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Monday, October 31, 2022

Tube of the Month : the 12E1


Today I have another rather uncommon tube to present: The 12E1 beam tetrode.

This beam tetrode was designed as regulator tube in power supplies, either for series or shunt regulation. 

But like many tubes not originally intended for audio applications the 12E1 might serve in audio amps as well and not only in the power supply but as output tube. The tube has an octal base (pin diagram shown on the left) and a small top cap which connects to the plate. The 12E1 has a healthy maximum plate dissipation rating of 35W. Triode connected it could serve as an alternative to the 6CB5A. It offers a higher plate dissipation rating as the 6CB5A and needs less heater current (1.6A vs. 2.5A). These beam tetrodes usually are quite tough and can be driven at their maximum ratings. But I admit I never looked in detail how well it would work. Check the data sheet for a complete set of technical specs. The plate curves don't look too shabby. Here the triode connected curves from the data sheet:

And the curves from an actual tube sample from my stash:

Since I never used this tube in a project I did not accumulate many of them. These 4 are all I have:

Let's have a closer look.

My 12E1s are made in England by ITT.

The base is made of micanol:

And lastly a 12E1 in operation:

The heated cathode and grids are nicely visible through the holes in the plate. View from the bottom:

An interesting tube that would deserve more attention. So many tubes, so little time.

Best regards