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In other words, if only one choke were used, the power supply noise would decrease greatly. But two chokes in series serve to decouple both the power supply connection and the ground.
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The sneakiest trick would be to use a dual center-tapped power transformer instead of the chokes. The transformer's VA rating should at least equal the amplifier's output wattage.
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Center-tapped choke and isolation transformer
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The transformer's core cannot abide unbalanced DC current, as it is not air-gapped. But by using a balanced current flow for the output tubes means that we have ensured that there is no net DC unbalanced current with which to contend. The B+ connection could be made at the primary's center-tap and the ground connection at the secondary's center-tap. Definitely, the low cost, small size solution.
If anyone experiments with these ideas, please share your results with us.
//JRB
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Voltage division within three voltage dividers
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Still, just the halving of the power supply noise is a worthwhile goal. In fact, this ratio could be improved upon by using a larger valued choke on the top portion of the circuit.
The cost and size of normal chokes is indeed prohibitive, but as this circuit uses a balanced current draw through the output tubes, a center-tapped choke or a common mode choke could be readily used. These chokes are smaller and less expensive than unbalanced chokes.
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www.tubecad.com Copyright © 2000 GlassWare. All Rights Reserved
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