Cathode bias calculator amplifier. The 7868 is only rated at 19 watts.

Cathode bias calculator amplifier It is a 5C5 circuit from 1953. So much for premium ‘matched’ tubes. 6. Cathode bias amps must run HOT. Install a jumper between the tip jack and the cathode. Those two Matchless amps are the only examples of cathode biased EL34 amps that I've seen. I would be more worried if you have low screen resistors on the tubes, but it looks like you have already replaced them. AMP GEEK NOTE: One of the reasons for the aforementioned differences could well be the fact that cathode-biased amps are often biased on the hot side. Your current values of capacitance are not unreasonable considering the impedance they are looking into. Amp is a 6v6 Plexi, AO43 chassis, Hammond original PT, 630v and a 30 watt OT. If your amplifier is cathode biased you must replace the cathode resistor to change the bias level. Although somewhat trivial, this design provides a quality audio amplifier that can be realized at a reasonable cost. V2's bias is set by R8. So for a cathode bias amp, the negative "grid" bias voltage is really the cathode's positive voltage. 2 times 25W is 50 Watt idle heat. [5] The power dissipated by the cathode bias resistor is the product of the square of the cathode current and the resistance in ohms. Mar 3, 2024 · The current flowing through the tube's plate, crucial for setting the correct bias. Jul 5, 2006 · Recently I had a 1960's 2x 6L6 cathode biased amp in for some work. Power Output Test. Cathode bias is mostly used in low cost valve amps that function from a Say the screen of the 6L6 is at 320v above the cathode voltage. You can also put a voltage divider on the screens to keep them down as that will also control plate current. (Schematic attached below) 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 The most widespread method to bias a cathode is to insert a cathode bias resistor between the cathode and ground, and connect the grid of the tube to the ground via a grid leak resistor. Fixed-bias amps, on Jun 26, 2021 · Break the existing cathode ground. Note that cathode biased does not automatically mean Class A, nor does fixed bias mean Class AB. High level block diagram of the amplifier ~ Un–bypassed Cathode Calculator ~ T his Calculator was originally made to support my Amplifier–Buffer project and can be used to calculate the a. Nov 26, 2019 · Assuming you have 4x6L6s in a 120 watt amp, that is 30 watts per tube. In the course of learning various biasing methods for his amps, some of which are cathode-biased, others adjustable fixed-bias, he has used a couple of online resources which have been useful, but I think can be confusing for new builders. Sep 21, 2018 · 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. Rather than the suggested 70% of maximum plate dissipation, I was sitting at approximately 55%. For this reason, the bias should always be checked, even with cathode-biased amplifiers. So if you see a big resistor between pin 8 and ground, it's most likely the cathode resistor, meaning the amp is cathode biased. Again, the "sweet spot" in between is where most techs set the bias. Dec 17, 2018 · Cool – glad it helped you. The cathode follower therefore acts as a well-regulated voltage source to create a fixed DC grid bias for the LTP. Especially NOS. 3 watts. I’m having an issue checking the dissipation on the EL34s in cathode bias mode. That means they let a lot of cathode current flow compared to Class AB biased amps. Most amps using this tube run between 430-450 volts DC. More specifically, it operates in Class A when the anode voltage is in the range from 190V to 410V. The CATHODE resistance is 1/transconductance which for 6c45pi is 1/(45mA/V) = 22R2. Fig 1. Jul 21, 2018 · Grid leak bias is usually used for one of two purposes: 1. Cathode biased amps can safely run at 100% plate dissipation at idle. Of all the pentode driven (WE91 type) amp schematics I found, 16uf was the lowest value shown, with the average being 63uf. I don't know what your B+ Plate voltages are, so I can only speculate, but any of the calculators out there will tell you if a bias point is good enough or not. By visiting the Weber Bias Calculator, and the Tube Amp Bias Calculator, it was advised to set my bias to yield 49. Capacitor C6 is a cathode bypass cap that helps decrease local feedback and increase V2's gain. It's rare to find an exception to that rule though The single-ended (SE) power output stage is the simplest form of power amplifier. I measured the amp's power output at 35. Drop of max output power is not a problem. In most common guitar amp circuits, cathode biased amps will self regulate plate current, in many cases plate I do use this same technique in the one solitary cathode biased se amplifier I have currently licensed, and it is very effective, but the amplifier does not use cathode