High Voltage Supply

The high voltage (HV) supply was one of the first items to be designed and constructed, and has subsequently been modified quite a few times to become what is now a flexible and reliable source of high voltage and current at the line frequency of 50Hz (UK standard), and up to sustained power outputs of 1600W, and peak power outputs up to 2500W.

Note: A high voltage supply is capable of delivering voltages and currents, even at lower powers, that are instantly lethal, and that any design and operation of a high voltage unit should be undertaken with great care by a trained and experienced individual. In my own case I was trained to work with high voltage equipment early in my career as an electronic engineer, and hence have opted for experimental flexibility, and maximum configuration, a power supply build that is accessible, open, and where high voltages could externally be exposed to the operator at certain key points. Careful design, implementation, and operation of such a supply is for the full responsibility of the individual concerned.

In the early days of this research it was unclear to me where in the experimental circuit interesting and unusual electrical phenomena originated from, whether it was the product of the generator, the tuning and driving units, the experimental coils themselves, the driven loads, the surrounding environment, or a combination of these factors. Later in the research I discovered that the generation of particularly displacement related events required a number of pre-conditions to be established, which involved the balance of the electric and magnetic fields of induction, which in turn involves all of the above factors, combined with a non-linear trigger, and with a defined load or “need” that cannot be met through the process of transference. These pre-conditions and the details pertaining to the generation of a displacement event will be considered and written-up in subsequent posts.

It was considered central to the early research, in replicating the key measurements and observations of other significant works e.g. Dollard et al[1], that the generator design be as close as possible to those used, and especially considering that actual units and components may not be easily obtainable e.g. an original H.G. Fischer diathermy unit. However for this unit certain videos, internal pictures, and schematics where obtainable online and formed the basis of the first stage of building a suitable generator using easily obtainable parts and components. The overall generator to be used for experimentation is a combination of the HV supply detailed in this post, and driving a range of subsequent generator stages that transform the supplied HV AC voltage and currents at the line frequency, into higher frequency ac, oscillations, impulses, bursts, modulated waveforms, and other such driving waveforms as may be useful to the study of the displacement and transference of electric power.

Figures 1 show the HV supply which currently drives the different types of generator stages:

The circuit diagram for the HV supply is shown in Figure 2 below, or click here to view the high resolution version. The schematic should be referenced for the subsequent circuit description:

AC line power at UK standard 240V 50Hz is fed via a high current (16A) 3-pin connector to a domestic distribution box with 3 circuit breakers at 6A, 10A, and 20A. The 6A circuit breaker feeds a low voltage switched-mode power supply unit providing 15V @ 3A and is used to power low voltage circuits in the HV supply and the generator stage including, pre-amplifiers, fans, control electronics, measurement devices, indicators, meters, and any other low voltage units. The HV supply is arranged with a number of low voltage two-pin power jack sockets to supply low voltage generator stage requirements on the upper level. The 10A circuit breaker powers filament transformers for vacuum tube generator stages, and auxiliary devices requiring line voltage AC, via a suitable mains output connector in the form of shielded 3-pin connector, and ceramic connection block for ad-hoc connections. The 20A circuit breaker feeds the high voltage transformers via a suitable power controller.

The distribution unit also has space for an incoming line RCD breaker, but has subsequently been removed, as it was found to be too sensitive to some experiments where power is reflected back into the HV supply, and causing the RCD to cut the power during the experiment. As an alternative a larger RCD was incorporated into the mains distribution for the laboratory, and separate mains circuits fed via a UPS (uninterruptible power supply) to measurement and test equipment, and computers. This arrangement prevents sensitive equipment from inadvertently being switched-off and/or rebooted during certain experiments when the lab RCD would disengage to protect the input supply. Having the test equipment running under these circumstances has proved key to understanding conditions and events within the experiment that have caused large reflections back through the mains supply.

