Everything you should know about Tubes for Effectrode Pedals

by Phil Taylor

This article outlines a little about Effectrode design approach behind using tubes and then explains how the tonal characterstics of our pedals can be tailored to satisfy user-specific requirements just by swapping tubes.

The Tube Advantage

Effectrode pedals utilize electron tubes as their active component for performing signal processing. Tubes offer clarity, richness and purity of tone that simply cannot be attained with crystalline silicon or germanium (marketed as "solid-state") technologies such as transistors, FETs, opamps, diodes and even the latest digital modelling technologies. To my ear, transistors and FETs often sound overbright, clinical and even brittle sounding. They are also susceptible to overload and clip in a harsh and unpleasant way splattering the audio-band with unrelated harmonic content. With careful design these effects can be minimized, however tubes are inherently linear, have greater headroom and soft-clip if overloaded. In my opinion this makes appropriate tool for the job of audio signal processing, which is why I established Effectrode. Effectrode pedals are very forgiving and musical, characterized by a wide open, natural sound that's full of warmth and clarity. It's just about impossible to get a bad sound out of them.

Tube Life and Servicing

The tubes operate at 300 Volts D.C. Our high voltage power supplies are fully regulated and smoothed to ensure low noise. There are some manufacturers of tube pedals are operating tubes at voltages as low as 12 volts. I guess this is for economic reasons or for lack of ability in H.T. (high tension) power supply design. It's certainly not for better tonal quality because low voltage operation (current starvation) of tubes sounds terrible - tubes are not designed to operate at low voltage.

To maximize tube life in our pedals, it is recommended that the pedal be allowed to warm-up for at least one minute after being switched on. This is so that the heater filament (the part that glows orange) in the tube to heat the cathode, which is coated with a layer of barium and strontium oxide. This oxide layer gets torn off the cathode, a process known as cathode stripping, if the cathode has not reached it's correct operating temperature. If operated well within their ratings, good quality signal tubes can last 100,000 hours or more; that's well over 11 years of continuous use. Should you need to replace a tube please be aware high D.C. voltages of up to 400 volts are present in the circuit. Whilst working on the power supply design for these pedals, I've experienced an electric shock or two and it's not a pleasant experience. Beware! To avoid an electrifying experience, refer servicing to qualified personnel only.

Tube Swapping

Customers often ask me what tube substitutions/equivalents they can use in their Effectrode pedals. I designed my pedals with this in mind, so the tubes are easy to access and replace. To remove a tube, first make sure that the pedal is disconnected from power. I advise that you undertake this job in a comfortable, well-lit situation - the kitchen table is a good place. This will help minimize the possibility of tubes being accidentally damaged and pins being bent during removal/insertion. A tube can be removed by gently wiggling with a circular motion and tugging it at the same time. There are several tube substutions that can be made in our Tube-Vibe and Tube Drive pedals.

Tube-Vibe

All Tube-Vibe (and Vibra Chorus) pedals ship with three tubes a 12AX7 tube and two 12AT7s fitted as standard. The 12AX7 is a high mu tube and is used as a gain and mixer stage. The 12AX7 tube is directly interchangeable with a few other miniature B9A double triode tubes including the European equivalent ECC83. I always recommend NOS JAN Philips Mil-Spec NOS, if they can be obtained. I cannot say enough good things about these tubes, they're mechanically reliable, electrically quiet and test well on my "Tube Imp" mini tube tester. The sections are well matched and the gains are usually measure closer to ideal than Russian and Chinese tubes. The JAN Philips 12AX7 is becoming a little difficult and therefore expensive to obtain as stocks become depleted, however the JAN Philips 5751 has aprroximately 70% and can be used as a substitution. The 12AD7 is also a superior replacement for the 12AX7.

Medium mu tubes, such as 12AT7, 12AU7, 12AY7 also work well in the 12AX7 position on the Tube-Vibe where they yield lower gain with the benefit of even more headroom.

Tube Drive

The tone and gain characteristics of the Tube Drive can be drastically altered by interchanging tubes - in fact the pedal was designed for easy access to the tubes for this purpose. It can be quickly and easily transformed into a hi-gain distortion beast, mellow blues driver or boost pedal by simply removing a tube and replacing it with a different type.

The tube in the 12AT7 position operates as an active tone boost and must be capable of high current drive. A 12AV7 will operate well here as substitute. This tube is not widely known and few people have caught on to using it, so there are still some very good bargins to be had on NOS (new old stock) tubes.

There are many possibilities for interchanging the tubes in 12AX7 position to customize the Tube Drive for specific applications or tailor the tone to personal taste. The Tube Drive ships with two high mu 12AX7 tubes for maximum gain which means the pedal produces creamy, super-saturated tones. If you find this a little "lively", you can tame things down by swapping them for lower mu tubes, such as the 12AU7 or 12AY7. For example, substituting the top 12AX7 for a 12AU7 takes some fire out the drive and the Tube Drive is transformed into a dedicated blues machine. Replacing the second tube with a 12AU7 reduces the gain even further, turning the Tube Drive into a clean boost pedal with plenty of headroom and dynamic range. The Volume and Drive contols have been designed to have a wide range to accomodate the use of different tubes in the preamp section of the Tube Drive. There are many other possibilities - medium mu tubes such as 12AT7, using equivalent and different manufacturers which yield variations in tone. The 12AV7 or 5965 is slightly lower mu then the 12AT7 with a different charactersitic curve. These work exceptionally well in the Tube Drive in position one and with a 12AX7 in position two to create an even, well-rounded overdrive response. I highly recommend trying one in there.

Tone Tip! I suggest all knobs set at quarter (9 o'clock) and use that as a starting point. All the control knobs on the Tube Drive have a wide range which makes it possible to achieve clean boost, blues, overdrive, distortion and modern saturated Soldano/Boogie tones from one pedal.