This is a power supply from the 80ies or even older. It contains a linear regulated power supply and a speaker. It offers 13.5 volts DC at 25 Ampere. Weight is about 10 KG, and this weight comes mostly from the big transformer.
There is plenty of space inside the casing. We can see the transformer. two large 10.000 µF capacitors, the speaker on the right. 4 regulator transistors are with their heatsink at the left. There is a small PCB for the regulation between speaker and capacitors.
On the front, we see a small 4 Ohms 3 watts speaker.
A small PCB contains the linear regulator driver stage. The scheme uses a TA7089M voltage regulator. The voltage regulator drives a single 2SD235 and this driven four 2SD114 transistors.
The PCB and the 2SD235 can be seen in the following image. 2SD235 is attached to casing bottom.
View on the four power transistors.
Closer look to the power parts.
I got this power supply from ebay. The power connectors were removed for some custom solution I guess, and some adapter case was soldered to the speaker input. The line cable seemed not the original one. The main fuse was broken.
I added the power connectors again and replaced the line cable. A first test with a variable AC transformer showed that the PSU works with no issues.
I moved the PSU into my shack to supply the RF power amplifier. I am a fan of these linear regulated PSUs, ok they waste energy, but are so simple in design and can be repaired easily and finally, they do not create any RF pollution.