The 20A circuit is first passed through a high current line filter which is used to prevent higher frequency electrical disturbances from being reflected back into the mains supply, and offer a measure of isolation between the two. The output of the line filter is fed to a power controller which enables the variable control of power supplied to the high voltage transformers. This HV supply was specifically designed around the use of the microwave oven transformer (MOT) as the high voltage part of the supply. MOTs are very readily available, and have proved to be a strong and robust transformer for this type of supply. The transformers used are all Galanz GAL-900E based which nominally produce 2100VRMS @ 900W ~0.45ARMS, and are quite common in UK domestic microwave ovens. The MOT represents a significant inductive load to the incoming AC supply, and uncorrected will reduce the power factor from the ideal 1 to ~0.6. To correct for this and reduce the draw on the incoming supply a power factor correction (PFC) capacitor can be used at the AC line input (after the line filter and before the SCR). A 20µF AC PFC capacitor can be used in order to correct for a single MOT. For 2-3 MOTs being used together this can be increased to 40µF.

The MOT is a transformer designed to drive a specific impedance load, (magnetron via a voltage doubler and tuned with a series capacitor), with the minimum quantity, and hence cost, of copper, and with the cheapest and simplest manufacture methods and components. This leads to certain drawbacks in the transformer characteristics, and most especially saturation of the transformer core when driven open-circuit, or connected to a higher than intended load impedance. The core is cheaply manufactured from steel laminate and then welded together which shorts the laminates out, greatly increasing the core saturation rate when adequate power is not drawn from the transformer. A detailed study of the characteristics of the MOT has been presented by Wokoun[2].

The easy core saturation requires the current to be restricted in the primary coil. This is not easily done directly with a variac, as is usual for variable output control of a transformer, since the core easily saturates at low input primary voltages leading to large run-away currents in the primary, rapid core heating, and ultimately destruction of the transformer from excessive heating, not to mention the dangerous risk of a transformer fire which is very hard to deal with due to extreme heating of the steel core even after the power has been cut-off at the input. Instead the current must be restricted either via an inductive load in the primary circuit, or much better, an SCR power controller.

A suitable simple series inductor is the primary of another MOT, (with the secondary shorted), connected in series with the primary of the MOT to act as the HV transformer. Alternatively the secondary of another MOT, (with the primary shorted), can be connected in series with the secondary of the HV transformer MOT, but more heating tends to occur in this configuration from the higher secondary impedance. The series primary connected MOT was found to limit the output current to a degree, and made adjustment with an input variac possible, with less chance of core saturation, but with however limited overall range of adjustment and suitability to changing load impedance. The advantage however of this first method is that the output of the MOT (not in core saturation) is a complete sine wave. In core saturation the output becomes progressively distorted towards a heavily clipped sine wave. It was concluded that this method of power control would be too limited for the wide range of generators that the HV supply would be driving.

The second and preferred method is the SCR based power controller, (similar to a light-dimmer controller but more powerful), which controls the on part of the sinusoidal cycle, and hence controls the overall power delivered to the transformer, which effectively restricts the core saturation whilst providing variable control of the output power. Suitable SCRs are very easily and cheaply available, and a complete unit with an output power of up to 3kW has been used in the HV supply. The disadvantage of the SCR is that the output is no longer a sine wave, but rather a distorted waveform that represents a small part of the total cycle. This has however provided some unexpected benefit in burst and impulse modes that will be discussed in the generator posts, but suffice to say here that the fast SCR turn-off can create very large voltage spikes in the MOT primary as the field collapses, which in turn produces strong impulses in the secondary at the line frequency. These impulses in the secondary, when fed directly to the experiment without a capacitor tank circuit, acts as one method of generating a non-linear trigger for a displacement event.

When working directly with the experiment at hand it is not convenient to keep walking backwards and forwards to the power supply to adjust power level or turn on or off the supply. To enable more distant control of the SCR the variable resistor used to control the power level was removed from the SCR circuit, and positioned in a small plastic box along with an on-off switch. The control box was then attached to the SCR via a long two-wire mains lead (5m), where on-off function is created by switching a higher resistance into the two-wire line, and hence holding the SCR in the off condition, which is also the case if the remote box is disconnected from the SCR power controller. Power control is affected from the variable resistor by reducing the resistance from 500kΩ down to 0Ω, which progressively turns the SCR on for a proportion of the ac line cycle.

Figures 3 below show waveforms from the HV supply at a range of different points in the high voltage supply, and including the high voltage rectifier and tank capacitor at the output to form a load.

