Panasonic RX-7700
The RX-7700 was Panasonic's top-of-the-line boombox. I'm pretty sure it was designed in the late 70s, when boombox build quality was still very high. This excellent build quality is why it weighs so much (over 25 pounds, and that's without the 10 D-cell batteries). It was probably better-suited as a tabletop set rather than as a portable. For more complete information about this model, you should visit National Panasonic RS-4360dft. The only difference between those two models is, the RS-4360 only came in black, while the RX-7700 came in either silver or black. The tuner dial is silver with the black models, and black with the silver models.
The service manual for this product can be purchased HERE.