Acquired an older Model T - How can I determine the year???

[TradeDataGuy]

Hi Folks,

Acquired a Model T from an ex-bass playing famiy member.  It needs to be cleaned up - new tubes, etc.  How can I tell the year, so I can get the correct specs, manuals, etc.  It has what appears to be the effects loop in the front - got the serial number as well.  Is there a reference anyone can suggest? Did the configuration change in the years around 69 - that's the year I'm assuming it might be.  Any info is appreciated.

[loudthud]

Does your Model T have the three position switch under the Mid control? That makes it 75 or later. It's not in the 72 catalog so the first Model T must have been 73 or 74. No way to date it from the serial number. Look on the inside for a little white and green inspection sticker about the size of a postage stamp. Unplug the amp first and don't touch any of the circuitry. It can shock you even when it's unplugged.