“Really early guitar amps were often designed for use with accordions, steels and microphones,” says Neil. “The earliest British one I’ve seen is from 1947 – the Vortexion model EG/10, which was advertised in Wireless World as the ‘AC/DC amplifier’. Valves in guitar amps are generally providing amplification (preamp valves), power (power valves) and rectification. In the UK, we often refer to a 12AX7 twin triode preamp valve as an ECC83, after the Philips/Mullard designation. Another wellrenowned preamp valve would be the British Mullard EF86 pentode you find in some classic Vox designs. Common power valves include the EL84 and EL34, which are Philips/Mullard in origin, and the American 6L6 and 6V6 found in Fender amps.
“Rectifier valves, such as the GZ34, EZ81, 5Y3 and 5U4GB and so on, convert AC mains supply to DC voltage. If the amp worked purely on AC, it would be very loudly humming at 50 or 60Hz. It’s also known as the ‘rectum frier’ because get things wrong and that’s what happens! When you hit the strings and draw power from the rectifier, the voltage of the whole system drops momentarily. People like that sag and compression – the way the amp squashes and then blooms a little bit.” [RB]