feedback. At idle this is 75mA per tube. This is a warm bias, but unreasonable. Nov 14, 2006 · One thing I should mention is that my amp is using a pair of KT-66's with cathode biasing. Then the composite sum acts as if it were the "real" 1/Gm. Since the bias supply draws very little current we only need one stage of smoothing in addition to the reservoir capacitor. The cathode resistor can also be bypassed by a bypass capacitor to reduce the negative feedback, introduced by the cathode resistor, and increasing gain. The schematic shows 6L6GC power tubes. If Vp is increased, Ip must DEcrease so the tubes don't melt. Having selected our operating point at 85V, we know anode, and hence, cathode current. The cathode bias or self-bias technique connects the grid to ground and elevate the cathode voltage above ground. The cathode resistor (and for a triode, Rk too) is in parallel with this but you can see these are trivial in comparison. Using the "Tube Bias Calculator," the calculated bias voltage and resistor value required to achieve the desired bias voltage are 32. Fixed bias amps have a bias circuit that puts a negative voltage on the power tube grid. So if the value you gave (120mA) is for the PAIR, that's in the ballpark. It's a relatively low B+ voltage on the plates around 340 volts and I got 30 volts on the 300 Ohm cathode resistor. Select your tube type and amp class (Class A, Class AB Low, Class AB, or Class AB High) and enter your Plate Voltage or B+. There are a lot of factors that determine the sound. Nov 20, 2010 · I've been helping a friend who is relatively new to amp building with various aspects of his builds. 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 Calculate Plate Dissipation Based On Plate Voltage And Cathode Current Readings. May 19, 2004 · This is a type of cathode follower that naive builders have done many times and has given CFs an undeserved bad reputation. Dec 22, 2021 · Heh, @JamesAM typed faster and was more concise. all the schematics call for it as well. This calculation is based on Langford Smith's formula from Radiatron Designers Handbook 4. Many amps which use "fixed" (negative grid) bias have provisions for adjusting the negative grid voltage upward or downward. Dec 26, 2024 · It needs to bypass the effective CATHODE resistance in parallel with the cathode resistor (your 124R). 6 Biasing techniques. Put the hot lead from your meter in the tip jack and find a ground anywhere on the chassis. Guitar Amp Circuit Design Calculators. I_plate = I_cathode - (I_cathode * Screen Current Percentage) Voltage Across Cathode Resistor (V_cathode) The voltage drop measured across the cathode resistor, used to calculate the cathode current. Sep 1, 2024 · this is a FIXED bias AMP NOT a SELF biased amp fixed bias is the VOLTAGE at the control grid (G1) that VOLTAGE controls the conduction of the tube the BIG "tell" fixed bias will have a negative VOLTAGE applied to the control grid and NO resistors at the cathode Self biased amps have a large power resistor at the cathode to ground connection and Jan 4, 2008 · Most cathode biased amps, especially those that are somewhat based on the AC30, overbias the tubes. (Actual Plate Voltage) Will calculate and display plate power dissipation and approximate plate current per tube. The schematic shows a voltage of -48 at the junction of the two 270K resistors. Some amplifiers don't have a bias-adjusting control (pot) but instead use a fixed resistor to set the voltage. It is basically the same as an ordinary gain stage, but instead of a load resistor we use an output transformer. With respect Jun 20, 2024 · For cathode bias the grid is grounded. 15v (53r) (12. The circuit The basic triode voltage amplifier, a 'common-cathode amplifier' is shown below: Calculator This extends tube life and helps make the tone difference between fixed-bias and cathode-bias a bit wider. Nov 30, 2020 · I am reviving an old WEM guitar amplifier which has push pull EL84s in what is rated (optimistically I thought) as an 18watt effort. so i had it replaced at the time. The calculator computes the -3dB bass cutoff frequency, the bias excursion ratio, the bias excursion time in milliseconds, and the bias recovery time in milliseconds. 5K resistor. From 360-400 to 480V, the load should be 1. Changes in the bias voltage will vary the conduction angle (that From Figure 49 we can see that the grid voltage bias, needed to obtain an anode bias current of 28mA, is around -12V. However, just as different tubes from different manufacturers will draw varying amounts of current in a fixed-bias amplifier, the same is true of a cathode-biased amplifier. By computing the resistor value, according to the wanted bias current, the cathode voltage is elevated so that the grid has the correct negative bias voltage. 