This SQ507X is for sale in the Netherlands, fixed price 550 Euros, cash and Local Pickup Alkmaar area as I do NOT ship, I only answer if you provide your phone number also, see the moving mail address on my main page.

Het type SQ507X heeft soms last van slechte bias dioden wegens ouderdom en ook wordt de ruststroom hoger bij hogere temperatuur.

Dit wordt m.i. deels veroorzaakt doordat de dioden niet thermisch verbonden zijn met de koelplaat. Hun gedrag wordt grotendeels bepaald door de eigen opwarming.

De bias schakeling is daarom aangepast.

Verder zijn de eindversterkers opnieuw bestukt met geschikte transistoren. De voedings-afvlakcondensatoren zijn vergroot tot 15000 microfarad, ze zijn van het merk BC.

De voltage selector hoeft niet per sé van 220V naar 240 volt, er kan ook geprofiteerd kan worden van enkele watts meer piekvermogen, indien gewenst.

Voor de goede orde is toch maar voor de 240V setting gekozen, omdat de versterker eventueel wordt verkocht en het wel zo netjes is als hij aan de huidige normen voldoet, zeker omdat wegens zonnepaneelgebruik de netspanning hier en daar boven de 240V uitkomt.

This Luxman SQ-507X is modified for a less sensitive null adjusting and good thermal behaviour, and it has more rigid power/main amp circuitry now.

Originally, bias compensation is done through the green sv3 diode, but as it is not mounted to the heat sink, it mostly reacts on warming-up by its own current.

Having the replacement transistors mounted, while the amplifier module was heating itself up using a dummy-load to over 55 degrees celcius, bias appeared to be raising too much, having the original diode solution employed.

All aluminium electrolytics are replaced, sometimes using metal-can tantalums of good quality (yes the tantalum audio usage discussion is known). The small tantalums were measured using a huntron tracker as well as a LCR meter to make sure they are okay. The metal-can tantalums are superior to the dropshape ones and do not have to be derated for voltage.

The main smoothing capacitors are 15000uF now (originals were 6800, the 15000uF value makes power supply smoothing capacity same as the L309V).

The main amplifiers are completely rebuilt using quality components.

The voltage selector needs not moved from 220V to 240V, so a few more watts peak power can be enjoyed (Mains power is 230 volts in NL ).

However, during 2023, I did put it on 240 for safety reasons, as the amp may be sold and excessive mains voltages may be apparent nowadays, due to solar panel use depending on the location in this country.

The old amp, and old preamp/power pictures

One of the refurbished amplifiers modules.

Observe the TO-126 type transistor mounted on the heatsink

The trimming potentiometers are high quality sealed metal ones.

The refurbished preamp/power boards: I then used metal case tantalum capacitors.

Aangepast schema van de eindversterker / modified schematic. Changes were written on a schematic, belonging to a SQ505X, as my 507X schematic is blurry. Apparently, a 505X has no Zobel filter coil.

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