Ciao vi contatto dall' italia ho in possesso un c.j.MV55 ho avuto dei problemi,
è andato in cortocircuito un trasformatore di uscita e purtroppo sono introvabili, ho contattato c.j. e hanno detto che non possono essere più forniti come ricambio, ho provveduto a farlo riavvolgere ma quando accendo imcomincia il motoboating e un volume troppo basso.
Sicuro che ho problemi con qualche parte del circuito e mi servirebbe il manuale di servizio, chi mi aiuta????
grazie!!
C.J.MV 55
Re: C.J.MV 55
Welcome to CJO. I don't speak Italian but... I think you are looking for the schematics for the MV55? You can download all our schematics here: https://www.conradjohnsonowners.com/vie ... f=17&t=128
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Home Theater in Member Gallery
Main stereo: ART Amplifier and ET7s2. 2nd stereo: PV-14L and MV-55. Previously Owned: PF2 preamp, Evolution 2000 Amp, PV-12AL preamp, D/A-2b Vacuum-Tube Digital Processor.
Home Theater in Member Gallery
Main stereo: ART Amplifier and ET7s2. 2nd stereo: PV-14L and MV-55. Previously Owned: PF2 preamp, Evolution 2000 Amp, PV-12AL preamp, D/A-2b Vacuum-Tube Digital Processor.
Re: C.J.MV 55
Thanks, I try to download the service manual I want to repair this amplifier because it is really amazing how I sound! 
Re: C.J.MV 55
Good luck with the repairs, let us know how it goes.
-admin
Home Theater in Member Gallery
Main stereo: ART Amplifier and ET7s2. 2nd stereo: PV-14L and MV-55. Previously Owned: PF2 preamp, Evolution 2000 Amp, PV-12AL preamp, D/A-2b Vacuum-Tube Digital Processor.
Home Theater in Member Gallery
Main stereo: ART Amplifier and ET7s2. 2nd stereo: PV-14L and MV-55. Previously Owned: PF2 preamp, Evolution 2000 Amp, PV-12AL preamp, D/A-2b Vacuum-Tube Digital Processor.
Re: C.J.MV 55
Hola EL34,
The motor boating oscillation usually comes from the B+ capacitor. Check the power supply capacitors, there is your problem.
The other possibility is that you need to change the EL-34s...when a tube is over bias, you might get a red plate or cause motor boating.
Here you might get some tips to find the culprit that is causing that oscillation.
https://www.youtube.com/watch?v=ThtE2hAuiIk
Happy liistening!
The motor boating oscillation usually comes from the B+ capacitor. Check the power supply capacitors, there is your problem.
The other possibility is that you need to change the EL-34s...when a tube is over bias, you might get a red plate or cause motor boating.
Here you might get some tips to find the culprit that is causing that oscillation.
https://www.youtube.com/watch?v=ThtE2hAuiIk
Happy liistening!
ML CLX BF-210 Stage X Motion 4. CJ 120SE amp ET7V2 pre, Holo May Kte Dac. Mac Pro. Power Cond. BPT Signature+ 3.5, Gaia II Feet. USB Lush^V3. Nordost SPM IC and Spk. Shun Mook, BCanto CD2 CD3. Linn LP-12/Unitrack tonearm/Denon DL103R MC.
Re: C.J.MV 55
Hi guys,
I wrapped both the output transformers, I mounted some new tubes but apparently it does not want to know how to work, I adjust the bias, I check a preamplified input source and from the speakers it is heard at very low volume, then the LEDs of the one channel bias fuse has blown! the capacitors and resistors are all intact! the bias goes up to -57 volts voltage of anode 498 ...... I don't understand what is happening! ideas? thank you
I wrapped both the output transformers, I mounted some new tubes but apparently it does not want to know how to work, I adjust the bias, I check a preamplified input source and from the speakers it is heard at very low volume, then the LEDs of the one channel bias fuse has blown! the capacitors and resistors are all intact! the bias goes up to -57 volts voltage of anode 498 ...... I don't understand what is happening! ideas? thank you
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AnotherJohnson
- Ultimate
- Posts: 5219
- Joined: Sun Apr 26, 2020 12:29 pm
- Location: Tennessee
Re: C.J.MV 55
Blowing out a bias resistor is often related to a runaway tube. A runaway tube can also lead to the type of oscillation you described. Motor boating is a good description because it is unlike typical transformer hum or typical failed cap leakage hum.
