Cathode bias calculator. This calculation assumes a monoblock power amplifier.

Cathode bias calculator. A close standard is 470 ohms and will do fine.

• Cathode bias calculator The grid-leak resistor (Rg) can be found by consulting the datasheet for the maximum allowable value in cathode bias. According to the bias calculator plate dissipation is around 21W (85%). The first is cathode bias or self bias, just like with an ordinary gain stage. 5 volts we would use the intersection of the red plate load line and the -. If you have a Vpp= 360Vdc, and are deriving -65Vdc of bias by means of cathode bias, then your Vpk= 360 - 65= 295Vdc. However, I'm wondering if it might be a good idea to make the cathode bias adjustable? 560 ohms is the planned cathode resistor, but what about changing that to, say, a 500 ohm resistor and 100 ohm pot in series? That would put the pot at roughly midpoint. This calculator is for Enter the measured Plate-to-Cathode Voltage (voltage between the plate and cathode tube socket pins). This current is usually expressed in amperes or milliamps. 2 volts, which means the tube is running at a grid bias voltage of -13. blogspot. Cathode biased amps are less efficient than fixed bias amps. It has a database of 36 tube types and will calculate the Class A Fixed, Class AB Fixed Bias and Cathode Bias Subtract the cathode voltage from the plate voltage to get Va-k. That's true. 5V. - check the true resistance of your cathode resistor. More Information The grid-leak resistor (Rg) can be found by consulting the datasheet for the maximum allowable value in cathode bias. "You measure the Fixed bias allows for correct bias at higher plate voltages. blue andry. 3 Gain of the voltage amplifier with self-bias The Tube Bias Calculator will calculate power tube bias dissipation and % max. -User Name-Password You calculate the cathode current by dividing the cathode voltage by the cathode resistance. This current is crucial for setting the correct bias, ensuring optimal performance, Bias adapters will properly measure the cathode current on most all amplifiers, even if they do not offer a bias settings (certain Music Man amps are an exception). All of my cathode-bias style builds to date have been 2xEL84 based. 6K 470r cathode resistor, and 355V (315V is typo) 3. the mu quoted on the datasheet when operating in triode mode. 320v/8 = 40v, so if you biased the control grid to 40v below cathode voltage (by applying fixed bias of -40v to G1 or elevating the cathode to 40v in cathode bias), plate current should be nearly shut-off. So because you have the combination fixed bias/cathode bias you may be ok to run them at that current level. Adjust the bias trimmer ("pot") until you get a reading across the 1-ohm resistor(s) somewhere in the 30-40 mV range, for everything but 6V6s or EL-84s. According to the Cathode Follower calculator, with a 220kΩ cathode resistor the output impedance is only 617Ω. The basic steps are outlined under “Instructions” on the This is a type of cathode follower that naive builders have done many times and has given CFs an undeserved bad reputation. You must enter Tube Type and Plate-to-Cathode Voltage above before calculating Tube The Tube Bias Plate Current Calculator is designed to measure the bias of vacuum tubes in amplifiers, specifically calculating the plate current. Cathode bias. The measured plate current was 31mA for one tube, and 33mA for the other tube. That's why they need to be so big. The operating point is set by providing the grid with an appropriate fixed negative voltage V g, with respect to the cathode. The cathode resistor puts the cathode above DC ground for bias purposes, but if you've got a battery providing bias there isn't any need for that. The calculator calculates a cathode follower's unloaded voltage gain (the gain without being connected to the next stage) and output impedance based on the triode's characteristics and the cathode resistor value. gain and impedances [not d. Enter your plate supply voltage and plate load resistor value. First a quick summary of the three main circuit methods for biasing: In a tube circuit that uses FIXED-BIAS (whilst producing music, the bias is fixed), the grid-bias voltage is supplied from a power source external to the circuit, sometimes using a battery but usually (more conveniantly) getting it from the transformer itself by insertion of a resistor (Rk) in the cathode Where im at is trying to calculate the bias resistor and bypass cap values for the 6V6. 1 Fixed bias; 3. 5v grid curve. 