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2017-08-20 Measuring Very Low Resistance 

From my FB comment 

Some comments say measure with a meter, but fractional ohm resistors don’t measure, or barely measure with the typical ohmmeter.   Instead, you should be giving better advice.  You should use the device between your ears to find the resistance.

The resistor should be put in series with another resistor of a known value, say a 100 ohm resistor.  Then connect both across a variable DC power supply, and set it so there’s 10 volts across the 100 ohm resistor, which gives 0.1 A through both.  Then measure the voltage across the unknown resistor.  Divide it by the current, 0.1A, and you should have the value of the unknown resistor.  Simple.

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2017-08-19 Emitter Base Breakdown Can Damage Transistor 

From YT reply to Neilgn  2017-08-20

Take any NPN transistor and measure the gain, and write it down.  Then put a 1k resistor in series with the transistor’s emitter and connect the emitter to positive and base to negative of a power supply.  Adjust the voltage until 2 or 3 volts are across the 1k resistor.  The voltage across the E-B junction should be more than 5 volts, maybe 7 or 8 V.  Now remove the transistor and measure the gain again.  When I did this years ago, the gain went from over 200 to less than 150.  I don’t know what causes this, but I’ve never seen any transistor that doesn’t do it.  When I did this, I cut off the leads of the transistor afterwards, because I was concerned about the damage to the transistor. 

The JT is only about 50 to 60 percent efficient, so if you have just a single current limiting resistor, it and the LED could be more efficient than the JT.

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2017-08-15 1950s Astor 7 Transistor Radio

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2017-08-13 Transistor Radio Technology Timeline

My post to FB Aug 14

Does anyone know about the timelines on what I’m talking about below?

The early TRs (transistor radios) were AM only because the germanium transistors available were not capable of FM frequencies.  The first TR was the Regency, and it used the Texas Instruments transistors that were similar to the Raytheon CK722.  I’m guessing this was ’54.

The early germanium transistors had enough collector to base capacitance to make it necessary to use neutralization in the IF amplifier(s) to prevent oscillation and get enough gain.  Not sure when, but the transistors (Ge or Si??) became lower capacitance and didn’t need to have so much neutralization, so they could be more easily assembled.

The cheap epoxy silicon transistors replaced germanium, and they could work adequately on the FM BCB, so AM/FM radios finally hit the market.  National Semi and Fairchild Semi were leaders in low price ‘jelly bean’ transistors in the 1960s, but I’m not sure exactly when.

Sometime after that, maybe the ’70s, the SAW filters replaced IF transformers so the IFs didn’t require tuning, thus saving on assembly costs.  The radios still required some alignment in the front end.

Eventually the radios became more integrated, more functions were done by a single chip.  I don’t remember what year I started seeing chips in radios.   I think the IF was changed to where it and the detector were using modern technology, like synch detection.  Tuning became digital so only a few buttons were needed.

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2017-08-12 Compilers Should Be More Helpful

From  FB comment 

More than 3 decades ago I took programming classes using a mainframe and minicomputer.  The error messages were numerous and cryptic, and those were for just a single mistake, such a missing right parenthesis.

One would think that since then, the compilers would be more helpful, but it doesn’t seem so.  I’m glad my career was in the hardware side of computers!  😵  👎

I’m not a software geek.  But it seems to me that a compiler could do better than give an error message and quit.  With today’s “Artificial intelligence” and “Fuzzy logic”, it seems to me that the compiler could learn what mistakes are common, and when an error occurs, it could give a list of possible solutions.

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2017-08-07 Low Quality Goods

From FB comment

There are many factors that affect price.  One part is getting things assembled by underpaid and child (illegal) labor.  Most discounters have been caught buying their goods from these illegal sweatshops, and they still turn a blind eye to these abuses.  The net result is that the quality of the components may not be so bad, but the overall quality may suffer because of quotas, sloppy assembly due to hurrying, or the use of the wrong parts.

Reminds me of long ago when I worked as a test tech.  Some boards wouldn’t pass tests, and had very strange problems.  Upon closer inspection we found that some of the dozens of diodes were, instead, zener diodes.  Someone had put a handful of the Zeners in the bin holding signal diodes. They look the same unless you read the markings with a magnifying glass.

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2017-08-07 Protoboards And Bypass Capacitors

From FB post

One important thing that people forget to do is consider what might happen with a circuit that has anything that draws power from the protoboard.
If you’re working with a few low power devices such as small LEDs and switches, then there is usually not a problem.

But if you have a buzzer driven by a transistor, the current may be high enough to cause the supply voltage on the protoboard to drop, and that may cause the device to sense that a switch was falsely pressed. The results may be very odd behavior.

The solution is to put a few bypass capacitors across the power supply lines on the protoboard.  Something between 0.1 uF up to 10 uF will usually prevent or cure the problem.

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2017-08-06 Seeing Digital Signals

From FB post about Arduino driving a ‘HC595 chip.

You don’t need an oscilloscope to see digital signals.  If you slow down the speed, you can see what’s happening by looking at LEDs.  Everything is digital, just on or off.

Plug two red LEDs, transistors, and current limiting resistors for LEDs (330 ohms), and for the bases (4.7k) and use those as probes to show what the signal levels are.

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2017-08-04 Cockroach Repeller Attracts

From FB comment

I got an ultrasonic cockroach ‘repeller’ from someone who had it on the kitchen counter. I opened it up and found it was full of cockroach carcasses.  Looks like it attracted cockroaches instead of repelling them.  They probably sprayed real cockroach killer in it. Since it was obvious that it didn’t work, I took it apart and dumped the infested case, but kept the PC board. It was labeled…

PANASONY

stupid maker would’ve had not one, but TWO corporations on their back for copyright infringement. Duh!

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2017-08-03 Wood Radio Cabinets

From FB comment in group Vintage Transistor Radios

 

I think we like the look of wood because of some primeval instinct from our distant past. Perhaps it has something to do with the trees being protective, under which we could take shelter during rain or shine. Or perhaps those prehistoric people who survived longer were spear makers and throwers instead of rock throwers – it doesn’t take any wood working to throw a rock.  Whatever it is, I just like to see and feel wood on tables, chairs, or any furniture, even radios.

Thanks. (more…)

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