44Ω, respectively. It is a conventional setup where the EL84 anodes are directly connected to the OP transformer while the screen grids run from HT via a 1. 440mV (example) Cathode Resistor Value (R_cathode) The tube will reach a stable point of equilibrium and stay there. Folks have ended up with really high values sometimes, which aren't wanted and shouldn't be needed -- a properly functioning amp like this should bias in the range of 470-500 ohms. When the capacitor is large enough, it acts as a short circuit for audio frequencies, eliminating the negative feedback, but is an open circuit for DC Amplifier Calculators; Tube Calculators; Tutorials; Read the cathode resistor value from the top of the calculator. Next, we can ignore screen current for this rough estimate. We simply pick the point along the plate load line that crosses the grid voltage. Oddly, 6V6 tubes seem to run hot with not much ill effects. supportive passive components for biasing and coupling duties. 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. The same amp in fixed bias would be about 40 Watts. 5v grid curve. The Fender 5F6A Bassman and most Marshall amps are fixed bias Class AB amps. Jul 27, 2022 · Now, before assembling final variant, would like to get rid of fixed bias circuit and switch to cathode bias, with 490 - 500V B+ and 520 Ohm cathode resistor (2 x 5W metal film resistors, 300 + 220 = 520 Ohm total). 4 to 1. Oct 4, 2008 · In fixed biased amps 70% is usually considered the max bias at idle. For fixed bias amps we can't calculate a cathode line because we can't divide by 0 ohms of cathode resistance. One annoyance caused by a simple bias supply is that when you turn the amp off, the bias caps may discharge faster than the HT caps. BUT they ran the tubes really hot. To get there we need 50W/330V= 0. Though not all amps with cathode resistors are cathode biased. Aug 17, 2015 · The measured plate voltage was 425VDC, and the measured plate current was 39mA. 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. 7M or 10M is used. 5% Total Harmonic Distortion. A ’cathode bias’ amplifier has a resistor going from the cathode to ground. My recommended bias measurement method is the " Output Transformer Resistance Method . Oct 30, 2008 · The bias shift that happens when a push-pull cathode-biased amp is driven hard has a time constant that determines how fast it recovers, typically a fraction of a second. The following steps are a way to figure the bias without a bias probe, and only a voltmeter. According to the plate transfer characteristics, a grid voltage swing of 0. This calculator allows you to compute and tune loadline and operating point of tube amplifiers’ power stages. This resistor is set to The cathode bypass capacitor in tube amp forms a filter that reduces the low frequency gain of the a common cathode amplifier. I used a 0. 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 Jun 30, 2014 · That will give you your target dissipation. Enter Plate Current: DC milliamps As long as you know (or can test) the plate voltage in your amp, and have a way to measure the idle current, you can determine where to bias it, using our calculator. Bypass capacitors cannot be counted on to provide a pole because the zero is usually so close in frequency. But don't chase your tail on obtaining the exact sound of your friend's amp. Dec 26, 2024 · A good approximation for degeneration is to imagine the cathode's 1/Gm as a "real" resistor, then add the external cathode bias resistor in series. This substantially increases gain. So long as you don’t mind the extra components needed. V1B's bias is set by R6. The EL84 If there is no plate current the voltage across the cathode resistor is 0V, so the other endpoint represents a 0V grid and 0mA plate current. The cathode is positive relative to ground because of the cathode resistor, thus the cathode is positive relative to the grid. 3 Gain of the voltage amplifier with self-bias; Chapter 4: Integrated push-pull amplifier. ) Screen resistors measure around 120r Around 270v coming from the amps HT at 228v wall voltage and amp set to the 245v tap (to lower the voltages slightly) I was thinking to try the following in that order: Sep 20, 2011 · According to the Weber Bias Calculator, that makes about 18W per tube, which seems awfully high. Aug 18, 2021 · Single ended 2A3 with -45V bias, and 2500 Ohm Primary gets 3. For an ideal amplifier, at FULL power it shifts (as TS said) to 150mA one tube, zero in other. Generally there are two types of bias arrangement used in guitar amplifiers. Oct 17, 2024 · I modified a princeton reverb to use Rob Robinette's micro power amp. 4mA for the one tube (minus approximately 5. In this way the grid voltage is negative with respect to the cathode voltage. It may be of help to some of you. 3 Gain of the voltage amplifier with self-bias; Chapter 4: Integrated push-pull vacuum tube amplifier. Figure 48: Schema of the amplifier output stage designed around EL84 tubes. Nov 24, 2022 · With cathode biased amps the most common way of setting the bias is adjusting the value of the cathode resistor. This gave me 100mA for the pair of tubes, so that makes it right at 50mA of bias current for each tube. Jul 24, 2019 · You have to know your plate voltage (fixed bias), or the difference between the plate and cathode voltages (for cathode bias). 