The Fairchild tube PSU is part of the Fairchild Perspectasound system first used on Disney's Fantasia.
While the EMI RS61 pairs are connected the heater voltage supply is measured to be 5.8V. This may not be bad as underheated tubes may make better and less noisy preamplifiers.
With both RS61 operating, the high tension output of the PSU is 340V.
One external voltage dropping resistor of 27KΩ for each preamplifier drops the voltage to 170V.
It was found by experiment that these RS61 operate more quietly at this order of HT and perhaps even lower. What were the original PSU requirements of the RS61?
Terminating the RS61 with a 560Ω resistor and a VTVM and singing very loudly the output could not exceed 20dBm.
When singing softly the output was around 0dBm. So it seems the Pleiades V0 drives them quite hotly.
Signal path setup:
Beyer M55 500Ω unbalanced, at 1in - 300mH (500Ω:50KΩ) inline transformer - Pleiades V0, 12V battery in series with 4R7 - EMI RS61 - 560Ω resistor shunt - Belco VT-250 VTVM
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