I have closely examined diagrams of power supplies that use rectifier tubes and have noted that they feed the filament with alternating current (AC). I have considered whether it might be an improvement to drive the filament with direct current (DC) instead.
The purpose of the filament is to generate an ionized field by releasing electrons, which are then attracted to the anode (I am disregarding the grid here). When current passes through the filament, a magnetic field is generated. With alternating current (AC), this magnetic field constantly changes direction, which can lead to changes in the geometry of the ionized field. This phenomenon could negatively impact the efficiency of ionization, as the free electrons will be influenced by the fluctuating magnetic field and may not move stably toward the anode. The constant change of the magnetic field could thus disturb the desired ionization process.
However, if the filament were driven by direct current (DC), the magnetic field would be constant, potentially creating a more stable ionized field. DC could therefore possibly improve efficiency by avoiding the disturbances caused by the fluctuating magnetic field from AC. The constant direction of the current would ensure more stable movement of the free electrons and more consistent ionization of the gas in the tube.
We are familiar with a similar phenomenon from old cathode ray tube (CRT) televisions, where a magnetic field could distort the image by altering the electron's path. This interference is an example of how a changing magnetic field can affect a process where the path of the electrons is crucial. In the same way, a fluctuating magnetic field in a filament tube can alter the movement of the ionized electrons and disturb the ionization.
The purpose of the filament is to generate an ionized field by releasing electrons, which are then attracted to the anode (I am disregarding the grid here). When current passes through the filament, a magnetic field is generated. With alternating current (AC), this magnetic field constantly changes direction, which can lead to changes in the geometry of the ionized field. This phenomenon could negatively impact the efficiency of ionization, as the free electrons will be influenced by the fluctuating magnetic field and may not move stably toward the anode. The constant change of the magnetic field could thus disturb the desired ionization process.
However, if the filament were driven by direct current (DC), the magnetic field would be constant, potentially creating a more stable ionized field. DC could therefore possibly improve efficiency by avoiding the disturbances caused by the fluctuating magnetic field from AC. The constant direction of the current would ensure more stable movement of the free electrons and more consistent ionization of the gas in the tube.
We are familiar with a similar phenomenon from old cathode ray tube (CRT) televisions, where a magnetic field could distort the image by altering the electron's path. This interference is an example of how a changing magnetic field can affect a process where the path of the electrons is crucial. In the same way, a fluctuating magnetic field in a filament tube can alter the movement of the ionized electrons and disturb the ionization.
No ions in a rectifier, unless it's a gas rectifier. The magnetic force is minimal compared to the electrostatic force from the anode-cathode voltage (also constantly changing), and would have little effect on the current waveform (though it may effect where electrons hit the anode). The path of the electron makes no difference - it hits the anode, a single piece of metal. The current waveform is mostly controlled by the capacitor or choke in the ripple filter.
This is not an issue in most unipotential cathode tubes. Herbert Reich (1) has this to say on the subject...
In short, the electric potentials filed between the cathode and plate dominate the electron path. Variations due to any stray magnetic field which may extend beyond the cathode surface is handled with electrode geometry (i.e. things like cylindrical plates) and structures like beam forming plates. Improvements in overall noise level due to DC heater power (within the tube) is generally far below the audible level.
(1) Reich, Herbert J, “Theory and Applications of Electron Tubes”, 2nd Ed., McGraw-Hill, 1944
In short, the electric potentials filed between the cathode and plate dominate the electron path. Variations due to any stray magnetic field which may extend beyond the cathode surface is handled with electrode geometry (i.e. things like cylindrical plates) and structures like beam forming plates. Improvements in overall noise level due to DC heater power (within the tube) is generally far below the audible level.
(1) Reich, Herbert J, “Theory and Applications of Electron Tubes”, 2nd Ed., McGraw-Hill, 1944
Define improvement.are you reffering to dht or indirect heated tubes. Theres a big difference in there construction. What works for one type may sound better or worse depending on the multitude of variables and of course preferences. Built it,try it.
Frank40, it helps if you do some technical document review, as this topic was described and assessed in the 40-50's.
For receiving tubes, the most noticeable 'improvement' related to AC heater filaments was the introduction of a double helix filament for indirectly heated valves in the early 1950's to suppress any noticeable influence of heater's magnetic field on tube operation for sensitive 12AX7 and EF86 type tubes used in low noise/hum amplifier applications.
For receiving tubes, the most noticeable 'improvement' related to AC heater filaments was the introduction of a double helix filament for indirectly heated valves in the early 1950's to suppress any noticeable influence of heater's magnetic field on tube operation for sensitive 12AX7 and EF86 type tubes used in low noise/hum amplifier applications.
Look at the bright side, we can have many threads and long discussions about which diodes, capacitor, chokes etc are best for the rectifier of the rectifier!