The 6AQ4 (CV417) is a miniature single triode for use as a grounded grid amplifier, and thus at high frequency.
This type of valve was designed for RF applications at VHF up to a maximum frequency of 250 MHz. These would include radio, television and radar. The equivalent noise resistance was given as 400 Ohms. The M8099 special quality version was made for critical applications.
The blue coating inside the glass is to suppress the emission of gas from the glass as in the EF91. This extends the working life of the valve. However, in this valve the anode is in the centre and encloses the grid this minimising the number of electrons available to reach the glass.
The anode face on. The control grid has copper supports and cooling U channel connected to the top of the supports but also that connects to the bright vertical strips. There is one bright strip each side. These could form a neutralising capacitor.
The thin glass tube envelope is 17 mm in diameter and, excluding the B7G base pins, is 46 mm tall.
