Motor transistors keep dying on me

[RoadrunnerOZ]

Not quite - the B77 uses triacs that are logic controlled - same idea different method

 

[map2112]

Yep! In my "childhood" in this biz, I first recall seeing that design in the Ampex MM1100 multitracks. Earliest versions were (in)famous for blowing up the Delco branded power transistors. Big clue....power up the recorder with no tape loaded and one (or both?) of the reel motors would run full torque.

Bri

Hi Brian

That is right, the venerable Ampex MM1000 used a very similar motor drive configuration:

Mark

 

[Brian Roth]

Hi Brian

That is right, the venerable Ampex MM1000 used a very similar motor drive configuration:

Mark

Indeed....earlier model MCIs (JH-100???) also used AC reel motors and the diode bridge design.

Bri