General:

Exellent designed and sounding power-amplifier made in Belgium around 1980.

Special features:

All properties a good medium powered high-end power-amp should have are in this design.
However Philips made some design concessions to keep the selling price acceptable, so there is some reason to improve it.
This power-amp is a member of the Philips "Black Tulip" range audio gear.
Matching: tuner 22AH170, pre-amplifier 22AH270.

 

Specifications:

Philips 22AH370.
Input voltage: 1 Volt per channel
Frequency range: 1 - 50,000 Hz (+/- 1.5 dB)
Harmonic distortion: less than 0.01%
Intermodulation distortion: less than 0.01%
Signal-to-noise ratio: 110 dB
Crosstalk damping: 85 dB
Output impedance: 8 Ohms
Output impedance: headphones 8 to 600 Ohm
Output power 2x 50 Watts RMS at rated values
Output power 2x 60 Watts RMS at 0.1% distortion
Power supply: 220/240 volts
Dimensions: 78 x 482 x 280 mm.

Front ^

 

User Manual:

Click here to download the user manual PDF format

 

 

Schematic:

The electronic schematic diagram is designed by Japanese engineers
and very much in the Luxman tradition way of design.
Many design properties are found in earlier Luxman designs like the L10 and the M12.
This makes the 370 a very good, stable and reliable amplifier with excellent sound.

Click here to download the service manual of the Philips 370

 

Restore on the way inside, updating the wires ^

 

PCB solder side ^

 

Modifications:

To get a fine high quality power-amp performance you have to do some upgrading:
The pcb design is rather poor and is crowded, many parts arte way to close packed together, so extra measures need to be taken:
Heatsinking the pre-driver & driver transistor-set is needed as temperatures of this driver-set can get near +65° C.
The wiring is a little awkward and you can get it better with less long wires. Also the practical setup is not as usually done, as usually
the power transformer is at the back and not at the front, this setup Philips used makes wires longer than usual with the main pcb placed at the front.
Separate the wires of the power amp section output and input, binding together as Philips did here is not a good idea.
Exchange the light bulbs of the meters for led's if you like led's light.
Since this is a DC-coupled electronic amp-design, use the capacitors at the input.

Set the transformer from 220V~ to 230 or 240 in Europe, due to the detrimental voltage rise from 220V to 240V~.
 

 

Updating the final stage : hatsinking the drivers and pre-drivers ^

 

Restore & upgrade ready, now you may exchange the DIN output sockets ^

 

Din output sockets exchanged. ^

 

LED's

 

Matching tuner 22AH170 ^

 

Matching pre-amp 22AH270 ^

 

Sound:

The sound of the restored Philips 370 is very good.