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Audio and Video Talk
Valves / Vacuum Tubes
De-constructing a burnt out vintage power transformer
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<blockquote data-quote="Mars" data-source="post: 617771" data-attributes="member: 817"><p>Things are coming to a head with the guitar amplifier. The power transformer has been manufactured and the amplifier is playing nicely. I measured some voltages, and they threw more light onto what the original design might have been.</p><p></p><p>I measured the voltage across the shared EL34 cathode resistor (25.6VDC). Thus the two EL34's conduct about 121mA. Voltage across anode to cathode is about 400V (a bit higher than expected).</p><p></p><p>When I return to the Duncan PSU designer, I can see why.</p><p></p><p>The lower current draw of the EL34's cause the B+ to climb. If I adjust the off load AC voltage of the PT to 350VAC per section, I get a better result:</p><p></p><p><img src="https://lh3.googleusercontent.com/-swLp1l06VzE/VhtuY2o4omI/AAAAAAAAHRc/BePVomTOEe4/s640-Ic42/EL34-PP-GZ34-kitaaramp-350-0-350.psu%252520%25255D.png" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p></p><p></p><p>I adjusted the design (increased the flux on the core to lower the Cu losses and balanced the Fe and Cu losses) on Yve's PT designer and got this:</p><p><img src="https://lh3.googleusercontent.com/-Ww3ro9GiRIU/VhtvO5DCgpI/AAAAAAAAHRs/twjMQIWKkH0/s912-Ic42/EL34PP-GZ34-kitaaramp-Cu-Fe-losses-dieselfde.psx.png" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p></blockquote><p></p>
[QUOTE="Mars, post: 617771, member: 817"] Things are coming to a head with the guitar amplifier. The power transformer has been manufactured and the amplifier is playing nicely. I measured some voltages, and they threw more light onto what the original design might have been. I measured the voltage across the shared EL34 cathode resistor (25.6VDC). Thus the two EL34's conduct about 121mA. Voltage across anode to cathode is about 400V (a bit higher than expected). When I return to the Duncan PSU designer, I can see why. The lower current draw of the EL34's cause the B+ to climb. If I adjust the off load AC voltage of the PT to 350VAC per section, I get a better result: [IMG]https://lh3.googleusercontent.com/-swLp1l06VzE/VhtuY2o4omI/AAAAAAAAHRc/BePVomTOEe4/s640-Ic42/EL34-PP-GZ34-kitaaramp-350-0-350.psu%252520%25255D.png[/IMG] I adjusted the design (increased the flux on the core to lower the Cu losses and balanced the Fe and Cu losses) on Yve's PT designer and got this: [IMG]https://lh3.googleusercontent.com/-Ww3ro9GiRIU/VhtvO5DCgpI/AAAAAAAAHRs/twjMQIWKkH0/s912-Ic42/EL34PP-GZ34-kitaaramp-Cu-Fe-losses-dieselfde.psx.png[/IMG] [/QUOTE]
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Audio and Video Talk
Valves / Vacuum Tubes
De-constructing a burnt out vintage power transformer
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