813 SE triode amps

Posted on Feb 6, 2014

This is a single-ended triode amp that I built using the 813 transmitting pentode, connected as a triode. It`s a fairly powerful SE amp that works very well. It uses a single pentode as the driver (a 12HG7 video amp tube), and a solid-state power supply with a microprocessor controller. This amp generates around 1000 volts, and the power supply d

813 SE triode amps
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escribed below can deliver a lot of current. The result is that there is a real hazard from the voltage and energy available. DO NOT TRY AND BUILD ANYTHING LIKE THIS UNLESS YOU ARE COMFORTABLE WITH HIGH VOLTAGES, AND ARE FAMILIAR WITH THE RISKS! Don`t come looking for me if you start a fire or electrocute the cat! When working on high voltages, keep one hand in your pocket, and NEVER LEAVE ANYTHING TURNED ON UNATTENDED! You`ve been warned. The main peculiarity of the amp circuit, I guess, is the single-tube pentode driver. I experimented quite a bit with the 12HG7 and 12GN7A tubes, both of which are high Gm pentodes designed as video output amplifiers for color TV`s. They are amazing devices, capable of providing very low distortion, high gain, and low output impedance all at the same time. much better than you can get with any single triode I`ve seen. The driver has a very nice harmonic profile, with the 3rd harmonic always below the 2nd. At lower levels, the 2nd is about the only harmonic that`s measurable. For some reason pentodes seem to have the reputation for creating more high-order harmonics, but it`s simply not true in a single-ended design. This driver tests, and sounds, better than any of the possible two-triode drivers I tried, like 6SN7 direct-coupled, or 6SL7 SRPP. It also does much better than a 6C45pi-E. I also tried these tubes triode connected with a CCS, and they did well that way - about the same as a...

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