12QR51 — Electrostatic Deflection Cathode-Ray Tube

The 12QR51 is an all-glass cathode-ray tube manufactured by Tesla, designed for high-performance oscillograph applications. It is specifically engineered to provide low deflection plate capacitance, making it suitable for demanding measurement setups requiring high writing speeds and a long screen persistence.

Design and Physical Construction

The 12QR51 features an all-glass envelope with a nine-pin base on a 25 mm diameter. To minimize parasitic capacitances and facilitate high-frequency operation, the deflection plates are connected to short, direct leads brought out through the side of the glass bulb. The accelerating anode ($a_3$) is similarly brought out via a side contact.

The tube utilizes electrostatic focusing and symmetrical electrostatic deflection. The screen is coated with a green phosphor characterized by a long persistence.

Physical Dimensions

• Overall Length: $390 \pm 10$ mm
• Bulb Diameter: $125^{+3}_{-1.5}$ mm
• Neck Diameter: $45 \pm 1.5$ mm
• Distance from Base to Side Contacts: $260 \pm 10$ mm
• Distance from Base to Screen Transition: 250 mm
• Useful Screen Diameter: 100 mm

Heater Characteristics

The tube incorporates an indirectly heated oxide cathode. The heater can be supplied by either alternating current (AC) or direct current (DC).

Interelectrode Capacitances

The design minimizes deflection plate capacitances to optimize high-frequency performance. The maximum capacitance values are specified as follows:

Operating Values

The 12QR51 can be operated at different voltage levels depending on the required writing speed and deflection sensitivity. The typical operating points are defined at three accelerating anode voltage levels:

Maximum Ratings and Operating Precautions

To ensure reliable operation and prevent damage to the tube, the following limiting values must not be exceeded:

• Maximum Accelerating Anode Voltage ($U_{a3}$): 4400 V
• Maximum Anode Voltage ($U_{a2}$): 2200 V
• Maximum Focusing Voltage ($U_{a1}$): 1100 V
• Control Electrode Voltage ($U_{g1}$): Maximum 0 V, Minimum -150 V
• Maximum Voltage Ratio ($U_{a3}/U_{a2}$): 2
• Maximum Peak Voltage between Anode and any Deflection Plate ($E$): 500 V
• Maximum Grid Leak Resistance ($R_g$): 1.5 MΩ
• Maximum Deflection Plate Leak Resistance ($R_D$): 3 MΩ
• Maximum Heater-to-Cathode Voltage ($E_{k/f}$): 125 V (DC or peak AC value)
• Maximum Continuous Cathode Current ($I_k$): 50 µA
• Maximum Screen Loading ($W_s$): 3 mW/cm²

Mandatory Operating Precautions

1. Cathode Preheating: Cathode current must only be drawn after the heater has been active for at least 1 minute.
2. Cathode Protection: To protect the cathode, it is highly recommended to insert a resistor of approximately 200 kΩ in series with the cathode lead.
3. Shielding: Proper operation requires shielding the tube from external fields. Electrostatic fields must be shielded using an aluminum cover, while electromagnetic fields require a cover made of magnetically soft material.

Related Designations

The documentation notes that the related 12QR50 cathode-ray tube serves as a replacement for foreign types, specifically the Mazda 30.C.2/P2 and the OE 411 PAV.