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From: baron on 23 Jun 2010 04:24
krw(a)att.bizzzzzzzzzzzz Inscribed thus:

> On Tue, 22 Jun 2010 05:56:43 -0400, JW <none(a)dev.null> wrote:
>
>>On Mon, 21 Jun 2010 17:42:21 -0500 "krw(a)att.bizzzzzzzzzzzz"
>><krw(a)att.bizzzzzzzzzzzz> wrote in Message id:
>><iiqv1650144gv9gu9kju00tl8ec8abqlau(a)4ax.com>:
>>
>>>On Mon, 21 Jun 2010 15:50:07 +0000 (UTC), Cydrome Leader
>>><presence(a)MUNGEpanix.com> wrote:
>>>
>>>>Phil Allison <phil_a(a)tpg.com.au> wrote:
>>>>>
>>>>> "Cydrome Leader"
>>>>>> Phil Allison
>>>>>>> "Cydrome Leader"
>>>>>>
>>>>>>>> I had a hard time recently locating a specific power transistor
>>>>>>>> in a TO-218 case, with the metal tab and not the lump of
>>>>>>>> plastic with a metal back like everything seems to be now.
>>>>>>>
>>>>>>>
>>>>>>> ** Why bother ??
>>>>>>>
>>>>>>> TO-218 is virtually the same pak and construction as TO-3P
>>>>>>> except you no longer need to use an insulating bush with the
>>>>>>> latter.
>>>>>>
>>>>>> to not have to modify existing heatsink clamps. The setup in the
>>>>>> product was a bit weird with a clamp holding the metal tab onto
>>>>>> the heatsink. I'm not sure why the transistor wasn't just screwed
>>>>>> down. There was a screw and nut for the clamp anyways. JW: Cue
>>>>>> AlwaysWrong!
>>>>>
>>>>> ** A well designed clamp does a far better job with TO-3P and
>>>>> similar single hole packs than using a bolt does. Normally the
>>>>> clamp supplies high pressure
>>>>> along the CENTRE line of the plastic body of the device. The body
>>>>> spreads the pressure evenly over the tab and there is then no
>>>>> tendency for it to lift up at the lead end as there is with a
>>>>> bolt.
>>>>>
>>>>>
>>>>>>> TO-3 is a whole nuther animal with many advantages over plastic
>>>>>>> paks.
>>>>>>
>>>>>> the TO-218 is actually somewhat compatible with the TO-3.
>>>>>
>>>>> ** The main advantage of the TO3 pak is that there is no plastic
>>>>> in contact
>>>>> with the chip which sits in a hermetically sealed environment -
>>>>> means chips have a much longer service life even when running near
>>>>> max temps.
>>>>
>>>>I'm not arguing that a TO-3 is better all around- it's just that
>>>>fewer and fewer semiconductors are packaged as nicely these days so
>>>>that's what you have to work with most of the time. The hermetically
>>>>sealed and welded metal can obviously costs more than some plastic
>>>>resin molded around a sliver of metal.
>>>>
>>>>Sanken uses to have the most exciting TO-3 cases. The base was
>>>>surprisingly thick and they felt like they were made of gold.
>>>>
>>>>> Internal feed wires can be sized to fuse immediately if a device
>>>>> fails - a valuable feature not seen in plastic paks.
>>>>
>>>>But the plastic ones explode and burn.
>>>
>>>Metal ones can explode and throw shrapnel around the room.
>>
>>A TO-3 explode? I've *never* seen that happen, and hope I never do!
>
> Yep. One failure mode the base lead came *though* the case like a
> bullet. In another the whole top of the case came off and ricocheted
> around the room. They ended up putting the power supplies in a
> bullet-proof test chamber for
> their christening. Secondary breakdown can be an impressive event.

I've had 3771's go bang and lift the top hat, but never blow it off
compleatly.

--
Best Regards:
Baron.
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