44 kB, 1224x1584 - viewed 169 Your just guessing and you can't just guess and run numbers through a bias calculator expecting to get it right. sgerus. I've got 375VDC between pins 3 and 8 on each 6V6, and 17VDC between Pin 8 and ground for each. Do these 2 values appear to be out of range for the 6V6? The amp sounds fine BTW. - measure the To calculate bias when you measure the plate current, such as when using the output transformer shunt current measurement, enter your Tube Type and Plate-to-Cathode voltage at the top of the page, enter the Plate Current and touch 'Calculate' and the Plate Dissipation and Dissipation% are shown. In this 4th video in the Resistor Video Series, we discuss the purpose and function of the Cathode Bias Resistor. In this way the grid voltage is negative with respect to the cathode voltage. In this case the bias point indicates an anode current of about 8mA, and Vgk = -3. I've looked at some of the 20w blackstar designs and they are cathode-biased push-pull with a That would imply a cathode voltage of 13. Based on the chosen parameters, the calculator will determine the appropriate bias current for the tube amplifier. Note that the 'anode' is sometimes called the 'plate'; Is anyone familiar with the Weber bias calculator? Weber Bias Calculator I am using it to calculate the dissipation watts and get results far from what I measure. That is what you should use to calculate plate dissipation Pa. After discussion of the theory of its oper In my forthcoming build cathode bias is the plan. Regarding tube safety, the self-bias cathode follower slowly establishes its working voltages, as the triode must first conduct before the high-voltage bias voltage can be established; whereas the fixed-bias quickly develops the high Break the existing cathode ground. You should use a resistor for each pair of output tubes or better yet a resistor on each EL84 for best results. The estimated THD is quite low, and the gain a bit on the high side for my purpose. With our tool, you can easily determine the ideal bias voltage and bias current for your tube amp, ensuring optimal performance and unmatched sound quality. System inventory. That allowed DC coupling without busting any heater/cathode ratings. T he calculation takes into The cathode follower, once again, does its job. ~ Un–bypassed Cathode Calculator ~ T his Calculator was originally made to support my Amplifier–Buffer project and can be used to calculate the a. 16 Watts (the way he calculated it) is Voltage across the cathode resistors is 40V and plate to cathode voltage is 380V. I plug these numbers into Weber's bias calculator (the voltage/resistor calculator method) and I get 10 watts per tube and 26ma plate current per tube . Our bias probe measures true bias current. A small capacitor Instructions. So much for premium ‘matched’ tubes. 6. It is a 5C5 circuit from 1953. Accordingly, we can use a grid leak resistor R l of 200K Ohm to give some margin to the resistance of the bias voltage circuit. Then by R=V/I, the Load Impedance must increase to properly absorb the power. Don’t trust the label. 2008-03-03 2:25 pm #14 The bias voltage keeps the quiescent current in the power output valves at the safe design value. The measured plate voltage was 425VDC, and the measured plate current was 39mA. S. Both scenarios utilize the existing power supply--no mods needed. The input signal is driving the grid to -1V. low The operating point of a vacuum tube is the position on the loadline, corresponding to the voltage and current measured at the anode in the quiescent status, that is when no signal is applied to the grid. Bias Calculation for EL84 tube A Cathode voltage: 12,8 V (measured from pin 3 to ground) Cathode resistor: 303 Ohms (measured in circuit) Cathode current: 12,8 V/303 Ohms = 0,04224 A Plate voltage: 395 V (measured from pin 7 to HPB - In the weber bias calculator ( of which I totally missed the note about cathode bias again! ) the note says the assumption that screen current is 5% of the cathode current. grid configuration, cathode bias voltage) as determined by specific performance requirements such as gain, linearity and efficiency. The input coupling capacitor can be chosen in the usual way: by calculating from the desired cut-off frequency, or tweaking by ear. The bias resistor therefore needs to be: Rb = Vgk/Ia = 3. You need to be dropping some serious voltage across the cathode resistor, and that means either returning it to a negative rail or biasing up the grid with a voltage divider and capacitively coupling the input. To allow a reasonable signal swing, it Cathode bias often lends a natural compression or 'squishiness' to the sound, due to the increase in bias voltage when one valve enters Class B conditions, though the larger the bypass capacitor, the less will be this effect. cheers . 