# 12ax7 cathode resistor

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Since the anode current here is 1.1mA and we need 1.5V bias, the bias resistor would be 1.5V / 1.1mA = 1.36k. A close standard is 1.5k. We don't have to get the bias voltage spot-on since the circuit is very self-adjusting. The output can either be taken directly from the cathode or from the junction of Rb and RK as shown. To use the Tube Dissipation Using Cathode Resistor Voltage Drop calculator enter your Tube Type and Plate-to-Cathode Voltage at the top of the page, then enter the Number of Tubes that share a cathode resistor, the measured Voltage Drop across the cathode resistor and the Cathode Resistor's Ohm Value and click Calculate. This is described in more detail below. We'll assume that the cathode bias resistor is bypassed with a capacitor, because that's almost always necessary to get the maximum gain and lowest noise. The absolute maximum input level is then determined by the voltage across the cathode resistor.

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Mar 04, 2008 · Im looking for some basic info... Lets say I havea gain stage with a 5.6K cathode resistor and a 1UF cap. If I change that to a 10K resistor and keep the 1UF cap, how might that effect the sound? Am I correct that the higher the resistor value the colder the bias? The only other thing Ive noted i... Cathode load resistor = 300V / 3mA = 100k ohm. Cathode bias resistor = Bias voltage / Idle current = 1V/1.35mA = 740 ohm At idle point, the tube will drop about 163V as seen from the graph. So the cathode idle voltage is equal to 300V - 163V = 137V. The grid will be at 1 V below the cathode so it will be running at 136V. Jun 06, 2016 · If I run the heaters in series not so much glow and less current consumption. I get better results with a 50K POT on the plate(anode) and a 10K POT on the cathode.

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Aug 31, 2012 · This, as we already know will lead to increased cathode current. Now we have a capacitor presented across the cathode resistor. The increased current WILL FLOW THROUGH the capacitor and charge it. That’s why we say that the capacitor is bypassing the resistor. Since this current does not flow through the resistor we have a steady cathode voltage. A resistor will increase voltage as the tube increases its cathode current, generating its own NFB. As the diode has the ability to change its forward current to maintain the voltage drop, it wouldn't fight the output so much, increasing gain for small-signal tubes and power output for output tubes.

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12AX7 cathode resistor values Hi, I must be missing something... I have used very low cathode resistor values, down to ~380 ohms on a 12AX7 preamp tube-second stage, with what I think are very pleasing distortion/gain results. The cathode voltage is elevated by connecting it to ground through the resistor R k, generally called the cathode resistor, as shown in Figure 12. Given that, generally, there is an anode current also at the quiescent state, the resistor R k produces a voltage drop from the cathode to ground so that the cathode voltage is above ground.

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Since the anode current here is 1.1mA and we need 1.5V bias, the bias resistor would be 1.5V / 1.1mA = 1.36k. A close standard is 1.5k. We don't have to get the bias voltage spot-on since the circuit is very self-adjusting. The output can either be taken directly from the cathode or from the junction of Rb and RK as shown.

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Since the anode current here is 1.1mA and we need 1.5V bias, the bias resistor would be 1.5V / 1.1mA = 1.36k. A close standard is 1.5k. We don't have to get the bias voltage spot-on since the circuit is very self-adjusting. The output can either be taken directly from the cathode or from the junction of Rb and RK as shown. (4) To force the bias-point, the correct self-biasing cathode resistor is chosen, or better, several tubes are set up in a rig, and the resistor is selected by experiment to put the bias-point in the best compromise position between the acceptable range of tube samples. Mar 04, 2008 · Im looking for some basic info... Lets say I havea gain stage with a 5.6K cathode resistor and a 1UF cap. If I change that to a 10K resistor and keep the 1UF cap, how might that effect the sound? Am I correct that the higher the resistor value the colder the bias? The only other thing Ive noted i...