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. The measured plate voltage was 456VDC. The Fender 5E3 Deluxe is a cathode biased Class AB amp. Putting in the voltages and cathode R valve, I get the bias reading from this calculator at idle: Plate cathode current 63. My preference for right now after only 2 hours of listening is that the high quality 18uf cap sounds best. 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. 7V creates a plate voltage swing of 0. The 5F1's V1 and V2 use "common cathode biasing", also referred to as "self biasing" or just "cathode biased. The amplifier operates in Class AB. The effective cathode impedance is equal to the 2. gain and impedances [not d. May 29, 2023 · Hoffman Amplifiers Tube Amp Forum, Bias Calculations for Cathode quiescent operating points and then be able to calculate what size cathode bias resistor based on Aug 14, 2015 · The measured plate current was 31mA for one tube, and 33mA for the other tube. There are other factors too, such as the grid return resistor to ground but I'd leave that one alone. For a cathode-biased amplifier the total current should not change much from idle to full roar. . I used the bias calculator and get a dissipation rate of 120%. looks like i need another pair of tubes. The common-cathode amplifier configuration - unbypassed cathode. 8 times higher, 7K to 9K. 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 data sheet recommends a 50μF cathode bypass capacitor. If the DC grid bias is -9V, then the cathode is at 9V and the screen-to-cathode voltage is 325V - 9V = 316V If the grid bias is -10V or -11V, then the screen voltage is 315V or 314V, respectively. Discover how to address gender bias with the gender bias calculator and bias amp calculator. These are discussed in the following: 3. The 7868 is only rated at 19 watts. Our bias probe measures true bias current. Jan 18, 2013 · The cathode of any octal based amp (EL-34's, 6L6's, 6550's, 6V6's, KT-88's, 7027's) is on PIN 8. For use with octal tubes EL34, E34L, 6CA7, KT66, KT77, 6L6, 6V6, 5881, 6550, KT88, KT90. You will need to look up the data for the particular tube your are using. 151 Amps total cathode current. Here, the cathode is connected to a resistor and capacitor. Single-ended amps are usually fairly low power (less than 15W say) and are invariably cathode-biased. If you have not been trained to work with high voltage then have an amp technician service your amp. Less clean headroom. The Fender 5F1 Champ is a Class A cathode biased amp. If this happens to you I assure you that my Tube Bias Calculator does nothing but calculate tube bias. For example, if our fixed bias grid voltage is -0. " With multiple tubes sharing the same cathode resistor, this calculator assumes the tubes are fairly well matched. You should use a resistor for each pair of output tubes or better yet a resistor on each EL84 for best results. the bias of the amplifier affects its tone. Feb 21, 2008 · Turn off the amp, jumper in the new cap, turn the amp back on and listen, then repeat with other caps. We will disc Aug 21, 2023 · Learn how to calculate bias with our online calculator. 5 volts we would use the intersection of the red plate load line and the -. james, thanks for the info. Jul 9, 2022 · Cathode bias: Smooth and compressed. Fixed biased amps require biasing to change power tubes as well as periodic bias checks to ensure they are working properly. WARNING: A tube amplifier chassis contains lethal high voltage even when unplugged--sometimes over 700 volts AC and 500 volts DC. 2w per tube depending on the voltage drop of the bias resistor. Most cathode biased amps are either deeply toward Class A, or completely to Class A. > what to bias the 6L6's at "Bias" includes plate voltage. May 12, 2013 · There's no good substitute for running at the "ideal" plate voltage, but in cathode biased amps boosting the cathode R even farther is useful. According to the 12AX7 calculator, the equivalent circuit with cathode bias has an 893Ω cathode resistor. So, 37mA is 100% for this plate voltage. I'm using a 12au7 as the power tube. Mar 20, 2021 · Cathode bias resistor 8. Dec 9, 2009 · It is fixed bias but doesn't appear to have adjustable bias. He says the 6L6GB is rated for 19 watts. I also installed a switch for fixed or cathode bias. The Granger Amp bias probe measures in milliamps by insertion into the cathode connection that conducts the current to the plate (anode) of the tube. Making the grids LESS negative will cause MORE current to flow through the tubes. Cathode biased amps are less efficient than fixed bias amps. They don't ever seem to really be an issue. 