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Adding a coupling capacitor allows us to compress the power supply voltage. In the previous circuit the B+ was 300 volts, while in this variation, it is 170 volts. Of course, all the benefits of using a lower voltage would obtain with the added advantage that the cathodes are electrically closer in this variation, which makes heater-to-cathode voltage limits less of a concern. |
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Next month we will continue the hybrid thread, as we have only just touched on a few of the many possible ways that solid-state and vacuum tubes can be married. High voltage solid-state devices: |
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NPN Transistors 2N6800 |
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PNP Transistors P-Channel MOSFETs 2N6800 |
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A low noise, high gain phono preamp could be made from this circuit. The RIAA equalization is achieved passively in between two stages for MM cartridges and between three stages for MC cartridges. |
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pg. 13 |
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