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Old 28th February 2012, 06:04 PM   #1
Kmet is offline Kmet  Croatia
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Location: east part of Croatia / Europe
Default 12AX7 in starving mode Dynaco PAS3X

Hi there..

I make Dynaco clone of the famous PAS3X preamp (only the line stage) and I am very pleased with sound of this preamp. Some recordings are truly natural and fine to listen. Now I want to make analysis of the circuit and to solve puzzle of this sweet preamp.

My mindcrunching question is: whay did designer of this preamp make heather of the 12AX7 tubes on smaller voltage, 12xx tubes are
12,6Vdc but in preamp it is 11Vdc on heather. One reason will be longest lifespan of tubes but it is unlikely..
How this particular tubes works in heather starved mode?

I found some schematics of the HP tube voltmeters with input tubes in starved mode. Please give me some hints..thanx

Solder smoke lover from Croatia
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Old 28th February 2012, 06:10 PM   #2
DF96 is offline DF96  England
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Slightly lower noise and smaller grid current?
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Old 28th February 2012, 06:22 PM   #3
Kmet is offline Kmet  Croatia
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Location: east part of Croatia / Europe
How aplification factor and internal resistance corespodent with lowering heather activity?
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Old 28th February 2012, 09:20 PM   #4
DF96 is offline DF96  England
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A cooler heater would mean reduced transconductance g<sub>m</sub>, higher anode resistance R<sub>a</sub>and probably virtually unchanged amplification factor mu.
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