You're a brave man even thinking about taking on one of these. I've been repairing domestic and professional audio for 40+ years and I won't touch these. Too difficult to work on, too 'clever' in the design department. I remember dismantling one once and I couldn't get it back together fast enough and back to where it came from. I've had others tell me they're not so bad, and I've said "well if you want to do it you're most welcome".
Interesting, thanks. I haven’t seen that. Just guys turning it on and measuring with no signal input. What volume knob setting would you typically use with the shorted inputs?
I have two Carver M-400t amps in storage. One I used in my home theater, and since I used to DJ, I used the other one for that. These amps would make your ears bleed from 100 ft through Klipsch LaScala speakers. They really are very good-sounding amps. I have a 120 WPC Yamaha receiver in my home theater now and it sounds blah compared to the Carver. No punch, no strong dynamics like the Carver.
Normally I wouldn't recommend recapping as a first or second step, but on these particular amps, I would. But I always check the triac first. If it's bad, you may be out of luck. You can find replacement parts, including the diac and triac, but Carver always insisted (I worked in a Carver-authorized repair center) we get these parts straight from them as they were hand-picked parts. Off-the-shelf parts might work for a year, a week, or a day, and then POP! BTW, the reason for the 201 wpc rating was that the FTC in America would not allow a home-stereo amp to be named with a model number that corresponded to its claimed wattage. Magnetic field amps must be tested with prayer only. No variac, no dimbulb. The power supply won't like it and will complain, but I don't think what you are seeing here is normal. It's been years since I worked on one. It may be that caps are all it needs.
Why is it called 'magnetic field amp'? And isn't a triac just a switching device? It's not like linear output transistors which might 'fight each other' and need to be carefully matched. So why wouldn't a triac with the same or better parameters just work?
John your knowledge and experience with SS is much more than mine! I graduated tech school in 1973 and by then SS was what they taught. I am a vacuum tube guy, mostly guitar amps. I do envy you for your ability to repair SS! Always love your videos, this one is no exception. Capacitors are the same in what ever they are in, so we are on the same page with them. I’ll be waiting for part 2 to see how you do with this guy. Love from NW Colorado. Thanxz
Standard practice for anything this old, atleast for me, replace every electrolytic and then troubleshoot. 85% of the time that clears out any issues the equipment has, or most of it.
Hi John, really enjoy your videos and this one caught my attention because I bought one of those amps new and used it for 9-10 years. Great amp, dead quiet (no buzzing or noise if the amp is working right). It really will do the 200W for extended periods. Mine eventually died, the big power supply cap blew and dripped corrosive capacitor blood on my finished wood floor; I was not amused. Sold it to a friend to fix, as I already had too many amps by then. He easily got it fixed; may still be working. In my opinion this amp is definitely worth restoring for its performance. BTW, I'm in Eaton, OH, not too far from you, and my wife went to UD for her EE degree.
I own a non functional cube. Blew it 15yrs ago running it mono, took it apart (was a service dillitant then) and it's still in that basket... I have more experience now and may finally attempt repair of that one. Unlike yours mine has ALL the writing ground off the metal case of ALL the T3 transistors.
carver said in an interview that not sure on this amp to decrease global feedback he was aiming for numbers back then to have it at 0.1% he indicated better sound quality that's a candidate for a switch mode power supply if I've ever seen one
Nice video, John. I like how you test the caps in circuit with an audio signal. I have a practical question. I opened up my 30 years old NAD (type 906) 6 channel power amp, to find one of the power supply caps on the edge of failing, it burst out of the plastic wrapper, it had a bigger diameter and increased ESR, while still working fine. I ended up recapping all the electrolytic caps on all channels. My supplier recommended also replacing all of the foil capacitors. I replaced them on one of the channels, but the ones taken out were as good as the new ones. Here’s my question, do you typically just replace the electrolytic ones or also these foil, or in this case polyester, caps as well? Do they ever fail or dry out? I appreciate your answer! Greetings from the Netherlands.
Poly caps rarely go bad. There is a plastic film and foil layers, so nothing to dry out. Having said that, it is possible for anything to fail. Caps across a high energy source, such as the mains can degrade from dielectric punctures due to voltage spikes. There have been bad batches that fail open, but that's rare.
I have a carver PM-1201 turns on everything seems fine except no sound from my speakers at all and that's not good seeing as it's 600 watts RMS at 4ohms per channel so something's not right with it
You're a brave man even thinking about taking on one of these. I've been repairing domestic and professional audio for 40+ years and I won't touch these. Too difficult to work on, too 'clever' in the design department. I remember dismantling one once and I couldn't get it back together fast enough and back to where it came from. I've had others tell me they're not so bad, and I've said "well if you want to do it you're most welcome".
