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Victor JVC M-L10 Restoration

Ren_

Ren_

New Member
Hello all, This is my friend restoration post here in Audiokarma. Please bear with my english as it is not my first language. Thank you :)

Recently I was able to get my hands on the Humongous Victor M-L10 power amplifier. The seller has mentioned that its in quite a bad shape and I can't agree more.
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As soon as I got back home, I took my meter and probed the unit. It was outputting at least 200mv of DC so then I took it up to my bench and start checking on the bias and the DC offset. As soon as I turned the unit on, the amp was not able to get out of the protection. Narrowing down it is the main board solder joints being dull and cracked. Thanks to my friend, he said that the cold solder joints can send the amp into oscillation and the amp protection mode is trigged. After painful hours of reflowing the joints, the amp is up and running again.
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Not long after, I decided that its time to restore the amp as best as I could. Thanks to the part list available online, I was able to get the parts ordered.

This is one of the few daughter boards connected to the main board, the board has been washed clean.
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Before:
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After:
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With the new capacitors installed, only the best for the M-L10 Nichicon UPW and UPM installed.
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After recapping Meter Circuit:
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After recapping the hard to reach Power supply Board:
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Now this is the Fun begins (actually not), the amp is also one of the few examples of it being in contact with the horrendous corrosive glue and poor worksmanship by the previous owner. The area around the Predriver filter caps has been cleaned as much as I can, the biggest problem is that 2 transistor and a polyester capacitor has been ate alive by this glue. The legs of it has been snapped off, both the transistor is the complimentary pair 2SC1775 and 2SA872. Both of which is replaced by the modern equivalents, KSC1845 and KSA992.
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Oh I almost forgot, this unit also has the known VD style diodes. So, I went ahead and replace it with 2x 1n4148 in series.
The transistor that has got its legged ate, X308.
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I had to give it to the glue as well as it has been tested that it has failed.
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This picture is before the rework so you can see the VD style diodes still in place. There is a polyester capacitor that has shown a sign of it being molested by a hot soldering iron and a resistor paralled with another resistor. Mind you, it is a 47k ohm resistor and the owner thought the original has failed so he or she was lazy to remove the actual resistor. But I had to thank god that he or she did not replace the whole resistor as the new resistor is a 47ohm not the 47kohm, Overall I do not know what the previous owner tried to achieve. The C201 polyester capacitor and the 47k Ohm resistor has been fully replaced and cleaned up of any mess.
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Replacement capacitor is small
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Nichicon LKG type 2 1000uF in place of the 820uF. Was trying to get my hands on the best of the best, Type 3 super through but mouser ran out of stock. Worst part of this purchase of this predriver cap is that I had to pay for the premium shipping Fee to Malaysia.
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The little difficulty of trying to work on the power supply board.Making sure the board is not stressed and snap as I work on it.
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For those that is interested in the Weight of the power supply transformer module, It has a fully sealed toroidal and a normal transformer. Both of which provide power to the different functions of the amp, the toroidal is on the Power stage of the amplifier. While the latter powers the protection circuit and such. I have not look too deeply into the schematics so please do not take up my words as I do not wan't to get bashed. :)
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The Amplifier has been through few stages of restoration on and off, so in some pictures some parts does not look like it has the described parts replaced. Most of the parts of the main circuit for example the output filter stage has its Mylar capacitors replaced with the Polypropylene capacitors.
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The amp is currently on 22mv of bias and the DC offset has been set to 1mv. Previously, it is at 12mv of bias but unstable. I suspected that with the VD style diode replaced, the bias is stable now. Even my boss at my workplace mentioned that it is extremely stable, he said the main obvious sound characteristic is being very fast sounding. When playing, it is comfortably at a temperature of 55c on the heatsink probed with an ambient temperature of 27 to 29c. So this is my first warm running amplifier, still can't believe I got my hands on one of the gem amplifiers from the early 80s.

Since this amplifier did not come with the ability to use banana plug, I went ahead and ordered some Cardas ACBP-S binding post to mod it into the amp. The amp originally came with the big bare wire only binding post. Since I do not have an electric drill, I painstakingly hand drill it with a step drill bit from 8mm to 14mm diameter hole
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Moving on, The wood case has also been reworked. This picture is the condition of the wood case, I know its horrifying for an amp of this calibre.
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The wood case took some time to work on as I do not have the required materials. Bought some sanding sealer and some high gloss lacquer. The internal case is slowly chipping off so the sanding sealer helped the wood not fall apart. I did not decide to darken the wood case as I wan't it as a reminder of what the amplifier went through before my ownership. The wood case has some signs of it being worked on aswell as there is few residue of lacquer that would not leave the factory QC.
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Total there is 5 coats of high gloss lacquer between each coat the case is sand leveled.
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The Final product:
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I Have to give a credit to the local headphone shop for giving me an opportunity to try my amplifier in their speaker room. Overall, everybody that is present at the shop is very surprised what the beast can do, monstrous bass and sounding fast and tamed while being elegant. In the small room, We were able to push the amplifier to 50-100 watt peak with the small ATC SCM7 and this is also the first time I hear an ATC. In the room, the ATC is very quick on it's feet and the mid detail is intoxicating, the highs especially is silky smooth.
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Currently, the amplifier is paired up with my Naim Allae. In the long run, I'm also looking out on a proper candidate to replace my preamp with a better one. This poweramp won't be out for sale for some time, as I love it to death.

Video is recorded by my mate with his stax.
 
