Port Czerniakowski in Vistula, is quick walk from the city center, and has a semi abandoned camping park.
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.
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.
The bits and bytes,
And the new expectations,
Filled with free speech,
Under ad lib virtualizations,
On a million sites,
Between a short screechs,
And any conditions.
Exploring the Royal Wilanow Palace in Warsaw, Poland.
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 of point and shoot around Warsaw.
An abandoned XIX century military fort became an canvas for the creativity of several street artists. Here are some pictures of Fort Bema in the north of Warsaw, Poland.
“Education is the key to unlock the golden door of freedom. “, George Washington Carver
“War is peace. Freedom is slavery. Ignorance is strength.”, George Orwell
These 2 quotes are the complete opposite yet they represent opinions about our idea of freedom. In one corner we have an idea of gathering knowledge to unlock the borders on the other the idea that not knowing perhaps makes us happier and more willing to risk.
Short urban exploration video in the abandoned SKRA swimming pools in the center of Warsaw.
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.