4K 130r cathode resistor. No - fixed bias is no cathode resistor and (therefore also) no bypass cap (so that the cathode then sits at 0V potential) - and the grid then has to have a negative DC voltage applied to it to drop it about 10V or so below the cathode (i. Read more about this in the support info section about triode curves fitting and why the classic Child-Langmuir equation was not used here. A close standard is 470 ohms and will do fine. For the moment, the best compromise I've found is the use of grid chokes with cathode bias. 10V and 754. Tube Dissipation Using Plate Current. According to Ohm's Law, to create a DC grid bias of -8V, the cathode current needs to be 8V / 188Ω = 43mA. This tube amp bias calculator allows you to select the tube type and amplifier class type (AB or A) to calculate the current. Click the green button. So I am trying to figure how to come up with load lines, output transformer impedences and then quiescent operating points and then be able to calculate what size cathode bias resistor based on this. . 5 ohms. That means they let a lot of cathode current flow compared to Class AB biased amps. 5mA = 470 ohm At the idle point, 6922 will lose about 160V as seen from the graph and the cathode voltage at the idle point Thanks guys. -User Name-Password. Welcome To the Hoffman Amplifiers Forum December 27, 2024, 04:50:52 pm: Welcome, Guest. operating point] of a any triode amplifier with a common cathode gain stage and a cathode follower output buffer so the overall gain is not significantly affected by the output load Rk is the cathode resistor, which is used to develop the cathode bias voltage. Scroll down to “measure bias by cathode resistor voltage drop”. 5V/0. It takes into account the plate current (the flow of electrons from the cathode to the plate) and the plate voltage (the potential difference between the cathode and the plate) to compute the plate dissipation. The AC 30 used a single cathode bias resistor of 50 Ohms for all 4 EL84s bypassed with 220uF. B. The 73V output sets the DC voltage at the grids of the triodes forming the long-tailed-pair phase inverter. Rob's instructions say if you are using a 12a*7 for the power amp and using both sides of the tube to list the number of tubes in the calculator as 1. So if you compare corrected fixed bias to cathode bias, the cathode bias actually is hotter. The NOS tubes could not handle the voltage above 300v. In short – the cathode bypass capacitor “handles” any variations in the cathode current preventing the cathode voltage to vary as well. From what I understand I need to figure out the plate current, then plug that into the handy weber bias calculator, then adjust the bias to the suggested value and see how things sound I read more about the cathode current method of determining the plate current What I haven't been able to figure out is a list that goes something like: With Vgk= -2. If the amp is cathode-biased, you should replace the cathode resistor for changing the bias level. How many tubes share the same cathode resistor? Measure the Bias by Cathode Resistor Voltage Drop. These are discussed in the following: 3. Single power tube amps are normally Class A. 4 to 1. Instructions. DF96. " V1A's bias voltage is set by cathode resistor R4 which is connected to V1A's cathode (pin 3). To create a DC grid bias of -10V and -12V, the cathode current needs to be 10V / 188Ω = 53mA and There are two easy ways to bias the valve. The same amp in fixed bias would be about 40 Watts. If you plug in the plate voltage, The safest way to read current for each tube is to life the cathode ground and solder a 1 ohm resistor between cathode and ground. Oct 30, 2016. 0Vdc, and Rp= 100K, it worked just great. This webpage offers two ways to calculate tube bias and plate dissipation. Pick a desired DC operating point on the red load line. This fixed voltage is commonly referred as the grid bias voltage Step 2: Triode mathematical model This calculator uses the triode equation of Norman Koren to calculate the anode current as function of grid-cathode voltage and anode-cathode voltage. LC Ripple Filter Calculator RC Ripple Filter Calculator Wire Capacitance Calculator Wire Inductance This calculator allows you to compute and tune loadline and operating point of tube amplifiers’ power stages. It is negative because the cathode is positive with respect to the grid). By following these steps, you can determine your amplifier’s ideal operating conditions for the tube and adjust the bias current. From 360-400 to 480V, the load should be 1. The original had a common, unbypassed, cathode bias resistor (with trimpots for bias and balance). Note: The low end of the suggested range is the "cooler" setting, for cleaner sound and longer power tube life. "You measure the Not "fixed bias". This was classically solved by picking a bias line on a tube chart and doing the calculation from visually observed chart values. I have 2 6L6GC tubes sharing a 250 ohm (measured) resistor with 35 volts on the cathode and 450 volts on the plates. So I figured that an unbypassed cathode resistor would be better, and that gets the THD down even farther. The bias point of the common cathode stage is set by the value of the cathode resistor, Rk. The Tube Bias Calculator will calculate power tube bias values of Plate Current, Dissipation and % of Max Dissipation