1965 and 1966

AC50s with Reverb

Below, the circuit of the JMI add-on reverb unit designed for AC30s - schematic OS/075.

Click to enlarge. Mention of the "Vib" channel indicates its intended use.

Whether at any point it was considered for the AC50 in any serious way remains to be seen. Only one AC50 has emerged so far with unit fitted - , large box, valve rectified - reverb certainly in place by the 1970s. Note that reverb's schematic - OS/075 - is close in sequence to the new schematic for the AC50 mark 3 - OS/072.

The units fitted to the amps below, however, were manufactured in the U.S.A., presumably being installed at a Thomas Organ Service Center. In contrast to the JMI units, these were transistorised rather than valve reverbs, as the picture immediately below shows.

The unit pictured above was removed from a defunct AC50. The reverb tank had long gone.

The height of the box indicates that it was designed expressly with the under-shelf of the AC50 in mind.

Valve rectified amps

Serial number unknown - currently in the USA

Solid state rectified

Serial number 4108 - currently in the USA

Serial number unknown - currently in the USA