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Audio and Video Talk
Valves / Vacuum Tubes
Ideas for MM valve phonostage
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<blockquote data-quote="Ampdog" data-source="post: 970199" data-attributes="member: 144"><p>Still not having checked back:</p><p></p><p>Long ago I read and used a slightly lower heater voltage on the heater of particularly the input stage - lower 'electron cloud' around the first grid and such. Worth a listen/measure test if one is able to do this, even with a pot in series with the heater . Some found about 5,7V most quiet, but a lot will obviously depend on the rest of the circuit. This could e.g. lower the operational valve Gm, which is again contrary to operation at maximum Gm for low noise.</p><p></p><p>Might be worth a test if one is able to control the heater voltage of the first stage only - - without again running wires all over the show. One must obviously give each heater test voltage/cathode time to stabilise at a new voltage before judging. Heater voltages of around 5,7V were reported best will depend on the valve apart from other matters.</p><p></p><p>Good test to examine whether heater voltage current and circuit layout et all has point is when powered up and listening, is to be able to suddenly turn off the heater supply and measure and listen for a low point in general hum interference as heaters slowly decrease down. </p></blockquote><p></p>
[QUOTE="Ampdog, post: 970199, member: 144"] Still not having checked back: Long ago I read and used a slightly lower heater voltage on the heater of particularly the input stage - lower 'electron cloud' around the first grid and such. Worth a listen/measure test if one is able to do this, even with a pot in series with the heater . Some found about 5,7V most quiet, but a lot will obviously depend on the rest of the circuit. This could e.g. lower the operational valve Gm, which is again contrary to operation at maximum Gm for low noise. Might be worth a test if one is able to control the heater voltage of the first stage only - - without again running wires all over the show. One must obviously give each heater test voltage/cathode time to stabilise at a new voltage before judging. Heater voltages of around 5,7V were reported best will depend on the valve apart from other matters. Good test to examine whether heater voltage current and circuit layout et all has point is when powered up and listening, is to be able to suddenly turn off the heater supply and measure and listen for a low point in general hum interference as heaters slowly decrease down. [/QUOTE]
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Audio and Video Talk
Valves / Vacuum Tubes
Ideas for MM valve phonostage
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