The output of the SCR power controller is passed through a system of connections to allow the MOTs to either be driven directly from an external source as required, or by direct connection to the SCR. Each individual MOT can be switched independently to the SCR output allowing the transformers to be used individually or combined in parallel or series combinations to increase the available output current or voltage. The output of the SCR is also fed to a 25W mains incandescent lamp which indicates clearly to the operator when voltage is applied to the input of the one or more of the MOTs. This is a simple but important safety factor when working in the experimental environment, and is a rapid but not exhaustive check to the running status of the high voltage supply. It must also always be remembered that considerable energy can be stored in the generator components, such as tank capacitors etc., and that a no visible lamp output is not a direct indication that it is safe to touch any part of the high voltage circuits prior to the appropriate discharge procedures.

The MOT is a cheaply manufactured component with minimum materials and quality, and hence the high voltage winding isolation to the steel core will not usually withstand voltages in excess of ~1.5 times the nominal designed output. This makes it difficult to combine MOTs in series where the core connected terminal of the secondary has been detached from the core in order to float the secondary, whilst keeping the steel core connected to earth for safety purposes. In this configuration the open-circuit peak voltage of the secondary can reach almost ~6kV from 2 series connected MOTs, which can easily arc-over to the steel core through the secondary insulation. When allowed to happen for any period of time the secondary coil is easily permanently damaged.

To overcome this problem and to enable two MOTs to be connected safely in series (both cores earthed), the MOTs are connected in series anti-phase, or center-tapped arrangement. In this configuration the two cores are connected together to earth, which also means the two core connected ends of the two secondary coils are also connected to earth. The primaries of the two transformers are then connected in reverse phase to each other, (as shown in the circuit diagram), such that one transformer produces +VHT out, and the other transformer produces -VHT out. The total output voltage of the series connected secondaries is 2VHT, and the maximum secondary to core voltage on either transformer is only VHT, preventing any secondary to core breakdown.

Of the three available MOTs in the high voltage supply, two are centre-tap connected, and one is floated from the core. This combination was found to be most flexible where the centre-tapped pair are suitable for driving spark gap based generators, and the floated individual is most suitable for driving vacuum tube based generators and if required in conjunction with a diode voltage doubler. In some generator configurations it was necessary to reduce the secondary current using a power resistor, which also in some specific cases helps to stabilise changes in power factor when driving varying or fluctuating high impedance loads from the generator outputs. When and where required a fan-cooled 100Ω 100W wire-wound resistor was used to reduce secondary currents and stabilise the supply output impedance to the next stage. For sustained outputs the MOTs and output components are cooled using a pair of low voltage fans which are manually switched as required.

Overall the high voltage supply has proved to be robust and versatile in providing high voltage in a variety of configurations to a range of different types of generator circuits. The design of the high voltage supply makes it easy to use in the experiments, with accurate and remote control of the output, and constructed with basic and readily available components.

Click here to continue to the 811A vacuum tube generator.


1. Dollard, E. & Lindemann, P. & Brown, T., Tesla’s Longitudinal Electricity, Borderland Sciences Video, 1987.

2. Wokoun, P., Investigations on Using a Salvaged Microwave Oven Transformer, 2003, KH6GRT Website

 

Vacuum Tube Generator (811A) – Part1

The vacuum tube generator (VTG) mainly used for experiments in the displacement and transference of electric power is based around a pair of 811A power triode vacuum tubes, of either RCA or Russian origin, and with electrical characteristics generally as defined in the RCA 811A datasheet. The 811A’s have demonstrated to be highly flexible, with high reliability, and good overall medium power performance, versus cost and availability, when used in a variety of different configurations. The final output of this generator with these tubes can provide a maximum sustained RF output power of ~600W, and peak output for short bursts (up to 10s) of 900W, and over a wide frequency band up to ~5Mc/s. In addition, the design and implementation of this generator has been arranged in such a way that it can be used in a variety of different configurations, including:

1. A tuned plate class-C Armstrong oscillator which derives automatic feedback from a pick-up coil placed close to the secondary coil.

2. A variable frequency Hartley power oscillator when combined with an independent oscillator drive module.

3. The output stage of a linear power amplifier, when fed with a suitable drive waveform in grounded grid, grid biased, or cathode follower configurations.

4. A modulator stage with suitable cathode keying via a mechanical or semiconductor switching circuit.

5. CW, burst, and modulated oscillation modes when used with or without a dc smoothing capacitor in the plate HV supply.

Other VTGs using the RCA 833A/C and Eimac 4-400A/C are more suited to higher power experiments including, telluric transmission and strong non-linear impulses for displacement experiments, and will be reported in subsequent posts.

