What a great series. Thanks Tony. I've just repaired and I'm now overhauling a TFM-55x. I felt like I was in the twilight zone when I first got the amp opened up. Now that I'm becoming more familiar with the design, I'm really beginning to admire it. Even with just a minimal repair, this amp sounds wonderful on a pair of 100W JBL's. Your videos have helped me to understand some of the things I've been seeing on the bench. The amp's owner is paying for parts and he has a set of speakers for me if I want them. Like you, I repair old stereo gear as a hobby. I repair automated handling equipment (electric forklifts and there ilk) professionally. Thanks again!
I like that you go into detail of how circuits work, very few UA-cam channel's do this. It is adding to my understanding of electronic circuit's - thanks. I also like the way you modded the meter circuit. Next time I hit a similar problem I'll bear this in mind rather than reaching for a standard solution..
"So, even though you're dealing with a 60 cycles signal, it modulating at changing the duty cycle thousands of times in a second." I beg to differ. It's a triac. Once you turn it on, it's going to remain on for the rest of the half-cycle. At best, it can adjust the firing every half-cycle of the 60Hz waveform. In order to get a power supply that can change "the duty cycle thousands of times in a second", you need a different device that can turn off mid-cycle and make the sine wave look like you're viewing it though a comb. In short, you'd need something that more closely resembles a conventional switching power supply.
I would love to hear the Carver mono blocks through y;our Klipsch speakers. I totally enjoyed the video series on the amps in the great detail you always provide. I have and have used Bob Carver electronic creations both Carver and Phase Linear for decades. There were problems like the Phase Linear 400 power amp that didn't have the safeguards you described and took out numerous JBL , Altec Jensen etc speakers in a micro-second .Thanks.
A little trick I picked up from an old industrial engineer involves Loctite. You just apply a generous portion across the plates of the transformer core. It fills in the tiny gaps and silences them. This works on noisy windings too. I've used this on everything from older amps like those two beauties to noisy inductors on the newest video cards for computers.
If the jfet is the weak point and it’s failed in one amp, replace them with new components in BOTH amps. One as a fix and the other as a precaution. Great video series.
I've been a fan of Bob Carver for a long time. I own a 5 channel Carver av705x home theater amp that is a wonderful piece. Though newer than the Carver designs you are looking at. Runs cool even after hours at high volume.
Thanks for utubing this, enjoyed all 4. Two things I would liked to have seen: 1. The output voltage waveform of one of the outputs of the xformer with that triac input pushing it at different levels. 2. Put the clamp-on amp meter on the line A/C cord to see what the actual current draw is at full output.
Really enjoyed your program on the Carver 9t. I have two 30-year old Carver M1.5t which have a similar design. Over the years I have had 4 failures for power caps, the thyristors, and the protection circuits. These guys still work, and have no headroom above 350 watts at 8 ohms. The other issue I discovered that moved me to much more robust and expensive amps is the amount of electronic noise/hash emitted. I discovered this trying to use the amp on some early synthesizers and digital samplers like the Ensonic samplers. The noise made the amp unusable so I went to an old Crown DC-300 class AB amp. I would be interested to see if other Carver users found the amps unusable in music production due to the noise.
Really nicely done series. Thank you. One question on the meter lighting - I was curious as to why you didn't just pick up working voltage off the power LED supply?
There's this musician called Anders Jensen, who's got royalty free music up in lossless formats... it would be interesting to hear some of his stuff through these amps.
Hi Tony, thanks for another great series of repair/review, really enjoy your methodical way of going about things. One question: those buck little buck converters are great value, I use them regularly myself. However, they are very noisy, any risk injecting this noise into various parts of the amp circuitry you think?
The buck regulator that I used operates at around 180kHz. At that frequency, the EMI is very low with respect to this type of application. Some buck regulators run at higher frequencies which produce higher EMI. At any rate, I would probably avoid using them in close proximity to a tuner or phono stage, as even the harmonics could possibly cause some interference. In this case, the power amp doesn't have very high gain, nor does it have as high of an input impedance as a tuner, etc. Therefore, it didn't seem to cause any problems. It is always a concern and should always be considered. Hope this helps. Thanks for the comment!
