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Old 26th March 2010, 10:00 AM   #1
Skorpio is offline Skorpio  Denmark
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Question Vintage reliability?

I have a very nice old Luxman solid state amplifier (from start 70'es) with output direct coupled to speaker terminals throug a 5A fuse.

I think it is one of the first with no capacitor i output and therefore (?) perhaps has no DC protection circuit?

Will it be safe to connect my speakers to this old product or should I take some precautions?
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Old 27th March 2010, 05:46 PM   #2
Mooly is offline Mooly  United Kingdom
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If it's working OK I would check it over for any drys... particularly any devices that run hot... drivers etc.
If there are any presets in the power stages I would look to replacing them.
Electroylitics... I would change them... but they almost certainly won't cause DC offset issues.

As an aside to all this, Japanese transistors for some strange reason often used to fail open circuit B-E. I don't know why that happened but I used to see it a lot in the TV trade... no obvious reason for it... absolutely no reason to suspect the Luxman of that... but worth a mention.

You could always run it with a couple of electroylitics back to back as speaker coupling caps for a while untill you are happy all is OK.

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Old 27th March 2010, 06:36 PM   #3
Spiny is offline Spiny  United Kingdom
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Hook it up to a dummy load (pair of 8ohm power resistors) attach a meter and power it up. if there is no significant offset then try it out on the speakers.

If this has not be tried for while I'd run it via a light-bulb tester first time. The lamp tester circuit can be found with a search but its just a 60/100 watt filament bulb in the live wire can save a lot of grief.
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Old 27th March 2010, 06:44 PM   #4
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have a look inside. If you see 3 large capacitors of near similar value it is probably a cap output amplifier. ex one 5000uf @ 50 or higher volts cap and 2 2500uf @ the same voltage as the single power supply one. If you see only 2 large caps probably dc coupled amplifier. Do you see any relays that connect to the speaker terminals? Commercial amps almost always had some type of protection for the amplifier as well as the speakers. If the fuses are speaker fuses you can try using lower values ie 2 amps for a while till you are sleeping better at night. fuses blow after the outputs fail and just about the same time as the speakers smoke but not always.

5 amp fuses for speakers means a high power amplifier 150 to 200 watts at 8ohms or 100 watts @ 4 ohms. See if you can find some info via google or post the model number here.
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Old 28th March 2010, 11:57 AM   #5
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state your model ...you may get a million repiar tips from me and many other forum members ....

In a few words vintage is what we do for years now .... meaning : a luxman amplifier that is made in Japan all ready been working properly for 20-30 years ...If serviced properly has an expectancy of at least another 30 years of happily working...

If your target is casual listening there is also a list of mods that you can perform to take this amplifier one step beyond hifi and one step closer to hi end ....

regards sakis
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Old 29th March 2010, 01:59 PM   #6
Skorpio is offline Skorpio  Denmark
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The model is this (507):

Luxman audio products

There is no protection circuit (and no output capacitor) and the amp is working fine, I have been playing for weeks on my test speakers...

Also both Iq and Offset values are perfect, nice for an amp age 40 years!

But will the fuse in series with speaker protect my bass units if the amp fails?
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Old 29th March 2010, 02:10 PM   #7
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the fuse will never work fast enough to protect any speaker connected to an amp like that if fails ....
\
electronics cannot be based on luck ...to be on the safe side you need to base them on facts

often while repairing vintage eventhough everything else was replaced a forgotten trimmer dirty or leacky could blow the amp to the moon ....
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Old 29th March 2010, 04:05 PM   #8
Mooly is offline Mooly  United Kingdom
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Will a fuse protect the speaker... answer as per Sakis's reply.

Will a DC offset protection scheme protect the speaker... it's not guaranteed as the relay has to "open" while the speaker is drawing a huge current. The bass speaker is inductive, so that will draw an arc at the relay contacts, possible welding them together.
Also nearly all protection circuits have a time constant formed by the integrator at the input to the circuit. That adds a delay of a few milliseconds too.
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