Sunday, May 9, 2021

Using a piezo element

The High Z element will require a high voltage low current drive. To control the frequency response we must adjust the coupling caps and the load resistance. The high R high C circuit gives good low frequency response but drops off on the high end.

Lowering the load resistance flattens the response.
Lower coupling caps cause the low end response to drop off. This will make a 'tinny' sound.      

Thursday, April 15, 2021

Turret board amp upgrade.


I will use the double row layout. First step is to layout the components.

I laid it out in spice so i could test the circuit. The sim works so I didn't miss any jumpers or cross fed any points.

My first build worked very well but left room for improving the layout.

I may want to put it in a box. The components on both side and the transformer mounted on the turret pins will not fit a box well.

This will install in a box much easier. The transformer on a separate board will allow it to be placed so the jack is accessible.

The little amp works nicely with a DBM.
I wound 9 turns of 3 strand wire. One coil is the primary. The other 2 form a tapped secondary. The taps are the AF output. RF and LO feed the primaries.
The platform is a pill bottle cap. The base is a piece of press board. I used turret pins to mount the diodes. I had the terminal strips on hand so I used them for the I/O connections. Turret pins would work just as well for the I/O.
This setup received a station in Texas and one in Tenn.
The 80 meter ham band was active.
WWV on 5Mhz.
Several shortwave stations around 6Mhz.
This was using my bench signal generator as the LO. Next step would be to build a generator.

Monday, April 12, 2021

Amp, Coil, Turrets, Board

 Had a little shop time. (rainy day) 

Took the lid off an ice cream carton and made a coil form.

I squared the material, Wrapped it around a suitable round mandrel. When heated the material melts and is sticky. (Think hot glue) I used a heat gun (hair dryer) to fuse one end. Pushed the form off the mandrel so it didn't stick to it. Fused the other end in like manner. Then fused the seem length wise.

I wound the coil with the wire on the bench. Then finished the coil with a dope made from ping pong balls and finger nail polish remover.   

The plan was to make a turret board for the amp build. This material is readily available and perfect for the job.

Look familiar? You will see it in the kitchen and bath. (If you do not have stone counters tops.) Formica was invented to be used as an insulator. It also makes some fine counter tops.

The plan is to use a turret board, These are ok but a little pricey. The formica is left over from a kitchen rebuild. The turret pins are 1 - 2 cents each.
Here are some examples of the turrets.

Here is the drawing for my amp. I used the scrap which was about 1" wide. I made 3 rows of pins. In the future I will spread the circuit out more. But I just used the piece which was already cut.

The pins were double ended so I put parts on both sides of the board. The little amp sings. It drives my earbud with the output of my AF generator all the way down and the 20db attenuator on.

I added a V cap and diode with test leads and it picked up a station which IDed itself as being 600 miles away. The prototype performs well. I will likely make another on a bigger board.

It may be worth looking into the formica. Last I bought was about $50 for a 4' by 8' sheet. Less than $2 a square foot is not bad?

Tuesday, April 6, 2021

Adding a pot to spice.

 symbol file .ASY


Version 4
SymbolType CELL
LINE Normal 0 -36 0 -48
LINE Normal 0 48 0 36
LINE Normal -20 -3 -9 0
LINE Normal -20 3 -9 0
LINE Normal -20 3 -20 -3
LINE Normal 9 -36 0 -36
LINE Normal 9 36 9 -36
LINE Normal -9 36 9 36
LINE Normal -9 -36 -9 36
LINE Normal 0 -36 -9 -36
LINE Normal -32 0 -20 0
CIRCLE Normal -6 32 1 25
WINDOW 0 16 -32 Left 0
WINDOW 3 17 -1 Left 0
WINDOW 123 16 26 Left 0
SYMATTR Value R=10k
SYMATTR Value2 T=.5
SYMATTR SpiceModel pot
SYMATTR ModelFile ..\sym\EXTRA\Misc\pot.lib
SYMATTR Description Potentiometer
PIN 0 -48 NONE 0
PINATTR SpiceOrder 1
PIN 0 48 NONE 8
PINATTR SpiceOrder 2
PIN -32 0 NONE 0
PINATTR SpiceOrder 3


Model - .lib file.


 .SUBCKT pot 1 2 3
.param tap=limit(T,.001,.999)
R0 1 3 {R*(1-tap)}
R1 3 2 {R*tap}




The ASY file defines the lib file location. Spice will look for the lib file in your lib directory. To allow spice to find the file either place it in the lib directory or modfy the line in the ASY file to locate it.



Monday, March 29, 2021

Sunday, March 28, 2021

The amp response


Click EDIT
Click SPICE Analysis
Fill in the 4 blanks to define the sweep.

Monday, March 22, 2021

Rod tube radio

 interested in rod tubes? This radio provides examples of their uses.

Friday, March 19, 2021

Emitter bypass cap

 When you begin to analyze a circuit the first step is to open the caps and short the coils. Then analyze the DC paths. Establish the bias to determine the Q points.

The AC function can be seen by adding the caps and coils back in the circuit. If you build a sim with no caps and then add the AC signal you will have degenerative feedback developed across the DC bias components. Build an alternate AC signal path with the caps allow the AC impedance to be different from the DC resistance.

So remove the bypass and look at our circuit.

The circuit is functional. It produces a good signal. (faithful, linear )

Not put the bypass back in.

We get a higher gain but the signal is less faithful.

You can remove the source bypass and get the same results.

We see builders who make (regenerative) receivers with audio amps. (or so they say)

If you have a strong station in your area you could connect an antenna to the input and receive the station. Is it a regen receiver?

Consider this before answering.

As the circuit was first presented you would have some 'drain bend' which could allow it to be used as a receiver. Try adjusting the source bypass and see what happens.

Some drain bend there.
So you can change the component values and see the effects.
The simulator will present garbage in - garbage out effects but more on that latter.
I will try and present some more sim function as we go through more circuits.

For now one point to consider is the lib is built by pro's and work quite well so after you built a circuit use the select component option to ensure you are using a 'full' representation.

Thursday, March 18, 2021

A series with mods to the grounding and size of drain cap

Setting the probe to reference the drain. With the sim running click on schematic to open the menu.
and set the reference.

 The point I want to make is the drain and source caps are 'juggling' the current. One charges as the other discharges. If they are small they limit the current. Set them to 25ufd and see what difference it makes.

A quick look at RC time constant

The natural log function defines the RC charge and discharge.

TC = R * C 

Things to consider:

As power is applied the current is limited by the resistor.

As the cap charges current drops.

Once the cap is charged current ceases to flow. (actually the cap never receives full charge but we call it charged after 5TC.)

My internet flaking in and out. Before I save the file somethings to consider.

Period = 1/T
Frequency = 1/P
The current flows as a cap charges.
If it is to small it will follow the wave form as it charges and discharges.
If it is to large it will charge and hold the peak.
In our amp we want the cap to be able to pass the AC component. Which means we do not want it to charge and hold.
So if we know F=1/P and TC=RC can we imply F=RC as the factor to determine the Cap size?
Would we set the low frequency = RC as the value to use?
More later....
Getting failed to update error.
Try again.

Wednesday, March 17, 2021

A little more on layout.


I'm putting this here so you can consider the fields. Maybe we will come back to it ?

Wednesday, March 10, 2021

more balanced current


Compare the current through R8 and R9. Increase R7 to get a more balanced current. 

Trace the current paths during a cycle. One cap charges as the other discharges etc.

How does this effect the current through R7?

vary the cap sizes


I set the battery resistance to 2 Ohm.

Changes the cap values improves the circuit.