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hifimaker 3rd January 2006 10:23 PM

Advangages of using new IRF240 in TO-204 package?
Just got the new Mouser catalog in the mail and noticed they are stocking IRF240's in TO-204 packages.

Are these similar to TO-3's and is there a compelling reason to use these over TO-247 designs? I'm wondering if they transfer or manage heat significantly better to justify the added cost over TO-247's?

The cost is almost $11usd each for quantities of 25.



PSz. 3rd January 2006 11:17 PM

Yup, the TO-204 package is very much like the TO-3. They do transfer heat better. Metal can devices are just cool. :cool: And the additional cost means they must sound better, right? Seriously though, you can find these devices in the SF Bay Area ridiculously cheap. I got bags of TO-3 irf130's and irf250's for a couple bucks per mosfet. You just need to look around a little.


MEGA_amp 3rd January 2006 11:38 PM

They do have the IRF140 in that package, these types are seemingly harder to get without the "N" designation at the end; which I understand is not good for audio use. At least theres no minimum bulk order.

BrianDonegan 4th January 2006 08:36 PM

You mean the IRFP140Ns are not good, or the IRFP140s?

MEGA_amp 4th January 2006 11:40 PM

As I understand from numerous threads, its the IRFP140N's which are not suited for audio use. I dont know personally, Ive never tried them. I'd like to try the IRF140 in the SOZ, it has 1660 Ciss vs IRFP140's 1700, dont know if that makes a difference, I'm assuming not. Also the IRF vs IRFP designation?? In the datasheet it says there well suited for audio use, Ive only seen that in 2SK1058/2SJ162 datasheets.

Another thing I dont understand, the TO-204 case max dissipation is at 125w vs the TO-247's 180w. I would think a metal case would allow higher dissipation.

MEGA_amp 5th January 2006 12:24 AM


Are these similar to TO-3's and is there a compelling reason to use these over TO-247 designs? I'm wondering if they transfer or manage heat significantly better to justify the added cost over TO-247's?
I just realized I asked the same question, oops. They have a slightly lower amperage rating than the TO-247 as well.

GRollins 5th January 2006 01:45 AM

As long as you can get the heat out of the device, there's no reason to get hung up on the case style. Be aware that metal cases are on their way out; the industry is moving to plastic cases.
The dirty little secret that people never mention is that metal cases are electrically live and can short to poorly placed wires, test probes, wedding bands, etc. Circuits can die a grisly death in this manner.
Granted, it's a purely esthetic thing, but I've gotten to the point where I kinda like the way the TO-247 case looks. In fact, a neat, orderly row of them looks as good or...dare I say it...better than a bunch of TO-3 cans. But that's just me being silly. Of course, life's about to get a little more complicated what with the TO-251 or whatever they call the LU1014D case, but that's just the way things are.
1660 pF vs. 1700pF doesn't strike me as being worth worrying about, though it leads me to a story...
Funny thing happened last week. I was listening to the big system. I'd gotten a phono stage where I though it was ready for the acid test. I'd listened to it under headphones, made changes, more headphones, another change, finally ready. Okay. Fine.
Something wrong with the tweeters.
Right side brighter than left.
Oh, hell! Don't tell me that I've gone and fouled up the RIAA EQ in this thing. I've put in too much time and effort and it's too late at night and all I want to do is listen. But...the imbalance won't go away. All right, dammit! I get out of my listening chair and prod my preamp (CJ Premier Three--has a MONO-STEREO-STEREO REVERSE switch on the front) to reverse the right and left channels. Hmmm...problem stays on the same side. Well, at least it's not the phono stage (I was running my phono into the AUX input--I had enough gain that I could have done without the line stage entirely, but no volume knob). Poke around. Poke around. Poke some more.
I'll bypass all the intermediate stuff and get straight to the punch line. The output devices in the left and right channels of the tweeter amplifier were different. (No, I didn't build the amp. Someone else did. They were gracious enought to donate the amp, so I'm not about to complain, so you just hush your mouth.) A moment's reflection led to the conclusion that the outputs for the right side--being brighter--would have lower capacitance than the ones for the left. And so it turned out to be. I dredged up the specs for the two devices and there was a two-to-one ratio between them.
Curiously, I'm not sure but what I didn't like the sound of the higher capacitance device (less treble) better. It was smoother. Less spitty. You could argue that the higher capacitance might make the distortion on that channel higher, but I don't think that's an issue here because there was plenty of current to drive the Gate. I'm still mulling this over. This gets into the realm of voicing a circuit. It's as much art as science. It's both fascinating and tedious, because it involves a lot of cut and try and experimentation. Theory helps some. Experience helps some. But in the end, you're just going to have to sit down and try it.
The moral of the story: Don't be too quick to assume that lower capacitance is always good, even in a dedicated high frequency amp.


EDIT: Mind you, I get away with bloody murder, running the absolute dog-widdle out of TO-220 output devices (IRF644s) because I water cool the bigger Alephs and can dump heat fast. That's an extreme case, and I don't reccommend it for everybody, but it's an option. Just something to think about.

BrianDonegan 5th January 2006 02:15 AM

Interesting. I just build two Aleph 30 channels with IRFP140s. Haven't listened yet (waiting for transformers). I'll have to give it a listen before I decide to change anything. Would be a waste otherwise.

PSz. 5th January 2006 02:36 AM


I had seriously thought about trying out headphones until I read your story.;)

Oh yeah, I must confess to liking neat little rows of plastic packages too. But the cost, impending scarcity, and dangers of an electrically live case make the metal cans that much more fun to play with. :cool:


mpmarino 5th January 2006 02:42 AM

I like the metal cases..I like the way they look. Kinda 'retro':) . Although they do get rid of heat faster, they are more difficult to mount effectively IMHO. You got some tricky drilling and bolting, not to mention you need a flat area front and rear. I think most people would actually end up with better heat transfer with a TO-247, bolt 'em or bar 'em down on the sink and away ya go :smash:

Edit: Brian, my '30 uses IRFP140' great!

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