Tuesday, January 30, 2018

CD4069UB amplifier

The CD4069UB is a very useful device it can be an oscillator or amp with a simple biasing system much like the one in the previous post. The datasheet offers this as an example circuit.
One CD4069UB contains 6 amps. This is a one chip stereo amp. Note the supply is 3 - 15 volts.

Sunday, January 28, 2018

Self bias and feedback

I have posted this 'type' circuit before without much comment. This is from a Bell Lab report from the late '50s. Not my invention.

It is especially good with MOSFETs because they will self regulate as they seek equilibrium.

Saturday, January 27, 2018

Manhatten pads with the pasta maker

First the disclaimer: If you get caught using mama's pasta maker I did not recommend it!!!
Get your own or borrow one from a clay worker. Folks that make clay jewelry use them to make sheets and strips of clay.

Now the project calls for Manhatten pads which I had none. You can buy them but not cheaply. So what to do? I happen to have some scissor cut board on hand and there is the pasta maker. It's not being used so here I go....

The idea is to turn this into....
These. One pass threw the maker gives strips. Passing the strips threw gives squares.

It took about 5 minutes to make these.

The question was asked about cleaning contacts and such. My answer is a fiberglass rod. I cut a piece about the size of a pencil from a 1/4" rod and filed the end to a screwdriver blade shape. It just took a minute or two to do this.
Just lay the flat side on the board and rub gently. The crud and oxide comes right off.

Friday, January 26, 2018

Build a circuit in spice and check the parameters.

spice has the curves built into it so you can display them and analyze the circuit. Common emitter is easiest so i started with it.
The common base works too!

here we have Ic vs Vbe. If R=E/I and Ic=Ie you could pick a point on the curve representing your operating point divide Vbe by Ic and determine your transistor input resistance at that point.
Now the problem is I am using a 2 volt supply and 100 ohm load. It will be different with a 12 volt supply and 10K load. So the circuit needs to be examined as you desire to build it.

One other thing to consider before closing the blog for the day. How do you handle a transformer?
I did a post a year ago on mutual inductance you might do well to look at it. What we are being told here is that the mutual inductance will cause our transformer primary to be loaded as the secondary is being loaded. In a power transformer we make the primary inductance high so we can load the secondary, draw power from the primary, and still not short out the primary. In the case of a tuned circuit the reflected change can cause the tank to detune as it loads. Some food for thought.

Thursday, January 25, 2018

Transistor circuit analysis

transistor circuit analysis
If you have a reasonable download speed this book is worth the trouble. It is only 250 pages but covers transistor analysis from the basics of insulators, conductors and semiconductors to actual circuit design.

You can click the link and preview without downloading.

Wednesday, January 24, 2018

Using the data from the previous post

Using the data

Figure 5.14 represents the circuit.
Step 1 uses the data.
Step 2 uses that result.

Tuesday, January 23, 2018

How to determine the parameters for a transistor?

This is the circuit in question.

What is the input Z? As the circuit is given we have a 100k base resistor, Vcc of 1.2 volts. The simple answer is assume Vbe=0.6 volt and Vb=Vcc-Vbe=0.6 volt. The base current is Ic/ß or Ic=Ib * ß. This implies Rbe=Rb/ß assuming ß=100 Rbe=100k/100=1k. BUT can we assume ß=100? A quick look at the spec sheet will tell us the ß has a range of 100 to 400? We'll get back to that. In the old days we had manuals full of data. We could run the test our self or let the factory have some one do it for us. How would you determine the resistance value for an unknown resistor. Measure the voltage drop across it and the current flow through it and apply Ohm's law. That's what we will do here first , then we'll look at the spec's.
Using this simple circuit, three meters and a variable power supply will get the job done.
I labeled the meters so you can see what they tell us.
The simple circuit disappears under all the test leads but it is as drawn except I used a fixed 100k resistor. I will just display the results. I set the supply for 1.0,1.2,1.5 and 2.0 volts. I did one series without an AC input to get the DC parameters and then did another with the AC.

