Prenton Prenton Sales Co, Pentron Electronics Corporation, Chicago USA

There are many references on the web to Pentron recording equipments (as early as 1949 if not before).  This combo amp appears to be quite rare.

Images courtesy of yellowbugman Dec 2008:

Pentron Sales Amplifier Serial Number Plate Pentron Sales Amplifier Model MA9 control panel Pentron Sales Amplifier Model MA9 Pentron Sales Amplifier Model MA9 rear