Figures 2 below shows an overview of the VTG apparatus, complete with the high voltage supply, the independent Hartley power oscillator module (HPO), the high voltage bridge rectifier (HVBR), and the supply dc smoothing capacitor.

The circuit diagram for the VTG and peripherals is shown in Figure 2 below, or click here to view the high-resolution version.

The high voltage supply VHT (described here), is connected to the input of the HVBR. The rectifier consists of 4 sets of 2 x HVP20 20kV 750mA high voltage diodes in parallel and arranged in a bridge configuration. The output terminal of the bridge B is connected to a tank capacitor 60µF 4kV k75-40a Russian pulse capacitor which results in a smoothed dc output suitable for rapid charging and discharging through a primary, or as a stabilised dc supply for the VTG plate circuit.

A dc meter is also so arranged on the output B to read from 0-4kV in configurable steps based on where the base terminal of the meter is connected to a resistor divider. The high voltage dc meter is a simple arrangement using a 1mA fsd (full-scale deflection) ammeter connected to a resistor divider with 4 x 1MΩ resistors. With all four resistors in series 4kV will result in a 1mA passing through the meter moving it to fsd, with one resistor in series 1kV will result in meter fsd, and accordingly for the 2 and 3kV scales. The meter face has been recalibrated to indicate needle reading in kV.

Before considering each of the configurations listed above in detail, it is necessary to cover the basics of the VTG design. The plate supply is provided by the HVBR output B+ and is a variable 0-4kV peak supply either smoothed or unsmoothed based on whether the rectifier tank capacitor is connected or not. The plate supply B+ is connected directly to the driven load LPCP, which in this case is the primary coil in parallel with the primary tuning capacitor. In this arrangement the primary load (parallel resonant circuit) would present the highest impedance to the vacuum tubes when at resonance. When the primary capacitor is so adjusted to set the secondary resonance frequency it is optimal for the impedance of the primary load to be equal to the output impedance of the dual 811A vacuum tubes in parallel. In this way maximum power is developed in the primary load or through the primary of the coil.

It is important to note that when using a VTG the primary circuit, (in this case the load LPCP), is NOT arranged to resonate at the same frequency as the secondary circuit, which avoids large primary currents being developed in the VTG which would lead to excess plate dissipation in the vacuum tubes, and rapid degrading or destruction of the tubes. Rather the impedance of the primary load at the resonant frequency of the secondary coil defines the driving impedance presented to the vacuum tubes, which in turn are adjusted by the grid bias or feedback to match their internal impedance to the driving impedance, leading to maximum power being developed in the primary circuit whilst not overloading the vacuum tubes beyond their maximum ratings.

Hence the VTG drives the coil in a linear sinusoidal CW mode with optimally arranged load impedance matching, as compared with for example, a spark gap generator where the primary and secondary resonance frequencies are arranged to be equal to allow maximum power transfer from the maximised primary currents during the ring-down phase of the primary tank discharge.

The load of the primary is connected to the plates of the vacuum tubes via high frequency chokes L1R1 and L2R2. These chokes quench very high frequency oscillations which can be generated by discharges within the vacuum tubes during overload conditions, and in turn help prevent very high frequency oscillation run-away conditions which can lead to rapid tube destruction.

The cathodes of the vacuum tubes are bridged by RF bypass capacitors to minimise the impedance of the high frequency signal path, and then connected via a sequence of jumpers J1-J3 to allow for different configuration modes. The cathodes are further connected to the heater power supply which provides a constant bias to the cathode combined heater element of the 811A. The heater power supply is a mains step-down transformer so arranged to provide an ac supply of 6.3VRMS @ 8ARMS for two 811A heater circuits in parallel. The heater supply transformer is fine adjusted in this case by R5 which reduces the voltage across the heater elements and has an RF bypass capacitor C5 to again minimise the impedance of the high frequency signal path. The ac voltage across the tube heater elements is monitored using a calibrated 0-10VRMS ac voltmeter, and R5 adjusted, (in this case 4 x 0R1 25W series connected resistors), to provide an optimal 6.3VRMS +- 5%.

