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Audio and Video Talk
Valves / Vacuum Tubes
SCC88/PCC88 heaters in series?
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<blockquote data-quote="Moonraker" data-source="post: 1095411" data-attributes="member: 24248"><p>What voltage is applied when the current draw is observed to be maybe 15% off spec? The voltage indicated on the data sheet? The point is, that voltage is an indicative value only and the 300mA is the overriding spec. </p><p></p><p>So ideally, one would use a 300mA current source to drive P- tubes for the correct heating power. They are tubes where heater current and not voltage is the primary spec. The current will be correct and the voltage should then be near the datasheet-indicated value. </p><p></p><p>If the voltage deviates, so be it. After all, consider the analogous situation : when E-tubes are driven off 6.3V the current drawn should be at or near the indicated value but deviations are seldom reason for anxiety, and indeed seldom observed in the first place.</p><p></p><p>For even lower hum one could use the U series tubes (100mA). Or even lower, as Neumann did with the VF14 microphone preamplifier. </p></blockquote><p></p>
[QUOTE="Moonraker, post: 1095411, member: 24248"] What voltage is applied when the current draw is observed to be maybe 15% off spec? The voltage indicated on the data sheet? The point is, that voltage is an indicative value only and the 300mA is the overriding spec. So ideally, one would use a 300mA current source to drive P- tubes for the correct heating power. They are tubes where heater current and not voltage is the primary spec. The current will be correct and the voltage should then be near the datasheet-indicated value. If the voltage deviates, so be it. After all, consider the analogous situation : when E-tubes are driven off 6.3V the current drawn should be at or near the indicated value but deviations are seldom reason for anxiety, and indeed seldom observed in the first place. For even lower hum one could use the U series tubes (100mA). Or even lower, as Neumann did with the VF14 microphone preamplifier. [/QUOTE]
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Audio and Video Talk
Valves / Vacuum Tubes
SCC88/PCC88 heaters in series?
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