The 25L6 is an octal-based

Tube socket

Tube sockets are electrical sockets into which vacuum tubes can be plugged, holding them in place and providing terminals, which can be soldered into the circuit, for each of the pins. Sockets are designed to allow tubes to be plugged in in only one orientation...

 vacuum tube

Vacuum tube

In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...

 of the beam-power tetrode

Tetrode

A tetrode is an electronic device having four active electrodes. The term most commonly applies to a two-grid vacuum tube. It has the three electrodes of a triode and an additional screen grid which significantly changes its behaviour.-Control grid:...

 type. It found common application in AC/DC radio receivers - such as those of the All American Five

All American Five

The term All American Five is a colloquial name for mass-produced, superheterodyne radio receivers that used five vacuum tubes in their design. These radio sets were designed to receive amplitude modulation broadcasts in the medium wave band, and were manufactured in the United States from the mid...

 type - and was also found in large numbers in early computers, such as the UNIVAC I

UNIVAC I

The UNIVAC I was the first commercial computer produced in the United States. It was designed principally by J. Presper Eckert and John Mauchly, the inventors of the ENIAC...

.

The tube used EIA base 7AC in common with many other power tubes. The tube was identical in design and ratings with the 50L6 with the exception of having a 25 volt 300 mA heater, whereas the 50L6 has a 50 volt 150 mA heater. The 12L6 and identical 12W6 were made with a 12 volt, 600 mA heater, and the 6W6 was made with a 6.3V, 1200mA heater. There was also a 35L6 with a 35V, 150 mA heater. Because of the slightly lower-power heater, the 35L6 has slightly lower output than the rest of the family.

This family is not to be confused with the 6L6

6L6

6L6 is the designator for a vacuum tube introduced by Radio Corporation of America in July 1936. At the time Philips had already developed and patented power pentode designs, which were fast replacing power triodes due to their greater efficiency...

 which has the same basing diagram

Basing diagram

A basing diagram shows or describes the “pins” of an electronic component. This part usually has more than two pins, so a basing diagram is needed to show which pin does what. Many basing diagrams also show dimensions....

, but has more than twice the power capability of the 25L6.

The 25L6 was introduced as a metal tube November 4, 1936, but most examples of this family were made of glass. The ST14 Glass 25L6G came out March 30, 1937, The T9 size GT version came out April 11, 1938. There was also a 25L6G in the smaller ST-12 glass envelope.

Computer equipment used this tube as a relay driver or to run the solenoid

Solenoid

A solenoid is a coil wound into a tightly packed helix. In physics, the term solenoid refers to a long, thin loop of wire, often wrapped around a metallic core, which produces a magnetic field when an electric current is passed through it. Solenoids are important because they can create...

s in key punch

Key punch

A keypunch is a device for manually entering data into punched cards by precisely punching holes at locations designated by the keys struck by the operator. Early keypunches were manual devices. Later keypunches were mechanized, often resembled a small desk, with a keyboard similar to a...

 machines. The heater in this case ran off the 24 volt power line in the equipment resulting in long life, and slightly lower power output. The industrial type 6046 is a 25L6GT rated for that application.

Also see All American Five

All American Five

The term All American Five is a colloquial name for mass-produced, superheterodyne radio receivers that used five vacuum tubes in their design. These radio sets were designed to receive amplitude modulation broadcasts in the medium wave band, and were manufactured in the United States from the mid...

.