The TS-520 was succeeded by the TS-520S and then by the TS-520SE.  The interface for Kenwood's external DG-5 digital frequency display is included and does not require installation of a kit.  The 160 meter band and a  separate channel for receiving WWV at 15 MHz were added to the 80, 40, 20, 15 and 10 meter coverage of the TS-520.   Much of the point to point wiring of the TS-520 was replaced with printed circuit boards and improved solid state devices.  Also added were a phone patch and a compression speech processor. The compression processing increases SSB average power without significantly degrading audio quality and intelligibility.  Like the TS-520, the TS-520S can be operated from 120 or 240 Volt power mains or from 13.8 Volts DC, so it is also suitable for mobile, portable, or emergency use.  The TS-520SE added some features and retired some.  It discarded the transverter connection and 13.8V DC operation.  It added a switch to select either of two crystal filters if installed, and a number of circuit refinements were made possible by improved solid state technology.  Its SSB crystal filter is adequate for casual CW operation, but an optional 500 Hz wide crystal filter can be installed for the dedicated CW operator.
These models remain very popular with amateurs because of their elegant design and reliability.  They are simple to operate, and frequently used functions are readily accessible from the front panel.  As with all the hybrids, band change tuning takes less than 30 seconds.  The audio quality both receive and transmit is excellent when properly aligned.