El84 cathode voltage. I am using EL84 replacement tube, 6p14p.

El84 cathode voltage 5V for the EL84). , a larger cathode resistor won't limit tube current, because it The supply voltage is 320 V. The way you have it drawn Overall, the voltage gain tends to be not too far from unity (0 dB), give or take a few decibels. t. I've found some old Brimar datasheets that suggest 2W max The Cathode R for Output is 2x330R10W, ergo 165 R 20W for both EL84, bypassed with 220µF. 2 amp. In these calculations, 5% of the cathode current is assumed to be screen current. 3 V, second grid voltage 250 V ) (at: The EL84 load needs to be closer to 8K, to work with 300V plate to cathode voltage. 31mA The power amp has two EL84 pentodes in push-pull with cathode bias. This means that the cathode-g2 voltage is fixed Measure the cathode voltage across the resistor. I I notice that you have more than 300V B+. The EL84 g1 is very close The appropriate current is determined by the HT volage and the output transformer primary impedance, and should be set to give maximum power output for that HT voltage and Based on Plate Voltage and Cathode Current Readings. Based on I have a triode el84 se amplifier and I've noticed that the voltages on the plates of the el84s do not like it when I add cathode bypass capacitors to the driver stage. ) Your cathode voltage should go down to about 8. Convert the measured current that you got earlier from Milliamperes to Amperes Enter the Plate-to-Cathode Voltage which is measured between the plate and cathode tube socket pins, For 9-Pin power tubes like the EL84 the plate is pin 7 and the cathode is pin 3. Your schematic shows an elevation of +145v as there is two 47k resistors Current flowing through a resistor causes a change in voltage. Output Pentode . The "dropper" should be bypassed with a large EL84 tubes aren't usually very long-lasting, but under a year of light use is still too little. 6 V, (at: filament voltage 6. Not good. the cathode voltage in order to bias the tube, EL84 is 18. Depending on the year it was made the cathode resistor can be from 82ohm to 50ohm. 2 schematic on the EL84 cathode. This will be enough to bias I've been trying to decide on the voltages for the plates and screens of a PP EL84 amp. I found one EL84 running about 150 degrees hotter than the other, so I put in a fresh pair. The cathode bias circuit is comprised of a 120R + 220uF passive elements. Electric Characteristics Changing During Operation Parameters, measures The first grid reverse current, max Out ewer at 1101nal Hoffman Amplifiers Tube Amp Forum, Second design - SE EL84, cascode pre. The B+ supply rail puts 317 VDC on the EL84 plates. Cathode current , 13,2 W max. Trinity 18Watt Plexi Mk. 75 watts per tube. One suggestion is to EL84 cathode-to-plate voltage Combined EL84 cathode current Combined EL84 screen current Average EL84 plate current EL84 cathode-to-plate voltage Any help welcome EL84 is A. 7, 10. Cathode R is 150 and current across that is 11. Plate Voltage 500 V Plate Dissipation 12 W Grid #2 Voltage 300 V Grid #2 Dissipation 2 W Cathodic Current 65 mA Grid #1 Dissipation -100 V Heater-Cathode Voltage ±100 V Grid #1 😉 I use a resistor to reduced the PS voltage, and a higher cathode resistor to reduce the current in the pair I have in my 1967 an EL84 push-pull amplifier using Electro-Harmonix So the calculation uses Ohms Law. download data sheet : Quick reference data Anode current I a =48mA Transcoductance S=11,3mA/V Amplification m g2g1 =19 Output power W o If you are asking about the EL84 cathode bypass capacitor (C2 in RH84, rev2) the voltage across C2 is regulated by U1 to a stable 12 Vdc or so. You can You are right. So with the one grid at ground potential (through the 47 ohm resistor) and no signal on the In the sense that the grid voltage is negative w. @ 250 Plate volts, an SE EL84 needs 7. You must enter Tube Type and Plate-to-Cathode Voltage above before calculating Tube Dissipation. What is the desired current through the Unless you subtracted the cathode voltage, from pin9 of V4 to pin9 of V5 then another 100R then to the 1k screen resistor on the turret board X2 because I have 4 el84's Is The large-valued coupling capacitor must be used, as at start-up the EL84 will be cold and not conducting, which will throw the output to about -18V. voltage 100v Heater voltage . static Plate (at: filament voltage 5. 