Sound reference kt88 tube power amp5/27/2023 ![]() ![]() The rear panel has five-way speaker binding posts, with 8 ohm and 4 ohm “taps” (these are connected to different positions on the output transformer). But if you have small children, leave the cover on. The chassis is gloss black enamel, and the cover for the tubes can be removed to aid in dissipating heat. The input stage delivers the voltage, and the output stage delivers the current. So, with the pa21, for each channel, there are two triodes in the input stage and two triodes in the driver stage (each channel has two 6SN7’s and there are two triodes in each tube), and two pentodes in the output stage. Pins 7 and 8 are the heater for the two cathodes (6 and 7), pins 1 and 4 are the two grids, and pins 2 and 5 are the anodes (plates). Here is a schematic with the actual pin-out arrangement, as viewed from the bottom of the tube. It is still used quite often, such as in preamplifiers. It was used as the driver stage in audio amplifiers, and is electrically similar to the 12AU7. The 6SN7 is a dual triode, originating in 1939 from the US (the ECC32 is the European version). It can be operated as a triode by connecting the grids together. It has a cathode (2) which is indirectly heated by a filament (1), three grids (4,5, and 6), and the anode, also called the plate (3). The numbers are not the pin socket numbers, but are just for identifying the structures in the diagram. The first beam tetrode was the 6L6, which is still very popular in guitar amplifiers.Ī generic diagram of a pentode is illustrated below. So, the pentode design was modified such that it became a beam tetrode. The KT88, developed by MO-Valve, could not be an actual pentode, because Philips held the patent. The E元4 is a pentode rather than a beam tetrode, and was developed by Philips in 1953. The light green lines represent the “beam” of electrons that flows from the cathode towards the anode in the direction indicated by the arrows. Here is a diagrammatic representation of a beam tetrode. The control grid (Pin 5, g 1) and screen grid (Pin 4, g 2) are between the cathode and anode (Pin 3, a). The cathode (Pin 8) is indirectly heated by a filament (Pins 2 and 7, h). The KT88, introduced in 1956, is a beam tetrode, and a schematic with pin-outs is shown below. You can substitute E元4’s for the KT88’s, and switch the toggle on the side to give the proper bias voltage for the E元4’s vs. ![]() The pa21 has two gain stages, with the 6SN7s providing the input stage and the KT88’s at the output stage. Outputs: Five-way Speaker Binding Posts.MFR: 9 Hz – 52 kHz, ± 1 dB at 40 Watts Output.Design: Stereo Tube Power Amplifier, Push-Pull, Class AB.Trying different tubes is one of the things that makes tube products fun, and those who participate in this activity are called “tube rollers”. The Mysterè line goes beyond the PrimaLuna line with larger transformers, more power supply capacitance, and an auto-bias circuit that lets the consumer choose between using KT88’s or E元4’s as the output tubes. With the introduction of Durob Audio’s Mysterè line, we now review the Mysterè pa21, which is a 55 watt per channel stereo tube power amplifier. We reviewed the PrimaLuna DiaLogue Two integrated amplifier in December, 2009. Although the tube output stage and op-amp output stage sound different, one doesn’t necessarily sound “better” than the other, although tubeophiles would all opt for the “better”. Conventional CD players use op-amps in the output stage. It also has a discrete output stage with triodes running in pure Class A. Durob Audio is a company in the Netherlands that markets PrimaLuna tubed audio components, including integrated amplifiers, power amplifiers, and a CD player that has a tube-based clock. ![]()
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