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From: john larkin <JL@gct.com>
Newsgroups: sci.electronics.design
Subject: Re: dumping a lot of heat
Date: Sun, 08 Dec 2024 10:38:02 -0800
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On Sun, 8 Dec 2024 17:34:56 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:

>john larkin <JL@gct.com> wrote:
>
>> On Sun, 8 Dec 2024 16:36:25 +0000, liz@poppyrecords.invalid.invalid
>> (Liz Tuddenham) wrote:
>> 
>> >Jan Panteltje <alien@comet.invalid> wrote:
>> >
>> >> On a sunny day (Sun, 8 Dec 2024 13:33:39 +0000) it happened
>> >> liz@poppyrecords.invalid.invalid (Liz Tuddenham) wrote in
>> >> <1r490yz.1xraied16vto76N%liz@poppyrecords.invalid.invalid>:
>> >> 
>> >> >john larkin <JL@gct.com> wrote:
>> >
>> >[...]>RL
>> >> >> 
>> >> >> Tubes were awful. Still are.
>> >> >
>> >> >The techniques for designing with them are quite different from
>> >> >transistors and ICs, you have to think a different way; they aren't just
>> >> >poor transistors, they have a different lifestyle altogether.  They also
>> >> >have some advantages over semiconductors:
>> >> >
>> >> >1)  Withstanding short term overloads without damage.
>> >> 
>> >> Thermal overloads depend on teh heatsink.
>> >
>> >Only slow overloads.  Fast ones depend on the thermal time constant of
>> >the bit being heated by the overload.  Some time later the energy
>> >reaches the heat sink but but then the damage is done.
>> >
>> >I've just accidentally mixed up the anode and grid pins of one of the
>> >triodes in an ECC91.  It drew about 100 mA for a few seconds with no
>> >damage.  That's equivalent to mixing up the Base and Collector
>> >connections on a transistor and subjecting the Base-Emitter junction to
>> >about 10 times the rated maximum Collector current.  How many
>> >transistors would survive that, even with the biggest heatsink
>> >available?
>> 
>> Mosfet data sheets usually have SOAR curves.
>> 
>> IXFH400N075T2 is rated for 1000 amps and 1000 watts (with astericks)
>> and 30 kilowatts for 25 uSec. 
>
>Into the gate?

Don't do that.

It's not hard to protect a mosfet from failure. The only way to
protect a tube from failure is to not use it.

A 1B3 makes a nice high-voltage capacitor, which is very reliable.

I have some beautiful tubes. 833 transmit jug. Some Blue Arcturus
things. A krytron. Some acorn and prox fuse tubes. A few gorgeous CRTs
and PMTs.

https://www.dropbox.com/scl/fo/m2ff4ty142v65omvmqf9k/ADvXu5nmmZ06w2hLulkZYL8?rlkey=z2tncdtgojshzogufp59xgxtw&dl=0