Vacuum Tube - 7A4 / XXL, Triode, Medium-MU
New-Old-Stock (NOS) tube.
Also known by US military identifier VT-192.
The 7A4 is a medium-mu triode using the lock-in construction. It is designed for use as an oscillator, detector, or amplifier. It is characterized by moderately high transconductance. It is particularly applicable for service in the higher frequencies.