is a TO3 case better?

[Jonny Hotnuts]

This may seem like a tard quesion but wondering if the TO3 was a better trans.

So few amps run them.....but the amps that do are usually VERY expenisve. Just wondering.....

[TheMG]

To assume a TO-3 transistor is higher quality than a TO-2XX equivalent would be an incorrect assumption.

I can see one advantage being better mechanical ruggedness and better thermal dissipation, but they also have their disadvantages such as more difficult mounting, more complex heat sink design, and higher cost.

As for the quality of the magic stuff (what's inside, where it really counts), there's nothing to be said about that. Just like any other transistor, there are fakes and knockoffs, and many varied specifications, no different than any other type.

[djQUAN]

in my own opinion, due to the rarity of TO-3 transistors in car amps, manufacturers are taking advantage of this and making people think "TO-3 is rare, it must be expensive, so it must be good!"

not sure if my assumption is right though.

but I do agree with TheMG's comments.

[tomtomjr]

I don't know if I would say better. Alot of the earlier TO3 amps are still in use. I have about 20 different old amps with them, and they all work but one.
TO3's are in alot of the vintage amps. later Linear Power (the first few models didn't have TO3's that I know of, early 80's Majestic, , early 80's Coustic , ect.
One thing that I remember about the older Linear powers with the TO-3's is the scream they made when doing a db test. The amps squealed loudly under a heavy note. Only heard this on Linear Power amps. Could have been the TO3's, not sure. Haven't strained one like that in 20yrs. Anyone else remember the earlier TO3 LP's screaming?

[1moreamp]

The "screaming" was most likely the loosely wound toroids that LP was famous for. I remember it well also, and on many other brands over the years.

TO-3's have a following mostly based on ten year lifespan testing where they seem to have the advantage. This along with thermal characteristics that seem to have some better advantages in some cases.
Manufacturers have come out with much better packages since then, and the margins between the packages has narrowed greatly over the years. With estimated MTBF being equal if not better with todays newer package designs.

There are a whole host of spec's to be considered, even the differences between a Aluminum case or a steel case TO-3 seem to hint at different quality standards, and lifespans. But there are so many variables to be considered, one would also remember that all these tech spec's are also in the hands of Sales Engineers also before we get them as end users.

Do I like them ? There OK, They pose different service related issues, mostly time consuming

[Workhorse]

TO-3 case offers THERMAL AND MECHANICAL advantages.

Ease of heat transfer/dissipation from the transistor to heatsink
I have seen plastic devices going into smoke at 90degC, but never seen a metal case device failure even at 120degC. Metal case offers much more thermal stability than plastic case devices.

If the ambient temperature is more than normal, TO-3 case devices always offer an edge over plastic devices.

[EWorkshop1708]

It's way easier to mount a big TO-264 and you get nearly the same performance and power handling.

TO-3 may be a bit rated higher, but with all the BS you go through mounting them, it's not much of a gain. Now if you have a GOOD TO-3 heatsink, that's different.

BUT IMO, TO-3 is still the toughest transistor. I've killed very few of them. I used to collect any high powered ones I'd find.

If you have a large heatsink with a THICK base, TO-264 is the way to go. Also, it's EASY to parallel TO-264, which works even better with the heatsink.

You can't mount a typical TO-3 with a thick base heatsink because of the B-E leads. Thermal flow in the heatsink is also way better when the base is thick, so the sink isn't just hot around the transistor. With a few flat pack TO264 devices, and a good thick heatsink, I can get better performance than with TO-3s. I can also fit more transistors on to one heatsink with the flat pack devices.

I just use my TO-3's as overkill transistors in low power stuff, so I don't have to use heatsinking. And running only 1A or so in a 20A device won't hurt

[thylantyr]

Ease of heat transfer/dissipation from the transistor to heatsink

Transistor -> goo/insulator-> heatsink

This is good


Car amps may do this.

Transistor -> goo/insulator -> thin metal bracket -> goo -> heatsink

not very good.

When the design is not executed well, the transistor case
is not the problem area.

Then you have a second variable. The amplifier design as a whole.

[EWorkshop1708]

Brackets really hurt thermal conduction. Heat doesn't go through the thin metal good enough. I've seen that done so many times with mostly TO-3, but others too. The bracket and transistors get hot first, before the sink gets warm

I agree with you, mounting directly to a thick metal heatsink is the best way.

Why don't they just make a flat-metal transistor with 3 leads coming out the top??? Like TO-3, but rectangle, and the leads in a much better place.

[TheMG]

Originally posted by EWorkshop1708
Why don't they just make a flat-metal transistor with 3 leads coming out the top??? Like TO-3, but rectangle, and the leads in a much better place.

$$$