F5 power amplifier

[bobodioulasso]

Beftus, may be you could use them as screws for mosfets mounting.

[Beftus]

Originally Posted by bobodioulasso

Beftus, may be you could use them as screws for mosfets mounting.

Good thinking, hadn't thought of that! I don't think it will be a good idea though. There's not much threading left if I account for a washer on top of the MOSFET and thermal foil under the MOSFET. Maybe 2 or 3 turns left...

[umut1001]

hi..i have 20 pieces of 2sj74bl 6g transistors...is last number 6g important for matching the transistors? should i use 2sk170bl 6g ? or only matching bl types enough? thx

[labjr]

Originally Posted by fishski13

i bought P.D.'s boards last spring and finally getting around to sourcing parts. found 10 of these for $50 - 11.25"x4.5"x1.25". i'll be using 2 sinks per channel, mounted vertically.
http://cgi.ebay.com/ws/eBayISAPI.dll...=STRK:MEWNX:IT

Doesn't seem like two per channel will do the job for the F5.

[fishski13]

Originally Posted by labjr

Doesn't seem like two per channel will do the job for the F5.

we'll see...

[fishski13]

Originally Posted by Brian Kingsbury

So lucky I looked at that listing (after it had ended ) and those heatsinks are coming from the same town where I live. Maybe I can drive over and hand the guy $60 and steal them before they ship!!

. sorry, you snooze you lose.

[labjr]

Originally Posted by fishski13

we'll see...

... fire !

[fishski13]

Originally Posted by labjr

... fire !

i'm confident that they'll be enough. anyone elese care to share?

i have access to lots of cheap drop cut aluminum. a slab of 1/4" thick on the flat side with the MOSFETs and thermal grease sandwich may be necessay.

[labjr]

Originally Posted by fishski13

i'm confident that they'll be enough. anyone elese care to share?

i have access to lots of cheap drop cut aluminum. a slab of 1/4" thick on the flat side with the MOSFETs and thermal grease sandwich may be necessay.

The manual recommends a 6" x 8" piece with 1/4" base and 2" fins per MOSFET as a minimum. That's 96 square inches of fairly heavy heatsink per channel. I guess you could keep adding aluminum until it runs cool enough. However the heat is pretty concentrated from only two MOSFETs so you'll need to devise a solution to spread the heat out fairly quickly.

[fishski13]

Originally Posted by labjr

The manual recommends a 6" x 8" piece with 1/4" base and 2" fins per MOSFET as a minimum. That's 96 square inches of fairly heavy heatsink per channel. I guess you could keep adding aluminum until it runs cool enough. However the heat is pretty concentrated from only two MOSFETs so you'll need to devise a solution to spread the heat out fairly quickly.

i haven't played around with this high level of thermal management before, but let's assume 30-35C above ambient. in the summer months, my house is 24C max and winter 18-20C. add these numbers and we're still under 1/2 of the 150C rated operating temp of the MOSFETs.

the actual square area of my heatsinks are greater than the recommended (50.6" vs 48"), but have shorter fins and less in number. the heatsinks will be mounted with the fins running vertically, and one heatsink per MOSFET. i'll be happy if my thermocouple readings at the heatsink/MOSFET junction is <60-65C.