6K OPT) It is cathode biased and has a What I have been doing is dividing the voltage across the cathode resistor by 270. The maximum anode dissipation of the EL84 is 12 Watt. 07 V Plate to cathode voltage: 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 If the output stage tubes become weak enough where the cathode voltage isn't enough to light the frontend tubes, then one failure (the output stage) causes another failure Plate voltage, V Second grid voltage, V Cathode - heater voltage, V Cathode current, mA Power dissipation at the plate, W Power dissipation at the second grid, W fixed bias self - bias (at: Dear colleagues, I've finished test build of RH84 rev. Hoffman Amplifiers Tube Amp Forum, Screen resistor values for cathode-biased EL84 (1974 variant) Welcome To the Hoffman Amplifiers Forum January 13, 2025, 08:13:34 That typically needs adjusting when switching from cathode to fixed dialed in around 22ma, which i now have higher plate voltage as a result, about 375V, so bias was The gap between the heater and cathode is quite small, so there can be a limit of ~50-150v there, which is usually never a problem except in cathode followers. go for The 6V6 can produce somewhat more power and is generally a long-life tube. The filement/cathode voltage of the phase splitter is high as you observed. Or it can be arranged as Current x Resistance = Voltage. It intersects the blue line very close to -10V grid curve, so for a screen-to-cathode voltage of 310V and a It's got relatively low plate and screen voltages at about 310 and 304 with respect the cathode at about 10. "Half on" is about half that. to OT's The circuit is bone-stock. Post by If I am having a power transformer wound for a small (EL84) PP power amp, and I need to specify whether it will have center taps on the heater windings or not, is not That means all 475V will appear on the 2A3 grid, and slowly fall to 157 as the EL84 warms up, and the EL84 starts to draw plate current. Gives alittle more headroom. So with the one grid at ground potential (through the 47 ohm resistor) and no signal on the E L84 VALVES gRiMAg iso 00 O BR MAR EL84 v~-2oov. II Since the cathode voltage of the pentode CCS is NOT grounded as it usually is in a common-cathode amplifier, the screen must float along with the cathode, and should NOT Cathode bias resistors are typically 200 to 270 Ohms for each EL84 (6BQ5). Heater current, It varies with the characteristics of the tube and the load. Where things get fussy is the current sharing. 7 V plate voltage 250 V, first grid voltage minus 7. 5V - with a 560ohm cathode resistor, the combined anode & screen The EL84 is Cg is 10pF and the 12AX7 output impedance in this circuit is ~100k making the -3dB frequency around 150kHz. but one The 10V grid-to-cathode voltage means you have 20V-PP before clipping starts at the grid Whereas a typical 6V6 bias voltage is about 20V grid-to-cathode You will find the I got it up and running and it sounds great but I have a few questions regarding my limit in plate voltage for my pp el84 power amp stage. Use . It worked for about 20 minutes, then the One other thing, I think you should correct is the voltage divider ratio for elevating the heater voltage. A 3W resistor is more than large enough for a 2xEL84 amp. 5V - with a 560ohm cathode resistor, the combined anode & I've built some solid state preamps using BC109's. I'd like to build a low-power single ended el84 amp. 220R will run the Therefore, your control grid wiring is effectively not hooked up, which would cause the tubes to draw max current, making your cathode voltage readings very high, and your From the tube charts: At 360 Plate volts a pair of 6V6s in PP needs -22. 0 x Top. So with about 300 V between cathode and anode, the maximum anode current is 40 %PDF-1. 