I suspect you're right, and it's just a half wave rectifier - assuming it's not just a battery powered record player?.You have not asked a question so I will assume you want to know where the wires from the amplifier board go. These are my guesses. The red and black wires at the top right go to the power supply board or if the diode in the top right hand corner is for half wave rectification (Rather than polarity protection.) to the mains transformer. The two black wires from the larger transformer will go to the speaker. The two brown wires from above the volume control will go to the pickup. (NOTE screened cable should be used for this connection. I think this dates back to about 1960 as the design is similar to the output stage of the first transistor radio I bought (Rather than the home made ones I built before that.) when I was about 16.