RO 5-Stage RCA Tube Preamp PUBLIC

Richter Original 5-Stage Guitar Preamp Using RCA Circuits

Richter Original 5-stage real-tube guitar preamp using circuit topologies from the 1965 RCA Receiving Tube Manual # RC-24 (p. 544, 545); "Low-Distortion Preamplifier" and "Bass and Treble Control Amplifier". Controls Include: Input Level, Bass, Mid-Center, Treble, Drive, and Volume. Intended for 6-string electric guitar. Both tube types are space-charge tubes designed for use with a single +12VDC power-supply for heaters AND plates (originally from a car battery). The tubes are available at The Tube Store. https://www.thetubestore.com . Experimental circuitry. Untested design. No simulation. Frequency Range 30 Hz to 16 kHz. Overall Gain +22 dBV (Vo/Vi = 10). Power-supply not shown. Requires a regulated single-polarity DC supply providing +12VDC @ >= 1A of current. Example: 12V DC 1000 mA Regulated Switching Power Adapter, Product ID: 798. $8.95. From the AdaFruit website. https://www.adafruit.com . Notes On The 12DZ6: The 12DZ6 is a space-charge pentode that works from a +12V supply-voltage on heater AND plate. Not originally designed for audio but is acceptable for audio due to grid-1-to-plate interelectrode capacitance <= 2 pF (being 0.15 pF). It is used here to provide a clean input stage with bright upper mids, low-noise gain of 5, an articulate vintage tone, and limited low-end. Notes On The 12U7: The 12U7 is a space-charge twin-triode preamp-tube which also works with a 12V supply-voltage on heaters AND plates. It was engineered to sound like a 12AU7 with a high-voiltage supply, and with the same gain (mu = 20), despite being a low-voltage tube. It is not a "starved" 12AU7, but is a different tube designed to work and sound like a 12AU7 but using a 12V supply, which the 12AU7 can use if starved fashion but sounds weak and thin, while the 12U7 sounds much the same as a 12AU7 operated normally. Thus, its overdriven tone is also the same; warm and smooth, with pronounced midrange, full gain, and emphasis on even-order harmonics, resulting in a sweet singing type of distortion, just like a 12AU7 at high-voltage. Here, the 12DZ6 input stage will be harder to overdrive than most input tubes, but the cascaded 12U7 triodes in subsequent stages will be easy to overdrive, depending on control the settings.