When the vacuum tube generator is used as a linear power amplifier in grounded grid (cathode driven) configuration it is necessary to prevent the RF input signal from feeding back into the heater supply and being dissipated in the low impedance power supply stage. To prevent this bifilar high frequency chokes can be used between the tube cathodes and the heater power supply. At low-frequency, (50Hz for the heater supply), current can pass through the choke from the heater supply to the tube cathodes, but the RF signal at the cathode is prevented from feeding back into the heater supply. Modulation and switching via cathode keying can also be arranged via mechanical or semiconductor switches, and allows for a range of “switched” experiments important in the comparisons of electrical phenomena experienced in the exploration of the displacement and transference of electric power.

The grid of the VTG is arranged with jumpers J4-J6 to allow for different configuration modes, and a current limit resistor R3 to restrict the maximum grid current below the nominally rated for the 811A, and according to the configuration it is used in. In addition both 811A’s are forced cooled by the fan driven by the auxiliary 15V supply. Force cooling allows for higher sustained power in CW modes, and affords an additional protection during peak power overloads. It is quite normal for the 811A plate to glow slightly red under higher sustained powers, and in peak power for short periods 0-10s for it to glow intensely red. Sustained high peak powers > ~650W will lead to plate dissipation overload combined with flash-overs between the plate and grid causing rapid grid damage. In most experiments in the displacement and transference of electric power I have found a comfortable sustained power between 400-600W, which leads to long vacuum tube life, and well sustained tube characteristics according to the nominal data.

Construction of the VTG and HVBR modules are shown in detail in Figures 3 below. For ease and simplicity of experimentation the VTG is open assembled on a simple board with simple insulated mountings and a combination of metal, plastic, and wooden mounts for the various components. Whilst this does lead to a very quick and flexibly modifiable prototype generator, there are significant EMC, interference, temperature, and stability benefits to housing the entire VTG build within a screened metal case, with directed cooling inlet and outlets, and with careful consideration to connection of high current and tension paths with minimal inductance copper bars etc.

Figures 4 show the construction of the Hartley power oscillator module which is considered further in configuration option 2 below.

The different configurations of the VTG module are now considered in more detail:

1. Tuned plate class-C Armstrong oscillator

This configuration is very well suited to investigations at the upper and lower resonant frequency of the coil being driven (FU and FL). In this case the VTG is a series-fed version of the Armstrong oscillator deriving the grid bias feedback from a pickup coil placed in proximity to the secondary coil. In the case of the flat coil this is a small 10 turn cylindrical coil (diameter 100mm) mounted behind the secondary coil and on axis with the coil centres. Oscillation via the pickup coil feedback automatically keeps the VTG on the resonant frequency being explored and adjusts automatically to maintain the resonant frequency when loading is applied to the secondary coil outputs.

In this configuration J1-J3 are left open and J4 is connected. Circuit operation is as follows. When first turned on the impulse current from the tank circuit B+ conducting through the vacuum tube causes a ringing oscillation (ping) in the primary circuit LpCp. This oscillation couples to the secondary circuit LsCs which is further coupled by the pickup coil to the grid bias leakage circuit. When the phasing of the pickup coil is the correct way round for positive feedback, the grid bias leakage capacitor C1 becomes negatively charged during the positive half cycle in the primary circuit, pushing the grid voltage down and progressively restricting conduction in the vacuum tubes towards the off state with much reduced plate current. The negatively charged grid leakage capacitor C1 then discharges through the grid leakage resistor R4. As this happens the grid voltage on the vacuum tube starts to rise progressively towards 0 volts turning on the vacuum tubes with an increasing plate current. The plate current through the primary circuit LpCp again is coupled to the secondary LsCs and the cycle repeats. With the grid bias leakage circuit correctly adjusted the VTG will oscillate with a linear sinusoidal output optimised for maximum plate voltage and current swing, (maximum power transfer at the resonant frequency of the secondary), whilst keeping the grid bias currents within the maximum ratings for the vacuum tubes used.