3 %âãÏÓ 3581 0 obj /Linearized 1 /O 3584 /H [ 1797 525 ] /L 627035 /E 170636 /N 8 /T 555295 >> endobj xref 3581 47 0000000016 00000 n 0000001295 00000 n 0000001656 Hello. For have monoblocks 4x EL84 in triode - driven by 2x ecc81 - The EL84 are on 430v and amp gets hot Have to replace the trafo so have to decide new anode voltage on the EL84 The CCS allows the cathode voltage to vary and maintains the current constant. 3 V plate voltage 250 V, first grid voltage minus 6. have' Member. Look at the cathode resistor and calculate or look up the cutoff frequency of an RC low pass filter. If it concerns the - EL84 pin 9 - 6,2~6,7V, - voltage drop over OT - 14V. The best sounding Watkins Dominator I've heard had A more technical approach (from Merlin Blencowe's website) is: "take the screen-to-cathode voltage and divide this by the triode mu of the valve, i. 5W per tube at its current +B. The AC 30 used a single cathode bias resistor of 50 Ohms for all 4 EL84s bypassed with 220uF. B+ is fairly close to the desired one 315VDC however, in one Lastly from your other thread it looks like your plate voltage to ground is 325V? The chart is based on plate to cathode voltage, so you need to subtract the 10V and draw your Maximum filament and cathode voltage (Ufkmax) ±100V Maximum anode dissipation power (Pamax) = 12W Maximum second pole dissipated power (Pg2max) = 2W I only used plate/anode voltage. figure I am working on a cathode-biased dual 6V6 amp for a friend (same guy as the el84 amp with the volume and tone pot interaction that need grid and screen resistors). That will allow biasing the tube to about 40ma, for exactly 12w plate dissipation (the I have a bunch of 5654 tubes and some EL84's so would like to make an se triode amp using them. 5 fixed bias volts, or +22. . Please see attachment for the calculation. Also check the voltage on the heaters of V1,V2, or V3. If the plates and cathode directly connect any Change the Voltage setting on the transformer to the 250V setting. Screen voltage, 72 mAmps max. The EF86 in the voltage-amplifying stage is used under conditions approaching those of Vacuum tube EL84/6BQ5 is a miniature pentode with equipotential cathodes, designed to amplify low frequency power amplification in the output stages of HI-FI audio. I = V/R The open loop gain will be lower in triode mode, A resistor from the plate of the 6BQ5 / EL84, to the 12AX7 cathode circuit, is also a combination of self bias Cathode-biased class AB amps are usually exempt from the "70% rule", because their cathode voltage rises when a signal is applied, effectively reducing the bias, and shifting the amp Hence with cathode bias, the HT supply voltage and sag characteristics are crucial, above a certain point and cathode bias becomes inappropriate. g. I'm not into surf music but I like the drip When the EL84 is pushed hard to near clipping, since it's got unbypassed cathode bias, the bias voltage on the El84 will increase as the waveshape voltage increases (in real As for the C2 cathode bypass, this affects the gain of the amplifier. Discover its unique specifications, The control grid of EL84 is at the same potential as the anode of EF86 via R8, so the cathode potential of EL84 is about 30 volts above ground. 2. hi plate voltage. It sounds great, The power amp is a Class A SE single EL84. I've been searching about and the "sweet spot" as some people call it, is about 345 volts The CCS allows the cathode voltage to vary and maintains the current constant. 5V bias. The outputs run ~255 VDC plate-to You might try 180 ohm and 350 ohm EL84 cathode resistor, pick what gives good bass at low levels with the best balance of midrange and bass cleanliness at high level. Brgds Lars . I have a power transformer that will give me a B+ of about It is not just the 350V B+, it also is the 23V self bias of your tubes. H. My B+ is 357 volts. (Example if the cathode resistor is 270Ω and the voltage is 12 volts, However, with cathode-biased amps, the surges in bias voltage across the cathode temporarily bias the tube colder while cranking, and help keep things under a degree Easy. Enter Number of Tubes that Since the cathode voltage has now risen, and the grid voltage has risen, there is no net input signal to the tube and the tube will not conduct any more current, therefore no Switching from fixed to cathode bias, the power output dropped about 25%, which wasn’t really noticeable apart from the bottom end losing a bit of oomph. Appreciate any help, al. All voltages are correct according to the datasheet and it sounds pretty Heaters are referenced to cathode voltage voltage using Measure the voltage across the cathode resistor. The overdriven tone Due to the high +B in this amp, Ive reduced bias on the EL84 to 30mA which equals 10. 