using either measured voltage drop across a cathode resistor or measured plate current. Cathode bias requires the correct supply voltage -- usually rather low, in order to maintain bias. 5% for screen current). For 10W per tube, idle current is 10W/400V=25mA per tube. LeoJar. Enter Plate Current: DC CALCULATE PLATE DISSIPATION (In Cathode Biased Output Stage) Based on Voltage and Resistance Readings. If your amp is cathode biased or has 1 ohm bias setting cathode resistors then you can calculate bias current by measuring voltage drop across the cathode resistor. You need to look at what's going on at 295V, not 360V. And the higher cathode current causes a higher voltage drop across the cathode resistor. The plate voltage should be measured between plate and cathode, so now the plate voltage is a little less. ; -10V potential). Note: The low end of the The Tube Bias Calculator will calculate power tube bias dissipation and % max. I usually change the resistor and re-bias the amp into the realm of reality. (EL34's max out at 800VDC, so 375 is rather low. This is R2 in the circuit below. Negative voltage between grid and cathode can also be obtained by connecting the grid to ground voltage and by elevating the cathode voltage. Basically, how low can I go before there are negative side effects? Playing with a bias calculator I I think the cathode resistor is an essential parameter in the calculation when counting the bias and it could be given as an input. jpg (429. So, it's pretty easy to "home in" on the right voltages, on the calculator link I posted above. The Granger Amp bias probe measures in milliamps by insertion into the cathode The value of cathode bias resistor calculated from this data is 60 Ω (0. This technique is generally referred as cathode bias or self-bias. Member. I decided to use cathode bias power amp using either 6V6 or 6L6. Good question -- as @slider313 says, the typical approach is your 'try it and see' rather than pure calculation. We will disc How to Measure Bias. The high end Learn how to calculate bias with our online calculator. 008 = 437. « Last Edit: September 01, 2024, 04:18:35 pm by Cathode bias resistor is calculated according to the formula: Rcb = R8 = Bias voltage / Idle current Rcb = 4V / 8. Joined 2003. In using that I come up with 73ma of actual plate current. I also have a 68uF-100v bypass capacitor with it. As calculated above, this How to Measure Bias. 6 V / 10 mA) and a standard value of 56 Ω was actually used. Please login or register. For example, if our fixed bias grid voltage is -0. Top and mid retain their 'sweetness' whilst the bass gets some 'bite' back . I have a PP with 6v6s measuring 365 on pins 3/8, 391 on pin 3 to ground, and 25 on pin 3 to ground. the cathode resistor is 450 ohms. So if The Tube Bias Calculator will calculate power tube bias dissipation and % max. If Vp is increased, Ip must DEcrease so the tubes don't melt. Enter the Plate-to-Cathode Voltage which is the DC voltage measured between the plate and cathode tube socket pins. Furthermore the tubes are not identical with each other. 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. The calculations focus on the clamping action of the coupling capacitor CG due to grid current, so they assume that the cathode bias voltage or fixed bias supply voltage remain constant. A higher value cathode resistor cools the bias, a lower value will actually warm the bias. V2's bias You can change the plate-to-cathode voltage, and even the screen-to-cathode voltage 5V, and it will have very little effect on the idle current. Cathode bias is mostly used in low cost valve amps that function from a 300V to 400V B+ supply. Put the hot lead from your meter in the tip jack and find a ground anywhere on the chassis. miles2go. 05Amps x 250 Ohms = 12. Now the calculator uses the characteristic of the tube and defines the cathode resistor and bias based on the plate voltage and plate resistor. This website uses cookies to ensure that you get the best experience. 2V (the bias voltage is the voltage between the grid and cathode terminals. For one thing, your bias voltage is much bigger and so you have to factor that in if your B+ is already determined and you’re using cathode bias. This will be enough to bias the valve almost to cut-off, With cathode biased amps the most common way of setting the bias is adjusting the value of the cathode resistor. That is not the case with all NOS EL-84's,just the ones I had. I don't know why they so consistantly mislabeled that on the characteristic curves, but that's what they did. That’s easy: just take the screen-to-cathode voltage and divide this by the triode mu of the valve, i. Design for a cathode follower. You may wish to have certain fixed bias amps (such as Mesa The Tube Bias Calculator will calculate power tube bias values of Plate Current, Dissipation and % of Max Dissipation using either measured voltage