PH3 phono preamplifier


My brother decided that now was the time to join the world of vinyl records and then needed a phono amplifier. We looked at different alternatives and ended up with a Audio Research PH3 clone as this looked promising and the schematic was to be found online.

My brother designed the amplifier according to the schematic found at and we decided to try to make our own regulated power supply as we had just discovered the high voltage (1,2 - 440V) LR8N3 regulator from microchip and wanted to try this. The regulator feeds a high voltage TIP162 darlington transistor to ensure enough current (30mA@210V) for the amplifier. We also use a PIC12F675 to delay the high voltage turn on until the tubes has pre heated for 30 seconds.

We had some difficulties getting genuine 2sk170gr, the first batch bought off eBay was not the real thing, they meassured more like 2sk170v's and a closer inspection made me suspicious as the surface looked grinded and irregular, take a look at for a more detailed description.

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