There’s a magic in building audio amplifiers that I’ve never found in a thousand microprocessor projects and — if that amplifier happens to glow in the dark with the soft light of vacuum tube filaments — so much the better.
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Capacitors C102/C202 are 0.01 µF 400V "Orange Drop" components from Antique Electronic Supply (AES). Unfortunately, the AES part number given, C-PD022-400, is for a 0.022µF capacitor — the correct part number for the 0.01µF component is C-PD-01-400. If you already bought the 0.022µF capacitor then there's no need to return it — it'll work just fine in this circuit, however you may have to "form" the leads a bit to get it to fit on the PC board.
In the power supply schematic the 47K 2W bleeder resistor is marked "R1" but it's actually R3 in the parts list.
Spare Time Gizmos is currently shipping Revision D of the 6T9 printed circuit board. This differs from the one described in the article in that an additional 47µF 450V filter capacitor, C3, has been added in parallel with C1. This will reduce residual hum in the power supply to inaudible levels. C3 is shown in the current schematics from our downloads page, but not in the article.
What’s in the zip?