the LC Oscillator. How does it work?

Click on the documents above to read it clearly. This forms the basis of understanding resonant circuits also.

The mechanical analogy of course is the flywheel. The analogy to supplying power to a fly wheel through a push rod is the transistor supplying power through the 'turn on' cycle.

Electronics workshop organization 2

Storage Boxes & Bins

Storage Boxes and Bins

Electronics Work bench

Example Spreadsheet

Part of the Master Alphabetic Control Sheet

Since my last post I am pleased to say that I have now completed my electronic workshop organization. The catalog system worked out pretty well. I struggled with the handling of misc items and ended up with two large Bins. One for misc small items and one for misc large items.

I then devised an alphabetic Master Sheet which has hyperlinks linking to each spreadsheet. It is a simple matter of clicking on the item in the alphabetic list. I am then taken to the correct sheet for the component category. The system has a large set of spreadsheets since i developed a spreadsheet for every component category. This will allow me to easily add components to each spreadsheet. It also makes the maintenance of the hyperlinks very easy. I have not counted the number of spreadsheets but I reckon there must be at least 40 spreadsheets in the workbook.

In a few cases I have found it necessary to point to a sheet which then points out the BIN number in different BOXES. For example MICROPHONES. Clicking on MICROPHONES will take me to the MICROPHONE sheet. On this sheet some large mics are stored in the misc large items bin and the smaller mics are stored in the plastic fishing containers. Phew! More difficult to explain it than to do it!

I have now used the system in the process of building my first project which is a Direct Conversion Receiver. It certainly is a pleasure to be able to pick resistors capacitors and wires directly from the a BOX and BIN. It is abit of a pain to update the catalog with the new quantity once the item is removed. This will require extreme discipline in order to maintain. I may in fact revert to a periodic stock taking method after a while.

Refer to the attached pics in order to get some idea of my new setup.

Electronics workshop organization 1

My next project will be to organize my electronics experimental workshop. Currently I have a good set of tools, test instruments and a large table equipped with good lighting. However my components are stored in the traditional and so called junquebox! It is extremely difficult and tiresome to hunt through the components in order to find a resistor or capacitor or transistor. In fact on many ocassions I confess to giving up and simply taking the easy but expensive way out. ie drive to Radioshack or order a new component online. As a result I have a fairly large pile of components accumulated over many years.

Searching on the internet does not show up many results on how to go about this organization of a workshop and associated components. I thought that someone may find it useful to follow my project as I proceed and as I 'learn by doing'.

I first laid out all my small components on my workbench. This allowed me to see what I have and to determine what size component storage I will need. I have also now embarked upon a mission to collect as many empty containers from the household trash as possible. Having paid a visit to the local container store I realize that most of those containers are far too expensive. Purchasing these containers would cost as much as the components for a complex radio would cost! I did go to Dicks Sports Store and purchased a number of fishing lure boxes for about $5.66 each. These provide about 34 storage bins for small components such as resistors and capacitors.

I started my organization with the capacitors. I soon figured out that the most efficient scheme would be to store components in designated BINS. Then link the BIN number to details about the components in a catalog on an excel spreadsheet. Having ironed out a few bugs I believe I now have a good and practical set up. Essential to the operation of the catalog is the ability to search. This means that even though the BIN numbers may be illogically numbered from a components perspective, at least it is possible to cross reference and search for the desired component. I have, to date, recorded approx 550 capacitors in the system and already this has given me insights into the power of a searchable catalog. The result of this project will be that all components will be searchable through the excel spreadsheet mechanism. This will enable me to quickly and painlessly try different components in the circuit in order to optimize my design.

To catalog a component my method works as follows. Using capacitors as an example:


Identify the capacitor spreadsheet in the excel components book.

Identify the capacitor value that requires storage.

Type in the capacitor value into the 'Find' function on the catalog spreadsheet. eg. 100pf. Typed in as '100'. If the value is greater than 999pf then type the value as mfd or microfarads. For example .001 as opposed to 1000pf. (Note that I need to note this rule on my catalog notes section.) Only type the number. Not pf or mfd.

If the computer shows a result I then increment the 'quantity' column, add any other known information such as tolerance or max working voltage.

I then identify the BOX number and the BIN number within that box from the spreadsheet.

Locate the BOX and the BIN and store the component if there is enough room in the BIN.

If there is not enough room or the component is a new component. Open a new line item in the spreadsheet and allocate a new BOX/BIN number. Enter the details of the component.

Store the component in the BIN.

To look for a component simply use the FIND feature on the spreadsheet to locate the component. Then if the component is removed then decrement the quantity in that BIN. If the BIN becomes empty then enter a replacement component requirement in the 'COMPONENTS TO BE ORDERED' Spreadsheet. The same procedure would apply to the case where a component cannot be located. In this case the Component should be added to the COMPONENTS TO BE ORDERED SPREADSHEET.

This method is very efficient from a space point of view since it allocates BINS only for components that exist. Since space is at a premium in my workshop I cannot afford to have empty BINS just in order to adhere to a logical list. The problem is that components of the same category. ie Capacitors may exist in many different boxes. However the computer search feature will find the BOX and the BIN. It means that the computer becomes essential to the operation of the system. The BOXES and BINS are only marked with a Number for the Box and a letter for a BIN within a box. This means that by looking at the BOX you cannot necessarily see inside what is in it. Another benefit of this system is that it is very easy to redesignate a BIN for another type or component. It is just a matter of changing the entry in the computer.