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Thanks for all the pics, they will pobably be usefull when I need to recap the one I was also lucky enough to find, about 6 years ago, it's been in my main system ever since, I use a Luxman C-12 pre with it at the moment (which sounds gorgeous), but I have a Luxman 5C50 (with the super rare optional wooden enclosure) to work on as a replacement, which I'm hoping will be an improvement. The matching P-L10 is supposed to be very good also, but equally elusive.

Great job on the case too, I decided to leave mine as is, it has some scratches, and a few chips, but still has most of it's origional lustre.
 
@GD70 is gonna enjoy seeing this thread. Glenn has the preamp and did a nice restore on the M-7050.

Nice unit, well done.

@AudioAvarice You have a couple nice preamps to enjoy while you continue your hunt for the P-L10. I read, as I have never seen one, that the optional cabinet for the 5C50 is vinyl clad. I was surprised to read that as the T-110/C-1000/L-100 and such have rosewood veneered cabinets. Can you confirm?

I also just found out the PD-441 has the rosewood vinyl on it. It looks most excellent and if the 5C50 wooden enclosure is like the side panels on this turntable, I'd be happy with it.
 
@Ren_ Yes I can confirm that they used vinyl on the optional case, it looks pretty good from a distance, and I has peeled a bit in one area, if I can't restore it, I'll try and find some decent rosewood veneer for it. I doubt I would bother with a P-L10 now, as I adore Luxman's version of tone controls in these two preamps, the simplicity of it's design, and discrete circuitry ensure minimal signal loss/degredation, even brought some Audio note resistors to see if I can hear a difference when I rebuild the 5C50.
 
I have some stuff which purpose is to protect vinyl office floors and make them shine again.
I used it after sanding some scratches in my bathtub. It is like new, again.
I also tried it on an old plastic binder, just to see.

Most probably it works for amp vinyl casings, too
no affiliation but here is a link https://cdn.hg.eu/media/vsslsaaw/0511300210006.pdf

I presume there will be alike products everywhere.
 
Blue Shadow said:
@GD70 is gonna enjoy seeing this thread. Glenn has the preamp and did a nice restore on the M-7050.

Nice unit, well done.

@AudioAvarice You have a couple nice preamps to enjoy while you continue your hunt for the P-L10. I read, as I have never seen one, that the optional cabinet for the 5C50 is vinyl clad. I was surprised to read that as the T-110/C-1000/L-100 and such have rosewood veneered cabinets. Can you confirm?

I also just found out the PD-441 has the rosewood vinyl on it. It looks most excellent and if the 5C50 wooden enclosure is like the side panels on this turntable, I'd be happy with it.
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The P-L10 is nice, but it uses modules for the volume control stage. Very complicated and also, as I have read, very troublesome. I suggest looking past the P-L10 for something a bit more "kosher" if you know what I mean ;)
 
Blue Shadow said:
I think AudioAvarice has a couple of great preamps already and I would not be moving those out for the JVC. Love the Linear Equalizer on the Luxmans, have that on my C-1000 with a nice, stepped Noble volume control easily opened and cleaned.
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For sure! Luxman preamplifiers of the era were extremely good and flew under the radar. Mostly completely discrete and well laid out. Unfortunately the prices on the used market are going up!

@AudioAvarice - I see you are planning on restoring your 5C50... I would like to draw your attention to the modules used in the Laboratory series of Luxman gear such as the 5M21 and 5C50... These can and will cause many gremlins including DC offset and noise. Luxman knew of this and published a critical service bulletin, outlining the replacement of faulty modules, in favor of an unpotted daughter board that was to be soldered in place of the old modules. Some of the Laboratory gear unfortunately slipped through the cracks, retaining the old style modules. These are the ones you have to look out for. Someone is actually making and selling replacement drop-in modules online. You can find them here, including more information about them. Let me know if I can be of any other help to you. Good luck!

Sorry for hijacking your thread, Kirin. I'm sure you understand ;)
 
The C-1000 was on my radar for a while just because it was another model with the Linear Equalizer, the C-12, and 5C50 use a similar rotary switch.

@Connor G Luckily both my UK model C-12, and Japanese 5C50 have the factory replacement DML-02 modules, I've got that site firmly in my favorites just incase, there's also a good youtube video of a guy servicing his 5C50, where he even sucessfully copies one of these factory replaced boards, might get a pair, just to have spares, and they come with a socket, so comparisons would be easy to make.
 
Connor G said:
The P-L10 is nice, but it uses modules for the volume control stage. Very complicated and also, as I have read, very troublesome. I suggest looking past the P-L10 for something a bit more "kosher" if you know what I mean ;)
Click to expand...
The P-L10 is a fabulous preamp, especially the phono section. The one main issue is one board that was not screwed to the chassis at the factory, that the main filter caps are on. When the unit is inside down on the bench, the caps can come in contact with the bench surface putting pressure on the pc board. It can crack, breaks traces, which looks to be a common issue with these. Mine had this problem and I believe Tims did as well, though his traces didn’t break. It can be repaired. First gluing the board, then running solid copper wires over the broken traces, and replacing the caps with physically smaller caps. Tom B. did this work on mine as well as replaced a few other parts and it’s been great. I wouldn’t shy away from it.
@Ren_ Fabulous work and documentation on your restoration! These JVC/Victor amps are sleepers and fantastic sounding! Granted most will need some work done at some point because of age. But so, will every other brand. I will suggest looking for the P-L10 as it’s designed to mate with the M-L10 & M7050s.
 
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