Tube of the Month : The 1625

Hi!

This months tube is a transmitting beam power amplifier, the 1625.

The 1625 was designed for use as AF amplifier or modulator as well as for RF amplification. Except for the heater it is identical to the 807.

The 1625 has a 7 pin base and a small top cap for the plate connection. It is an indirectly heated tube with a 12.6V heater which consumes 0.45A. It is electrically and mechanically identical to the 807 with the only exception that the latter is heated with 6.3V / 0.9A. While it was intended to be used in Class AB2 configuration where it can deliver up to 120W, I have seen 807s used in singe ended amps and in triode connection as well. I never built anything with these tubes, so cannot share any practical experience but I am sure these are some excellent amplification devices. Since I have some of them in my tube stash I thought I write up a tube of the month post about them. As always let's have a look at the plate curves:

The data sheet also shows the triode connected curves:

Actual curves taken from a tube with the tracer:

These don't look too shabby. Let's have e a look at the tube.

I have some RCA 1625 in the beautiful world map boxes:

Probably the most beautiful tube box ever made.

The tube is wrapped in protective cardboard inside:

Inside the cardboard is some detailed documentation:

Some details of the tube：

More photos of a 1625:

The military designation is VT-136:

A National Union 1625:

The plate obstructs most of the glow when the tube is in operation:

On the bottom part of the grids is visible:

An interesting tube worth considering for an amplifier project if you don't mind the top cap.

Best regards

Thomas