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Friday, 15 January 2016

Luxman L&G L2800 Amplifier.

This arrived ... "Can you have look mate, been in the attic for years, plugged it in and it hums loudly and gets hot"...

... Yeah, why not.

I initially thought it was some sort of cheapo Japanese "nomark" amp...









Closer inspection reveals it to be made by L&G ... nope, me neither! A google search reveals it's made by Luxman, a well thought of brand in hifi circles, and this is from their L&G "more affordable" range. Apparently designed by Kimura-San of 47Labs & Gain-card fame.






It's of bog-standard 70's Japanese construction. Thankfully you can get to the print side of the board through a hole in the bottom.







A close look at the board shows there's either been some leakage of electrolyte form the caps, or there's been some sort of spillage. It certainly smells like a cat's litter-tray..








More signs of spillage.





This is a bit weird... there are two caps, mounted upside down, despite having more than enough space on the board... Here's one, there's the same on the other side of the board....







Nothing unusual about the output pair, NEC 2SD388A & 2SB541A on the left hand channel ...

nothing unusual that is, unit you look at the right hand channel....
















... which is fitted with Toshiba 2SD371 & 2SB531 ! Apparently it's never been repaired before , so it must have left the factory like this! Perhaps they switched supplier and ran out halfway through making this amp!















A few cursory checks, and on with the mains, don't hold out much hope for the caps, but let's find out how bad things are. Left hand channel has a horrible 8V DC offset, and it's all humming very unpleasantly.

I think we'd better look at those caps. One by one, they are removed, tested and replaced. Some are open, some electrically leaking, many are physically leaking, and none are to tolerance, except the main split-rail smoothing caps, and those two caps mounted upside down!


After a comprehensive re-cap, things are improved, the DC off-set on the left channel is still way too high at 2V. I measure the bias of the right-hand channel at the 0.33 ohm emitter resistors. It's set for 80mA. I set the left the same, and then set the balance up for both channels. DC offset is less than 5mV for both channels.

Now the switch-gear and pots are all noisy, but really nicely made. A good clean up with some switch-cleaner and repeated operation sorts any switching issues and noisy pots are no more.

I soak test the amp for a couple of hours with some fine Yes music, re-checking the bias and offset after an hour, and it's all well. Sounds great, the phono stage is quiet, and it makes a good 50 watts into 8 ohms. Despite different transistors in each channel, I'm damned if I can tell!

The guilty parties ....


5 comments:

  1. I have listening to this amp last night. Well done you have made my mate a very happy man. Lovely sound.

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  2. I have the same amplifier (and the matching tuner) since shortly. it plays very well for about 15 minutes and then gives a "plop" in the right channel and stops playing. i suppose my caps have reached the end of their life also. but upon opening there are soms resistors with the "shield" completly gone... so i have no possible way to now there resistance. do you have a shematic of this amplifier ? if it plays its a lovely sound. regards from Belgium , Peter

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    Replies
    1. Hello Peter,
      I'm Dirk H. from Antwerp, Belgium, and I have the same amplifier. It was on a clauset for many years, and now I Tried to get it to work, it failed. Do you know any good repair people?

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    2. Peter, I am Dirk H. from Antwerp and I have the same amp. My does not work anymore. I am desperately looking for a fine repair. Can you advise me?

      Delete
  3. Hi Peter,

    You may wish to look here :

    http://images.google.de/imgres?imgurl=http%3A%2F%2Felektrotanya.com%2FPREVIEWS%2F63463243%2F23432455%2Fluxman%2Fluxman_5-l-15_stereo_pa_sch.pdf_1.png&imgrefurl=http%3A%2F%2Felektrotanya.com%2Fluxman_5-l-15_stereo_pa_sch.pdf%2Fdownload.html&h=2521&w=4065&tbnid=imiPBAlDJYgopM%3A&docid=TW49v16R2vL1sM&ei=e4FAV-CfGIeGU7GuhvgK&tbm=isch&iact=rc&uact=3&dur=325&page=1&start=0&ndsp=44&ved=0ahUKEwigyfS9wOvMAhUHwxQKHTGXAa8QMwgxKAowCg&bih=971&biw=1855

    ReplyDelete