I don't care what he says his design goal is. What he's actually doing has nothing to do with Jensen transformers. The guy's a quack and a charlatan. Not surprising that you'd be taken in by it.
I think SY still has one of their stupid Vero headphone cables unless he sent it back to my friend.
se
Thanks, Scott.
The style 1 and style 2 are quite large compared to the exposed area on the BD139s. Plus $72 just isn't in the budget right now. I'll see if I can find some thermally conductive epoxy here locally and try gluing the thermocouples I have on hand to the case.
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Yes. And again, his "articulation poles" is a gross misrepresentation and misapplication of real technology. But that's how a lot of the hucksters operate. So if some naive schmuck Googles it, they'll find that it's "real" but simply won't know enough to know that it's being misrepresented and misapplied.
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I was afraid of that, it's a tough problem. We bought a very expensive IR thermometer with a tiny spot size but it was over $1000.
I'll figure it out. Like I told SY, I've plenty of time at the moment, some TO-3Ps, and four or five thermocouples. I think I'll be able to work out a fudge factor for the thermocouples and get a close enough answer.
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Thanks. I'll fool around with the IR thermometer and a simple touch of the thermocouple first and see if I can get some consistency with that and if it doesn't pan out, try the JB Weld (I have some here as well as some unloaded two part epoxy).
I'd simply do the "just turn it on and see what happens" as I have plenty of output devices, but I only have two pre-production circuit boards and want to build two pre-production amps, so I don't want to risk output device failure damaging the circuit board.
se
If you want to be creative, you could measure the Vbe drop vs temperature of the transistor on its own with the operating base current when the device is externally but uniformly heated in a temperature chamber of some kind, without collector current. Then measure the Vbe drop when the circuit is operating (assuming you have a way of knowing what the DC base current is). I think that should get you the die temperature at the EB junction (I'm sure someone will chime in if that's wrong!). We used to use a variation on that to measure PIN diode die temps when conducting big RF currents (gated the RF off briefly, look at the voltage drop on a scope).
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I think there are a few details, but the principle should work
you can fit to a diode model including base, emitter resistance http://ieeexplore.ieee.org/xpl/logi...://ieeexplore.ieee.org/iel1/101/6598/00261890
like a band gap reference you could use 2 test currents in a fixed ratio in a short enough time to avoid too much heating/cooling
you can fit to a diode model including base, emitter resistance http://ieeexplore.ieee.org/xpl/logi...://ieeexplore.ieee.org/iel1/101/6598/00261890
like a band gap reference you could use 2 test currents in a fixed ratio in a short enough time to avoid too much heating/cooling
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Thanks, but I simply need the temperature of the plastic case, not the die or the junction temperature.
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I have both an IR thermometer and thermocouple temperature probes. But simply touching the thermocouple to the case won't necessarily give me the case temperature. And the devices are BD139s which are rather small and much of the front surface area is covered by the head of a 6-32 pan head screw which rather complicates using the IR thermometer.
That's why I'm thinking of getting a TO-3P (plastic version of a TO-3), heating it up and measuring it with the IR (it's a much bigger target than the little BD139s). Then I can touch the temperature probe to the surface, get a reading and determine how far apart the two are.
Then I can use that to calculate the actual case temperature of the BD139 when I similarly apply the probe to it.
se
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