Hi guys, i have some 2n3055 transistor TO-3 package. It has only 2 pins; base and emitter. The "tab" is the collector. So let's say i want to use it in a circuit such as attached. How do i connect with the collector or is the tab grounded ?

 

They are usually mounted on a physically isolated heatsink inside the chassis. The heatsink will have voltage on it in reference to the chassis ground. The case of the transistor, as you guessed, is the missing connection.

 

Use a screw, nut, and wire on a ring lug to connect to the xstr case. An internal tooth lock washer is also useful for maintaining the connection between the ring lug and the case.

 

There are mounting kits available for the TO-3 case, such as; http://www1.futureelectronics.com/doc/AAVID%20THERMALLOY/4804SG.pdf

 

I see . I just need to connect a wire to the case.

So, just curious, if the collector is not connected, is it grounded by default ?

 

if it is in contact with a grounded surface - it is.

 

If you get a socket for the T)-3 can and use an insulating washer, then the transistor can be placed on a grounded heat sink or case, but still have a voltage present on the collector. If that voltage is dangerous, then it is also possible (or was) to get a plastic insulating cover to protect users.