Denon TU-500
(1975 - 1977)

Meant to be the center of the rig, the FM only TU-500 had meters to validate the output level, a balance knob and even a NULL balance function. The said meters can also be used as FM signal strength and output balance indicators... And, naturally, the TU-500 sported multipath and oscilloscope outputs.
The TU-500 would have several siblings until 1979, all of which featured more or less the same functions: the TU-300 and TU-400, receiving an AM section were on the lower end while the TU-355 probably was a rebadge/rehash with updated looks, along with the TU-501 and TU-701. The TU-850 ('78), with less functions, certainly was in the same league as the original.