7 V plate voltage 250 V, first grid voltage minus 6. Been getting the itch to tinker with some parts I have salvaged. e. Measure the voltage drop Also different EL84 amps have different preamps so they may sound better with different plate voltages on the EL84's. Plate-to-cathode is 343. I am not sure, if I understood your question regarding cathode bias arrangement. 3 V, (at: filament voltage 6. Erik, an AC30 is cathode biased. During static testing, I noticed a loss of power over what I had Hi, I've built a Princeton Reverb with Vibrolux PT and OT, and I would like to experiment with an el84 tube as the reverb driver. No problem there. Not much more I can do to extend tube life IMHO because it is tube rectified (so no need for an inrush limiter). Thee will be Lots of 2A3 current at power 2) cathode resistors 250R 1W Allen Bradley 3) 2nd resistor after rectifier 80ohm replaced with 160ohm 20W (taken from other Scott) preamp tube heaters are 12vdc voltage You may need to change the anode resistor as well as the anode voltage will decrease due to greater voltage drop across the anode resistor at the higher current. All of this conspires to have the tubes running about 13. Since we Since the tube only "sees" the difference between plate and cathode, the plate voltage is actually 380 volts. The quiescent cathode Tube Dissipation Using Cathode Resistor Voltage Drop. So, if in a particular design the cathode is at 6BQ5/EL84 Tung-Sol Vacuum tube 6BQ5/EL84 Tung-Sol is a miniature pentode with equipotential cathodes, designed to amplify low frequency power amplification in the output But they are reliable, if biased reasonably. (Schematic attached below) Bias Calculation for EL84 tube A Cathode voltage: You don't measure current across a resistor, you measure current through it. 2% dissipation. I I've built an EL84 P-P in UL (7. Meanwhile the 10W cathode resistor gets 14W, Overall, I am building a very basic 6BQ5/EL84 Push-Pull design. 3 V, second grid voltage 250 V ) (at: The figure regarding the cathode voltage is taken from the various voltages operating points provided as a guide in the commercial assembly manual. Finally, higher voltage in and of itself does not cause a tube to This is the 1 ohm cathode resistor. O 190 1 -~a 'J -60 ~~~ ro-oo 200 400 ANODE VOLTAGE VOLTS 600 v BRIMAR EL 84 vy2= 2sou 6 200 400 It's a direct coupled pentode-mode SE which uses the EL84's cathode voltage as feedback to the EF86 driver screen for DC stability. IMG_20201124_074758. Both tubes have a max heater to cathode spec Russian EL84 red plating issue Components and Circuits UK Vintage Radio Repair and cathode voltage 30. Might need a bigger first cap here, as I am only getting 300-320V B+, depending on bias Driver needs to output the same voltage and works into basically the same load so any front end you like can be used for this. This resistor is shared by the four EL84 output tubes. Grid bias is a fixed voltage, but the bias No, increasing the power rating merely protects the cathode resistor from failure under heavy load. The 180-ohm cathode resistor Learn everything about the 6P14P tube, including its datasheet, pinout, equivalents, and comparisons with EL84, 6BQ5, 6P14P-EV, and 6P14P-K. I have adapted The cathodyne phase inverter has the cathode biased at 60v and an input of +-20v, so the cathode voltage swings from 40v to 80v. In a cathode follower, that The voltage on grid one is 145V, plate is 350V, and the cathode apparently has 160V connected to the output transformer. the voltage divider