On numerous occasions, I have been asked for Luxman repairs. Feel free to ask questions, but I will NOT do repairs for others, being retired and not looking for "work". I only (may) react to mail if accompanied by your phone number, see the "moving mail address" on my main page.

Gemakshalve is deze pagina alleen in het Engels geschreven.

This page was written using English language only.

Luxman L-308, refurbished November, 2023 .

The L-308 is alike my L-309V. It produces 55 Watts per channel specified, 20 W less than the 2 x 75W L-309V. Apart for the wattage difference, there are other electronic differences, too. Generally, for normal use, the differences are not apparent.

This L308 having scratches and dents on its woodcase, suffered from a missing big power supply smoothing capacitor, and it was repaired, before.

According the previous owner there was a problem getting the proper size smoothing capacitors, as they are obsolete and the size of them is quite uncommon.

Apart from the small woodcase issues and the missing capacitor, the unit was in reasonable good shape, for its age.

Sanding the woodcase, applying "stain" and "antique wax" made the case acceptable again. I does not bother me it is not totally new.....

Its refurbishment started Autumn 2023. Obvious is one of the two big capacitors is missing:

The RIAA turntable pre-amplifier PB-726

The picture on the left is of the card before refurbishment. It resides at the side on the right-hand side of the amp, more or less hidden behind the power smoothing capacitors.

Two "frog"-greenish color electrolytic capacitors did not really fit well, as the circuit card was designed for smaller ones.

Several capacitors were glued using strong glue, including the two big green mylar ones. The glue also attacked the circuit card itself, over the years, leaving a brownish discoloring.

This type of glue has to be removed always as it can get conductive and attract moisture, and attack the metal leads of components.

There was enough room for mounting two nice yellow axial capacitors.

Due to lack of space, the little blue tantalum capacitors remained being tantalum ones, although these are professional metal case ones, now.

Of course, the pink and shining-metal polystyrene capacitors were retained, new ones are not better. The nomenclature on the card differs a bit for two of them on each channel, but their value does match the published schematic.

All 5% tolerance carbon resistors were replaced by quality metal film resistors having a maximum of 1% value tolerance, a few even 0.1% tolerance.

On the side of the card, goldplated connector pins were installed, to ease wire connections.

Electrolytics are Nichicon KA audio capacitors, and Panasonic FC.

Of course, new transistors were mounted.

The Filter and switch card PB-728

This card contains the toggle switches.

It is hardly accessible, and short messy wiring makes ik hard to define how the wires run. Care should be taken to make sure wiring information does not get lost. Taking pictures does help.

It is the last card removed from the three ones sitting on the front panel, and it should be the first one to mount, again.

The card was depopulated, and the toggle switches were cleaned.

On the side of the card, connector pins were installed, to ease wire connections, as can be seen on the picture on the right.

The wires are cut off at the ends, goldplated connector sockets are mounted, and then covered with heatshrink tube.

Observe on the old situation there are four blue little Tantalum electrolytic capacitors, two each in series, for proper derating. Those are replaced by single axial metal ones, which do not need the derating, as per specification. Information on these can be found in Sprague 150D and alike datasheets.

The two 1% tolerance yellow film caps are repurposed ones, scavenged out of some expensive aircraft device. You can not buy them anywhere, such 1% tolerance types were probably built to spec for companies buying a lot of those.

Linear equalizer PB-778

The linear equalizer has limited possibilities, just "tilting" the frequency response, yet it has a lot of components.

Also here, components were replaced and the switch was taken apart and cleaned.

The tone control board PB-777

As the PB-778, also this card is the same as the one specified for the L-309 amplifier.

The following shows a switch taken apart.

The refurbished card. I presume, it can compete with just about any other Luxman refurb on the www .

Amplifier modules PB742

As always buying an old Luxman, at least one defect was catered for, in the past. As found in a L309V, also here a repair was done using EIC brand transistors.

I do not see this EIC brand used elsewhere, maybe this brand was an official Luxman supplied replacement, it does not look the Bangkok "EIC semiconductor" manufacturer existing today was its manufacturer.

Because of serious connector deterioration, I reworked the connector and fitted female pins in it of another connector type, mating those of the also modified power supply board.

The connectors fit nicely. The output transistors were changed to 2N5631/2N6031.

The VBE multiplier transistor fits better if it is a TO126 type, as it can be bolted to the heatsink. A BD329 is used for this. It is a fast, high HFE low saturation type, perfectly suiting this purpose, I suppose.

Care must be taken to keep its collector plate isolated from the metal heatsink.

The TO66 drivers are 2N6420 and 2N3585 now, the output power transistors are 2N5631 and 2N6031.

The power supply and power supply/protection card PB-731A

The power supply card was in good shape, except for the corroded pins supplying the amplifier modules.

As all current goes through these contaminated pins, these could well be have contribued to the failure in the past.

There was a little card carrying the four power rectifier diodes, I removed it.

The "Hifi special" diodes (whatever it means) are of a 3 Amps package type, probably not suitable for withstanding peak currents of the new big capacitors.

The terminals of the missing big capacitor were chemically attacked. Crimp terminals were used to connect the big Philips ones.

The card carrying the rectifier diodes was replaced by a single chassis-mounted high power rectifier.

Again, I used same type of big Philips capacitors already used in two L309V refurbs. They are dated 1999 and I kept them stored charged.

Also in this Luxman, I had to remove about 3 millimeters from the aluminium terminals, to make them fit in the amplifier without sticking out from the chassis.

Noteworthy is the fact, while in a L-309V the Philips capacitors double the amount of energy storage, in this L-308 it triples it, as the originals in this one are 10000 Microfarads, compared to 15000 in the L-309V.

At the solder side of the power supply/protection card I put two bypass capacitors of 100 microfarad, to have low impedance closest to the grounding terminal at the chassis.

To compensate for larger capacitor values all over the place, the timing for the relay is extended to some 10 seconds.

It allows voltages to stabilize, before the loudspeakers are connected.

Sturdy goldplated connector pins were mounted to cater for the amplifier modules to be connected.

Several leisure pictures of the finished amplifier.

It has a bottom side, alsoo! This one is equipped with nice white mounting sliders, I do not remember seeing them in my other Luxman amps.

The front:

Innards of the amplifier:

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