Rebuilding a 1960s Antenna Tuning Unit — Converting from SPC to T-Match

After years of gathering dust, my vintage Amateur Radio Antenna Tuning Unit (ATU) from the 1960s has finally been given a new lease of life.

The original unit was built around the SPC (Series–Parallel Capacitor) configuration — a popular design at the time, but one that can be a little finicky when dealing with modern transceivers and a wide range of antenna impedances.

During the rebuild, I decided to convert the design to a T-Match configuration, following the excellent information and circuit details provided by PA0FRI’s T-Match page