Luxman L-507 refurbish and variations of the 507 series

[sonavor]

I am moving to this thread with postings from another Audiokarma thread I started in July, 2010 - http://www.audiokarma.org/forums/showthread.php?p=5402159#post5402159

At that time I dug out my Luxman L-507 which had been in storage for a while because I wanted to see if it worked. I wasn't really surprised that it didn't. I bought the amplifier second-hand from an authorized stereo store in 1976. A couple of years later it developed a problem in the right channel where the amplifier had to warm up before it would work. The speaker protection relay would click on and off while the warm up process took place. I started just leaving the amplifier on all the time. It never had any problems when I did that. On two occasions I had a (supposedly expert) technician look at it to fix the problem. They never could find the problem. I finally stopped using it around 1988.

In 2010 when I decided to see if I could resurrect this nice vintage amplifier I started looking for a service manual or a schematic. That was when I started the Audiokarma thread. I couldn't find a service manual but I found a couple of schematics. One was for the SQ-507 and one was for the L-507 (my amplifier). I also found the ton of information on this site about refurbishing vintage audio and the necessity to replace the electrolytics. So that was the first step.

As I started on the recap I found that my L-507 didn't really match either the SQ-507 or the L-507 schematics. They were close but not the same. One clear difference was on the output amplifier schematic. The SQ-507 shows eight transisitors. The L-507 schematic shows nine transistors. My L-507 has ten transistors.

There are pictures of the schematics and latest recap on the other thread. http://www.audiokarma.org/forums/showthread.php?p=5402159#post5402159

The recap went smoothly and I was impressed when the amplifier came to life. It still needed a good cleaning of the switches but it was working. I also discovered a problem with the speaker protection relay. Its contacts were really corroded so I replaced it. The old L-507 was pretty much back to the way it was when I put it away....the warm up problem on the right output amplifier module was still there. I had hoped that was a capacitor related problem but it wasn't. I verified it is a heat issue on the suspect output amplifier module by using a heatgun (carefully) to heat up just that board before first turning on the L-507 for the day. When I did that the problem didn't occur. So I did some more trouble-shooting in vain and decided to shelve it until maybe I could find another L-507 to compare to.

A few weeks ago I aquired a second L-507 amplilfier. It was a unit that was advertised as having problems driving speakers. It turned out to be a really nice amplifier. It is in excellent shape....better cosmetically than mine I think. I did a quick test on my variac/dim bulb tester and it passed. When I had power on it I could hear the protection relay click just once as it is supposed to and stayed on. So I swapped the right channel output board of this new L-507 with my old one. Sure enough, the warm up problem in my old amplifier went away. So I was in business.

The recapping of the new L-507 and description of circuit differences start in the other thread - http://www.audiokarma.org/forums/showthread.php?p=5402159#post5402159

I will now continue them here. Audiokarma users: ecluser and Alienz have been providing me with some great information and help. Alienz has a Luxman SQ-507 and posted a couple of pictures of his output amplifier module. I have a couple pictures of mine. You can see they are similar but different. Because there isn't an accurate schematic of the L-507, I traced out my board and created one. That picture is also posted in the starting thread. One thing that was interesting in determining the real schematic was that the closest Luxman output amplifier schematic to the L-507 is the L80V. The actual component physical location in the L80V is completely different but the circuit is really, really close. I have a couple of pictures of the differences and a cross-reference of the circuit parts (output amplifier only) of the L-507 and L80V.

Sorry for being so long-winded on this posting but I hope other Luxman vintage amplifier owners will find the information useful. I will be adding the rest of the L-507 recap and any new schematic information in this thread.

-Sonavor

 

[ryuuoh]

Nice story, and congratulations on getting your vintage amp up and running~
I have an L-80v, and I like it a lot.

 

[Alienz]

Hi sonavor,

Did you also replace the big PS caps on your Lux amps?

I'd like to replace mine with some Mundorf M-lytics but they are only 3 by 4 cm but I wonder how to get them mounted in there.

I read about people re-using the old caps, getting the old stuff out etc or using some pvc piping to support the caps.

 

[sonavor]

I didn't replace the PS caps. I figured if I did, I would go with the heavy duty, long lasting power supply caps. The datasheets on those larger caps state a rated life of hours at some temperature (usually 85 degrees Celsius - 185 degree fahrenheit). Those hours are around 2000 to 5000 for the less expensive caps and up in the 10,000 to 15,000 range on the expensive ($50 - over a $100).

Don't they sell circular, metal mounting brackets for the larger cans?

When I get around to fixing up my L-100 I hope those PS caps are okay. They are huge, custom ones that Luxman had made for them I think.

 

[Alienz]

I like the idea of re-using the old caps as mounting, just not looking forward to getting all that goo out of there, i also have no idea how toxic this stuff is.

BTW there's this german guy who has a site full of old brochures, including luxman, i think the L-507 is in there somewhere too. If you need any german translation just let me know

http://new-hifi-classic.de/Gallery_MO/index.php?cat=168

 

[sonavor]

I have decided to change direction on the recap of my second L-507. The person I bought the amp from had said it lacked power and was distorting the output. I recapped the two output amplifier modules and tested them on my first L-507 where I adjusted the idle and DC offset. No problems, no distortion. Satifisfied with that I had intended to move right along with recapping the rest of the new L-507 electrolytics (and tantalums). However, tonight I decided to try the recapped output modules back in their original places to see how the second L-507 actually sounded ... and see if there was anything else wrong. I re-verified the power to the amp using a dim bulb tester (plus variac). Everything was fine. So I hooked up speakers and a little mp3 player to see how it sounded. It sounds great. I mentioned before that this new L-507 appears to, overall, be in better condition than my original one. I have attached some pictures of it. You can see the muting protection relay looks new (maybe it was replaced once already). However, it must have been a while back unless someone found some NOS for the relay. Two years ago I couldn't find an exact replacement anywhere.