No doubt there are catalog systems available out there. I thought that by developing my own I would have a very clear idea of what type of catalog system I need. Once I know this I can transfer my data over to another more robust and user friendly system. Should not be a problem.

Once I have all my existing components cataloged and therefore some control over my workshop environment I will then look at storing the catalog on my website in order to be able to access from any computer. This will be particularly useful when I am on the road and I am working on a design for a project. Having a master database online will mean that I do not have to contend with the headache of keeping multiple versions up to date.

One Tube 6L6 Transmitter experiments 6

Having completed my 6L6 project for the time being with no doubt in my mind that I can improve the design still further with improved understanding. I read the RSGB Handbook 5th edition section on Transmitters and in particular tube oscillators. Revealed the link between the output impedence and how it impacts the behaviour of the oscillator. It states that you need to increase the capacitive load in order to stabilize the Transmitter. This is because the TX is only in the positive feedback stable condition when the feedback from the load is slightly capacitive. I found just the opposite on my TX ie as I increased the capacitive load the oscillator became less stable. I think this is due to a slight mismatch to the antenna load, meaning that in fact the load was still slightly inductive. Note that I did not try this test using a dummy load but instead I used my attic dipole which is not a perfect resistive load. However more analysis is required before I can be sure.

I was able to make a number of very good QSOs with stations all over the US this wekend and I received reports ranging from 459 to 589. Examples of contacts being WB3T, WB2PPQ, WA$DAX, KF8R, K9LWA. I find that even running full power at 4.5 wats still yields a stable transmitt signal although it is important to monitor the signal to be sure that it is indeed stable.

One Tube 6L6 Transmitter experiment 5

This evening I wound a 'final' coil which consists of 21 turns for the loading coil and approx 9 turns for the link coil. I noticed that the link coil turns were not that sensitive to the performance of the Tx.



Measurements as follows:



Power output into my attic antenna = 4.2 watts

Cathode current keydown = 30mA

Cathode current keydown with crystal removed (ie not oscillating) = 36mA

Plate voltage key up = 339 volts

Plate voltage key down = 326 volts

Screen voltage key up = 163 volts

Screen voltage key down = 148 volts

Frequency of operation = 7041.98 Khz

Cathode voltage key up with crystal removed (ie not oscillating) = 34volts

Cathode voltage key down with crystal removed = 8 volts

Cathode voltage key up with crystal operating ( ie oscillating) = 34volts

Cathode voltage key down with crystal operating (ie oscillating) = 8 volts (frequency changed when probe placed (indicating impedance loading)

Control grid voltage key up = 0 volts

Control grid voltage key down = - 18.8 volts (I assume this is an inaccurate RMS value?)



NOTE: Most interesting was that the frequency of operation was shifted to what appears to be the natural operating frequency of the crystal. ie 7040Khz when I connect the voltmeter across the control gris. Could it be that the additional load impedance of the meter was driving the control grid properly negative biased. In other words perhaps the negative bias of the control gris is not sufficient.



Next try adjusting the negative bias. I tried a number of combinations but in the end I was not able to really improve the performance.

I completed the coil construction and reassembled the Tx back to its original form. Now working very nicely at the above parameters. Next I will take some pics of my current vintage station including my HQ180 Hammarlund RX.

One tube 6L6 Transmitter experiments 4

This evening I experimented with various coil settings. Eventually settling on a configuration providing 4.5watts and 29mA Anode current. Reasonable signal with small signs of freq drift at the beginning of the transmission. Heard by NN5O but not able to complete the QSO. Freq of operation was 7042.11Khz.

A better quality signal is given at 3.5watts. About 31mA. Frequency of operation 7041.39Khz.

Next I will rewind the coil to the same specifications and clean up the installation. Reinstall the coil and test again.

One Tube 6L6 Transmitter experiments 3

Now decided to try playing with the plate current. Tried putting a 220ohm resistor in parallel with the existing 220ohm cathode resistor to see what happens. Result. No appreciable change. Plate current measured as 29.8mA. Removed the resistor.

Now back to the original circuit and now trying a new tank coil with looser coupling. ie winding the link over the cold end. Seems to be better than the previous coupling.
9 turns. Coupling still loose. Sharp resonance and sharp dip. Power 2 watts. Stable freq.

Now tried tighter coupling. Got it very stable and looking good! Output power = 4watts with Anode curent at max dip showing a nice dip to 30.2mA. Keydown voltage =325volts. Therefore input power to plate = 325*30.2mA = 9.8 watts. Output power = 4 watts. Efficiency now 40%. Can I do better? Output freq = 7042.18Khz.

Further adjustments now very interesting since I am getting very close to the point where max dip on the input current is corresponding to max power output indicating a point of maximum efficiency and therefore stability.
29.7mA plate. Keydown plate voltage = 326volts. Input power = 9.68 watts. Output power now 4.75 watts. Efficiency = 49%. Excellent.

Now try raising the screen voltage and see if can get more power? Raised it back to original spec. ie 191 volts on key down. Now raised the plate current to 35mA with no difference in power output and freq not as stable. ie less effieicnt now.

Now feel like I have arrived at a good result for the tank coil. Next step is to wind a solid coil using the same dimensions.