Here is the compiled data.

Just for the fun of it you could use Ohm's law and see what the resistance is. For example the first test R=E/I=1.072/.0011=975 Ohms. My 1K guess was fairly close? Now let's look at the data sheet.
Hfe, gain, ß = 100 when the collector current is 0.3ma at their test conditions. They used 10 volts where I used 1.2 volts. You could just measure Ic for your circuit and use the chart. What else will the datasheet tell us?
Wow, input Z vs Ic. Earlier I "guessed" about 1K. My test gave a result of about 1K? Look at the chart the Z is 1k at about 4 ma. What's up with that? Examine the chart I posted and you will notice that the current increases with and increase of Vcc. Again they used 10 volts where I was using 1.2 volt. If R=E/I and and R is held constant doubling E would double I. In the transistor the relationship is not linear. The chart is on a log scale. Increasing the voltage 10X give a change more like SQRT(10)increase. Anyway. some food for thought. If you download and study the datasheet it may become more clear.

Friday, January 19, 2018

IC AF amp wiring with microscope

I was using the microscope to wire this little circuit. The microscope has a button I can push and capture the image so I did a series. The question was asked on TRB about using a camera to work with surface mount components. The USB scope is a camera with a lens to enlarge the view.

Biasing the BF2040

I biased the proto board with a 5volt regulated supply and divider. The three resistors have .5ufd caps across them.

This is the 3 stage board.

closeup with some labeling.  The source should go to ground. I used a 4 ohm resistor in the test circuit so I could read the drop across it to check channel current. If you use a 6 volt supply you could connect the drain to it. Check the spec sheet. I think it would allow 8 volts on the drain. I had a 9 volt supply so used the 5 volts.

Monday, January 15, 2018

Remote charging at 80 feet

Charge you phone or tablet within an 80 feet radius

I thought the chief designer might find this interesting. Since I posted to the cloud to link it decided to share with all.

Sunday, January 14, 2018

K669 Amp construction

The school teacher says build the DC circuit first. Once the bias is good add the AC components. So this is the goal.
I will be using some three terminal strips to make four assemblies.
The center terminal is grounded so I connected the 10 ohm resistor to it. When I mount the strip my ground will be established.
The gate will be on the left so I connect a 100k resistor from it to ground and the gate resistor is installed.
I connect a 100k resistor across the two outside terminals. This and the drain resistor form the self bias network. Now connect one end of the 2k2 resistor to the drain.
With the four resistors in place I solder them in place. I solder them before adding the transistor to prevent overheating it. The transistor installation is fairly simple. The source is the center terminal and it is to be tied to the 10 ohm resistor on the center lug. All I need to be concerned with is getting the drain on the lug with the 2K2 resistor.

The basic circuit is complete. I will need to at the AC coupling components to finish my amp. I will do a test of the amp first.
As i said the 2K2 resistor is the drain load so I connect the positive lead to it and the negative to the center terminal. All that's left is to put a signal on it.
I set the power supply to 9 volts and applied a signal to the gate through a capacitor. I have a good strong signal but at what input?
I moved the scope lead to the input. 220mv.

I moved the lead back to the output and adjusted it for 1 volt. Now to see the input.
Back on the input and I see it is 94 mv. So 94 mv in produces 1000 mv out for a voltage gain of over 10.
Is it enough? Well 1 stage = X10. 2 stages = X100. 3 stages = X1000. 4 stages = X10000. How much gain should you need in an amp?
I made this circuit with 3 stages and put an AF transformer on the output. When I shunted the input with a diode and attached an antenna I could hear my local radio station. It was actually to load and will need a volume control. So again this circuit repeated three or four times and find an AF source to attach.

Add a capacitor to feed the Gate and one to couple the next stage or load and have fun.

Oh if you don't have any terminal strips just drive three pins in a board and hook it up.