how to mount output devices of amplifier?

[Wagener]

I am going to build the leach amp (4-channels) for one of my design projects. I have finally copied both the PCB layouts into tango. One with the transistors mounted on the PCB and the other with transistors wire linked to the PCB.

Which one should I use considering that I will run the leach amp into 4-ohms. This will obviously make it run hotter and I will most probably use fans on the heatsinks.

I heard that the L profile heatsinking is not very efficient.

It will be nice to have the output transistors on the PCB but I want the best heat transfer.

[Frank Berry]

A big heatsink is what you need.
The "L" profile heatsinks are not very efficient.
I do not recommend that you rely on a cooling fan. Fans tend to fail. Use very large heatsinks that can radiate the entire heat load. You'll be glad that you did.

[Wagener]

So what you are saying is that I should keep with Mr. Leach's approach of using wire links to connect the transistors to the PCB.

For 4 channels this is quite a lot of wires :-)

[Frank Berry]

Absolutely correct.

[gmarsh]

I've done "sandwich" construction on numerous occasions - first bolt the output transistors (and thermal tracking transistor, if there's one used) in place on the heatsink. Bend the legs outwards, lay the stuffed amplifier PCB on top of the transistors (with the legs facing upwards through the board now) and solder the board in place. I also have short pillars and screws securing the 4 sides of the board.

The effect is that you have a "sandwich" - the amp PCB is parallel to the heatsink and stands about 1/4 inch from it, and the output transistors are sandwiched in between the two. This results in neat, compact construction and very short lead lengths... though replacing blown output devices is a bit of a pain

[slowhands]

If you use TO-3 devices per the design, you will probably need either the L-bracket, lotsa wires or another approach. One that worked well is sockets with extended pins to reach your board.

Heathkit used these sockets on some of their receivers in the early 70s to mount TO-3 outputs on a heatsink, yet still have 1 inch breathing room between the board and heatsink. For the collectors, they used 1 inch standoffs, and for emitter and base the socket had long pins which soldered to the board. There were no wires to the output transistors, so it was easy to assemble. The collector standoffs also mounted the board. At the time I thought it was pretty slick.

[mcp]

This may help.

Mounting TO3

Mounting Flatpacks

Regards

[moving_electron]

Here is a related thread in case you have not seen it.

redesign of leach amp pcb for integrated TO-247 output devices

[lucpes]

Here's a nice article on heatsinks/mounting:

http://sound.westhost.com/heatsinks.htm

& a nice mounting method (not for TO3 though...)