Your MV55 needs time on the bench. You say the capacitors and resistors are “intact” but I’m not clear on the intended meaning. To a native English speaker, intact might mean that they do not show visually recognizable signs of failure. Or it could be interpreted as meaning that they’ve all tested good.. but under what condition?
The MV55 is a very old model. If it’s been more than 10 years since it was recapped, recapping would be a good place to start.
As for wrapping transformers, again I’m not clear on your meaning. Did you mean you’ve put them in some sort of blanket? Or have you dealt with insulation issues by rewinding them. Transformers do fail with age and heat, and those of the MV55 era were even more prone to this than those currently used as OEM. Rewinding transformers is tedious work, and seemingly minor details can affect performance.
There’s probably something at the root of this … but without having it on the bench in front of us, and if Roberto’s excellent video didn’t help, it’s just very hard to make a diagnosis. Best of luck.
Your MV55 needs time on the bench. You say the capacitors and resistors are “intact” but I’m not clear on the intended meaning. To a native English speaker, intact might mean that they do not show visually recognizable signs of failure. Or it could be interpreted as meaning that they’ve all tested good.. but under what condition?
The MV55 is a very old model. If it’s been more than 10 years since it was recapped, recapping would be a good place to start.
As for wrapping transformers, again I’m not clear on your meaning. Did you mean you’ve put them in some sort of blanket? Or have you dealt with insulation issues by rewinding them. Transformers do fail with age and heat, and those of the MV55 era were even more prone to this than those currently used as OEM. Rewinding transformers is tedious work, and seemingly minor details can affect performance.
There’s probably something at the root of this … but without having it on the bench in front of us, and if Roberto’s excellent video didn’t help, it’s just very hard to make a diagnosis. Best of luck.
It’s just stuff. I like mine. I hope you like yours. I probably like yours too.
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Big Dog RJ
- Ultimate
- Posts: 2361
- Joined: Sun Sep 07, 2014 6:30 am
- Location: Melbourne, Australia
Re: C.J.MV 55
Yes, very correct.
In fact it's not an easy task to refurb vintage gear but it's possible with the right tech and skilled hands. So many stories of this in personal experience, not sure which one to mention... but one stands out with previous Quad ESL 2905's that I had.
When multiple panel failures started happening approx right during and after warranty, just around the third panel failure, one of the ESL's had two transformers failing. One was the mains HT (high tension) tranny and the other the low tension one. Anyway, after I got a full panel refurb done on both, the trannys required skilled hands. They were replaced with the same Chinese toy looking trannys but never sounded like an original Quad ESL. So I sent both trannys off to a chap out of state. They returned with fine precision skill done on them, just by holding them you could tell the difference straight away!
After my Quad tech assembled the ESL's back, the overall performance was such a fantastic experience for both of us, that at one point I was wondering what on Earth is the IAG group referring to QC... when clearly their QC is out of whack! Anyway, this tranny refurb and winding skill requires decades of experience and a steady hand, can't have a few beers and give it a go on a Sun arvo...
Hope the OP can restore this gear and get it back to reasonable spec, afterall during its hay day, it was a wonderful sounding amplifier.
Cheers and all the best, RJ
In fact it's not an easy task to refurb vintage gear but it's possible with the right tech and skilled hands. So many stories of this in personal experience, not sure which one to mention... but one stands out with previous Quad ESL 2905's that I had.
When multiple panel failures started happening approx right during and after warranty, just around the third panel failure, one of the ESL's had two transformers failing. One was the mains HT (high tension) tranny and the other the low tension one. Anyway, after I got a full panel refurb done on both, the trannys required skilled hands. They were replaced with the same Chinese toy looking trannys but never sounded like an original Quad ESL. So I sent both trannys off to a chap out of state. They returned with fine precision skill done on them, just by holding them you could tell the difference straight away!
After my Quad tech assembled the ESL's back, the overall performance was such a fantastic experience for both of us, that at one point I was wondering what on Earth is the IAG group referring to QC... when clearly their QC is out of whack! Anyway, this tranny refurb and winding skill requires decades of experience and a steady hand, can't have a few beers and give it a go on a Sun arvo...
Hope the OP can restore this gear and get it back to reasonable spec, afterall during its hay day, it was a wonderful sounding amplifier.
Cheers and all the best, RJ