When you measure the speaker output for DC, it’s typical to short the inputs. Most service manuals specify this.
Interesting, thanks. I haven’t seen that. Just guys turning it on and measuring with no signal input. What volume knob setting would you typically use with the shorted inputs?
I have two Carver M-400t amps in storage. One I used in my home theater, and since I used to DJ, I used the other one for that. These amps would make your ears bleed from 100 ft through Klipsch LaScala speakers. They really are very good-sounding amps. I have a 120 WPC Yamaha receiver in my home theater now and it sounds blah compared to the Carver. No punch, no strong dynamics like the Carver.
Normally I wouldn't recommend recapping as a first or second step, but on these particular amps, I would. But I always check the triac first. If it's bad, you may be out of luck. You can find replacement parts, including the diac and triac, but Carver always insisted (I worked in a Carver-authorized repair center) we get these parts straight from them as they were hand-picked parts. Off-the-shelf parts might work for a year, a week, or a day, and then POP! BTW, the reason for the 201 wpc rating was that the FTC in America would not allow a home-stereo amp to be named with a model number that corresponded to its claimed wattage. Magnetic field amps must be tested with prayer only. No variac, no dimbulb. The power supply won't like it and will complain, but I don't think what you are seeing here is normal. It's been years since I worked on one. It may be that caps are all it needs.
Why is it called 'magnetic field amp'?
And isn't a triac just a switching device? It's not like linear output transistors which might 'fight each other' and need to be carefully matched. So why wouldn't a triac with the same or better parameters just work?
John your knowledge and experience with SS is much more than mine! I graduated tech school in 1973 and by then SS was what they taught. I am a vacuum tube guy, mostly guitar amps. I do envy you for your ability to repair SS! Always love your videos, this one is no exception. Capacitors are the same in what ever they are in, so we are on the same page with them. I’ll be waiting for part 2 to see how you do with this guy. Love from NW Colorado. Thanxz
Standard practice for anything this old, atleast for me, replace every electrolytic and then troubleshoot. 85% of the time that clears out any issues the equipment has, or most of it.
Hi John, really enjoy your videos and this one caught my attention because I bought one of those amps new and used it for 9-10 years. Great amp, dead quiet (no buzzing or noise if the amp is working right). It really will do the 200W for extended periods. Mine eventually died, the big power supply cap blew and dripped corrosive capacitor blood on my finished wood floor; I was not amused. Sold it to a friend to fix, as I already had too many amps by then. He easily got it fixed; may still be working. In my opinion this amp is definitely worth restoring for its performance. BTW, I'm in Eaton, OH, not too far from you, and my wife went to UD for her EE degree.
A whole lot of recapping and Bingo two nice amps !...cheers.
Awesome, just awesome. Roll on part 2.
Avid viewer of all your vids.
When I saw that bulb flash briefly on the good amp on initial power up, I thought it was just the inrush into the transformer.
These TO-3-Adapters are pretty hot *.*
PSU are very tricky to repair all the caps should be replaced i recommend you get the service manual
I own a non functional cube. Blew it 15yrs ago running it mono, took it apart (was a service dillitant then) and it's still in that basket... I have more experience now and may finally attempt repair of that one. Unlike yours mine has ALL the writing ground off the metal case of ALL the T3 transistors.
Thank you.
carver said in an interview that not sure on this amp to decrease global feedback he was aiming for numbers back then to have it at 0.1% he indicated better sound quality
that's a candidate for a switch mode power supply if I've ever seen one
Nice video, John. I like how you test the caps in circuit with an audio signal.
I have a practical question. I opened up my 30 years old NAD (type 906) 6 channel power amp, to find one of the power supply caps on the edge of failing, it burst out of the plastic wrapper, it had a bigger diameter and increased ESR, while still working fine. I ended up recapping all the electrolytic caps on all channels. My supplier recommended also replacing all of the foil capacitors. I replaced them on one of the channels, but the ones taken out were as good as the new ones.
Here’s my question, do you typically just replace the electrolytic ones or also these foil, or in this case polyester, caps as well? Do they ever fail or dry out? I appreciate your answer! Greetings from the Netherlands.
Poly caps rarely go bad. There is a plastic film and foil layers, so nothing to dry out. Having said that, it is possible for anything to fail. Caps across a high energy source, such as the mains can degrade from dielectric punctures due to voltage spikes. There have been bad batches that fail open, but that's rare.
I have a carver PM-1201 turns on everything seems fine except no sound from my speakers at all and that's not good seeing as it's 600 watts RMS at 4ohms per channel so something's not right with it