Uploaded March 2025 | Updated September 2026, 3 weeks ago
Once upon a time there were gas filled rectifiers. These have been completely replaced by silicon diode, but it is interesting to revisit them to see how they worked. The vacuum diode held on a little longer for high voltages applications. Gas filled rectifiers work on the same principle of hot cathode emission, but the addition of a gas or vapour allows a larger current to flow that wouldn't be possible in a high vacuum device. The gas can also transport the heat away from the anode better. Mercury was commonly used for this purpose but helium, neon and argon were also used. The mercury rectifier here is of an early open design, allowing us to see the glow discharge in action.
The full-wave rectifying circuit used here was also a common set-up with diodes tubes. It made the transformer more expensive but saved on two tubes and simplified heater supplies. This circuit can still be found in low voltage supplies where diode volt-drop may be an issue.
CONTENT:
00:00 - Intro, high vacuum diode
00:50 - gas rectifier
02:20 – circuit diagram
03:12 – test setup
03:53 – running
08:08 – What not to do with heater voltage
08:55 – images during cycles
Once upon a time there were gas filled rectifiers. These have been completely replaced by silicon diode, but it is interesting to revisit them to see how they worked. The vacuum diode held on a little longer for high voltages applications. Gas filled rectifiers work on the same principle of hot cathode emission, but the addition of a gas or vapour allows a larger current to flow that wouldn't be possible in a high vacuum device. The gas can also transport the heat away from the anode better. Mercury was commonly used for this purpose but helium, neon and argon were also used. The mercury rectifier here is of an early open design, allowing us to see the glow discharge in action.
The full-wave rectifying circuit used here was also a common set-up with diodes tubes. It made the transformer more expensive but saved on two tubes and simplified heater supplies. This circuit can still be found in low voltage supplies where diode volt-drop may be an issue.
CONTENT:
00:00 - Intro, high vacuum diode
00:50 - gas rectifier
02:20 – circuit diagram
03:12 – test setup
03:53 – running
08:08 – What not to do with heater voltage
08:55 – images during cycles
