Let’s plug in a few guesstimated values and see what we get:
Let’s assume:
Power Dissipated = 80 W
Ambient Temp = 25 C
Theta(Heatsink-To-Air) = .3
Theta(Bracket-To-Heatsink) = .1
Theta(Case-To-Bracket) = .3 (Kapton & Grease)
Theta(Junction-To-Case) = .7 (Guess For Super TO-3)
That would give us a chip temp of:
TA+PD*(THA+TBH+TCB+TJC)
=25+80*(.3+.1+.3+.7)
=25+80*(1.4)
=137 C
Let’s assume:
Power Dissipated = 80 W
Ambient Temp = 25 C
Theta(Heatsink-To-Air) = .3
Theta(Bracket-To-Heatsink) = .1
Theta(Case-To-Bracket) = .3 (Kapton & Grease)
Theta(Junction-To-Case) = .7 (Guess For Super TO-3)
That would give us a chip temp of:
TA+PD*(THA+TBH+TCB+TJC)
=25+80*(.3+.1+.3+.7)
=25+80*(1.4)
=137 C
It's normal for the case of the transistor to feel much hotter than the heatsink, one will be touchable, the other will not. It's possible your thermal interfaces are fine, but you can't know for sure until you measure. The temperature probes that come with inexpensive DMM's would be adequate, maybe even a cooking thermometer if you have one of those around. Have fun
Some images: on the VFET, on the T bracket close to VFET and on the heatsink close to T bracket (at 1.5A bias)
I combined two mica of TO-247 size for insulator. Unfortunately, the new material insulator from Panasonic (graphite) is so thin (the thickness is 0.5mm = 0.01mm graphite + 0.506mm adhesive) => easy to short circuit and thermal conductivity is hard to transfer through thick adhesive layer. I bought a new graphite (0.1mm) without adhesive and test later.
I combined two mica of TO-247 size for insulator. Unfortunately, the new material insulator from Panasonic (graphite) is so thin (the thickness is 0.5mm = 0.01mm graphite + 0.506mm adhesive) => easy to short circuit and thermal conductivity is hard to transfer through thick adhesive layer. I bought a new graphite (0.1mm) without adhesive and test later.
I build this amp for my friend. I told him this amp from Mike and I want to mark VFETRON on the front panel but my friend is a fan of Nelson, so I used the STOP font for thatVery nice Nagini, love the enclosure. How did you produce your frontpanel? Is it two 10mm plates on each other?
The front panel is a copy of Pass XS series and it's 15mm thick.
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