How To Build A 12AX7 Gain Stage Part 3 HD

Trenton Blizzard shows you how to build a 12AX7 Gain Stage on an Electronics Breadboard. Web: www.trentonblizzard.com Blog: www.trentonblizzard.blogspot.com Share this Video: https://youtu.be/qi1JoKZ6umU Subscribe To My Channel and Get More Great How-To Videos SUMMARY A 4 part video series showing how A single common cathode 12AX7 amplifier stage is designed that could be used as the front-end stage of a DIY tube amp or a DIY vacuum tube guitar amp. Part 1 Multisim spice simulation is used to create and simulate a single stage 12AX7 vacuum tube gain stage. The basic model used by Multisim does not require any heater power to simulate. A high voltage DC source of 250V is used as the simulated power supply. A 100k ohm plate resistor along with a 1k ohm cathode resistor are used to set bias. A grid resistor of 1M ohm is used as the input resistor so a guitar can be easily plugged into it without signal loss. A .01uF capacitor is used as the AC coupling cap and forms a high pass filter around 15Hz. PART 2 The 2 channel oscilloscope is used to view both the input and output signals. The oscilloscope is DC coupled at first. But, then switched to AC couple to view the output signal. The stage output is almost 40Vpk or 80Vpk-pk with an input signal of 1Vpk at 1kHz. An AC "Bode" plot is performed that shows both gain and phase versus frequency. The phase plot confirms the 180 degree phase change that happens with a single common cathode gain stage. The AC Bode plot shows the output, in db, versus frequency from 10Hz to 100kHz. Markers are used to determine the -3db point of the low frequency response. A DC plot was performed to demonstrate the DC potentials on the plate and the cathode. The DC current was used to explain that a vacuum tube amplifier stage is a series circuit for DC currents. PART 3 A common cathode 12AX7 gain stage is constructed using vacuum tube breadboard adapters. These adapters were once available to DIY audio builders back in 2007. The equipment, such as a high voltage tube power supply, is described for operation and hook-up. PART 4 The DC and AC performance are measured using a DMM (digital multimeter) and an oscilloscope. The results from the real world 12AX7 gain stage is compared to the simulation results. White papers for biasing 12AX7 and 12AU7 tube stages can be found at www.trentonblizzard.com Ask Me A Question http://trentonblizzard.blogspot.com