Analog Applications Journal Texas Instruments Incorporated 4Q, 2013 www. HighPerformance Analog Products Lowcost solution for measuring input. Power Supply Design for Vacuum Tube Amplifiers using Rectifier tubes. Power Factor The power factor of an AC electric power system is defined as the ratio of the real power to the apparent power, and is a number between. Do you have any additional comments or suggestions regarding SAS documentation in general that will help us better serve youVacuum Tube Power Supply Design. Introduction Tube Power Supply Design. Its time for a little confession I dont always spend as much time on my power supply designs as I should. Sometimes I get excited about my latest circuit and after looking for just the right tubes, output transformers, coupling caps, and low noise resistors, the power supply design becomes almost an after thought. Sometimes things turn out ok and there are no problems. Other times I end up with bad voltages, unacceptable power supply sag, channel crosstalk, or worst of all, a hum that I just cant seem to eliminate. Its at these times that I always wish I had taken a little more time to get it right. Offline Activator For Windows And Office Kmspico Setup Edition'>Offline Activator For Windows And Office Kmspico Setup Edition. The truth is, there is no reason to suffer power supply set backs like this. The design of basic tube power supplies is actually very straight forward. And, if we rely on the excellent work of those whove come before us O. H. Schade, N. H. Roberts, D. L Waidelich, H. J. Reich, we dont even need to tackle any advanced math or taxing mental gyrations to arrive at some truly excellent power supply designs. What Id like to do here is to walk through a design process first recommended by O. H. Schade. 1. in 1. Herbert Reich. 2 in 1. Theory and Applications of Electron Tubes. Now, the state of electronics has changed somewhat in the 6. Schade first published his landmark work. As such, I will present again, a somewhat modified version of this process more suited to todays amp builders and hobbyists. This process uses only simple equations and Schades original graphs as modified by Reich. Even those builders who are unfamiliar or uncomfortable with advanced mathematics should have no problems using this approach. The entire process relies on assuming that the rectifier, when conducting, acts like a resistor. So if you can figure out how this resistance acts at your planned load current, you can get your power supply design just right. I am going to work through the procedure by designing a supply for a mythical low power stereo amplifier. Its a stereo single ended class A design Ill refer to as the Ghost amp. I will first present the process for each step and then fill in some numbers to show how the process works. I urge readers to read the entire design process first and then go back and look closely at the math. Its not advanced, but it can be a little intimidating the first time through. As I work though the process, I introduce new variables and identify them with unique letters and symbols. References. 1Schade, O. H., Proceedings of the I. R. E, 3. 1, p. 34. Reich, Herbert J, Theory and Applications of Electron Tubes, 2nd Ed., Mc. Graw Hill, 1. 94. Table of Contents. Part 1 The Basic Power Supply. Power Factor Correction Calculation Example Pdf' title='Power Factor Correction Calculation Example Pdf' />Part 2 The Smoothing Filter. Part 1 The Basic Power Supply. Power Supply Constraints and Choices. The first step is to determine the total load for your power supply. This is the B voltage required by your amp, and the total load current for all plate supply and screen supply voltages. If you are building for a stereo amplifier, be sure to include both channels. I will refer to these as VL and IL respectively. Also required is the mains voltage and frequency where the amp is to be used. This will affect your transformer selection and your overall power supply design. Power Factor Correction Calculation Example Pdf' title='Power Factor Correction Calculation Example Pdf' />These I will refer to as VM and f. M respectively. For the Ghost amp, each channel requires a B voltage of 2. I Up Pro Activation Key'>I Up Pro Activation Key. A at idle and 6. 5m. A at peak output. So VL2. 50v and IL 2 6. A 1. 30m. A. Here in North America the main power is 1. Hz so VM1. 20v and f. M6. 0Hz. These will be our starting points. So summarizing, we are starting with the following conditions. Now we need to choose a topology. Our basic options are a single diode half wave rectifier, a dual diode full wave rectifier center tapped transformer secondary, or a dual diode full wave voltage doubler. There are other topologies of course, but these three are the most suitable for high fidelity amplifiers. For the Ghost amp I will choose a full wave dual diode rectifier. This topology has advantages over the half wave circuit in that the ripple is lower and the ripple frequency is twice as high making it easier to filter. The dual diode voltage doubler shares these characteristics but since the required VL is fairly low by tube amp standards, there is no need to deal with the added complexity of the voltage doubler. I am also going to choose to use a capacitor input filter. I could also use a choke input filter, however the choke would require a much higher transformer secondary voltage and a larger choke than the capacitor input filter. This would drive up the size and cost of the power supply and small and cheaper is better than large and more expensive. The First Calculations Currents and Voltages. Now that we have the basic electrical constraints and have chosen a topology, its time to start estimating the electrical parameters which will drive the power supplys operation. The first of these are the diode plate currents. Once calculated these will allow us to choose a suitable rectifier tube for our amplifier. The. average plate current in our full wave rectifier is simply one half the total load current one half for each diode. The peak plate current is more complex. Because the input capacitor only partially discharges on each half cycle, the diode can only conduct on that portion of the following cycle when the plate voltage exceeds the voltage to which the capacitor discharged between cycles. This means that the capacitor charging current must be significantly greater than the average plate current. Here we are going to make an assumption. Based on the typical performance of vacuum tube rectifiers we are going to assume that the effective peak charging current per plate is four times the average current. Later we will refine this estimate based on our preliminary results. So using this estimate yields the following result for the peak plate current. Now that we know the peak plate current it is time to choose a rectifier tube. Making this decision requires checking the tube data sheets, looking at max ratings and voltage drops, and applying some judgement and experience. There are some basic rules to apply which make this task easier. First, and most importantly, the maximum tube ratings must not be violated. We already have an estimate of the maximum plate current. But what about the diode peak inverse voltage. The diode will see this voltage when the capacitor is at max voltage, i. VL, and the transformer winding is at the peak opposite voltage. An Algorithmic Approach To Hemostasis Testing. Since we cant as yet estimate voltage drop in the rectifier, it is good to assume its zero so the peak inverse voltage on the diode will be the load voltage plus the peak AC voltage from half of the center tapped secondary. Since we dont know our secondary voltage yet well estimate its RMS value as the the same as VL. This means that the peak inverse diode voltage will be as follows. There is one other important parameter which is the diode voltage drop. While the amp is at idle, the voltage drop across each diode will be one voltage, and when the amp is approaching full power the current draw will be greater and the diode voltage drop will be greater. This will result in what is known as power supply sag. For class A operation such as our Ghost amp, sag is generally not a major consideration current change is only 1. AB or B operation, sag can become a major issue. Because we are shooting for a high fidelity amplifier we will want to limit sag as much as possible.