It gets plenty loud when I use other preamps. The problem is that I am using a 6 channel preamp so there are other, more powerful, amps in the mix when I use multiple channels. I just need to make a good stereo pre dedicated to the F6..
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Ya that's what I'm thinking.
If R1 and R2 are there for stability (and for setting bias) what benefits would there be to removing or lowering them other than wasting a little less power?
Nelson says it better than I do. Here's a paragraph from the F6 DIY article from 6moons (R13 & R14 = R1 & R2 on the Mosfet schematic). Just wondering if there's a value with the Mosfets under which it isn't recommended to go. 😱
Yeah. There certainly is. Going where no man fears tread is what a FAB is about.
When he wrote that article he was referring to semisouth devices with much friendly temperature coefficients.
I built an F5 with no current limiting circuit or thermistor to control bias and the bias certainly does want to creap up in value. Setting the bias was a slow process. That was using 0.47 ohm source resistors on irfp240/9240
I'd take a guess and say 0.3 ohms might be achievable with irfp240/9240, but wouldn't bet my house on it till I had actually tried it.
So would setting those resistors too low result in thermal runaway or something more catastrophic? Basically would some thermal sensors which trip a relay controlling power prevent catastrophic failure if one wanted to experiment with different values?
Forget over engineering and controlling everything.
Just experiment to find what's safe.
Nelson might provide some further advice but there's nothing stopping anyone doing their own tests. That's what its about. It doesn't take long to swap in and out different source resistors.
Normally On thermal sensors mounted on the heat sink are probably ok.
You'll burn out the mosfets way before anything catches on fire unless you used ridiculously thin gauged wiring intended for small currents.
I had no issues on that board either, dont know how much bigger one would want to go with cap, the Panasonic version I used on BA-3 boards are much smaller, even at 103 degree version.
Russellc
I know this has been covered, but I can't find the info I'm after.
I know NP posted a thread about this, just can't find it at present.
Transistor insulators.
I know mica is much preferred, But I'm having trouble finding any in the to-247/to-3p size.
Mica ~ 0.7wm/k
I can however get these
Aluminium oxide 15.06 W/mK @ 75° (solid pad)
Thermalsil III 0.92 w/m °C (silpad)
Thermalfilm™MT 0.379Wm/K (kapton)
Would that not mean the aluminum oxide is far superior ?
Second choice, thermasil or thermafilm ? noting there rated as celcius or kelvin, does that make a difference overall ??
Thanks..
I know NP posted a thread about this, just can't find it at present.
Transistor insulators.
I know mica is much preferred, But I'm having trouble finding any in the to-247/to-3p size.
Mica ~ 0.7wm/k
I can however get these
Aluminium oxide 15.06 W/mK @ 75° (solid pad)
Thermalsil III 0.92 w/m °C (silpad)
Thermalfilm™MT 0.379Wm/K (kapton)
Would that not mean the aluminum oxide is far superior ?
Second choice, thermasil or thermafilm ? noting there rated as celcius or kelvin, does that make a difference overall ??
Thanks..
Aluminium oxide is very brittle. The best compromise is the Keratherm type.
It's also important to use the right level of mounting torque, if you use a screw. A clamp is better.
10 Keratherm® Red Insulators - Parts
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Yup. After having a look, those red keratherms are 6.5w/mK
Pretty impressive. So thats what I'll get.
Thanks all.
Pretty impressive. So thats what I'll get.
Thanks all.