Low Power Vacuum Tube PreAmp

I have wanted to learn more about vacuum tubes for years but was always put off by the extremely deadly power requirements. Working with low power sources for so long, I have blown my fair share of capacitors, which is scary enough for me.

Recently I discovered the world of sub-miniature vacuum tubes and the meager power requirements of some. Enter the Raytheon JAN 6418 pentode. Not only can you run this thing on 9 – 30 volts of power, but it is the size of a medium capacitor. We are talking about a mere 1 1/4″ glass bulb with 5 trimmable leads. Very Small.

6418 tube data sheet page 1

From the JAN 6418 datasheet:

The 6418 is a filament-type pentode of subminiature construction designed for use as a power amplifier in portable and wearable equipment. The flexible leads may be soldered directly to the terminals of circuit components without the use of sockets. Standard subminiature sockets may be used by cutting the leads to a suitable length.

Filament voltage – 1.25 volts
Max plate voltage – 30 volts
Max grid #2 voltage – 30 volts
Max cathode current – 0.5 ma

Grid #3 is composed of two deflector plates, one being connected to lead 3 and the other to lead 5.

Project #1 with the Raytheon JAN 6418 pentode will be a simple guitar preamp/booster

When I was researching these tubes (or valves as they are called in the UK), I found a few great projects that I plan on building. From RIAA phono preamps to condenser mics, I have my work cut out for me.

The first design I settled on building is a simple guitar preamp design attributed to P. Woodland (I found it here). I knew this would go together quickly on a stripboard with a super-low parts count; 3 resistors, 2 caps, a small battery, a socket, and a tube. The 1.25-volt battery is not the most elegant solution, but it will power the filaments.

5.3.2022 – This design is not yet verified; I am waiting on some 18r resistors, and I don’t have anything even close.

05.05.2022 – VERIFIED! I added an LED resistor, changed the C1 value, and reoriented the ground wire. A fun build and a great way to learn about tubes without the risk of killing yourself.

This thing sounds pretty killer, it adds a beautiful clean boost to my signal and some nice gnarl to my Fuzz Face, Super Fuzz, and Bazz Fuss pedals. The more I play with it, the more I love it!

JAN 6418 guitar and bass boost
Watch out for the cuts on the capacitors.

Need JAN 6418 tubes? I got you!
5-Pack NOS!

Learn more about sub-mini vacuum tubes.