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2023: My restoration / recap / refurbishment of a Luxman L-308 amplifier.
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.
Its original owner explained he wanted to fix it himself as it did look easy and nothing was burnt, but never started to do it.
Most probably he was not able to get the proper size smoothing capacitors, as they are obsolete and the size of them is quite uncommon.
Apart from the 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".
Its refurbishment started Autumn 2023.
The RIAA turntable pre-amplifier PB-726
One picture 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 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, leaving a brownish discoloring.
There was enough room for mounting two nice yellow axial capacitors.
Due to lack of space, the small blue tantalum capacitors remained tantalum ones, although these are metal case ones, now.
Of course, the polystyrene capacitors were retained. 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, connector pins were installed, to ease wire connections.
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.
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.
Linear equalizer PB-778
The linear equalizer has limited possibilities, 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.
Amplifier modules PB742
As always, 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.T
I do not see them used elsewhere, maybe this brand was an official Lumxan supplied replacement?
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.
The TO66 drivers are 2N6420 and 2N3585, output 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 pins supplying the amplifier modules.
There was a little card carrying four rectifier diodes, I removed it.
The terminals of the missing big capacitor was chemically attacked. Crimp terminals were used to connect the Philips ones.
The card carrying the rectifier diodes was replaced by a single chassis-mounted 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, too!
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