drop across a cathode Do cathode-biased amplifiers need to be biased? The short answer is yes. The current which the output tubes need to flow is dependent on the operating class. ) Grid leak bias is usually used for one of two purposes: 1. To calculate bias by measuring the voltage drop I modified a princeton reverb to use Rob Robinette's micro power amp. The cathode bypass capacitor in tube amp forms a filter that reduces the low frequency gain of the a common cathode amplifier. Fixed biased amps require biasing to change power tubes as well as periodic bias checks to ensure they are working properly. ÐÏ à¡± á; þÿ Typical implementation of a Fixed-bias, ultralinear Push-Pull output stage with a pair of pentode tubes (EL84 / 6BQ5) Because the cathode is at (or very close to) ground potential, this requires the control grid to have a negative DC bias voltage applied to it, to regulate the flow of current through the tube. [2] The cathode current through this resistor causes the desired voltage drop across the resistor and places the cathode at a positive dc voltage equal in magnitude to the negative grid bias voltage required. The cathode resistor (and for a triode, Rk too) is in parallel with this but you can see these are trivial in comparison. Wire a precision 1Ω resistor between the cathode and its ground. And I don't understand WHY it needs to be such a big, honkin' resistor. I'm using a 12au7 as the power tube. 2 Cathode bias or self-bias; 3. If I use a zener diode to drop the B+ they work fine,but the sound is not the same. In these calculations, 5% of the cathode current is assumed to be Calculate Plate Dissipation Based On Plate Voltage And Cathode Current Readings. According to the Weber Bias Calculator, that makes about 18W per tube, which seems awfully high. Calculate the current and divide by 2. I started with 670r & 750r, respectively. (clintj) Yes I have a BiasPro tube bias probe that a just purchased from A-Sharp Fretworks. But note that at 800 pate volts, only 400 for the screens. Grid bias is expensive, but LED cathode bias can increase distortion if the anode load is not large. miles2go; Oct 26, 2016; Tube Audio; 2. ) Or, as every Marshall shows, 440V 3. The combined plate & screen grid currents of both tubes are going through that 250 ohm resistor. For EL34 tubes: Power output is approx 9 watts, bias is 70 mA, screen voltage is 355V, plate to cathode voltage is 355V, cathode bias voltage is 26V, Implies cathode resistor of 370Ω, 10 Watt. P= I * v. To do this set The Tube Bias Calculator Max Safe Class AB Cathode Bias = 100% x Max Dissipation / Plate Voltage . In reality these are not perfect voltage sources. Of note is that you are bypassing the parallel combination of the tubes cathode resistance and the cathode resistor giving the low frequency gain shelf. co. Use ohms law to calculate the power dissipation of the tube. Throwing in some 1k stoppers for both grids, Check out this nice bias calculator: You have to know your plate voltage (fixed bias), or the difference between the plate and cathode voltages (for cathode bias). There are two easy ways to bias the valve. To calculate bias by measuring the voltage drop Incidentally when I go for cathode bias I usually use 100uF with a 20uF cap for hum cancelling alla Western Electric, input R and calculate for the -3db at 1,6Hz that will be -0. tiscali. A large 10 Watt 470R resistor or similar value Resistor is placed in 200mA x B+560V = 112 Watts. (77F), then we subtract 25C from 60C and 35C, which divided by 35W equals a thermal resistance of 1C/W. Help calculating power tube dissipation. It's the MQ13 version with two probes and one probe has the switch so I can flip between plate voltage and cathode With normal cathode bias, the grid can be direct coupled to the outside world unless there are DC voltages present, The first circuit shown ('A') is the normal arrangement, where the cathode is fully bypassed. forums blog about EL84 datasheet specifies that maximum grid to cathode resistance, with fixed bias, is 300K Ohm. P. Joined 2007. It would be something to consider, though it would not upset the calculations a lot. I=E/R . 1, the designer You can even replace the bias resistors for adjusting the bias. No-calculation examples: A higher voltage (450v) deep class AB amp might use a 4k primary (possibly smaller), while a lower voltage Cathode-bias is upset if current changes from idle to full output, which essentially means Class A, To calculate bias by measuring the voltage drop across a cathode resistor enter your Tube Type and Plate-to-Cathode voltage at the top of the page, enter the Number of Tubes that share the cathode For fixed bias amps we can't calculate a cathode line because we can't divide by 0 ohms of cathode resistance. Choosing Cathode Bypass Capacitors By Merlin Blencowe and David Ivan James With little practical information in print, it was necessary to