Wonderful and unique fat smooth overdrive: Pentode tubes!

Bands like The Beatles, Rolling Stones and guitarists such as Brian May from Queen, Peter Green from Fleetwood Mac, or more recently Rory Gallagher from Oasis, are known users of Vox AC-30 guitar amplifiers. Turned up loud it has a fat smooth overdrive, harmonic and unique, but whats the secret?

Most of the recent versions use parts that are quite standard and the same as any other valve amplifier, meaning noval triodes tubes in the pre-amplifier and pentodes in the power amplifier, but the most favored and sought after AC-30 tones, are the in the late 1950’s and early 1960’s versions, the main difference being the EF86 tube in the pre-amplifier.

So what is so special about the EF86?

The EF86 (datasheet) is a high-gain pentode designed to amplify low-level audio signals in the late 1950’s. It is usually found as a pre-amplifier tube in audio equipment and instrument amplifiers. The EF86 is much more sensitive than other common preamp tubes like the 12AX7, and achieves more gain. Pentodes still offer with a little more odd-harmonic content and a ‘glassy’ sound. Their overdriven  sound is an expressive compression effect.

What is the issue with pentode tubes?

A complex mechanical structure, combined with a high gain design, make a pentode like the EF86 very susceptible to vibration and the resulting microphonics, meaning noisy, which is not very good for music in busy loud stages.

How do reduce the noise floor of a EF86 pentode?

The easiest ways, if you really want to use a EF86 pentode quietly ( some ways are cheaper  than others) : add dampers, shock mount the tube, buy a few tubes and test until a quiet one is found.

Another way? 

But lets think a in a non linear way, perhaps we can find a pentode that can allow us to have all the good things like the glassy compressed overdrive but with low microphonics.

I started looking around datasheets from  both from east (USSR) and west ( rest of the world) and started noticing that some tubes would withstand greater amount of G-force . The submini tubes, specified  for reliability and designed for long service life under conditions of severe shock, vibration (up to 20,000G), high temperature and high altitude. These tubes were some of the most meticulously built and most rigorously tested of all tubes, as their main intended use was extreme military applications.

The cheapest and easiest submini pentodes for me to obtain  were the russian made ones, I found and tested a few, in the first tube position of a guitar amplifer, submini pentodes such as the 6S31B (datasheet; in cyrillic 6С31Б), 6P30B (datasheet; in cyrillic 6П30Б-P), 6J5B-V (datasheet; in cyrillic 6Ж5Б-В).

But just for standard size tube enthusiasts I also tested a few noval and heptal options.

I will keep improving the circuit until it sounds great and  is stable. A post about it soon.






How to build a valve guitar amplifier?

Fast track video showing the build of an MJ style guitar tube amplifier. I had some NOS tubes laying around, the 6N2P-EB ( datasheet) and 6N6P (datasheet), made in the CCCP in the 70’s.

The 6N2P-EB is direct replacement of the 6AX7 (datasheet) , or with the 12AX7 (datasheet)/ECC83 (datasheet)  if we change the filament heaters ( like this). The 6N6P is equivalent to the 12BH7 (datasheet)/ECC99 (datasheet) if we make the same filament heater mod, mentioned before.

The amplifier is inspired in the Tiny Terror, but with a few changes to accommodate different tubes.

A bit more reach… with a Koy Boost!

A clean boost is a very useful guitar pedal since it can raise the output of quiet guitar pickups to deafening levels rock levels.  For this essential pedal project and often made in a basic way, I decided to embellish it with koy fishes  using an acid etching technique.


The Skulptor sounds O.K. recorded with a phone?

In our modern world here is evidence that size is not everything. A small blues demo with a concentrated tube amp recorded with a low quality phone camera (and microphone) through a 1×12 open back speaker cabinet, still I think it sounds great ! Thanks to Machinarium pub in Warsaw for providing the space for the No To Gitara meetings.

Dynamic Prototyping Pedal – Sound UNIQUE not CORPORATE nor BOUTIQUE!