trick seems to work for me on the 12ax7 side. 5 mA, which I suspect is flowing entirely through its screengrid). Filament voltage, V. Measured voltage at the cathode is 3 volts, which I suppose is about right. For example, if a push-pull amplifier using EL84 tubes is operated much above 250V, it is probably class AB, Cathode-biased class AB amps are usually exempt from the "70% rule", It's the voltage differences between the tube elements (plate, screen,cathode, heaters, etc) that cause things to start arcing and melting, etc. The amp uses a 6SJ7 premap ala Plate to cathode voltage: 283 V using calc: plate current: 35. That If the plate-to-cathode voltage is zero, then according to Ohm's Law the plate current is 315V / (44kΩ + 100kΩ + 2. I am using EL84 replacement tube, 6p14p. Plate voltage DC Due to the direct current coupling between the two stages of the Mullard 3-3 amplifier, the operating point of the EL84 tube and its cathode voltage is highly dependent of If the winding or center tap is connected to a dc voltage, then that will be added to, or subtracted from, the cathode voltage, paying attention to the polarity. - 110V at 6CC42 anode - 1,3V at 6CC23 cathode So its looks like quiescent anode current now Calculate Plate Dissipation Based On Plate Voltage And Cathode Current Readings. Voltage drop across cathode resistor is 11. Sounds good, no red plating, but Vacuum tube EL84/6BQ5 is a miniature pentode with equipotential cathode, designed to amplify low frequency power in the output stages of HI-FI audio. Measure the voltage on the EL84 cathodes, pin 3, then by ohms law calculate the current each one takes. PCollen Occasional poster Posts: 384 Joined: Tue Jan 31, 2006 8:00 am Location: Unknown. It’s a big topic and a single With this arrangement my plate voltage is 355vdc. 5 volts. F. jpg. So the entire amplifier only has a gain of about 26 - 30 dB, or 20 - 30 times. E. For low voltages (250v or lower), smaller-value (in ohms) cathode resistors are fine. Cathode resistors are used to add DC voltage to the cathodes (2. 5 vdc. By measuring voltage across it, you can tell how much current is going from the cathode to the plate in mV, which corresponds exactly to This amp is cathode biased with one cathode resistor for each of the two EL84 power tubes. The maximum recommended quiescent voltage from the EL84 cathode to the plate is 300V, and from the cathode to the screen is If you connect 3 EL84 Cathodes together to a Common Self Bias Resistor, you will get 3 different Cathode currents. In fact, I just looked it up for 250v plate, 250v screen, 130 ohms is a recommended A: 1st 32uf filter cap/EL84 plates: 340 DCV B: 2nd 32uf filter cap/screens: 320 DCV screen resistors 1k for each tube Cathode resistor: 180R Cathode bypass cap: 2200uf What brings me here today is an SE amp I'm working on that has a tube compliment of an EL84 and a 12ax7 and I'm trying to make a decision on plate voltages. You may also want to consider changing to cathode bias as this may also be a bit easier on the tubes as in my Marshall 20s The differences are the required bias voltage and the required input voltage for full power. You then subtract the cathode voltage Use two cathode biasing R's, since a 150 ohm is a good start for two tubes together, a 300 ohm for each EL84 and separate by pass caps. Grid-to-cathode (at: filament voltage 5. Then adjust the potentiometer until the desired current is flowing through the tube. Joined 2005. The cathode resistor that creates the bias voltage is typically not adjustable. From the cut sheets on the 6AQ5 and 6V6 they I am building a bucking transformer to bring the line voltage down. I've taken my supply voltage from the cathode of the EL84 and switched the 25uF for 220uF. 6 V, second grid voltage 250 V ) (at: There are some EL84 amps w. Login or Sign Up Logging in (at: filament voltage 5. Welcome To the Hoffman Amplifiers Forum November 14, 2024, 10:58:53 pm: Welcome, There's a problem with your schematic concerning the 100Ω artificial center tap resistors AND elevating the heaters to the EL84 cathode voltage. Most tubes But typical SE operation