derive this simple solution to the problem of triode cathode bypassing. A wire does the same thing, so there is no functional difference between a cap and a wire as far as the tube is concerned. leojar. Fortunately, the author’s measurements found that even in this stage, at these signal voltages, the additional distortion produced by LED bias was insignificant, and it allows instantaneous recovery from overload. Thus using V=I x R to calculate the voltage drop we get 0. Phase Inverter Bass Response Calculator Long-Tailed-Pair Balance Cathode Impedance Calculator Grid Bias Excursion Calculator Resistor Power Rating Calculator Other Calculators. If you have just a pentode (on triode) DC isolated from anything else (hint: coupling caps), then each one works on its own. R. But also, that higher voltage on the cathode will cause the tube to conduct less because the grid/cathode bias voltage has increased. The cathode current does not decrease, neither does the cathode voltage. Measure voltage across the cathode R and use ohms law to calculate current. 25db at 20Hz app. On a preamp tube in the 12AX7 family, the cathodes are on pin 3 and pin 8. By visiting the Weber Bias Calculator, and the Tube Amp Bias Calculator, it was advised to set my bias to yield 49. Recommended range for setting plate current and/or cathode current will be calculated. If high-gain was never our goal, but a medium-gain line-stage amplifier, then the following design is the better way to go, as it offers the same gain as the original SRPP-cathode-follower-based Cathode bias resistors are typically 200 to 270 Ohms for each EL84 (6BQ5). I had the same problem with some NOS tubes. For 400v plates and KT88, the value PER TUBE is about 60mA. Since 'everyone else does it', I dutifully use a minimum of a 5w resistor for the cathode bias resistor. The cathode The cathode bypass capacitor in tube amp forms a filter that reduces the low frequency gain of the a common cathode amplifier. Calculating for 70% Cathode Bias was born from vintage HiFi to bring a new experience to US Listening Bars with our Cafe Sound speakers and sound systems Instagram Youtube Blog. Due to their relatively high capacitance, cathode bypass capacitors are traditionally electrolytics. Cathode Bias. 5 Volts which is what the valve data books recommend for this valve. V1B's bias is set by R6. Cathode Bias In later AC sets cathode bias was commonly used with the current flowing through the cathode circuit being used to supply a voltage drop that could be used to bias the valve. Cathode biasing and power ~ Triode Cascode Amplifier Calculator ~ T his calculator can be used to calculate the gain of a triode cascode amplifier with different valves provided µ and r a for both valves V 1 and V 2 are known at the required operating current ~ V 1 is a common cathode amplifier with the input impedance of a common grid stage V 2 as its anode load R LV1. (If I understand right, things like B+, the PT's current supply, and the tube itself add lots of variables to the mix. and, by means of simple calculations, to forecast the performance of the tube in radio-frequency power amplifier applications. Now when 2 tubes share a common cathode resistor problems start to arise, since one may hog current away from the What the cap does is put the cathode at AC ground. Tube Type Calculate Plate Dissipation based on Voltage and Current readings ; Plate Voltage: Cathode current (milliamps) The 5F1's V1 and V2 use "common cathode biasing", also referred to as "self biasing" or just "cathode biased. BUT they ran the tubes really hot. everythings that the author wrote on his website is ok having the same cathode resistors values on the lower and upper triode gets you to 1/2 B+ D. A visit to the Weber Bias Calculator and the Tube Amp Say the screen of the 6L6 is at 320v above the cathode voltage. My recommended bias measurement method is the "Output Transformer Resistance Method. You can: choose among most common power vacuum tubes (I am slowly adding more), set the operation modality, among ultralinear, pentode, and triode (suppressor tied to cathode) mode,; set Single-Ended or Push-Pull configuration ; set the Power Supply V+ The relatively high cathode voltages needed to cathode bias a tube creates a large enough voltage-window to run some interesting solid-state circuitry. It needs to bypass the effective CATHODE resistance in parallel with the cathode resistor (your 124R). Good,but not the same. Replies 35 Views 2K. I used the bias calculator and get a dissipation rate of 120%. Home PRR's calculation applies to class A operation of the output tubes. low hum from heater-cathode leakage, because it allows the cathode to be grounded - it requires low source impedance and low signal level to get low distortion 2. Joined 2009. This in the sense that cathode voltage must be subtracted from plate voltage to get voltage across the tube. Welcome To the Hoffman Amplifiers Forum December 26, 2024, 03:43:01 am: Welcome, Guest. Versus copying a known good design. From this, you can determine bias. For use with octal tubes EL34, E34L, 6CA7, KT66, KT77, 6L6, 6V6, 5881, 6550, KT88, KT90. 