Transistors

[Mark Hennessy]

But interesting that the main resistor values (4k7 and 1k) are exactly the same as my calculation 

Great minds

[Nowhere-Man]

Just been running through some random puzzles. Such as (1) you have the Beta of 150 and collector current of 0.00397 Amp. Question: What is the emitter current? How did I do it? I calculated the Alpha and multiplied it by the collector current.
(2) Pretend we have an emitter current of 0.004 Amp. The Beta is 150 and the task is to find the collector current. For this I discovered I can use the Alpha and divide the current.
It's always good I find these days to create puzzles. My next stage may be to throw in a few resistances. I do know the base collector impedance will be high due to bias and that part of the power output is created by the dreaded holes.

[Terry]

Ah, yes - the dreaded holes!

Fast rewind to 1965 when Rank Bush Murphy introduced their first hybrid TVs, the Bush TV135 series.

We had a visit from an RBM field engineer who told us that some of the older engineers - I was a mere youngster then, of course! - were having trouble getting their heads round these new fangled transistors.

Valves were easy, he said. They produced electrons - which exist. Transistor have holes, but these don't really exist. Now these holes, they move ....

[Nowhere-Man]

The "hole" story is it got back to Mark's diagram, except a similar schematic online. You have to find the base voltage from Vin 12. I used the potential divider and got the same as the answer. Good idea for me is to do the voltages and currents. Funny but this basic classroom stuff is never fully addressed in amateur books. Even ARRL will give just one example. Neither did ARRL give resistance values in the examples.

[Nowhere-Man]

I found this tutorial I will try and upload on my old mobile.
http://www.learningaboutelectronics.com/...transistor

[Nowhere-Man]

Good! It worked. First comment. Very poorly explained. I have revised Mark's pointers and his system was indeed far simpler. One issue I have is the base supply voltage here is 3 volts DC but the base current is going to be something like 0.00002 typically. Multiply that by 30K and you get about 0.6. Are we to put this 3 v and 0.6 down to the junction resistance?
Anyway, according to this we have 3 volts supply on the base. I just got to the part where I finally managed to get the 4 milliamp value. Yet I think it's very poorly explained with some showing off perhaps? It assumes we all know the conventions of mathematical formulae.

[Terry]

I have revised Mark's pointers and his system was indeed far simpler.

At the risk of asking a stupid question, why then do you not keep using Mark's methods?

It seems strange to me that you have been given simple, accurate guidance, which you find easy to understand but persist in looking for other confusing sources to criticise.

[Nowhere-Man]

Simple answer. I don't just follow one system and that's it. I tend to take from a lot of systems or compare. I did manage in the end to follow the tutorial quoted above but was puzzled by the lack of verbal support to it. I had to mess with the figures till I could tie it together. I got as far as the 4 milliamp value and have yet to finish.

[Nowhere-Man]

Best method of all I guess is practical application. Using a meter and so forth. In fact my belief now is radioo engineering advances pretty much came about via trial and error and observation. Then the mathematicians and physics students made the effort to explain why and wherefore. So we got sums to work out resonant frequency or factors. You can swat on this stuff online in spare moments without a soldering iron at hand. It has some value (better than watching TV) but I don't over rate it.

[Nowhere-Man]

Consider it took thousands of years to discover an inductance and capacitance can resonate. A lot of it was down to Tesla, I think. In the war, soldiers typically made very simple radios using just a diode, winding and v capacitor. It took centuries to discover you can use electric power to transmit AF. So, I think the maths came later on to explain in textbook terms how it works. I always found these books a bit choppy. So many of them just throw out a few sums and use a lot of jargon. For actual understanding to date the best source I found was F J Camm.