Rectifier - Half Wave ·Rectifier
Philips directly heated gas-filled industrial half-wave rectifier for magnetic-chuck supplies, providing substantial current with the low forward drop characteristic of gas-discharge rectification.
A directly heated, gas-filled, double-anode rectifying tube designed for industrial power applications, specifically optimized for driving magnetic chucks.
The 1725A is an industrial gas-filled double-anode rectifying valve designed primarily for medium-power rectification duties. Its primary documented application is the excitation of magnetic chucks, where it is rated to deliver an output current of 1.3 A per valve. The tube features a directly heated, oxide-coated filament and is housed in a glass envelope with a specialized base.
The 1725A utilizes a gas filling to achieve a low and stable internal voltage drop during conduction, making it highly efficient compared to high-vacuum rectifiers in low-to-medium voltage, high-current applications. To ensure reliable operation and prevent damage to the internal structure, the tube must be operated in a vertical, base-down position.
The 1725A is constructed with a robust glass bulb and a specialized base designated as Base A. The physical dimensions of the tube are characterized by a maximum overall height of 135 mm, a maximum seated height of 119 mm, and a maximum bulb diameter of 71 mm.
The tube has a net weight of 75 g. For industrial distribution, they are typically packaged in quantities of 25, with a total shipping weight of 5500 g.
The tube incorporates an internal screen (s) to stabilize the gas discharge and protect the electrodes. For proper operation, this screen must be connected to the cathode (filament) via an external current-limiting resistor:
The base diagram provides connections for the two independent anodes (a and a'), the directly heated filament (f, f), and the screen (s).
The 1725A features a directly heated, oxide-coated filament designed for AC operation. Because the filament is directly heated, it also serves as the cathode of the rectifying system.
| Parameter | Value |
|---|---|
| Filament Voltage (Vf) | 1.9 V |
| Filament Current (If) | 3.5 A |
| Calculated Filament Power | 6.65 W |
| Heating Supply | AC |
| Filament Type | Oxide-coated |
| Recommended Pre-heating Time (Tw) | 15 s |
The pre-heating time (Tw) of 15 seconds is the recommended duration to allow the filament to reach its proper operating temperature before anode current is drawn. In urgent circumstances, this pre-heating delay may be decreased to 0 seconds, though adhering to the recommended 15-second delay is standard practice to maximize tube longevity. The calculated filament power consumption of 6.65 W is derived directly from the nominal filament voltage of 1.9 V and the nominal filament current of 3.5 A (1.9 V * 3.5 A = 6.65 W).
The gas filling within the 1725A results in distinct electrical properties, notably a low arc voltage drop and a specific ignition voltage required to initiate conduction.
In a typical full-wave rectifying circuit configuration (referred to as circuit 'a'), the 1725A operates under the following nominal conditions:
| Operating Parameter | Value |
|---|---|
| Transformer RMS Voltage (Vtr / Veff) | 150 V |
| Output DC Voltage (Vo) | 110 V |
| Output DC Current (Io) | 1.3 A |
This operating point demonstrates the tube's capability to deliver a steady 110 V DC output at 1.3 A from a 150 V RMS AC supply, making it highly suitable for powering industrial magnetic chucks and similar inductive loads.
To prevent premature failure or immediate damage to the gas-filled structure, the 1725A must be operated strictly within its absolute limiting values. These limits represent the maximum stress the tube can withstand under any circumstances.
| Limiting Parameter | Absolute Maximum Value |
|---|---|
| Peak Inverse Anode Voltage (Vainvp) | 470 V |
| Average Anode Current (Ia) (Averaging time Tav <= 5 s) | 0.65 A |
| Peak Anode Current (Iap) | 4 A |
| Minimum Surge Limiting Resistance (Rt) | 5 Ω |
| Ambient Temperature Range (tamb) | -55 °C to +75 °C |
The minimum surge limiting resistance (Rt) of 5 Ω is critical to protect the oxide-coated filament from excessive peak currents during start-up or transient conditions. The average anode current limit of 0.65 A is specified per anode, integrated over a maximum period of 5 seconds, ensuring that the thermal limits of the individual anodes are not exceeded during continuous operation.
The 1725A is a specialized, gas-filled, double-anode rectifying valve designed for industrial applications, particularly magnetic chucks requiring a reliable 1.3 A DC supply. Operating with a low filament voltage of 1.9 V and a current of 3.5 A, the tube features a directly heated oxide-coated cathode. It exhibits a very low typical arc drop of 10 V and an ignition voltage of 22 V.
When configured in a standard rectifying circuit with a 150 V RMS supply, the 1725A delivers a nominal 110 V DC at 1.3 A. Designers must ensure the tube is mounted vertically (base down) in a 40465 socket, connect the internal screen to the cathode via a 10 kΩ, 0.5 W resistor, and respect the absolute limits, including a 470 V peak inverse voltage, a 4 A peak anode current, and a minimum series resistance of 5 Ω.
General specifications
Properties common to every published source and operating point.
Electrical assignments shared by every tube using this base designation.
No verified pinout is recorded for this base designation.
1 physical section, each with unique specifications.
Section 1
Directly heated gas-filled rectifier for magnetic-chuck rectifier service.
Source-dependent data
Each block preserves the test conditions and published values from one reference. Values from different sources are intentionally kept separate.
Data set 01
Published operating points and test conditions from this source.
Arc voltage drop
10 V
GasFilled
Maximum peak inverse anode voltage
470 V
Maximum average anode current
650 mA
Maximum peak anode current
4 A
Application
magnetic-chuck rectifier service
Heater voltage
1.9 V
DirectAC
Heater current
3.5 A
DirectAC
Data set 02
Published operating points and test conditions from this source.
Maximum average anode current per anode
650 mA
Tav max 5 s
Minimum series resistance
5 ohm
Permitted mercury/ambient temperature
-55 to 75 degC
DC output voltage
110 V
DC output current
1.3 A
RMS anode supply voltage
150 V
CircuitA
Ignition voltage
22 V