12V tubes

Did you know that a series of 12V tubes were made for car use? The tubes are designed to not require HT but instead uses an acceleration grid to boost the electrons from cathode to anode.

I built a headphone amp using such tubes. Check it out at on my website (URL shortened):

https://bit.ly/2koJDkU

Also, check out this page on so-called "Space Charge" tubes:

http://www.junkbox.com/electronics/lowvoltagetubes.shtml