Luxman SQ 700, X, G amplifier

General: 

This amplifier produced in the early 1970’s. .

Photos:

 

Special futures:

Schematic:

         click here to download the user manual with schematic diagram of the SQ700X

Pilotlamp update: the led lasts for many years and gives perfect light.

 

Owners manual

       click here to download the user manual with schematic diagram of the SQ700X

 

Burnt capacitors, the above has completely deformed and has no real value anymore in µF. ^

 

Modifications:

The SQ700X is a very nice amplifier and easy to upgrade and repair. Hardly ever the ampplifier breaks down.
If it does break follow below advise, upgrading is after 40+ years a must, the electrolytic caps are mostly out of specs.
Replace broken power transistors with TO-66 transistors 2SC1445 and PNP 2SA765 (Sanken) instead
of 2SA616 and 2SD155 (NEC), mail me for info on limited NOS stock,
or use plastic transistors like 2SB595/2SD525 (Toshiba) or 2SA1694 & 2SC4467 (Sanken) or equivialent.
On other places in the amp you can use 2SC1775 as predriver and/or BD139/140 as drivers.
The transistors of the pre stages are often noisy. Use BC550/560C or 2SC1845/2SA992 or equivialent,
you can get the noise figure below the original specs of Luxman.
Screening of the phono stage is another update:
humming is much lower when transformers of other gear are close to the amp.

The main power capacitors of 2200 uF are often in bad shape,
in this amp they had only 1400 uF capacity left, replace with 4700 uF or equivialent.

Unexpectedly all other caps were in perfect shape and all had more than the specified capacity, I left them in the amp.
 

On this photo you see the inside of the amp, the uMetal screen at the phono stage is an update to prevent humming.

 

Sound:

These series of "High Quality" audio components soon got legendary of their outstanding quality and excelent sound performance.
 

Bottom of the amp with uMetal screen update.

 

original power transistor

Revision ^

 

Another revision ^

A warm white led is the perfect replacement for the bulb. ^

 

Test in Dutch language:

© Hans Hilberink - PE1MMK ® 2003- Last update: 10-05-2020.