Re: 70w 23cm amp build, question.

Neil Smith G4DBN

The ninety-odd  spreaders I made were tapped M3. I assumed the idea was to clamp the PCB to the spreader using an M3 screw in the tapped hole for soldering, then discard the M3 and use the M3 tapped hole as an M2.5 clearance (just) hole to fix the whole thing to a heatsink.

Just guessing mind, although I made all those spreaders, I haven't made an amplifier for myself.

Neil G4DBN

On 30/09/2020 21:02, militaryoperator via wrote:
No, the instructions are the other way,  drill tap 3mm then fix with 2.5mm.

i think the copper tapped to 2.5 was to secure the spreader while the fet is soldered,
Then the holes opened to 3mm to take bolts to compression fit the board and copper spreader to the heatsink, it would not be possible to get the spreader compressed to the heatsink with threads in the copper,
de alec
On Wednesday, 30 September 2020, 18:29:49 BST, militaryoperator via <military1944@...> wrote:

A bit unclear. 

Notes on fitting the heat spreader to the G4BAO/G7NTG 70 watt PA
It says:

The centre holes in the PCB should be opened out to 3mm and secured to the heat spreader with a smear of solder paste in between them with two short M3 stainless steel screws 

then says:

The screws are then removed and then the pcb can be fixed to the heatdink with 2 x m2.5mm screws.

If I have tapped two 3mm holes how can 2.5mm bolts fit?


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