The US Government VT-137 is the commercial 1626. It was designed as an RF power oscillator for conditions where good frequency stability is important. The operating condition was class C and that explains the high negative grid bias. The valve was only designed to provide short pulses of power in the anode tuned circuit. The circuit itself would then ring and generate sine wave outputs.
Recently this triode design has been pressed into service within an audio amplifier design.
The 1626 is etched into the envelope.
The base is printed with the makers name, and both Type designations.
The anode is carbonised for good heat transfer by radiation and fixed rigidly to the mica supports to minimise vibration.
The box is typical of the period, plain white card on the outside but a security feature inside. Along the length of one corner is a card flap at 45 degrees that has a gap in the middle. The card liner has a flap that engages with this gap and locks the valve in place. Extracting the valve damages the liner and thus indicates if the package has been tampered with.
Another 1626 held in the card liner. The one piece card slots together once the valve is in place.
The locking dovetail. The right edge shows the damage inflicted in removing the valve from the outer sleeve.
The slots that hold the liner together.
The classic envelope is 38 mm in diameter, and excluding the IO base pins, is 89 mm tall.
Reference: Datasheet. Type VT-137 was first introduced in 1941.