Beginners' Aleph-X Production Diary

lscangus · 24th June 2006, 09:51 AM

IRFP044 Paired in 8 fets, all the way from Germany!

Thanks for one of the user in diyaudio.

lscangus · 24th June 2006, 09:52 AM

Capacitors are from RS

lscangus · 24th June 2006, 09:54 AM

BHC 47000 uF 25V X 8

lscangus · 24th June 2006, 09:55 AM

Paired Fets

lscangus · 24th June 2006, 09:57 AM

The Progress.

lscangus · 24th June 2006, 09:59 AM

Progress 1 Another angle of those gigantic heatsinks

EUVL · 24th June 2006, 11:29 AM

Glad to see you making progress.

Patrick

lscangus · 24th June 2006, 08:33 PM

I am sorry that i didn't contact you for so long, as i havn't done anything to those fets, now i have mount them onto the heatsinks and make sure them they are all insulated.

The next step is to connect them up to the board.

Angus

jleaman · 24th June 2006, 08:43 PM

Take you'r time It will pay off

EUVL · 25th June 2006, 04:56 AM

I assume you use thermal grease.
Do you have mica insulation in between (I would recommend) ?

Use the thermal grease sparringly. You should only smear on a thin layer uniformly on both sides of the mica with your finger. The grease is actually not very thermal conductive compared with metal, as it contains silicone grease and aluminium oxide particles. So you only need just enough to bridge any uneven gaps. The mica will do the insulation for you.

If you have a laboratory supply, set the voltage to your working voltage (per FET) and current limit to just over your bias current. Use a separate 9V battery with a 1k trimpot to set bias across gate and source resistor (starting from less than 3V and increasing slowly to something like 4V). After it is operating at the right voltage and current for say 5 minutes, measure the temperature at the heatsink and at the transistor METAL case. The difference should not be more than 8 degC. Then you know your thermal grease is not excessive. Of course check the insulation first between transistor & heatsink with a multimeter. Many multimeters also have temperature measurement (thermocouple) capabilities.

Patrick

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24th June 2006, 11:29 AM	#7
EUVL diyAudio Member Join Date: Oct 2003	Glad to see you making progress. Patrick

24th June 2006, 08:33 PM	#8
lscangus diyAudio Member Join Date: Oct 2005	I am sorry that i didn't contact you for so long, as i havn't done anything to those fets, now i have mount them onto the heatsinks and make sure them they are all insulated. The next step is to connect them up to the board. Angus

24th June 2006, 08:43 PM	#9
jleaman Banned Join Date: Apr 2002	Take you'r time It will pay off

25th June 2006, 04:56 AM	#10
EUVL diyAudio Member Join Date: Oct 2003	I assume you use thermal grease. Do you have mica insulation in between (I would recommend) ? Use the thermal grease sparringly. You should only smear on a thin layer uniformly on both sides of the mica with your finger. The grease is actually not very thermal conductive compared with metal, as it contains silicone grease and aluminium oxide particles. So you only need just enough to bridge any uneven gaps. The mica will do the insulation for you. If you have a laboratory supply, set the voltage to your working voltage (per FET) and current limit to just over your bias current. Use a separate 9V battery with a 1k trimpot to set bias across gate and source resistor (starting from less than 3V and increasing slowly to something like 4V). After it is operating at the right voltage and current for say 5 minutes, measure the temperature at the heatsink and at the transistor METAL case. The difference should not be more than 8 degC. Then you know your thermal grease is not excessive. Of course check the insulation first between transistor & heatsink with a multimeter. Many multimeters also have temperature measurement (thermocouple) capabilities. Patrick

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