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From: Jan Panteltje <alien@comet.invalid>
Newsgroups: sci.electronics.design
Subject: Re: dumping a lot of heat
Date: Mon, 09 Dec 2024 06:25:29 GMT
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On a sunny day (Sun, 8 Dec 2024 16:36:25 +0000) it happened
liz@poppyrecords.invalid.invalid (Liz Tuddenham) wrote in
<1r499nc.1l79pftrqcriyN%liz@poppyrecords.invalid.invalid>:

>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?

The 100 mA is a current limit due to the limited electron emission possible from that cathode
at those settings.
You can get flash-over with anode voltage at the grid of toobs.
I understand you love toobs, sure toobs were nice
some arguments against using those:
1) glowball worming,
2) slow startup time of your system
3) bad efficiency, heater needs power all the time
4) fragile
5) toobs are BIG, imagine your smartphone electronics done with tubes,
   it would take a whole room or even building, and a special power station to power it..
   if you could get it working at all.
6) weight
7) sockets, bad contacts toobs thrown out of sockets
8) CRTs versus LCDs or OLEDs? smartphone with a color CRT?
9) touch screen????
10) X-Ray emission from the monitor HV stabilizer tubes..
etc etc
I have designed with toobs
In the early sixties in school I got hold of an old tube based CRT TV, round CRT tube at that time.
Then 'teletor' appeared in a Dutch magazine, all transistor TV with scope CRT as screen.
I modified it to drive that real old  magnetic deflection TV set with transistors
HV tronsformer, the works.
Was an interesting learning curve...
Never longed back to toobs after that.
Had to work with those up into the late seventies every day in the studios.
plumbicans, vidicons, CRT monitors full of tubes... racks full of tubes, video recorders...
CRT based Tectronics scopes everywhere...
35 mm film scanners with tubes, all the sync stuff, audio stuff,
Transistors slowly made their way, Ampex AVR1 as the most complicated all transistor I worked on.

Toobs are pretty much dead... for consumer producs.
Imagine drone electronics, may as well get a 747 to carry the power pack...
GPS receiver with toobs? 
LOL