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70w 23cm amp build, question.


militaryoperator
 

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?


Ben


a a
 

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 groups.io <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?


Ben


militaryoperator
 

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 groups.io <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?


Ben


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 groups.io 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 groups.io <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?


Ben
-- 
Neil
http://g4dbn.uk


militaryoperator
 

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
-------------------------------


Ok Neil, I get the idea. Only have some copper sheet here so have cut 2 bits, will solder them together, then drill/tap 3mm, and bolt to pcb and device and solder, remove 3mm and then drill/tap 2.5 into the heatsink. 

Lot of faffing about, hi. I hope the blasted thing works after all this.


Much easier to buy one already done (aka PW  Nov20) 


Ben 


Paul Randall G3NJV
 

I have two of these to assemble and as I understand it first job is temporary clamp the copper piece tight against the PCB so the copper, the FET and the board can be soldered together with low melting point solder.

The suggested method is put M3 threads in the copper and use M3 stainless screws for temporary clamping (stainless, so they won't take solder, and can be removed after soldering).

For final assembly, you must clamp the PCB with attached copper piece tight to the heatsink. A warning is given against using large screws (M3) for final assembly because the big screw heads reduce clearance to the RF "hot" matching lines on the PCB. Recommendation for final assembly is M2.5.

So, the heatsink must be tapped M2.5 to accept final assembly M2.5 clamping screws passed thru the PCB and copper. The M3 threads in the copper are no longer used because the M2.5 clamping screws pass thru and only engage with the tapped heatsink.

Or .....you could drill clearance holes for M2.5 (thru PCB and copper) and use M2.5 stainless screws, nuts and washers to hold everything together for soldering, then discard the nuts and washers for final assembly using the M2.5 screws into the tapped holes in the heatsink (avoids need for M3 drill & tap and hardware).

Or ... you could drill and tap the copper piece M2.5, holding together with M2.5 screws for soldering then just drill out the threads in the copper using M2.5 clearance drill for final assembly using the M2.5 screws into the tapped holes in the heatsink (avoids need for M3 drill & tap, M3 hardware and M2.5 nuts).
 
That's my understanding, I hope this post clarifies with options.

See you on AO100!
Paul




From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of a a via groups.io <celad2001@...>
Sent: 30 September 2020 20:10
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] 70w 23cm amp build, question.
 
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 groups.io <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?


Ben


militaryoperator
 

Thanks Paul. 

I did suspect that was the case, just a bit unclear but fine now. 

I have bought a hotplate so will mount all the components first, hotplate it, then attach the fet and spreader. and try and keep the other components away from plate while soldering them. 

cheers, Ben.



Subject: Re: [UKMicrowaves] 70w 23cm amp build, question.

I have two of these to assemble and as I understand it first job is temporary clamp the copper piece tight against the PCB so the copper, the FET and the board can be soldered together with low melting point solder.

The suggested method is put M3 threads in the copper and use M3 stainless screws for temporary clamping (stainless, so they won't take solder, and can be removed after soldering).

For final assembly, you must clamp the PCB with attached copper piece tight to the heatsink. A warning is given against using large screws (M3) for final assembly because the big screw heads reduce clearance to the RF "hot" matching lines on the PCB. Recommendation for final assembly is M2.5.

So, the heatsink must be tapped M2.5 to accept final assembly M2.5 clamping screws passed thru the PCB and copper. The M3 threads in the copper are no longer used because the M2.5 clamping screws pass thru and only engage with the tapped heatsink.

Or .....you could drill clearance holes for M2.5 (thru PCB and copper) and use M2.5 stainless screws, nuts and washers to hold everything together for soldering, then discard the nuts and washers for final assembly using the M2.5 screws into the tapped holes in the heatsink (avoids need for M3 drill & tap and hardware).

Or ... you could drill and tap the copper piece M2.5, holding together with M2.5 screws for soldering then just drill out the threads in the copper using M2.5 clearance drill for final assembly using the M2.5 screws into the tapped holes in the heatsink (avoids need for M3 drill & tap, M3 hardware and M2.5 nuts).
 
That's my understanding, I hope this post clarifies with options.

See you on AO100!
Paul




From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of a a via groups.io <celad2001@...>
Sent: 30 September 2020 20:10
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] 70w 23cm amp build, question.
 
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 groups.io <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?


Ben


Neil Smith G4DBN
 

I use low-temp Bismuth/Tin solder (Adafruit Makerpaste or Chipquik 138C) to fix power devices so I can change them without melting the Pb/Sn/Ag solder used for the rest of the components. I use a slab of aluminium on my hotplate as a low-pass filter/heat capacitor to give a smooth control of temperature.

Neil G4DBN

On 04/10/2020 10:25, militaryoperator via groups.io wrote:
Thanks Paul. 

I did suspect that was the case, just a bit unclear but fine now. 

I have bought a hotplate so will mount all the components first, hotplate it, then attach the fet and spreader. and try and keep the other components away from plate while soldering them. 



militaryoperator
 

I bought a slab of ali as well Neil. Seems I'm thiking right, hi. 

I have some 183deg solder I was going to use. I see on bay there is some 138deg type so maybe I should treat myself. 

Ben G4BXD



Subject: Re: [UKMicrowaves] 70w 23cm amp build, question.

I use low-temp Bismuth/Tin solder (Adafruit Makerpaste or Chipquik 138C) to fix power devices so I can change them without melting the Pb/Sn/Ag solder used for the rest of the components. I use a slab of aluminium on my hotplate as a low-pass filter/heat capacitor to give a smooth control of temperature.
Neil G4DBN