I was a UYK-* repairman too.

It was a good time to get an education.

 

The one vacuum tube you still have in your house, other than those who still have CRT TVs or Monitors, is the magnetron in your microwave. I don't see that one being replaced any time soon.

As for general electronics, yes, semiconductors have a serious advantage. That being said, in the last 15 years, I gone back to tubes at the hobbyist level. I find modern electronics a bit to "sterile" sometimes. Especially now, with programmable devices. I work with microcontrollers and CPLDs. But when I want to play, I want to get my hands dirty. Nothing like building a tube amp. And if you're a tad lax while probing with your meter, the high voltages will bite you !

As for the 0A2: There is the 0A2 regulator tube, which is filled with an inert gas, at low pressure. As mentioned it works like a zener diode, and comes in a glass miniature 7 pin package. But there was also the OA202 semiconductor diode (germanium ?). In the old days, before computers, zero and the letter "O", were commonly interchanged. For the regulator tube its properly zero-A-two, since the first digits indicate the filament voltage, and the 0A2 is cold cathode (no filament), hence zero. But we all know, when ordered one, a lot, if not most people said OH-A-2, and the guy on the other side knew what you wanted. When your dealing with human beings, and they know their business, they get the right item. When computers got involved, then you had to specify. Before "Word", or "Word Perfect", or "WordStar", there was this thing called a typewriter. On many portables, they did not have a zero, nor "one" key. For a zero, you used the capital-O, and a one, the lower case L. Since it was read by humans, there was no confusion.

 

Vacuum tubes? - You guy's had it easy.

I had to use a cats-whisker wire probe on a lump of gallium rock crystal and a pair of headphones to receive a radio signal (in the cardboard box I lived in, on the side of the freeway!)

I jest, but I do recall doing Uni lab experiments with a single OC71 transistor (tested and signed for in and out of the storeroom) each of which cost about the same as a tradesman's weekly pay.

Gawd I'm getting old!

Now I buy Arduino Nano 3 modules with USB connectivity from China for less than $3ea post free, with maybe 1 million transistors in them!

 

Now I buy Arduino Nano 3 modules with USB connectivity from China for less than $3ea post free, with maybe 1 million transistors in them!

Yeah, but 95% of them are counterfeit!

 

I was a UYK-* repairman too.

I sure bench pressed a lot of R390s into rack cabinets in the day! I got so I could do it single-handed.

 

Tubes had their place, in their time just like core memory did. We still have a few for HV regulation in machines making transistors today.
http://forum.allaboutcircuits.com/threads/tube-creep.113198/

https://en.wikipedia.org/wiki/High_Frequency_Active_Auroral_Research_Program
HAARP has 720 4cx10,000D tetrodes.

 

With a real world bipolar transistor you actually can swap the C and E and it will still work as a transistor, albeit with a much reduced gain of about one.

The input stage of evert TTL gate works in this mannor, so there are real applications for this.

I thought the multi-emitter input of TTL was just a simulation of the diodes used in DTL.. No transistor action actually.

 

I thought the multi-emitter input of TTL was just a simulation of the diodes used in DTL.. No transistor action actually.

Actual transistor action is actually evident, but strangely enough it is forward action when the input is low.

During the transition the input transistor is briefly in its active region; so it draws a large current away from the base of the output transistor and thus quickly discharges its base. This is a critical advantage of TTL over DTL that speeds up the transition over a diode input structure.

Source: https://en.wikipedia.org/wiki/Transistor–transistor_logic#Fundamental_TTL_gate

 

why can't I swap the emitter and collector in a circuit?

you can. the resulting device has very low beta.

 

See
.MODEL ZTX690B NPN IS=1.5p NF=1 BF=1000 IKF=3 VAF=60 ISE=4E-13 NE=1.37 NR=1 BR=123 IKR=1 VAR=14.5 ISC=4E-13 NC=1.34 RB=0.1 RE=0.045 RC=0.027 CJE=250p VJE=0.68 MJE=0.36 CJC=59p VJC=0.49 MJC=0.36 TF=0.77n TR=18n RCO=0.93 GAMMA=5n QUASIMOD=1 XTB=1.4 TRE1=0.002 TRB1=0.002 TRC1=0.002 Vceo=45 Icrating=2 mfg=Zetex
.MODEL ZXTN25012EZ NPN IS=9E-13 BF=990 NF=1 VAF=25 IKF=3.8 ISE=8E-14 NE=1.35 BR=410 NR=1 VAR=8 IKR=1.25 ISC=8e-14 NC=1.35 RE=0.0117 RB=0.1 RC=0.0081 CJE=168p VJE=0.7 MJE=0.38 CJC=61p VJC=0.52 MJC=0.31 TF=0.5n TR=1.7n XTB=1.4 Vceo=12 Icrating=6.5 mfg=Zetex
.

 

If an NPN transistor is just a layer of P type material between two N types why can't I swap the emitter and collector in a circuit? I remember doing this with some JFETs, source and drain could be swapped.

As a point of interest, certain 'power type' or otherwise low beta BJTs (e.g. many 'TO-36 packaged' germanium types) do indeed manifest significant 'polarity dysphoria' - to the extent that they exhibit greater gain in small signal operation in the 'wrong' 'polarity mode' --- Of course such operation is inadvisable (to say the least!)...

Apologies should the above point have been previously 'touched upon' -- I hadn't time to thoroughly read the thread


Best regards
HP

 

Some circuits will work, most wont