Transistors

[Nowhere-Man]

"Because collector current is less than emitter current by factor α."
The same site had collector current slightly lower. The emitter is forward biased so current should have less resistance.
I think I got a touch sunburned working today. I've had to keep up the pace. I must say the boat looks nice but it's been hard work.

[Craig]

"I won't say what I think of that tutorial because this is a family-friendly site. Similar comments apply to just about every other article I've read on there. Unfortunately, because it's quite well presented and search-engine friendly, a lot of beginners cite pages from that site when really they shouldn't."

I'm with you there Mark. They don't explain how to calculate the parallel value of the two bias resistors, why that is relevant, and of course linking all that together via Thevenin. Then they use the beta transform to move that parallel combination to the emitter side, again without an iota of explanation. They leave re out of it, which is probably reasonable because at 4mA is it just 6.5 ohms.

And then they have the effrontery to call the site "Learning about Electronics"; when it actually teaches precisely nothing at all.

Craig

[Nowhere-Man]

This is quite common though. I already made a start juggling that circuit to see what I could deduce. I may also access other explanations. Personally I think it's crucial to explain these things with a view to others understanding. I learned from that site but I think they were being a bit "clever" and showing off long winded digits.
I noticed in my other schematics emitter is at + chassis.

[Mark Hennessy]

Personally, I think it's crucial to actually build some circuits and see how they behave in reality, but perhaps that's easier said than done sometimes...

[Nowhere-Man]

I agree with you there. While working on my boat the other day someone told me to "take away" a radio and radiogram. This turned out to be fake with a modern PCB board inside. Still it had a small AM LW ferrite aerial and stuff to add to my scrap box. I figure I have enough stuff to make a radio (on the cheap). Once boat work is complete and the weather turns. I would make it the old way on a chassis and my spare GE transistors. Far better than reading books.
Of course the boat project has gone very well and I hope to move on soon and put my steel boat up for sale. If it works out hopefully I can expand the radio work although I now need to build a workshed. I'll be sad to lose the steel boat but my glass fibre alternative will be less stress and money plus I will get better signals.

[jimmc101]

It might be worth looking at the 'GE transistor manual 7th edition' from 1964.  A quick Google will turn up a download.

It includes sections on Unijunction Transistors, Tunnel Diodes and Silicon controlled Switches, unfortunately nothing on Field Effect Transistors.
Covers basics to quite advanced theory, but also has a lot of practical circuits.

An example below shows a complementary astable which can be used as a simple continuity tester

   

Jim

[Nowhere-Man]

I was just readung an article and will quote from it:
"When radios became more complex, with the introduction of SSB and FM, the era of home made gear mostly ended. A decent radio is a significant financial commitment now; it's expensive enough to be a barrier to young folks, and the act of purchasing, rather than building, limits the educational experience."
Personally I find the transistorised circuits a "step up" from your typical mid Fifties valve radio. I was comparing a Hartley oscillator with a triode vs a transistor equivalent. By comparison the triode design was much simpler.
I am a bit off topic here but the article above states that the 1960's students actually built all sorts of gear because circuits were engineered and point soldered. Lots of mistakes were made too. The punchline is I think the interest amongst the general population today has shrunk so much as maybe they feel the digital era is way too complex to relate to. So kids are learning web design and code, rarely making radio equipment. The good news is the vintage scene offers a different perspective. You can even build a transistor radio close to the valve principle (mixer, IF, detector and so on). Sadly, this is not being conveyed to the population so teaching is very theoretical (possibly semi reliant on IT).
It's the same with mechanical engineering. All the old Kelvin, BMC and Perkins boat diesels can be worked on but modern car engines are computerised. It tends to stifle interest.

[reset]

"I won't say what I think of that tutorial because this is a family-friendly site. Similar comments apply to just about every other article I've read on there. Unfortunately, because it's quite well presented and search-engine friendly, a lot of beginners cite pages from that site when really they shouldn't."

I'm with you there Mark. They don't explain how to calculate the parallel value of the two bias resistors, why that is relevant, and of course linking all that together via Thevenin. Then they use the beta transform to move that parallel combination to the emitter side, again without an iota of explanation. They leave re out of it, which is probably reasonable because at 4mA is it just 6.5 ohms.

And then they have the effrontery to call the site "Learning about Electronics"; when it actually teaches precisely nothing at all.

Meaning no disrespect sir but did you actually review the site? After reading these comments I checked the site out. If you go to the home page and click articles it starts with what is a resistor, how are resistor constructed, what are resister used for.... Then capacitors and coils etc. If you took the Radio Engineers Handbook as your textbook and flipped to page 1000 to start reading you would be were this thread is. No they can\'t reteach the basic theory on every page. They start with we know nothing and build on the subject. It would be like taking calculus without taking basic math or algebra when you jump to the end of the book to start.Don't hit me! I was an electronics instructor and had students come in day one wanting to ask about the third weeks material. They had read an article in Popular Electronics and thought they could bypass the basics. I'm just saying maybe you should start on page one of the book before passing judgement?

[Craig]

It was never cheap though. Practical wireless 1970 issues have an advert for transistor radio kits. Traditional superhet, 7 band(long, 2 medium, 3 short and one "trawler" band). That particular "Romer 8 Mk1" was £6.19/6 with a whopping 7/6 shipping. Age 14 I thought that was an astonishing amount of money. And indeed it was - it was a day's average salary before tax

Putting that into today's money is £106. So again about a day's average salary.

But it is both a lot less straightforward (surface mount parts, advanced digital stuff) and more straightforward at the same time (superb op amps that cost not much and a lot easier to apply instead of individual transistors). With coding and software - something I abandoned back in Fortran/Algol/Basic days. Today's script kiddies can run rings around any of us old farts.

[Nowhere-Man]

Hmmmm, money. I am notorious for recycling. I even make my own paint. I scavange all sorts of wire. Only yesterday I found 2 small speakers (and they aren't cheap new). So, from what I scavanged so far I could build a simple radio. It may or may not work. I would prefer to make a valve receiver but lack the spares and bit and pieces. To help me I have a basic idea of very old radio design. I mean one of my sets merely uses a wire for the aerial. So amplify signal, mix to IF, amplify, demodulate, amplify and hope for the best. I do have the IF cans but would doubt my spare AF117's would be good at HF frequency.