Re: R4C power supply question
¿ªÔÆÌåÓýDoug, ? Yes it had to do with reducing audio hum.? The whole power supply was poorly designed from day one with too much ripple in the 150 volt, -70 volt and 14 volt supplies.? In this case I think it reduced 120 Hz hum and made 60 Hz hum worse which wasn¡¯t reproduced as well by the speaker.? ? I must have sold 500 or more total replacement power supply boards that got rid of the ripple (hum) and eliminated the two 5-watt dropping resistors.?? Once the 12-volt three-terminal regulator came along, I never understood why Drake never redesigned the power supply.? Eliminating the heat from those two dropping resistors, plus replacing the power? hog audio amplifier, made the PTO more stable. ?The replacement boards were the RPS-4 and AMP-4. ? Rob, NC0B ? From: [email protected] [mailto:[email protected]]
On Behalf Of Doug Crompton WA3DSP
Sent: Tuesday, March 21, 2023 12:02 PM To: [email protected] Subject: [DRAKE-RADIO] R4C power supply question ? In comparing early and later R4C power supply schematics, a capacitor (C201) was added going from the output of the low voltage diodes to the high end of the filament string. It is listed as 20uf 150V. I am attaching a schematic showing
it. I was wondering what its purpose was and why it was added. Does anyone have any ideas? I thought it might have something to do with audio hum.?
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Rob Sherwood