Anyone got recommendations for screw torques on the modushop chassis running 1stW clones and other Class A circuits? Have a bit of an annoyance of the chassis making kricking noises due to thermal expansion. Going to tear them apart this weekend and retighten everything. Suggestions?
If you're talking about tightening the transistors to the heat sink, surprisingly little torque is needed. 0.5 Nm is the general recommendation for M3x0.5mm. That's barely beyond finger tight.
I always put serrated lock washers on the bolts that hold the brackets to the front and rear panels and tighten the screws pretty snug. I've never had issues with pinging during thermal expansion.
Tom
I always put serrated lock washers on the bolts that hold the brackets to the front and rear panels and tighten the screws pretty snug. I've never had issues with pinging during thermal expansion.
Tom
Yes, the actual chassis, not the MOSFETs to Heatsink interface. Went and bought one of those fancy torque drives for that. I have loctite handy so I'll give that a go with re-tightening everything. I'm wondering if it is the top and bottom plates shifting against the heatsink brackets given the dissimilar metals. Will have to try some troubleshooting to narrow down the offending joints.
In addition to the good advice above, sometimes a flat washer or two are needed to keep the back panel from bowing when attaching to the sink brackets. Also, if it helps, I‘ve put a flat nylon washer or a small silicone o ring under the top panel screws for some extra clearance if the panel rubs or makes noise.
0.8Nm
even more (if bolt quality allowing) with mica pads ..... say 1Nm
Keratherm and other squishy ones, 0.8Nm
and yes, split washer in all places, except fancy screws for covers
I suppose the mounting torque of the transistor screws will depend on the transistor package. What you're after is a specific pressure across the thermal interface. That would depend on the torque on the screw as well as the area of the transistor package. I think my 0.5 Nm was for the LM3886 which is similar in area to a TO247, possibly a bit smaller.
Tom
I do that as well. If you don't have enough fingers to keep everything together give the washers a small drop of super glue (cyanoacrylate).
Tom