The Mark Levinson No. 26S Dual Monaural Preamplifiers used Teflon circuit boards to supposedly differentiate the No. 26 and the 26S models, produced between 1991 and 1994 by Madrigal Audio Laboratories. This unit utilizes Camac coaxial connectors (except for the XLR balanced ones), which were used in the medical industry as well, because they break hot before they break ground when you unplug them. No shorting electronics means a safe preamp and safe ER patients. An external power block, the PLS-226, was used to keep interference to a minimum.
The No. 26S came in 3 versions, a Balanced audio version, a Phono version, and vanilla version that could do neither. There was only space for one expansion board inside the unit, so you could not put in the phono and the balanced board. This made the phono and balanced inputs on the unit shared, only one set could be active in the unit based on which board was present.