronics as an amateur, on and off since my school days around 50 years ago. And I still haven't learned to not burn myself with a soldering iron!
Hi Wakh,
Yes, mostly correct. The centre voltage is set to a little less than 1/2. The supply sags under load, so the proper way to set it is to adjust for equal clipping at full power using an oscilloscope. Setting it to 25 VDC with a 55 V supply might be closer. 1.4 VDC at TP 4 would mean a 234 mW dissipation in the 2N3904, it's going to get pretty warm. 1 VDC at TP 6 will mean pretty high bias current in the output and the TIP32A is conducting less current than the 2N3904.
I would confirm R4 and R5 are not open. If either was, you would get very high bias current in the outputs. By open, I mean even a bad solder joint or broken trace would do the same thing exactly.
Hi oscroft,
lol!
I usually get it with a splash of molten solder, or by having to hold something still. When I had really long hair (remember those days?), I used to burn my hair with the iron when it fell forward. Stinks.
Yes, mostly correct. The centre voltage is set to a little less than 1/2. The supply sags under load, so the proper way to set it is to adjust for equal clipping at full power using an oscilloscope. Setting it to 25 VDC with a 55 V supply might be closer. 1.4 VDC at TP 4 would mean a 234 mW dissipation in the 2N3904, it's going to get pretty warm. 1 VDC at TP 6 will mean pretty high bias current in the output and the TIP32A is conducting less current than the 2N3904.
I would confirm R4 and R5 are not open. If either was, you would get very high bias current in the outputs. By open, I mean even a bad solder joint or broken trace would do the same thing exactly.
Hi oscroft,
lol!
I usually get it with a splash of molten solder, or by having to hold something still. When I had really long hair (remember those days?), I used to burn my hair with the iron when it fell forward. Stinks.
Before measuring, you need to set the output voltage as close as possible to half the supply from +55V. how exactly to do that ?
if i set trim to show 25v then bulb is glowing if i put it to the left to 38-40v then its not glowing, and i get bit of volume. but thats only for q5 if i am right other 2n3055 does not have same voltages