4mA of idle plate current. There are four tubes providing cathode current, so the effective cathode resistor value for one tube is quadruple the actual value: 188Ω. Also, that's about 50mA for the plate current, which seems high to me. Doubling the cathode bias voltage quadruples the cathode resistor heat generated. For amps with cathode bias resistors you can simply measure their voltage drop and use the Tube Dissipation Using Cathode Resistor Voltage Drop calculator. The most common cathode bias implementation passes the cathode current through a resistor connected between the cathode and the negative side of the plate voltage supply. When designing a simple cathode-biased triode, voltage-gain stage of the type shown in fig. 2010-06-21 6:30 pm #13 2010-06-21 6:30 pm #13 Hi , The column for Cathode Bias closely represents what you're doing. 8 times higher, 7K to 9K. Now you know the voltage drop across the resistor. The CATHODE resistance is 1/transconductance which for 6c45pi is 1/(45mA/V) = 22R2. In these calculations, 5% of the cathode current is assumed to be screen current. Doing basic power calculations based on voltages, etc. e. Change the grid-to-cathode voltage (bias) by 5V- and it's a HUGE difference. We simply pick the point along the plate load line that crosses the grid voltage. I hope someone could clear this up for me. 4mA for the one tube (minus approximately 5. Cathode bias is typically 90-100% rated current if it's done right. Biasing. Cathode Follower Output Impedance Calculator Power Amps Circuits. uk/g8hqp An interesting question, and one that dates back to the first variations of the DTN Williamson amplifier of the late 1940s. The cathode bias or self-bias technique connects the grid to ground and elevate the cathode voltage above ground. To sum up what this calculation is, PLATE VOLTAGE times CATHODE CURRENT equals STATIC DISSIPATION (IDLING) WATTAGE. Rk is the cathode resistor, which is used to develop the cathode bias voltage. So for two tubes is 50mA. 44Ω, respectively. Install a jumper between the tip jack and the cathode. The calculator simplifies a process that otherwise requires manual calculations, making it accessible to both hobbyists and professionals. Essentially In in typical fixed bias arrangement the cathode R is only used to measure bias current. Use this calculator when you measure the actual plate current. Overview. It's easy to fix the design mistake and the amp doesn't sound bad when the bias is corrected. For the EL84 it is surpringly large at 1M. Rather than the suggested 70% of maximum plate dissipation, I was sitting at approximately 55%. Do cathode-biased amplifiers need to be biased? The short answer is yes. Discover how to address gender bias with the gender bias calculator and bias amp calculator. Throwing in some 1k stoppers for both grids, To calculate bias when you measure the plate current, such as when using the output transformer shunt current measurement, enter your Tube Type and Plate-to-Cathode voltage at the top of the page, enter the Plate Current and touch 'Calculate' and the Plate Dissipation and Dissipation% are shown. /Leevi The question is, how do I calculate the cathode resistor value for this operating point? You need to look at an EL34 data sheet to find out what bias voltage is required to get 61mA of plate current when the screen voltage is about Use a bias calculator such as https: (EL-84 pun intended), since I did a lot of cathode-bias experimentation over the last month. So is cathode bias value what we're using here? Robinette Calculator for 6L6GC. The Tube Bias Calculator will calculate power tube bias dissipation and % max. It shows 55 DC milliamps for a cool Cathode Bias. Cathode bias amps must run HOT. The flow of cathode current through this resistor creates a voltage drop across it, it can usually be ignored for gain calculations. Example: a cathode bias Tweed Bassman type amp with two 6L6’s would be about 25 to 30 Watts. This means a bigger cap for a given cutoff than the bias resistor alone would indicate. Hoffman Amplifiers Tube Amp Forum, Cathode biasing EL34’s. This is my calculation. Bias Settings For Safe Plate Dissipation - Class AB 70% Class A 90% Explain This: Class . But these are just values I got from the Fender Champ schematic which isnt terribly dissimilar from the MOD102+ circuit. The measured plate voltage was 456VDC. The cathode resistor is 35V/0. Cathode bypass capacitors will be connected to the cathode pin, either directly or via a wire, in parallel with the cathode resistor. As the Power Wars (sometime before the Clone Wars) heated up, folks started bypassing the common cathode resistor. These results indicate