Modifying Preamp Circuitry Page 1 This is a great dissertation on how to modify and change guitar amp preamp circuits to your liking. I don't remember where I found this on the internet; I've had it for several years. The cathode bias resistor value is found by dividing the absolute value of the operating point grid voltage by the operating point cathode current (plate current plus screen current). The power dissipated by the cathode bias resistor is the product of the square of the cathode current and the resistance in ohms. The 12AX7 in V2 may not be the best choice for a cathode follower, since the 12AX7 is designed to be a high-gain voltage amplifier. It’s not designed to supply significant amounts of current. It also has high internal impedance, which is part of the problem we’re trying to solve in the preamp/tone stack interface.

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It uses a 12AX7 with a 280V supply voltage, 10k unbypassed cathode resistor and a 100k plate load resistor. The following circuit load is a 470k attenuator resistor and 470k grid leak resistor in series for a total impedance of 940k. In other words, if you are careful, you can easily get excellent performance from a cathode follower. This doesn't mean that the stock cathode follower cannot be modified or improved. For example, we can replace the cathode resistor with a constant-current source, either a tube-based or solid-state effort—or even an inductor. The cathode voltage is elevated by connecting it to ground through the resistor R k, generally called the cathode resistor, as shown in Figure 12. Given that, generally, there is an anode current also at the quiescent state, the resistor R k produces a voltage drop from the cathode to ground so that the cathode voltage is above ground. In other words, if you are careful, you can easily get excellent performance from a cathode follower. This doesn't mean that the stock cathode follower cannot be modified or improved. For example, we can replace the cathode resistor with a constant-current source, either a tube-based or solid-state effort—or even an inductor. After finished my simple 12AX7 tube preamp, I decided to try other medium mu tubes, including this 12AU7 and also the 6922. The design is exactly the same as the 12AX7 preamp, it is a single gain stage triode tube with cathode follower. Mar 22, 2011 · This is achieved by choosing a plate resistor of twice the internal plate resistance of the tube, which for a 12AX7 is approximately 50k requiring a plate resistor of 100k, then choosing a bias resistor so that plate voltage is 2/3 of B+.

Mar 22, 2011 · This is achieved by choosing a plate resistor of twice the internal plate resistance of the tube, which for a 12AX7 is approximately 50k requiring a plate resistor of 100k, then choosing a bias resistor so that plate voltage is 2/3 of B+. Calculate Plate Dissipation In Cathode Biased Output Stage Based On Voltage And Resistance Readings In these calculations, 5% of the cathode current is assumed to be screen current. With multiple tubes sharing the same cathode resistor, this calculator assumes the tubes are fairly well matched. Recommended configurations for the 12AX7 are below: Since the cathode resistor is bypassed for audio frequencies by the 100uF capacitors, gain will be set by the transconductance of the tube under the operating conditions, as shown in the above diagram.

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You would not get much of an increase from eliminating the resistor but you should be aware that a 12AX7 is like two triode sections of a 6AV6 which has been used in radios for ages. In radio use, the cathode is grounded and the bias comes from contact potential, the impingement of electrons from the cathode on the grid. The ECC83 / 12AX7 is a weakling in this regard, although for guitar applications it is often 'good enough'. Designing an AC Cathode Follower For the following example we will design a cathode follower to act as a buffer for an effects loop.

12AX7 circuit, biased at 2 mA, with a plate load resistor of 100k, next stage grid resistor 470k. Cathode biased using 1k bypassed with a big capacitor + 470 ohms additional unbypassed resstor. Cathode biased using 1k bypassed with a big capacitor + 470 ohms additional unbypassed resstor. A 12AX7 voltage amplifier with a 100kΩ plate load resistor and a fully bypassed cathode resistor has become ubiquitous in guitar amplifier design. The Preamp Gain and Output Impedance calculator displays familiar values: 36dB and 38kΩ for unloaded voltage gain and output impedance. Jun 14, 2014 · In this milestone video (Rusty and my 100th) Cathode Bypass Capacitors (CBC) are discussed, with emphasis on their influence upon both gain and tone. Audio spectra associated with several values ...