I don’t think I’ve ever seen such a wide range of opinions on a specific brand of electronics. When it comes to Carver you get “biggest pile of crap I’ve ever heard” and you also get “I’ve always loved them and I’ve had several different pieces of Carver equipment with no issues whatsoever”. Come on people . You can’t have it both ways. It’s either good or bad or just ok.
The 300hz signal does not look clean initially at all. It looks severely clipped until the power supply catches up, unless that is an artifact from the scope.
9:48 You know you've been working on old tech too much when... you say "capstan tape" instead of "Kapton tape" ;) *chuckle* On a more serious note, I don't think the 130-odd mA dissipation is actually required, I guess it was merely done like that in order to have symmetric loading on both rails and avoid unbalancing the power transformer. They tend not to like that too much, potentially starting to hum and whatnot. BTW, 130-odd mA on +/-31 V actually is about 8 W, so if that's already included in the 21-ish W at idle, this thing is surprisingly power-efficient. Isn't lighting a bit uneven with just one LED instead of two bulbs? It's also looking quite bluish, which isn't exactly my preferred tint but tastes may vary.
What a great series. Thanks Tony. I've just repaired and I'm now overhauling a TFM-55x. I felt like I was in the twilight zone when I first got the amp opened up. Now that I'm becoming more familiar with the design, I'm really beginning to admire it. Even with just a minimal repair, this amp sounds wonderful on a pair of 100W JBL's. Your videos have helped me to understand some of the things I've been seeing on the bench. The amp's owner is paying for parts and he has a set of speakers for me if I want them. Like you, I repair old stereo gear as a hobby. I repair automated handling equipment (electric forklifts and there ilk) professionally. Thanks again!
Thank you for showing how you found the culprit. Yes, I would love to hear how they sound on your Klipsch speakers!!!
I have The RF3 Klipsch speakers and they Rock with the silver 7t's I hadd mine rebuilt a few years ago.
Can't wait to hear both hooked up to speakers.
I like that you go into detail of how circuits work, very few UA-cam channel's do this. It is adding to my understanding of electronic circuit's - thanks.
I also like the way you modded the meter circuit. Next time I hit a similar problem I'll bear this in mind rather than reaching for a standard solution..
"So, even though you're dealing with a 60 cycles signal, it modulating at changing the duty cycle thousands of times in a second." I beg to differ. It's a triac. Once you turn it on, it's going to remain on for the rest of the half-cycle. At best, it can adjust the firing every half-cycle of the 60Hz waveform. In order to get a power supply that can change "the duty cycle thousands of times in a second", you need a different device that can turn off mid-cycle and make the sine wave look like you're viewing it though a comb. In short, you'd need something that more closely resembles a conventional switching power supply.
Your a good teacher you explane things so well
I would love to hear the Carver mono blocks through y;our Klipsch speakers. I totally enjoyed the video series on the amps in the great detail you always provide. I have and have used Bob Carver electronic creations both Carver and Phase Linear for decades. There were problems like the Phase Linear 400 power amp that didn't have the safeguards you described and took out numerous JBL , Altec Jensen etc speakers in a micro-second .Thanks.
aka "Flames Linear".
Getting old is not for the fainthearted, but it beats the alternative.
A little trick I picked up from an old industrial engineer involves Loctite. You just apply a generous portion across the plates of the transformer core. It fills in the tiny gaps and silences them. This works on noisy windings too. I've used this on everything from older amps like those two beauties to noisy inductors on the newest video cards for computers.
This sounds like the modern version of potting a transformer in tar. 😀
If the jfet is the weak point and it’s failed in one amp, replace them with new components in BOTH amps. One as a fix and the other as a precaution. Great video series.
I've been a fan of Bob Carver for a long time. I own a 5 channel Carver av705x home theater amp that is a wonderful piece. Though newer than the Carver designs you are looking at. Runs cool even after hours at high volume.
Thanks for utubing this, enjoyed all 4.
