Transistors

[Nowhere-Man]

I will join in later today. I now have to test another water pump to use as shower tray drain. I used bitumen on the support timber to protect from damp. Sadly as the roof is low and the tray needs to be raised a bit, you'd have to shower with knees bent.
Last night I came across an AVG meter circuit. Very strange. American circuits bias the anode of the AVG diode. The milliameter has to be shunted to read 0.0025 amp at full scale and will follow the AVG. Works on a bridge system.
Back to work......

[pwdrive]

The National HRO used a bridge circuit for it's S meter:

http://www.cryptomuseum.com/df/hro/files/hro_manual.pdf

Lawrence.

[jimmc101]

Oh dear my last post was very badly worded.
What I was trying to say was that the common emitter configuration has both voltage and current gain either of which can be stabilised by the appropriate feedback, whereas the common collector/emitter follower configuration intrinsically has 100% voltage feedback and the common base configuration intrinsically has 100% current feedback.


On reflection, although I think of a bipolar transistor as fundamentally current driven, I have no problems in treating it as a 'black box' and using whichever model suits my purpose on a case by case basis.

Jim

[Crackle]

Sadly as the roof is low and the tray needs to be raised a bit, you'd have to shower with knees bent.

Fit an opening hatch above the shower.

Mike

[Nowhere-Man]

A fair few people have commented the boat is looking nice inside. Weather lately a bit dull for working on it but I have to keep going. With transistor radios I will need soon a signal generator and a diagnostic method. Chas Miller wrote a book on transistor radios and it must be good as it costs about 90 quid. My ARRL only devotes the odd few pages to transistor circuits.

[Nowhere-Man]

I had a good night messing about with PNP transistor jargon. I winded up with a method that seems to be working, so far as you don't expect miracles. Taking a graph base current of 50 microamps from ARRL and a collector current of 2 milliamps, I set out to simply calculate the Beta. Or add collector and base to get the emitter. I didn't quite follow ARRL's system so I looked online. All of this was for common emitter.
I know this is a bit dated and not accurate in real life but the fun is in going through the old school. I also had to learn to do Logs as well. I wonder if kids still do logs at school.
I expanded on Mark's hints as well so often work out voltage drops to get terminal voltages.

[Nowhere-Man]

I just did a test question that gives you the Beta and emitter current values and, by that, you have to work out the collector current. This approach I found online and it helped me a lot. By a bit of division, I was able to find the base current too. I did notice how emphasis is on current whereas valves tend to stick to voltage stats. The ARRL sixties edition was dreadful for Beta explanation and I even wonder if it wasn't so well understood.

[Craig]

Well the closest transistor type to a valve (well, a pentode to be specific) is the FET. It is voltage controlled like a valve, and the characteristic curves are very similar.

And regarding understanding bipolar transistors, you need to keep away from old references, because they could be considering Ge transistors - whose operation is much more complicated that Si.

[Craig]

I had a good night messing about with PNP transistor jargon. I winded up with a method that seems to be working, so far as you don't expect miracles. Taking a graph base current of 50 microamps from ARRL and a collector current of 2 milliamps, I set out to simply calculate the Beta. Or add collector and base to get the emitter. I didn't quite follow ARRL's system so I looked online. All of this was for common emitter.
I know this is a bit dated and not accurate in real life but the fun is in going through the old school. I also had to learn to do Logs as well. I wonder if kids still do logs at school.
I expanded on Mark's hints as well so often work out voltage drops to get terminal voltages.

That is definitely a Ge transistor. Beta (=Ic/Ib) is only 40, which is typical of germanium. A half way decent silicon transistor will typically have a beta in the range 200 to 900.

You'll drive yourself bonkers trying to get to grips with an old reference trying to understand germanium. These things had a leakage current in the range 100 to 300 microamps, and it doubles for every six degrees temperature rise - and that temperature rise can be due to heating of the device because of the current flow! So setting the bias point is a real black art.

I applaud your fixation on understanding the roots of transistor operation from the 50's and 60's, but get a solid understanding of modern transistor operation and circuits around that first.

[Nowhere-Man]

It's pretty clear really. A good exercise is to either find the Beta or use Beta and emitter values to get collector value. Online tutorials give Betas of 150 or 200. Sat with my dog in the garden last night I winded up with emitter at 4 milliamps and collector about 3.97. For me the downside is the GE transistor supply is dominated by Ebay. Maybe later I'll look into cases where silicon was used with circuit modification if possible. Another fun idea might be to make my own simple receiver one day as I have spare ferrite rods and tuners, even speakers.