Playing with electrons with the CV2269 tube

At your own risk. A 1.2V battery is used but a series fuse should always be used with a battery for safety.


It was decided to write this post at the same time the experiment is done as there is a lot of things happening. There is change of behaviour of the electrometer CV2269 electron tube depending for example on the past history of applying voltages. For example heater before anode voltage etc.


The CV2269 is at the moment on a small bread board. Very convenient, the downside is that the contacts are usually not great leading to systematic errors.


The connections are straightforward.


The YFE digital multimeter black cable is connected to battery -.


Heaters are connected to 1.2V from an AA battery, see below, by means of small flying wires, making heater disconnection easy.


The battery fuse + is applied to the top of the breadboard. There a micrometer is connected, it's other terminal connected to the breadboard rail just below. So anode, Pleiadss bias resistor etc are to be connected to this second rail. One of the heater terminals is connected to the upper rail bypassing the micro ammeter.


The red lead of the millivoltmeter is connected directly to the control grid.


Before connecting the battery there is a positive potential difference. The 1GΩ input impedance of the millivoltmeter at its small range showed after a few minutes 50mV and increasing. Photoelectric effect?


By connecting the heater voltage (before connecting anything to the anode) the grid voltage goes immediately heavily negative. This should be due to the missing electrons on the cathode leaving the positive protons lonely. It passes through the voltmeter's range of -330mV? and the voltmeter automatically changes range and the recorded voltage is reduced as the voltmeter at a higher range goes to a 10MΩ input impedance. So there is oscillation as the voltmeter goes back to a lower potential difference by its shunt effect. The voltmeter goes back to the more sensitive range the voltage starts to go more negative... and voltmeter oscillation.


Nevertheless let's assume the grid potential is slightly lower than -330mV.


Now reapplying heaters. For some reason now the voltmeter steadily shows -400mV at the grid.


Next an 8.2MΩ resistor is connected from grid to positive rail (below the top breadboard rail line). The voltmeter shows -174mV at the grid.


Next the anode is connected to the positive rail. The grid measured potential is now decreased to -310mV. Why? The anode attracted many of these electrons?


Next the anode cable is disconnected. the grid potential jumps to a high of 700mV and then starts decreasing until it becomes -160mV. Connecting again the anode makes the grid -310mV without an overshoot. Disconnecting the anode there is overshoot again to 700mV and then going toward -160mV. How a relaxation oscillator would sound like using this property?


Next heaters were disconnected. And after some minutes the grid can be measured 20mV and increasing. This must be the time constant of the 1GΩ voltmeter. Now it shows 40mV and increasing. This should be the photoelectric effect. Ambient light or photons falling on the electron tube. Now the value is 60mV and increasing. Now more than 100mV but bringing a light torch near the tube did not make much change as it did on the EF183 electron tube. Torch abandoned. Now the grid is 140mV and increasing.


Heater is connected. Grid goes immediately to -410mV.


There is a viewer. Hello to France.


Anode lead is connected to the positive rail. The grid potential shown on the voltmeter is -457V. There is very faint movement on the anode tiny meter watched by a magnifying glass, indicating a very small anode current.


Now the 8.2 MΩ resistor is connected to the positive rail. Ie from anode to grid. The grid potential becomes -311mV. There is more anode current witnessed by a larger deflection on the anode micro ammeter.


Now a 2.7MΩ resitor is connected from anode to grid. The grid potential becomes -200mV. Anode current further increased as expected.


In an attempt to measure anode current the ammeter was accidentally connected from positive rail to grid. It showed 30μA or grid current. This mistake is a Pleiades resistor of close to 0 Ω. The tube seems to have survived.


But another mistake of connecting the grid to cathode. There seems to be a problem with the tube. Repeating the previous experiments now when connecting the 2.7MΩ resistor the grid potential becomes 1V. There is very little anode current. Poor tube will you survive?


Repeating experiments. The heater is applied, voltmeter oscillation. Good sign. Applying anode voltage the grid potential becomes -65mV.


Gently rocking the tube pins in case there is a bad contact.


Connecting the 8.2MΩ Pleiades bias resistor to positive rail. Grid potential becomes -300mV. Anode current is a bit higher? The changing to the 2.7MΩ Pleiades bias resistor. Grid potential is -200mV. Anode current higher. Is the tube destroyed? Or will it make a better microphone amplifier?


A not very good thing happening to an electron tube is the cathode short connected to grid. It is like short circuiting a source of voltage. A large grid current should flow. It is the missing electrons from the cathode rushing to come back externally to the positive cathode to meet their beloved protons. The grid potential is forced by the short circuit to become 0V contrary to the self assumed negative value.


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Measured anode current. With the Pleiades bias resistor of 8.2MΩ from grid to anode Ia is 10μA. To cathode or negative side of heater it is 7μA. With Pleiades bias resistor of 2.7Ω connected to anode it is 13μA, connected to minus or cathode it is 9μA.


Now a 330kΩ Pleiades bias resistor is connected from anode to grid. The anode current doubles to 20μA.


The irony here seems to be that the anode current can't become large not because of the small anode voltage. But perhaps because of a not sufficient pull up voltage to liberate the electrons from a sufficiently self assumed negative grid bias.


Now a 2.4V pull up potential will be connected to grid through the 8.2MΩ bias resistor. Values of Ia of 11μA, 17μA, 27μA were obtained by the 3 Pleiades biasing resistors respectively. Not as great a difference as expected. So it seems anode voltage is low too. But it may sound great.