This quote was the inspiration behind this build, because guitar amplifiers, effects, and music gear in general, in recent years has forked into 3 lanes ( from the same road ) :

  • The mass corporate production, which has millions of dollars for marketing, R&D, production and distribution. The benefits are consistency, warranty  and availability ( often they are not cheaper so I’m not going to add it as benefit). The downside is that they might not have high end quality parts, the musician gets a generic sound, low resale value, and some might be just copies of other well know products.
  • The boutique industry is smaller because it has small production runs, has little money for marketing and usually relies  on word of mouth and social media for promotion. The positive  things are non generic sounding ( usually), small production runs which means that less people have it, passionate people with specialized expert skills run the company, possible higher re-sale value if the brand gets more famous, and often durability and features are better. The negative side are high prices, limited availability and limited warranty.
  • DIY ( Do-It-Yourself) and craft industry, well, there are huge communities about it, these are people who build their own gear, from kits or  they find all information online and use the standard methods for electronic prototyping. On the upside there is the satisfaction and pride of making things, people learn new  facts and skills, yetrhave no limit of customization. The dark side is lack of consistency, the kits are usually copies of corporate and boutique gear, quality control is low, and they might be built just by someone who can pick up a soldering iron and not very unique because of that.

I personally wish to have unique tone, and created that opportunity by developing a portable Dynamic Prototyping Pedal. The original idea was:


Then I built it and looked like this. I realized that with it I can change the parts and play the result immediately in a true bypass fashion.


After using it for a while I realized it needed something more and I decided to add a second proto board.


Camera: Nokia Lumia
Year : 2016

Room .55 Guitar Amplifier – Perfect for any home!

A guitar and the desire to rock with great tone from luxurious tubes, at home without the concert volumes?

Half a watt of pristine clean and  aggressive rock gain in one tiny box: Art is…Room .55

Loud .55 Guitar ampifier

Art is… Room .55 specifications:

Power:  0.6 Watt

Technology: Tubes

Type: Class A ( Single Ended)

Topology: Head

Controls: Gain and Volume ( also has Treble switch)

Channels: 1 Channel ( From Clean to Crunch using the Gain knob)

Input: 1 for instrument

Output: 1 to 8 ohm or 16 ohm speaker

Pre-amp Tubes: 1 x 12AX7 ( But it can be swapped by 12AT7, 12AY7, 12AU7)

Power tube: 12AU7 ( But swapped by 12AT7 or ECC99)

Special Features: SMPS High voltage control knob ,  hand-wired point to point, Feed-Back-Loop with control (FBL), FBL / Bypass / Hi-Gain switch and Country Knob

Power supply: 12V DC with 1.5 Amperes (minimum)

Size (Height x Width x Depth ): 11cm x 18cm x 11,5cm

Weight: 0.9Kg

The Skulptor 1 Watt Vacuum Tube Guitar Amplifier – Short Clean Demo

“A image is worth a thousand words, and video is a thousand impressions.” By M.

Before my home becomes a museum of the things I build , I decided to demo in a very informal, and experimental fashion the amplifier I built. This post is connected to my previous post about my little 1 watt amplifier design,  THE SKULPTOR.  Thank you to my friend from the polish band Astronauta for playing.

The filming and edition were made with “my feet” , this how I get the best unadulterated footage. The “can-do” attitude is everything 😀







The BOSS RC-3 is a compact loop station in a stomp box format that allows up to 3 hours of recording in stereo, and is compatible with a multitude of instruments and devices. Overall I think its a great jamming tool, either alone at home or with a band.  It can be operated with the in-built footswitch, or, with an additional external footswitch that makes it even easier to use in a live scenario because it opens up the possibility to scroll around the memory banks and set the rhythm with a foot. This video is a great tutorial.


The BOSS external foot switching in this pedal works in continuity mode, and the changes happen when the circuit continuity is broken. In other words the circuit is operated with a N.C. switch ( Normally Closed Switch ) which opens when the button is pressed.


