January 02 2006

Projects Subminiature Tubes

A collection of obsolete technology links.

What are Sub-Miniature Tubes?

Sub-miniature tubes, also referred to as pencil tubes or hearing-aid tubes, are among the last generation of vacuum tubes designed and built. They’re typically very small, and instead of being socketed they have flexible leads like passive components. Some are designed to be run off of batteries (the hearing aid tubes), with very low heater & B+ voltages, while others were designed for military & industrial use.

They’re not the smallest generation of vacuum tubes – that distinction probably goes to Nuvistors, but they maintain the classic glass envelope, letting you see the heater glow and internal structure of the tubes. It’s just not right if you can’t see the tubes glow.

I’ve always been interested in small & miniaturized things. I first got interested in small tubes with the 6AK6, which I purchased a bunch of intending to build Doug Hammond’s Pentode Driver, but built the Micro Champ instead. I knew about sub-miniature tubes then, but didn’t get around to getting any until I saw Zachary Vex’s Nanohead amp and at the same time I found a box of 6021W tubes on eBay, which immediately triggered my mania!

Potential 6021W Projects

  • Overdrive pedal, Matchless style
  • Overdrive pedal — sky’s the limit (dumble style? 3 tubes & 6 gain stages, fuuuullll shred?)
  • Tube Buffer, like the Valvulator
  • Tube Tremolo pedal, like the Matchless Vibrobox
  • Standalone preamps
  • Micro amp, like the Nanohead or PowerMan
  • Hi-Fi — headphone amp, computer audio amp, preamp
  • Tube microphone preamp

High Voltage Sub-Minis

This is a table of some of the sub-miniature tubes which run on 6.3V heaters and high voltage (>100V) B+ and are probably well suited to guitar projects.

Tube Type Ih (A) Gm mu Ra P(W) Pdiss(W) eBay Datasheet
6021 Dual Triode 0.3 5.4K 35 6.5K 1.1 6021 6021
6111 Dual Triode 0.3 5K 20 4K 6111 6111
6112 Dual Triode 0.3 1.8K 70 38K 0.3 6112 6112
6814 Triode 0.15 6K 29 4.8K 2.2 6814 6814
5719 Triode 0.15 1.7K 70 41K 1.3 5719 5719
5744 Triode 0.2 4K 70 17K 1.3 5744
5840 Sharp Cutoff Pentode 0.15 5K 1300 260K 1.1 5840 5840
5899 Remote Cutoff Pentode 0.15 2.5K 650 260K 5899 5899
5902 Beam Power Pentode 0.45 4.2K 15K(Zout 3K) 1 3.7 5902 5902

Guitar Amp Projects

Hi Fi Amp Projects


Tube Data

Small Speakers

Tiny combos need tiny speakers. This is a listing of speakers I’ve found sized 6" and below. The smallest speakers specifically designed for guitar seem to be 6" (with the exception of the Ted Weber 5" unit). Below that you need to check frequency responses for something which tails off after 5-6KHz. Sometimes small woofers or midranges have a good response curve for this.

Commercial Products