F5m Redux

[bdbender]

@Cheng: olé! 😉

 

[N Brock]

the fan was running and heatsink was slightly warm, even though the I had the power witch in the off position (I hope nothing else was damaged).

Very strange behavior. Perhaps the switch FETs have failed open?

BUT, also before I go through and double check everything, I wanted to ask/double check and make sure since I have extra keratherm around; Is it okay to use keratherm vs the grease on the bigger, ie IRFP 140s etc?

I don't have a ton of experience with silicone pads, but per the spec sheet, Keratherm red has adequate thermal conductivity for this amp. I've read they are more sensitive to clamping pressure than mica / alumina with grease, but they're pretty widely used on diyAudio builds and not many complaints. @MistyBlue started a thread comparing different thermal pads / pastes that's worth a look if you want to dive deeper.

 

[birdbox]

Is it okay to use keratherm vs the grease on the bigger, ie IRFP 140s

I used Keratherm 86/82 on my F5m and other amps. Works great. I used what was in the kit for my F5m Redux --> Mica and grease I think?.

Make sure to torque the IRFP140/9140 to spec (1 N-m if I'm not mistaken) and use appropriate lock washer so the bolt can't loosen under thermal cycling.

 

[Cheng]

I would also be very careful when handling and soldering the fets. I suspect my failed fets could be due to static while handling them during soldering and not due to manufacturer issue.

My F5M runs warm to a little warm, but the fan take care them and it sounded very nice on my setup after warm up 🤓

 

[birdbox]

3D printed brackets hold two or four supplies side by side with a bit of air space around them (they don't get all that warm but it can't hurt). Pips on the bottom of each supply hold the brackets in place. Braided 1/4" sleeving and some heatshrink completes the package. Files suitable for printing or editing are attached here and on the first post.

I printed 4 of these for another member. They work so well that I'm going to print 4 more for myself 😎 Simple and effective! Thanks Nelson for sharing the design!

 

[Cheng]

Very nice! Does your supply blocks get hot to touch after hours of playing music?

 

[birdbox]

I've never checked. I'll check them next time I play tunes for a few hours.