MTH Protosound Boards:

 

Protosound 1 board:

Protosound 1 (Top board):  (Used in Old O gauge engines)

Protosound 1 (Bottom board):  (Used in Old O gauge engines)

 

Protosound 2 boards:

Example 1:  3v Board (Used in O gauge and some G scale engines)

 

Example 2:  3v Board  *Modified*   (Used in some G scale engines, modified at factory for remote heat-sinking)

 

Example 3:  3v Board  *Modified*  (Used in some G scale engines, modified at factory for remote heat-sinking of two components)

 

 

Protosound 3 boards:

Example 1:  PS3 board (O Gauge / One-Gauge)  (Used in O and G scale/One Gauge)

 

Example 2:  PS3 board (HO Scale)  (Used in HO scale engines only)

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