When setting up this mode of operation it is most important to ensure correct phasing of the pickup coil in connection to the grid bias leakage circuit, and that the values of C1 and R4 are suitably adjusted to allow maximum swing of the plate circuit whilst keeping the grid bias within the maximum ratings. For this VTG with 2 x 811A vacuum tubes R4 is optimally between 1-1.5kΩ and C1 between 1.5-3nF. Considerable power dissipation occurs in R4 when running the VTG at higher powers > 400W, hence the need for a wire-wound power resistor (100W), and preferably as part of the forced cooled air circulation. Excessive or too little grid bias current will lead to a distorted and clipped oscillation, or in extreme cases, no oscillation at all and rapid vacuum tube degradation or destruction. Initial setting up is best done with low plate voltage ~ 500V and higher values of R4. R4 can then be progressively reduced to increase grid bias whilst ensuring a clean and stable output oscillation.

As seen in previous impedance measurement posts for the flat coil (1S-3P) the resonant frequency of the secondary can be adjusted by changing the capacitance of the variable vacuum capacitor in the primary Cp. When adjusted the oscillating frequency of the VTG automatically changes to track the changes in the secondary resonant frequency. At high values of Cp > ~650pF the impedance of the lower resonant frequency FL is dominant and the final oscillating frequency can be adjusted around this frequency FL in the range 1.5-2.2Mc/s. At low values of Cp < ~650pF the impedance of the upper resonant frequency FU dominates  and the final oscillating frequency is in the range 2.7-3.8Mc/s.

Adjusted in this fashion this configuration of the VTG is very well suited to continuous linear measurements for single wire currents, displacement and transference of electric power, and telluric transmission experiments. This configuration is best suited to exploring frequency regions centered around FU and FL, where oscillation is stable and conduction currents in the secondary of the experimental coil are > 10mARMS. This configuration is not suitable for exploring frequency regions far from resonance, at very low bias currents, or between the transition between FU and FL. In these cases it is necessary to use the VTG in modes 2 or 3 where accurate progressive frequency control is provided by an external source and the VTG acts as a power stage, whether that be as a tuned power oscillator, or as a linear power amplifier.

2. Variable frequency Hartley power oscillator

The Hartley power oscillator converts the VTG to a linear oscillator which can be adjusted for variable frequency in bands defined by the combination of band capacitors connected on the HPO module. The frequency of oscillation of the VTG is now determined by the resonant circuit formed on the HPO board, the pickup coil of configuration 1 is not connected in this arrangement. This configuration is suitable for measurements across the entire frequency band of interest, in the case of the flat coil 1S-3P between 1.5-3.5Mc/s.

The HPO must be manually tuned or retuned to a specific frequency of interest and particularly when changing the loading of the secondary coil circuit. The resonant frequency of the secondary coil is very sensitive to electrical loading, temperature, material losses, changing boundary conditions and proximity, which all cause deviations of the configured frequency. Any change in this tuned frequency  requires re-adjustment making the HPO configuration not well suited to experiments designed to explore different loads and operating conditions. It is however very suited to exploring circuit operation where the loading conditions are relatively fixed, and particularly in off-resonance, low current, and frequency transition regions.

In this configuration J1-J3 are left open and J5 is connected to the Hartley oscillator module along with the plate voltage and RF ground as shown on the circuit schematic of Fig 2. The bands of frequency can be adjusted by hardwired jumpers on the HPO module, where the static band capacitors are combined with the 1000pF variable capacitor, and form a parallel resonant circuit with L5 the HPO coil with an inductance of 3.0uH. The available bands are broadly as follows (static combinations of capacitors shown only):

a. 1 x 500pF = 2.4 – 4.1Mc/s

b. 1 x 1000pF = 2.1 – 2.9Mc/s

c. 1 x 500pF + 1 x 1000pF = 1.8 – 2.4Mc/s

d. 2 x 1000pF = 1.7 – 2.1Mc/s

e. 1 x 500pF + 2 x 1000pF = 1.5 – 1.8Mc/s

The setup of the HPO again requires a balance between largest plate swing (output power) without distorting the output wave, whilst restricting the grid bias within maximum parameters. The required frequency band is first configured using the hardwired jumpers, and the HPO grid bias variable resistor is set in the higher halve of its resistance range . The VTG plate supply is first set low at 500V and the HPO coil tapping point starts close to the RF ground end. The tapping point can be progressively moved upwards towards the plate voltage end of the coil until a point is reached where the output of the VTG is stable, clean, and with good power output as the plate supply is progressively increased up to the maximum ratings for the vacuum tubes. The HPO grid bias resistor can then be progressively reduced keeping the grid bias current within the maximum recommended. If no oscillation can be obtained the grid bias resistor can be progressively reduced until oscillation starts, whereupon the other adjustments discussed can be continued with.

