2stageEF high performance class AB power amp / 200W8R / 400W4R

[thimios]

If you find the right black magic marker you can colour the end of the screws black to blend in. Marksalot brand are good for this here. Many others come out purple.

An option to increase thread life in aluminum is to use long set screws as studs and leave them in the heat sinks.

Hi Jeff and Andrew, thanks for the tips.
Do you mean screwing bolts on heatsink and fixing the heatspreaders using washers and nuts?

 

[jwilhelm]

Hi Jeff, thanks for the tips.
Do you mean bolts on heatsink and nuts in the other side on the heatspreaders?

Install the studs/set screws in the heat sink and attach whatever to the heat sink with nuts. No wear/damage to the aluminum threads this way.

 

[AndrewT]

This also helps where a tall capacitor blocks access to the bolt/screw head. A spanner can remove the nut/s

 

[Vrystaat]

Why are you guy's not using clamping bars. You can use bigger diameter screws. Much easier to tap as well.

 

[thimios]

Why are you guy's not using clamping bars. You can use bigger diameter screws. Much easier to tap as well.

Hi Vrystaat ,have you seen post #2341,2347?

 

[Vrystaat]

Sorry Thimios, I did not see the transistors mountings below the board.

 

[thimios]

Sorry Thimios, I did not see the transistors mountings below the board.

Never mind, i know what you say but this isn't my problem now.

 

[astx]

Install the studs/set screws in the heat sink and attach whatever to the heat sink with nuts. No wear/damage to the aluminum threads this way.

IMHO good idea if you often need to replace/exchange the transistors e.g. during test phase...

BR, Toni

 

[Dave Zan]

...I have tools as in picture 2.

Another option is to use a tap that "forms" the threads rather than cuts them.
These work well in Aluminium, no chips and the tap is less likely to break, not weakened by chip clearance slots.
Should be available in your country or easy to send in a plain envelope for mail order.

Best wishes
David

 

[thimios]

Another option is to use a tap that "forms" the threads rather than cuts them.
These work well in Aluminium, no chips and the tap is less likely to break, not weakened by chip clearance slots.
Should be available in your country or easy to send in a plain envelope for mail order.

Best wishes
David

Something like this?Osg Tap, Right Hand, Thread Forming, M4, 0.70mm Pitch, Cobalt, Bright Finish - | eBay.
Looks fine but very expensive option!

 

[AndrewT]

The drill size for a thread forming tap is bigger than the drill size for a thread cutting tap.
You will need to find out what drill size to use for the material you are working with.
Aluminiums are quite different formulations and I suspect this affects the drill size.

 

[jwilhelm]

Thread rolling taps are better for sheet metal. In blind holes they are more prone to stick. They do form a tough smooth thread though.

I'm not sure if Sowa will ship to Greece but they have a good selection of aluminum taps and a reasonable priced. SOWA - Homepage

 

[astx]

Another option is to use a tap that "forms" the threads rather than cuts them.
These work well in Aluminium, no chips and the tap is less likely to break, not weakened by chip clearance slots.
Should be available in your country or easy to send in a plain envelope for mail order.
...

Yes - that's a good alternative to standard screw tapping ...

I will try using this one: gewindebohrer.de - BAER HSSE-TIN Forming Tap M 3 x 0,5 - DIN 371 with oil grooves 34TD70320601
You will need a

• 2.8mm drill for M3
• 3.7mm drill for M4
• 4.65mm drill for M5

BR, Toni

 

[thimios]

IMHO good idea if you often need to replace/exchange the transistors e.g. during test phase...

BR, Toni

I can't see any reason for heatspreaders removing when transistors fail.
BTW. My country not included in his shipping catalog but i see very expensive shipping cost for such a small thing

 

[astx]

Thread rolling taps are better for sheet metal. In blind holes they are more prone to stick. They do form a tough smooth thread though.

I'm not sure if Sowa will ship to Greece but they have a good selection of aluminum taps and a reasonable priced. SOWA - Homepage

Not those parts some posts ago - especially designed for blind holes.
But one must use oil during forming the tapping ...

BR, Toni

 

[jwilhelm]

Not those parts some posts ago - especially designed for blind holes.
But one must use oil during forming the tapping ...

BR, Toni

I was just looking at the ones you posted the link to. They look a lot higher quality than the versions I've been using. I've only used Sowa/Chinese junk to date. Notice the ones you linked to are for high speed power tapping only.

 

[thimios]

Looks like i have another option when the drilling is between fins (no blind holes required).

 

[Dave Zan]

...Notice the ones you linked to are for...power

I suspect this is only if you push the limits, they list stainless steel - which is extremely difficult.
For Aluminium I have never seen a "power only" limitation.

Looks like i have another option...

That's a sensible option too.

Best wishes
David

 

[SGK]

I don't trust myself to get one hole in the right place let alone two or more so I just have Modu do it in my case, it is money well spent.

 

[astx]

I don't trust myself to get one hole in the right place let alone two or more so I just have Modu do it in my case, it is money well spent.

Dear Steve,

yes - another good option. I personally use the services from schaeffer-ag.de
Any news about your new location - profile still shows London? Timezone?

BR, Toni