Two things I would liked to have seen:
1. The output voltage waveform of one of the outputs of the xformer with that triac input pushing it at different levels.
2. Put the clamp-on amp meter on the line A/C cord to see what the actual current draw is at full output.
Excellent series Tony!
Really enjoyed your program on the Carver 9t. I have two 30-year old Carver M1.5t which have a similar design. Over the years I have had 4 failures for power caps, the thyristors, and the protection circuits. These guys still work, and have no headroom above 350 watts at 8 ohms. The other issue I discovered that moved me to much more robust and expensive amps is the amount of electronic noise/hash emitted. I discovered this trying to use the amp on some early synthesizers and digital samplers like the Ensonic samplers. The noise made the amp unusable so I went to an old Crown DC-300 class AB amp. I would be interested to see if other Carver users found the amps unusable in music production due to the noise.
Really nicely done series. Thank you. One question on the meter lighting - I was curious as to why you didn't just pick up working voltage off the power LED supply?
Great end to the series !...cheers.
Strange amps!! Thanks for sharing and educating!
There's this musician called Anders Jensen, who's got royalty free music up in lossless formats... it would be interesting to hear some of his stuff through these amps.
Nice work. I'd have liked to see a square wave through this amp.
Hi Tony, thanks for another great series of repair/review, really enjoy your methodical way of going about things. One question: those buck little buck converters are great value, I use them regularly myself. However, they are very noisy, any risk injecting this noise into various parts of the amp circuitry you think?
The buck regulator that I used operates at around 180kHz. At that frequency, the EMI is very low with respect to this type of application. Some buck regulators run at higher frequencies which produce higher EMI. At any rate, I would probably avoid using them in close proximity to a tuner or phono stage, as even the harmonics could possibly cause some interference. In this case, the power amp doesn't have very high gain, nor does it have as high of an input impedance as a tuner, etc. Therefore, it didn't seem to cause any problems. It is always a concern and should always be considered. Hope this helps. Thanks for the comment!
I don’t think I’ve ever seen such a wide range of opinions on a specific brand of electronics. When it comes to Carver you get “biggest pile of crap I’ve ever heard” and you also get “I’ve always loved them and I’ve had several different pieces of Carver equipment with no issues whatsoever”. Come on people . You can’t have it both ways. It’s either good or bad or just ok.
The 300hz signal does not look clean initially at all. It looks severely clipped until the power supply catches up, unless that is an artifact from the scope.
9:48 You know you've been working on old tech too much when... you say "capstan tape" instead of "Kapton tape" ;) *chuckle*
On a more serious note, I don't think the 130-odd mA dissipation is actually required, I guess it was merely done like that in order to have symmetric loading on both rails and avoid unbalancing the power transformer. They tend not to like that too much, potentially starting to hum and whatnot.
BTW, 130-odd mA on +/-31 V actually is about 8 W, so if that's already included in the 21-ish W at idle, this thing is surprisingly power-efficient.
Isn't lighting a bit uneven with just one LED instead of two bulbs? It's also looking quite bluish, which isn't exactly my preferred tint but tastes may vary.
Got a decent record player and a disk that UA-cam has no problems with? Use that. The detail at lowish volume would be interesting.
I am looking to try to get a Harmon Kardon av r 25II fixed and was wondering how I might be able to get into contact with you.
Tony
Do you work on other Carver amps?
Such as the TFM series ?
Nice to see another classic ready to be put back into service.
Did the PLL IC I sent you arrive safely?
Just got it yesterday. Thanks again! Now I just need some time to get back on that project :)
Hmmmm, the voice sounds a bit like Bob Carver.... :)
Play them!
Play something for us, please.
I had a pair of these back in the early 90s What a giant steaming pile of s#%t they were. Sound horrible no matter what you do
Not to me..... what are you comparing them to, a Krell? I have the Silver 7t's that bass Rock.
Sound great to me!
You should have had the (op-amps)4558's upgraded to NJM2068's. 4558's are notorious for current noise.
@@christophero1969 Nope I just threw them in the trash where they belonged. I have owned transistor radios that sounded better