3 Gain of the voltage amplifier with self-bias The bias point for 6L6GC tubes depends on the plate voltage that the amplifier is designed to use. This is with a cathode biased amps of course. Jan 31, 2024 · If you calculate only combined bias current using cathode resistance and its voltage loss you don't know what is the difference between tubes! Making bias hotter is easy installing resistors parallel with what there originally is and then they can be "few kilo ohm class" and often 0. The grid of cathode biased amps will be at 0 volts. In these calculations, 5% of the cathode current is assumed to be screen current. i May 28, 2010 · Therefore 2 output valves that are Cathode biased is described as Class A push pull. I suspect that likewise, a good 6V6 SE amp, and a good 6V6 Push Pull amp will have different operating conditions. estimates the needed cathode resistor, if you want to use self-bias The 73V output sets the DC voltage at the grids of the triodes forming the long-tailed-pair phase inverter. A visit to the Weber Bias Calculator and the Tube Amp Bias Calculator both suggested a bias measurement of 38. 4mA of idle plate current. Oct 27, 2013 · Cathode bias resistors are typically 200 to 270 Ohms for each EL84 (6BQ5). On the other hand, cathode bias shows a more smooth amp - biased on the hot side ~ 100mA's per tube @ 430V on plates 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). Cathode Bias: This self-biasing method allows the tube to automatically set its bias level. IMPORTANT: Screen stops should be a minimum of 1k-1W flame-proof for all tubes and this is especially important in cathode-biased amps. Just plug in your cathode voltage and cathode resistance value (250 ohms) into Ohm's Law. c. I have a 6550 p-p amp (my fav big bad tube) with ability to switch from fixed to cathode bias and although they behave differently, in fixed bias mode there seems to be a kinda punch which is not present on cathode bias mode. Jul 18, 2022 · I put a 6L6GB in my Vibro Champ, used Rob's calculator to bias the amp. A DC operating point SPICE simulation 3 indicates that the DC grid and plate voltages are -780mV and 108V, respectively. 1 Fixed bias; 3. 1. The power section overdrives quicker and has more “sag” (a spongier, looser response), especially in the low end. Both capacitors are typically 10u to 100u –they’re not critical. This can make cathode-biased amps sound "woozy" when handling large signals. 2 Impedance of an output transformer estimates the grid bias voltage, estimates the expected output power at max displayed Grid Voltage, when max Grid Voltage is 0, when operating in Class A or A2, and at the selected output voltage headroom. According to the Cathode Follower calculator, with a 220kΩ cathode resistor the output impedance is only 617Ω. For 400v plates and KT88, the value PER TUBE is about 60mA. DC voltage measured between plate and cathode. i just popped a sovtek, and the JJ's i have have small pins. Cathode Impedance Calculator Grid Bias Excursion Calculator In DC terms, the result is that the two 10-ohm cathode resistors effectively double in value, acting as if a single 40-ohm cathode resistor were used to cathode-bias the triode. 3mA, so I believe I had hit this sucker as close as I’d care to. These results indicate that the required resistor value to achieve the desired bias voltage is much higher than the typical range for 6V6 amplifiers. 1v peak-to-peak 400Hz sine wave into the Normal Hi jack, plugged in a dummy load (4 ohm 50 watt resistor) to the speaker jack, connected my oscilloscope leads to each end of the dummy load resistor, turned up the volume until the top of the sine wave began to flatten out then backed off until To adjust a fixed bias, you usually need to access internal controls on the amplifier. 1 Output stage, or power stage. 1 Single Ended vacuum tube amplifier; 4. The AC15's value is 25μF. 5 Watts @ 5% 2nd Harmonic Distortion. The tube will reach a stable point of equilibrium and stay there. And Madison's estimated 440V ain't very different from the Clubman running 430V. Running hot may be part of the magic. Aug 26, 2006 · TYPES OF (FIXED) BIAS CIRCUITS. He's right. 2 Cathode bias or self-bias; 3. A "cold" bias means that the tubes are running much colder, the tone is cleaner and a bit more sterile, but the tubes last much longer. Wire a precision 1Ω resistor between the cathode and its ground. The AC 30 used a single cathode bias resistor of 50 Ohms for all 4 EL84s bypassed with 220uF. 2kΩ cathode resistor in parallel with the reciprocal of the tube's transconductance. low cost - distortion not a major consideration In most circuits 4. My longer version: First, don't just keep boosting cathode resistance to 'fix' the redplating. After having built EL84 amps using both Fixed and Cathode bias, I’m convinced that fixed bias is the way to get the absolute maximum performance out of them. 8mA. More interestingly, the type of bias arrangement that the amplifier manufacturer chooses also affects the sound. Example: a cathode bias Tweed Bassman type amp with two 6L6’s would be about 25 to 30 Watts. 