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 |
Links
Guitar Amp Projects
- Superfly, and one built in a stombox enclosure.
- 3W Tube Power Amp uses a 6021 in the preamp, and a pair of push-pull 6AK6 in the output stage.
- MiniTubeAmp, a tiny 6021 project using an external switched mode power supply (not guitar, but it's very cool).
- JJS Class A submini amp, using 2 6021Ws with SE output stage. Looks very much like the ZVex Nano, and uses a switching power supply.
- JJS Class AB submini amp, using 6112, 6021W, and a dual 5902 PP output stage, with toroidal transformers (sound samples available). Both very impressive!
- Jon Anderson’s 5902 submini guitar amp, using a 6112 for the preamp and an SE 5902 output stage (sound samples available)
- Micropower subminiature tube guitar amps with reverb and vibrato, a collection of SPICE-modeled circuits replicating classic guitar amps in submini-form. These would be an interesting starting place for a build.
- Mark Lavelle’s PowerMan 6021 amp in a PC power supply.
- Another Powerman build, using a pair of 6021s for output.
- Pencil Pusher
- Pencil Pusher II
- Nabla, with 6N17B, 6N21B, and 6P30B tubes
- Miniature tube amp
- Subminiature Express at Amp Garage. T-Wreck circuit with 5902 output.
- A4 ‘Wreck made with 6112 and 6AQ5, also on Amp Garage. Spiffy.
- The Reduced Princeton (PDF), a class project for UIUC’s Physics of Electronic Musical Instruments course.
- Fred Nachbaur’s Tea Tin Amp
- Micropower subminiature tube guitar amps with reverb and vibrato
Hi Fi Amp Projects
- Mini-Amp mit der Miniaturröhre 5902
- Tube CAD Journal – Balanced line stage using subminis, and part 2 — Balanced phono stage
- Kolibri, another 5902 stereo amp.
- 6021W Tube DAC
Radios
Tube Data
- WA2ISE sub-miniature tube page
- The Virtual Valve Museum can be searched for pictures of many tubes, including some sub-minis. It’s also got pictures of just the weirdest tubes, so it’s great to browse.
- The National Valve Museum
- A Japanese page on submini tubes
- Another RIAA phono preamp with sub-minis
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.
- Weber Speakers has four 6" models and one 6"x9" model.
- Jensen has several 6" speakers: MOD 6-15, P6V, C6V and one 5" speakers - Mod 5-30.
- 6" woofers from PartsExpress. I made a small cabinet out of two of these.
Commercial Products
- ZVex Effects makes the Nanohead guitar amp, and the iMPAMP stereo amplifier, both using JAN 6021W tubes.
- Audioaero’s Prima amplifier used 6021Ws (although they’re inside the case, soldered to a PCB board – not nearly as cool if you can’t see them).
