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Autona AL125 - VAS and current drive

Autona AL125

As promised – the Autona AL125

The Autona AL125 was the workhorse of the 70s and possibly even early 80s in the DJ arena.  The amplifiers compared to what we see today were well made but I would not be surprised if the engineers pushed the SOA (Safe Operating Area) to the limits, the DJs even more so.  As promised in our previous article on the 2N3055 here are some pictures I have of three of these delightful little amplifiers.

Article as promised from the Silicon Bubble – the 2N3055

autona al125
The famous “little” Autona AL125

Note the one above on the RHS which has an interesting tale to tell. See below.

autona disco amp the AL125
Autona AL125

The amplifier on the RHS used to be used at a hotel for the PA system.  Using the amplifiers without an additional aluminium heatsink was just inviting trouble as can be seen by the very burnt fibreglass board where the 2N3055s are seated.

autona 125
A better looked after module
heatsink supplied with AL125
Autona AL125 with supplied heatsink

AL125 heatsinking

The alloy heatsink supplied with these modules were supposedly good for 50W into 8 Ohms. As a rush job this may well have sufficed but looking at the image above,  continuous playing into a load very much higher than 50W was a big no no.  The overheated one drove an entire floor of PA speakers, perhaps about 10 x 8″  8 Ohm drivers through a line transformer with no additional heatsinking – for more than 12 years.

Most teenagers during the 70s and 80s bought, built, modified or blew up replicas of these amplifiers. Not having a directly coupled output stage had its merits.

Autona AL125 - VAS and current drive
Autona AL125 – VAS and current drive

Further Reading:  The Quasi Complimentary Power Amplifier Autona AL125

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Good evening all - first time I have been here. These 125W amplifier modules should have a temperature compensation transistor mounted on the heatsink. Just wondering how the amplifier in photo could have got so hot unless it is faulty yes?

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