Anyway, I will get to the recap of this second L-507 eventually. But after working on its output amplifier modules in my original L-507, I think I want to re-work my original L-507 first. I never did get the warm up problem on the right channel output amplifier board fixed. There has also been some scratchiness on the left channel when the unit first powers up.

I feel safer now messing with my original L-507 since I have a good, working spare. The first step will be to take apart and retest the components on the PB-742 output amplifier module that requires warming up. There were also a bunch of tantalum caps on the original L-507 that I didn't replace so I will be removing them this time.

 

[sonavor]

Here is one more picture. While I switch over to work on my original L-507 I plan on getting familiar with the sound of the new L-507 (with just the output amplilfiers recapped). I would like to see if I notice any difference later when I recap the rest of the board. Of course it is very likely that my brain won't remember the details well enough to notice but I figure I'll try since I have the opportunity.

 

[sonavor]

Looking at the picture again of the muting protection board, I don't think that relay has been replaced. The board looks undisturbed. The blueish-green lock-tight type glue on the mounting screws is still there. When I replaced the protection relay on my original L-507 I had to pull that little board out to de-solder the old relay and solder in the new one. I really think this amp has had a pretty low stress life compared to my first one.

 

[mrflex65]

Looks like you have a burned up resistor in front of the relay....:scratch2:

 

[sonavor]

You mean the 100 ohm resistor? It is a little discolored but it is okay. That picture is of my latest L-507 that I have recapped the output amplifer boards on. I listened to it for about three hours last night and it sounds great. Once I get my first L-507 reworked, compare the two for a bit, I'll finish recapping the second amp.

 

[mrflex65]

Nice lookin unit by the way:thmbsp: I've yet to own and listen to a luxman.Maybe one day soon....:yes:

 

[sonavor]

I picked up a Luxman L80V in need of repair this week. While I am in the Luxman mode right now I felt that I had to buy it. Plus I've been wanting to get an L80V for a while.

 

[sonavor]

T0-3 socket replacements

Back to my original L-507 amplifier.

I removed all of the components from the PB-742 output amplifier board that has had the strange warm up problem all of these years. I even removed the TO-3 sockets for the power transistors that attach to the heatsinks. On one of the sockets there was a crack in the plastic housing. I has been glued and the metal part is solid. However, since this has been a problem board I would like to replace it with a new T0-3 socket. I haven't been able to find a T0-3 socket with the collector post straight down in the center of the metal frame like these. The current T0-3 sockets all have the collector post off to the side of the frame and coming down at an angle. While I can probably rig a new socket to fit, I would rather find one with the same layout as the original.

Does anyone know if these kind of TO-3 sockets are available anywhere?

 

[ryuuoh]

I found a pdf for sockets with the center pin:
http://www.keyelco.com/pdfs/prod22-trans-sockets.pdf

 

[sonavor]

I found a seller in Taiwan that is selling them so I went ahead and ordered some (minimum was 10). I have attached a picture. I can continue with the recap while I wait for the sockets to ship.

 

[sonavor]

L-507 PB-742 bare board

I removed all of the components from the troublesome output amplifier board (PB-742). Here are pictures of the component side and the trace side. There are some left over ink discolorations on some traces where I had made some marks during the original recap.

 

[sonavor]

Here is the PB-742 board with new non-electrolytic caps installed.

 

[sonavor]

I decided to change the non-electroytic caps again. Except for the two 47pF caps, the others are polypropylene. The 47pF caps are ceramic. The resistors are all changed out as well with metal film resistors. I am planning on re-using the two output emitter resistors though (R21 and R22). I am also reusing the diodes (D01, D02 and D03). I have replaced the two trimmer pots (for idle and DC offset) with a pair of Bourns 5K pots. I am planning on resusing the existing driver and output transistors (Q05, Q06, Q07 and Q08). On the other six transistors I am deciding whether I want to change those out or not. I'm leaning towards changing them. If I don't change them all then I will at least change the Q03 and Q04 (NEC C1103A) NPN transistors. The reason for that is they had a bunch of the brownish glue on them and one of them doesn't always measure when I connect up my Peak transistor tester. It is likely just due to gunk on the leads but I have cleaned them a couple of times and the measurement still messes up occasionally. Q03 and Q04 are also difficult to replace after the T0-3 sockets are on the board. So if I am going to change them, now is the time.

I have attached a picture of the current state of the PB-742 board (small caps, resistors and diodes installed). There is also a picture of the Q01, Q02, Q03, Q04, Q09 and Q10 transistors (and their possible replacements).

 

[sonavor]

The goal of reworking this PB-742 board is to finally eliminate a nuisance warm up problem it has had since 1978. That being the case I decided to replace all of the small transistors. The two output transistor emitter resistors I am keeping. For now I am also keeping the three diodes. It is hard to find replacement SV-02 and SV-03 varistors so if the problem still exists after this work I will have to find some or make substitutes per echowars' guide.

The next step is to install the electrolytic caps, resolder the board connector and install the driver and output transistors. It will be at least ten days before I will be able to complete this however. The new TO-3 sockets I ordered for the two output transistors aren't expected to arrive until then.

Attached is a picture of the board with the new small transistors.

 

[sonavor]

Here is the board with the electrolytic capacitors installed.