Picture of required materials.
Picture of required materials.

List of materials:

  • Enclosure ( Plastic or metal,according to your budget )
  • 2 x Heavy duty SPST momentary footswitch
  • 2 x SPST latching toggle switch
  • Stereo 6.3mm jack
  • 22AWG cable
  • Soldering iron and solder.

To wire it up you can use this schematic.



Finished box.
Finished box.


After drilling and soldering it all together grab a stereo jack cable plug them together, and the result will be a switch that will help your methodical inspiration to come out and stay for eternity, somehow.


Switch and pedal together
Switch and pedal together




The Chime in a box, call it TAVTIB!


The Tweed American Vintage Tone in Box, I call it TAVTIB! The carry around brush to color your tone and sound like your self without breaking your back carrying a huge and heavy amplifier around.

The idea came to existence after finding a few articles about how some FET transistors have a tube-like transfer characteristic and produce harmonic distortion similar to tube triode, this meaning that they can sound a bit like a tube amplifier at low voltage.


After looking around the web for a while I found RunOffGroove and a project called the Fetzer Valve. This project was the first of many projects concerning adaptation of tube amps in to preamp/distortion pedals , the circuit it self is a popular DIY booster and  building block in larger circuits such as amplifier emulations in pedal format. Visit the page you will find lots of options.

I wanted american vintage sound with heavy mids and sweet highs of a Tweed era amp that could be styled easily due sensitive touch response with my P90 pickup. There are a few pedals in the market that could be purchased but the price was so high that motivation to close the wallet is instinctive.


TAVTIB specifications:

Technology: Vacuum Tube Emulation at low voltages with N-channel JFETs

Controls: Gain, Bass, Middle, Treble,Volume and Input selector

Input: 1

Output: 1

Special Features: True-bypass

Power supply: 9V DC with 100 mA (minimum)

Size (Height x Width x Depth ): 55mm x 83mm x 110mm

Weight: 150g

The Skulptor 1 Watt Vacuum Tube Guitar Amplifier

For quite a while, I wanted to own a small, low power all tube guitar amplifier that would sound very Tweedy or tonally american, like the well known sounds from SRV. An amp that I could use at home with a small or BIG cabinet,  would be eco friendly because it would be made of recyclable materials and with low power consumption, easy to move around yet sturdy, and that I could play in a neighbor friendly volume, without it sounding dull.

The first step, was to look for something online, through a few web shops and publications. I researched and ended up finding mainly 5 watt,  also some lower wattage options that costed a lot more than what I wanted to spend.

I searched in few DIY guitar gear websites and forums and found a few possibilities, some easier than others, some required more money than others, some had no information concerning the the first run with flying colors.

In the end I found a lot of suggestions at a few forums. I was advised that sometimes transformers are 70% of the cost of non replaceable parts. If I would use an alternative to a power supply transformer I would save 35% of the total cost. Went to the Warsaw Polytechnic talked with a power supply specialist  and he provided me with the recipe for a SMPS Boost supply that took 12VDC to 220VDC quietly. I calculated all the tube parameters, and the end result is the amplifier you can see in the pictures ! I will try to make a low-fi video eventually.

Art is… Skulptor specifications:

Power: 1 Watt

Technology: Tubes

Type: Class AB ( Push-Pull)

Topology: Head

Controls: Gain, Tone and Volume ( also has Treble switch)

Channels: 1 Channel ( From Clean to Crunch using the Gain knob)

Input: 1

Output: 1 to 8 ohm or 16 ohm speaker

Pre-amp Tubes: 2 x 12AX7 ( But V1 or V2 can be swapped by 12AT7, 12AY7, 12AU7)

Power tube: 12AU7 ( But swapped by 12AT7 or ECC99)

Special Features: Cooling Fan, SMPS High voltage control knob , Effects loop with send level, Hardwired point to point.

Power supply: 12V DC with 2 Amperes (minimum)

Size (Height x Width x Depth ): 16cm x 22cm x 14,5cm

Weight: 1.6Kg