Marshall JCM 800

Marshall made several amplifiers under the "JCM800" name, but most noticeably were the 50 watt 2204 and the 100 watt 2203. Because the valve industry had begun to fade and Marshall became worried that the standard power valve, the venerable EL34 would soon become unavailable, a number of JCM 800s were factory equipped with the 6550 beam pentode power valve, a valve with a different tonal character. Some people (notably Ozzy Osbourne guitarist Zakk Wylde) loved the resulting sound, but it was generally considered to be a downgrade in sound quality. The 6550 is a high power tube that is more common in valve-driven bass amplifiers because it allows a higher output power over the EL34 for a given distortion level and because it has a very crisp low and high end sound. Because many players desired more power amp distortion (which is considered more "pleasant" than pre-amp distortion, which these Marshalls still had plenty of), the prices for EL34s, especially vintage ones, skyrocketed for use in Marshalls. Marshall would not return to full time use of the EL34 in all of its valve amps until the rise of vacuum tube factories in the mid and late 90s when former Soviet countries made most valve types plentiful again.