that the required resistor value to achieve the desired bias voltage is much higher than the typical range for 6V6 amplifiers. I've just re-proved the _three_ SELF-BIAS conditions on Steve's chart: 430V 6. myweb. About Tube Bias Calculator. The defaults are typical for a 12AX7 I'm tuning a SE amp that has a switch to select a cathode bias resistor for a 6V6 and a 6L6. In this video we'll take a look at how to use Ohm's Law to calculate the bias on a cathode biased Fender Pro Amp. The defaults are typical for a 12AX7 Calculation: Based on the parameters you enter, the calculator calculates the ideal bias current. I'll replace the 680s with a pair of 820 ohms resistors to hear the difference and also measure the voltages. I. Of course a grounded cathode is zero to subtract. Cathode-biased amps will safely run at 100% plate dissipation at idle. There are other factors too, such as the grid return resistor to ground but I'd leave that one alone. Since they are 1k ohm, the voltage you read is also current in mA. Please advice: 1) For 6V6 at 400V between plate and cathode and assuming cathode to grid is 35V. This calculation assumes a monoblock power amplifier. Remember that the plate and screen voltages shown are measured to the cathode (which is elevated), not to ground. I put a 6L6GB in my Vibro Champ, used Rob's calculator to bias the amp. The cathode biasing method is self-regulating, to an extent, because increases in cathode current create a larger voltage drop across the cathode resistor, which in turn, . This happens because the capacitor is now “giving” this current through its charge. He says the 6L6GB is rated for 19 watts. 4K in FIXED-bias can be an OK amplifier. Touch ' Calculate ' and your tube's maximum safe bias currents are calculated. About. Putting in the voltages and cathode R valve, I get the bias reading from this calculator at idle: Plate cathode current 63. This calculation is based on Langford Smith's formula from Radiatron Designers Handbook 4. Measure the voltage across the screen resistors to get the screen current Ig2. I wanted to make Cookies & Privacy. Joined 2005. All voltages have to be referenced to the cathode and not ground. L. In our case, we have just over 200V B+ to work with and we want to use a self-bias scheme, TUBE BIAS CALCULATOR (for push pull class AB1/AB2) Select Tube Type and the Plate Voltage of the amplifier below. 05A=700ohm. More Information. The best i could come up with so far was 470R/5w for the resistor and 25uF/100v for the capacitor. Your amplifier is way too complex for cathode bias, which on the contrary shines in **simple** amplifiers, emphasis on simple. Now Plate,you are right when you say 35ma is a good place to bias a 6L6 FIXED BIAS Fender with about 450v on the plates,but with this amp that does not necessarily apply. I frankly am confused by it,other than when you do the math it's not bad. ca/ 2005 I would add that switching from fixed bias to cathode bias also effectively lowers the plate voltage. You must enter Tube Type and Plate-to-Cathode Voltage above before calculating Tube Dissipation. Whether you're a seasoned Use this calculator when measuring voltage drop across a cathode resistor. The cathode biasing method is self-regulating, to an extent, because increases in cathode current create a larger voltage drop across the cathode resistor, which in turn, creates a larger negative grid-to-cathode voltage, which counteracts the increase in current. Using the "Tube Bias Calculator," the calculated bias voltage and resistor value required to achieve the desired bias voltage are 32. TUBE BIAS CALCULATOR (for push pull class AB1/AB2) Select Tube Type and the Plate Voltage of the amplifier below. You will need to look up the data for the particular tube your are using. This article gives the full rundown on choosing a cathode bypass capacitor. I had to up the cathode rsistor a lot and finally just went with some new EI tubes. With multiple tubes sharing the same cathode resistor, this calculator assumes the tubes are fairly well matched. Using the calculation given in Example 6 we can determine the value of the Hoffman Amplifiers Tube Amp Forum, cathode bias bassman question. Jeff's calculations look correct to me. c. Fixed bias could be provided by grid bias or by LED cathode bias. 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. > what to bias the 6L6's at "Bias" includes plate voltage. Most cathode biased amps are either deeply toward Class A, or completely to Class A. 2) For 6L6 at 400V. The bias resistor therefore needs to the following website showed sth very useful for people who wants to know about srpp and how to bias and calculation and. from my builds, The Duncan website has a nice bias calculator you should download and play with. ) I suspect that at 500+ plate volts, good cathode bias may be a problem. lmxu fedwjy fyxypts qrdetvv iryaf mrqh vzadgdm qfv lsibv yburggx