No, temperature of pin 2 right up at the case- as close as you can get to measuring junction temperature. That is the case temp, so .83 times dissipation above that is junction temp.
I'm dumb sometimes 😛, ok, before changing res I'll check temp at fet pin2 (Drain), the amp is starting up 😉Ok, after 40min of burning here the results:
R13 = 47.5K
Voltages:
R40 = -.291 (2V caliber)
R39 = -.284 (2V caliber)
V- to -G = -4.40 (20v caliber)
DC offset (Out to Gnd) = -12.2 (200mv caliber)
Ifet = 0.291/0.47 = 0.62A
Total Bias = 0.62x3 = 1.83A
Temp:
Sink = 50°C
Irf240 (Pin2 drain) = 71°C
Junction temp = 0.62x32x.93+71= 89.45
R13 = 47.5K
Voltages:
R40 = -.291 (2V caliber)
R39 = -.284 (2V caliber)
V- to -G = -4.40 (20v caliber)
DC offset (Out to Gnd) = -12.2 (200mv caliber)
Ifet = 0.291/0.47 = 0.62A
Total Bias = 0.62x3 = 1.83A
Temp:
Sink = 50°C
Irf240 (Pin2 drain) = 71°C
Junction temp = 0.62x32x.93+71= 89.45
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you're good
understanding that :
DC Offset is in mV ,
Sink T is measured in area , say , somewhere convenient for grabbing it with hand
Irf240 T - good , if not having more then 10C then surrounding heatsink surface
understanding that :
DC Offset is in mV ,
Sink T is measured in area , say , somewhere convenient for grabbing it with hand
Irf240 T - good , if not having more then 10C then surrounding heatsink surface
Yes DC offset is in mV
I'm not sure I understand what you mean here
I think the only thing left before doing the second board is to catch some 100K res to replace the erroneous 10K ones on R2 and R15 (If I understood what you told me, those res sets the amp gain, so the max amount of volume it can deliver, right?)
I'm not sure I understand what you mean here
I think the only thing left before doing the second board is to catch some 100K res to replace the erroneous 10K ones on R2 and R15 (If I understood what you told me, those res sets the amp gain, so the max amount of volume it can deliver, right?)
temperature difference between IRFP's case (mid pin , whatever) and heatsink right near to mosfet - is measure of quality of temp transferring mechanismus
in other words - if screwed lousy - mosfet will be burning , while heatsink will stay cool
if tighten as needed , mosfet will be moderately hotter then surrounding heatsink area
yup for 10K , gain , blahblah
edit : another important data , needed for temp rise understanding :
you wrote Tsink is 50C ; what's T ambient ?
in other words - if screwed lousy - mosfet will be burning , while heatsink will stay cool
if tighten as needed , mosfet will be moderately hotter then surrounding heatsink area
yup for 10K , gain , blahblah
edit : another important data , needed for temp rise understanding :
you wrote Tsink is 50C ; what's T ambient ?
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You have about 20 W in each fet. You're seeing a 20 degree rise from sink to FET, which is across your isolators. That is a thermal resistance of 1°C/Watt, which is 10 times what Keratherm ought to give you. Worse than mica and goop. Could be right for a silpad. Tighten the FETS and hopefully you'll see less rise across the isolator.
also measure temp of heatsink on top , middle
Bill - we'll see what's happening tomorrow , when he measure temp near mosfet
I believe 50C is somewhere further
Bill - we'll see what's happening tomorrow , when he measure temp near mosfet
I believe 50C is somewhere further
You're right Zen Mod, I took sink temp on one of it corner (where there was a disposable Hole to put the probe on 😉 )
I will take the temp right next to the fet later today (I'm at work now.....have to earn some money to DIY 😱)
Bob Ellis, you are right too, I haven't tightened the fets enough, I had some margin left , so i fastened them even more ( I can't do further without damaging fet/taping)
As for the Keratherm pads, those are the White ones (thin and flexible), I only found TO220 pad (witch fit tightly, but fit nonetheless)
KERATHERM - Isolant pour boitier TO220 - Lot de 12 - Accessoires pour dissipateurs (french page)
check again non-continuity between mosfets and htsnk, just in case
knowing Papa's logic - hand-test was most probably with hand either at center-side of heatsink , or top side
Treshold SMs , for instance , always mentioned top-back-screw hole , for putting temp probe
so , context and known routine are important things .......
knowing Papa's logic - hand-test was most probably with hand either at center-side of heatsink , or top side
Treshold SMs , for instance , always mentioned top-back-screw hole , for putting temp probe
so , context and known routine are important things .......
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Will I see large benefits by replacing White Keratherm pads with brown ones (with FiberGlass) Feuille thermoconductrice 70/50 TO 247 0,25mm Kerafol KERATHERM BRAUN 70/50 - Vente Feuille thermoconductrice 70/50 TO 247 0,25mm Kerafol KERATHERM BRAUN 70/50 sur conrad.fr | 180346 (those are TO246 format)
Are the red ones sold in the diyAudio store available? 4 times the conductivity should make a difference.
They are in stock but I found that too, It's red keratherm sheet (have to be cut) 100x100
Feuille thermoconductrice 86/82 rouge 100X100X0,25 mm Kerafol KERATHERM ROT 86/82 - Vente Feuille thermoconductrice 86/82 rouge 100X100X0,25 mm Kerafol KERATHERM ROT 86/82 sur conrad.fr | 189056
Feuille thermoconductrice 86/82 rouge 100X100X0,25 mm Kerafol KERATHERM ROT 86/82 - Vente Feuille thermoconductrice 86/82 rouge 100X100X0,25 mm Kerafol KERATHERM ROT 86/82 sur conrad.fr | 189056
Easy (I use an office paper cutter)
You can make the holes with a punch for leather.
(trivia info : a couple of commercial manufacturers now use Keratherm red)
Argh! those insulators film cost an arm and a half.....
I own some Noctua NT-H1 thermal paste (witch is known to be as good as Arctic Silver 5), will it be good enough with mica pads?
I own some Noctua NT-H1 thermal paste (witch is known to be as good as Arctic Silver 5), will it be good enough with mica pads?
if not electrically conductive ( as Arctic Silver was in one iteration ) , why not
though - common white goo(p) always was good enough for Mighty Moi
😉
though - common white goo(p) always was good enough for Mighty Moi
😉
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