DATVPA@groups.io | fitting a heat spreader to the G4BAO/G7NTG amplifier for 23cms

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fitting a heat spreader to the G4BAO/G7NTG amplifier for 23cms

James Smith All Messages By This Member #288 Notes on fitting the heat spreader to the G4BAO/G7NTG 70 watt PA The heat spreader should be made of copper sheet 3mm thick or greater as in the drawing below. 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 screws such that the screw does not stick out on the other side. I use 138 degree Edsyn CR11 solder paste for this. The assembly is then placed copper face down on a hotplate with the transistor set in solder paste in the square hole – make sure you get the transistor the right way round! The hotplate is then switched on and heated to 160 degrees C or until the solder melts. Remove from the hotplate and gently press down the transistor until the solder sets – be patient it might take a little while. I have the luxury of an accurate hotplate but there are many ways to do it; A ceramic hob whilst the wife is not looking, a clothes iron ,on a large piece of aluminium plate on a gas ring or even as I used to do , with a blowlamp or gas torch heating the underside of an aluminium plate with the PCB on top. I never had a device failure doing this! If the PCB comes without a rectangular hole in the centre then just drill a 4 or 5mm
Rod Smallwood All Messages By This Member #290 Drawing? On 26/06/2020 11:34, James Smith via groups.io wrote: toggle quoted message Show quoted text Notes on fitting the heat spreader to the G4BAO/G7NTG 70 watt PA The heat spreader should be made of copper sheet 3mm thick or greater as in the drawing below. 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 screws such that the screw does not stick out on the other side. I use 138 degree Edsyn CR11 solder paste for this. The assembly is then placed copper face down on a hotplate with the transistor set in solder paste in the square hole – make sure you get the transistor the right way round! The hotplate is then switched on and heated to 160 degrees C or until the solder melts. Remove from the hotplate and gently press down the transistor until the solder sets – be patient it might take a little while. I have the luxury of an accurate hotplate but there are many ways to do it; A ceramic hob whilst the wife is not looking, a clothes iron ,on a large piece of aluminium plate on a gas ring or even as I used to do , with a blowlamp or gas torch heating the underside of an aluminium plate with the PCB on top. I never had a device failure doing this! If the PCB comes without a rectangular hole in the centre then just drill a 4 or 5mm
James Smith All Messages By This Member #291 look in files toggle quoted message Show quoted text On 26 June 2020 at 11:40 "Rod Smallwood via groups.io" <rodsmallwood52@...> wrote: Drawing? On 26/06/2020 11:34, James Smith via groups.io wrote: Notes on fitting the heat spreader to the G4BAO/G7NTG 70 watt PA The heat spreader should be made of copper sheet 3mm thick or greater as in the drawing below. 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 screws such that the screw does not stick out on the other side. I use 138 degree Edsyn CR11 solder paste for this. The assembly is then placed copper face down on a hotplate with the transistor set in solder paste in the square hole – make sure you get the transistor the right way round! The hotplate is then switched on and heated to 160 degrees C or until the solder melts. Remove from the hotplate and gently press down the transistor until the solder sets – be patient it might take a little while. I have the luxury of an accurate hotplate but there are many ways to do it; A ceramic hob whilst the wife is not looking, a clothes iron ,on a large piece of aluminium plate on a gas ring or even as I used to do , with a blowlamp or gas torch heating the underside of an aluminium plate with the PCB on top. I never had a device failure doing this! If the PCB comes without a rectangular hole in the centre then just drill a 4 or 5mm -- there is a driver amp PCB on Ebay - QO-100 ES'HAIL 30 WATT AMPLIFIER KIT
James Smith All Messages By This Member #292 Hi Gareth The expensive solder paste does not dry up if you keep it in a resealable bag - I have used my tube for about 12 amplifiers now over about 18 months and it is still fine! I get your point though - the device is extremely tough and should be ok - go with your favorite method - I used to use normal solder paste and a blowlamp , even on 300 watt 2,4GHz devices with never a problem! I always check the transistor for shorts as soon as the solder sets with a Fluke 75 on continuity range - sometimes random solder blobs can get under the tabs to ground - if so, reheat, clean up and try again. MAKE SURE THE TRANSISTOR IS THE RIGHT WAY ROUND! haha Jim
James Smith All Messages By This Member #294 Heat spreaders ready to use can be obtained for the G4BAO amplifier from Neil Smith who emailed me with; I found some 3/16" busbar in my stock bin that will do nicely. Milled flat and square to 3mm thick, drilled and tapped, £5 plus £1 postage for 1-4 spreaders. £1.64 for larger quantities. I have enough bar in stock to make 24. Neil neil@...

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