2N3055 transistor

audioguru said:

The transformer does not have a secondary voltage rating nor a power rating. It is drawn backwards.

R1 and R3 are not needed.

The value of C1 is too low.

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You missd out that a 741 can't provide enough current for the 2N3055, but really it's an appallingly bad 'design'.

audioguru said:

Then Multisim is backwards.
The 20VAC is rectified into 26.3VDC. Then the 2N3055 transistor needs a proper heatsink with many fins and maybe a fan.

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A proper heat sink is what we have been trying to get, we need to know how large it needs to be to handle the power dissipated by the 2N3055. Eric suggested a heat sink with a surface area of 120mm^2, I didn't catch whether that measurement was per fin or the over all minimum size.

Here's a site that shows how to estimate the heat sink area for a give required thermal resistance.