The HPO can then be varied across its band frequency range according to the experimental requirements of the circuit, and the output power adjusted using the plate supply voltage. If the loading on the secondary coil changes significantly the HPO will need to be re-tuned and/or re-adjusted to provide stable power oscillation. Off resonance of the secondary coil in the experiment may require the HPO tapping point to be re-adjusted towards the RF ground to prevent excessive power dissipation in the coil. During continuous operation the temperature of the HPO inductor coil should be monitored in order to prevent over-heating. Re-adjustment will be required when moving often and rapidly between on-resonance and off-resonance operating points. As previously stated this configuration mode is best suited to exploration of operating points not accessible with configuration 1, and where the operating conditions do not change rapidly during the measurement cycle.

3. Linear amplifier output stage

The VTG can be operated as the power stage of a linear amplifier when correctly configured and connected to a suitable frequency generator with power amplifier output stage. No pre-amplifier stage is currently provided in the VTG so the driving signal source will need to generate an output between ~ 1-10W in order to the drive the VTG output to a usable output power. In this configuration the VTG can be driven in grounded grid, grid biased, or even as a cathode follower with some change of circuit connection and setup.

For grounded grid operation J1 is connected to the external signal source, and J6 is connected directly to RF ground. For grid driven mode J1-J3 are open and J5 is connected to the external signal source which in this case also needs to arrange for the driving signal to provide suitable dc grid biasing for the vacuum tubes used. For this reason grounded grid operation is preferred for simple linear amplifier operation.

When correctly setup and driven the VTG in this configuration can provide a very stable oscillation output which can be easily and finely adjusted by the external signal source, overcoming some of the adjustment problems of the HPO, but not exceeding the very good power output levels of the HPO. It has been found that the HPO is better when higher power experimentation is required, but the linear amplifier is better for overall signal stability and accurate adjustment.  This configuration also allows for non-sinusoidal waveforms to be applied to the experimental system.

4. Modulator stage

Modulation of the VTG is currently by cathode keying, allowing conduction through the vacuum tubes to be switched at low frequencies via mechanical switches and relays, or at higher frequencies < 100kc/s  by semiconductor MOSFET switches. Modulation of this kind was originally considered to be important in the exploration of the displacement of electric power where non-linear events play a very significant part in the unusual electrical phenomena observed within an electrical system. It has since been found through experimentation that the non-linear impulses generated by this modulation method are not of sufficiently low transition time and low pulse width to be particularly useful in the generation, observation, and measurement of displacement phenomena.

5. CW and burst oscillation modes

The VTG can be arranged in any of the configuration modes 1-4 and then operated in CW or burst modes simply by removing the plate supply tank capacitor at B+. When the tank capacitor is connected at the output of the HVBR a constant plate supply voltage B+ is applied to the primary load. In this case the output of the VTG in oscillation will be in CW mode providing a constant and continuous oscillation wave to the primary circuit LpCp.

When the tank capacitor is removed from the HVBR the output is an unsmoothed full wave rectified supply at 100c/s (based on UK line frequency). Applied to the VTG this produces bursts of oscillation inside the supply envelope, and has proven to be useful in establishing certain operating conditions in experiments orientated to displacement of electric power. These operating conditions and experiments are currently work in progress and will be reported in subsequent posts.


Overall the VTG has proven itself to be a versatile and reliable linear power source suitable to drive a wide range of experiments to explore the displacement and transference of electric power, and also some preliminary lower power telluric transmission experiments. Over several years of operation only 1 x 811A has been replaced after grid flash over destroyed one of the tubes when being used in configuration 2 with the HPO at an off-resonance operating point, with large output mis-match and high reflected power. The VTG has also sustained reliably through high power experiments where both plates of the tubes are glowing bright red for short periods of time. The 811A in RCA and Russian forms have proven themselves to be robust and reliable provided the heater element (spring tensioned) has not broken during extended storage. VTGs with other vacuum tube types and configurations will be presented in subsequent posts.

Click here to continue to part 2 of the 811A vacuum tube generator where the operating characteristics for each of the defined configurations are measured, optimised, and tuned.