5 Amplifier classes; 3. 1 Fixed bias for vacuum tubes; 3. This calculator is for a single tube. 2 Cathode bias or self-bias for vacuum tubes; 3. Use this calculator when you measure the actual plate current. If you have a May 17, 2010 · Completely removing the cathode bypass resistor on the EL84 will reduce output power by reducing the overall gain of the stage, because without a bypass cap there is nothing to keep the cathode voltage constant, and the cathode voltage will then be pulled up and down slightly, in synch with the rise and fall of the plate voltage, thereby Apr 10, 2010 · This amp is cathode biased with one cathode resistor for each of the two EL84 power tubes. 80-9. 3. The Grids are referenced to ground (chassis) by a 220k resistor. That's why they need to be so big. 4. 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 The cathode resistor in a typical triode preamp is bypassed with a large capacitor to eliminate a form of negative feedback known as cathode degeneration. 5E3P Amplifier Build. The calculation below shows how to properly determine these values and next, how to calculate the amplificiation as function of frequency. I would not be afraid to copy that schematic. 10V and 754. Aim at 70% for fixed bias, or closer to 100% for cathode bias. 1 Output stage or power stage. From this, you can determine bias. Not all tube amps have adjustable bias, but most larger tube amps do (output power of 40 watts or greater, typically). 7-13. The defaults are typical for a 12AX7 Oct 25, 2019 · The bias setting for any amp depends on the actual voltage the amp runs at. 2 Impedance of an output transformer The common-cathode amplifier configuration - unbypassed cathode. 1 Single Ended configuration; 4. Apr 19, 2010 · The current which the output tubes need to flow is dependent on the operating class. (cathode // cathode bias resistor) Most power grid tubes used in AF or RF amplifiers can be operated over a wide range of grid bias voltage (or in the case of grounded grid configuration, cathode bias voltage) as determined by specific performance requirements such as gain, linearity and efficiency. Then by R=V/I, the Load Impedance must increase to properly absorb the power. Due to this configuration, cathode bias is simpler to maintain because it requires no manual adjustments. Few questions regarding new setup. Most output valves in HiFi valve amps (40 Watt and less) are Cathode biased in the same way that pre-amp valves are biased. A "dumb" calculation by me would say ok the B+ is 500V, that means 30/500 = 60 mA. 5W is enough. Mar 2, 2008 · This is taken from a post I posted in another thread. Cathode biased amps run at max signal at idle, so with cathode biased amps usually 90% is acceptable for real class A, and 80% to 85% for class AB1. Now you know the voltage drop across the resistor. Power-supply voltage is provided by dual half-wave diode rectification of 120 VAC stepped up by a magnetic transformer. " V1A's bias voltage is set by cathode resistor R4 which is connected to V1A's cathode (pin 3). You must enter Tube Type and Plate-to-Cathode Voltage above before calculating Tube Dissipation. Oct 22, 2007 · when i got the amp, the board under the 10 watt resistor was burned, could've been a tube or resistor failure, right. 'course, I ain't gonna be changing tubes every 3-6 months either. Push pull 2A3 with -62V bias, and 3000 Ohm plate to plate primary gets 15 watts @ 2. This is not entirely correct since these values depend on the DC bias. i've done work on my other amps, but none of them are cathode biased. In AC terms, the cathode is loaded by a constant-current source and whatever external load impedance is driven times two. 5% for screen current). The single-ended (SE) power output stage is the simplest form of power amplifier. A higher value cathode resistor will cool the bias, a lower value will warm the bias. (In triode anode and cathode currents are equal). Following is a schematic of a typical common-cathode amplifier stage with an unbypassed cathode resistor: This circuit is similar to the bypassed cathode configuration with the exception of the removal of the cathode bypass capacitor, Ck. As with fixed bias amps, cathode biased amps sound their very best when biased correctly. It was certainly running higher voltages than originally intended, maybe by 40-50V due to higher mains voltages, and sitting right on 100% plate dissipation. fcng soyhs zwkouvq dmhzmjt msha szju znmvi icwvt pmrwois zfb