Power Supply TO220 vs TO3?

[danial stocks]

The TI linear ccts/ voltage regs databook 1989 has a fairly comprehensive 
power supply apps notes..
here's some typical pkg to heatsink data mentioned..

TO3 - metal to metal 0.52'c/w
    - mtl/mtl with thermal grease 0.14c'w
    -mica washer + thermal grease 0.36'c/w

TO220 - mtl/mtl 1.1'c/w
      - mtl/mtl with grease 1.0'c/w
      -mica washer + grease 1.7c/w

as you can see, TO3 is a better option if high dissipation is needed.. this 
data applies to the thermal gradient BETWEEN the device and the [presumably 
aluminium] heatsink.. as such, this should be valid for pretty much any Al 
heatsink, provided that there is a flat contact surface between device and 
h/s.. the heatsink to air thermal is of course totally dependent on 
type/size of h/s, environmental factors etc..
Cheers,
Dan
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