THE POWER AMP SECTION Unique two stage cascaded power amp The first stage comprises a pair of EL84s in a self biasing class A push-pull configuration. This stage generates fantastic tone whether the amp is run clean, bluesy or flat out.The second stage uses two (G120 model) or six (G400 model) KT88s which deliver masses of power over a very wide frequency spectrum. Individual bias controls and current meters On the back panel there are six separate bias controls and six digital meters (two on a G120), one for each power amp valve. When you buy a matched set of valves they are selected to have similar plate dissipation characteristics, however, these change throughout the life of the valve. Within a couple of weeks the valves are no longer matched. With an OX amp the valves do not need to be matched. They can be matched in the amp and then readjusted at regular intervals throughout their lives. Harmonic switch Changes the character of the power amp by increasing the ratio of even to odd harmonics giving a smoother, less abrasive sound. Triode switch The power amp valves can be switched between pentode and triode mode. This reduces the power, and again gives a uniquely different character to the sound which is more mellow with less headroom. Bass boost switch This is not just a switch to alter the character of the preamp tone controls. It is an integral part of the power amp and drops the lower cutoff frequency by about 15Hz. Massive transformers Both the power transformer and the output transformer are huge. Most valve amplifier transformers limit the bass frequencies because they just don’t have enough iron in them. This means that the flux induced tends to saturate and limit the power which makes it all the way from valve plates to the speakers. We use M6 grain oriented steel in thin laminations which increases this low frequency efficiency very significantly. Output transformer protection The most common cause of major damage to valve amplifiers is running them either without, or with an incorrect load. This can be because a cable has become damaged or even in some cases because a speaker fails. All our power amps monitor the speaker load and will revert to standby mode if a problem occurs. This protects the output transformer and valves before they are damaged. Point to point wiring and hi-spec components We only use high grade audio components which are rated well beyond the use to which we put them. These components are point to point wired by hand using traditional tag strips mounted on a unique star connected grounding frame. About the preamp design