40CB4 1½" Viewfinder CRT
The 40CB4 1.5 inch diagonal television tube first appeared in the early to mid 1970s and is probably one of the most widely produced and used miniature television viewfinder tubes. The 40CB4 (and its smaller brother the 1 inch diagonal 30FB4) are true television tubes, as opposed to more conventional viewfinder tubes, and are constructed in the same way as much larger ordinary television tubes. The tubes employ a cavity type side-connector for the final anode connection, internal aluminising and a part-external aquadag graphite coating, as is common with all television tubes the external aquadag is grounded and the capacitance formed by the conducting films on either side of the envelope is used to smooth the EHT. In this design the EHT is approximately 5kV. This is a very high resolution picture tube with very small spot size and is capable of rendering fine detail in the picture. The electron gun employs electrostatic focusing and magnetic deflection, again in common with most modern television tubes. The 40CB4 is a very common tube and has been produced by numerous manufacturers. Slightly shortened versions, the 40CB4M and 40CB4S are available for use where space is at a premium at the expense of resolution and a slightly higher deflection power requirement. These tubes are around 10 to 12 mm shorter than the standard 40CB4. The 40CB4 has been adopted by hundreds of manufacturers for use in camera viewfinders, miniature televisions, monitor applications and various hand held communicators. The tubes were employed in Panasonics 'TR' range of miniature hand held pocket television sets and are still made today and find uses in high-end professional video and studio camera viewfinders. The tube's heater and cathode are shared and this requires that a separate winding in the power supply supplies the 2.5 to 3.0 Volts for the heater across pins 4 and 5. With this floating heater supply, the cathode (either pin 4 or 5) can be driven normally.
