Does heatsink need to be grounded?

[Steve Blackdog]

Hi folks,

I am working on my Proamp Viper (like Music Man RD210 / KMD GV60). It has two T220 power transistors (tip41c). The transistors are screwed down to the chassis (insulated by mica).

For reasons I will not bore you with, I have changed this so that the two transistors are no longer screwed to the chassis, but are fitted upright with a single vertical aluminium heatsink.

I am wondering whether I need to ground the heatsink to the chassis ground, or to leave it floating. It is quite close to the Power Transformer and I don’t want to create any interference.

thanks in advance.

cheers

steve

[The Dude]

If the transistors had mica insulators on them, they weren't getting ground through the tab anyway, so I see no reason you'd need to ground the heatsink. It shouldn't matter either way.

[Enzo]

Just because I am anal, I might at least connect a small value cap between heat sink and ground just to head off potential RF issues.

[The Dude]

Not a bad idea,............ especially if you don't like BBC radio.

[g1]

There are modern units that insulate the entire heatsink from the chassis so they can bolt the power chip directly to the heatsink, and it sits at one of the supply rail voltages. No problems that I'm aware of, as long as no one forgets the insulators.

[Mick Bailey]

Many Ashdown amps do this - the heatsinks each sit at the respective +/- rail voltages. The first time I ever worked on one of these I was checking the comparative heatsink temperatures with my fingers and got a nasty shock as soon as I touched the second one. I should have known better.

[Steve Blackdog]

Not a bad idea,............ especially if you don't like BBC radio.

I once had a Carlsbro Super Stingray. Great amp, but it had an annoying habit of picking up local taxis. Nothing more atmospheric than “anyone in the Broomhill area? Pickup for Central Station.”

[Enzo]

Hot heatsinks are not that rare. Some Marshall TDA7293 models did that. Some Peavey "wind tunnel" amps had whole heat sink at rail. Thing is when they do that, the heatsink is "grounded" for RF through the low impedance of the power supply.