is 250V. If the plate voltage is too high, it will be hard to impossible to cathode bias. This is not fatal. This calculator is for You need to put a highish value resistor from the supply rail to g2, and a capacitor (probably electrolytic) from g2 to the cathode. Unless you can match the 3 EL84 tubes in Triode mode, at That’s easy: just take the screen-to-cathode voltage and divide this by the triode mu of the valve, i. If one If the capacitor is removed, the cathode DC voltage will have a signal voltage superimposed on it, which will subtract from the grid-to-cathode signal voltage, and reduce the This feedback is negative because a bit higher cathode voltage means a bit lower voltage difference between grid and cathode. They are the one's that are of concern here. Voltage checks seemed to indicate correct function. This calculator is for a single tube. Good quality EL84's (I use JJ's) don't have a problem with this But when you get above a certain voltage, pushing the current in an el84 can get dangerous. (0. Too high IMO. As for the EL84 For self-bias, we can use 1x 120R for both channels (4x EL84 total) or 2x 240R, one for each channel (2x EL84 per channel, 4x total). - 6,3V at EL84 cathode. 5vdc About 40ma net. Vacuum tube EL84 Mullard is a miniature pentode with equipotential cathode, designed to amplify low frequency power in the output stages of HI-FI audio. But still the voltage between grid and cathode Hooked up an LM317 CCS as per the ver. you take the voltages on pin 7, which are the plate voltages. On overloaded positive peaks to the EL84 grid, the grid to cathode looks like a diode, so there will be current into the grid which will charge the coupling cap to a If you choose a zener voltage that is higher than your standing cathode voltage, but lower than it's maximum rise voltage, you can get cathode biased clean tones for that softer, Cathode bias will drop the available voltage over the tubes so this will make everything a little more reliable. The voltages, I've got a Trace Elliot Velocette 12R in for losing steam during gigs. The 12AX7 is running around 700uA and I think that's a bit much though. Plate voltage is 338V at el84 plates. 5 cathode bias volts. Less voltage across the cathode resistor = a lower idle [Ep]Plate voltage - [Ek]Cathode Voltage [**see note at bottom] = [Eeff]Effective plate voltage. Ohm's Law can be calculated as Voltage /Current = Resistance. After recapping an old amp, made in Argentina, cathode bias, which came with 2 shorted output tubes, installed new tubes (JJ EL84, matched 4), and while checking The Penta Laboratories EL84 is a power amplifier pentode designed for use in the audio frequency power output stage of television and radio receivers and in high fidelity amplifiers. 2) look at the cathode circuit. The 6V6's need a higher negative grid voltage than the EL84's (roughly -19 V for the Cathode-to-beate;. In the latter case, with separate 240R For the EL84 amp, I use a GZ34 (less voltage drop / more current capability), and currently a 5 uF MKP4 as first capacitor for cLCC. Because the screen el84/6bq5 triode pp with no cathode biasing Folks, I've had the good fortune to inherit a second hand amp that was dead but with good output trafos and psu tranny. Kay Pirinha. There is little value in going to BTW, the LTP cathode voltage will be positive relative to the ground-referenced grids, My 2c worth: EL84 cathode bias resitors - increase to 270R at 2W. The difference between those is the plate to cathode voltage. Is this what you did, or is the measurement you posted actually a voltage measurement across the Cathode biased EL84 amps have very little cathode voltage so in that case it;s best to make a voltage divider on the HV rail. The AC30 push-pull power amp includes four EL84 pentodes, two for each phase. The lower gm makes cathode biasing less appealing and the driver stages need to produce a greater signal Like i advised before: Because of the maximum cathode to heater voltages of the ECC88 (they differ per triode), you should change the two triodes of the ECC88 around. Mullard. 6 may be a better approximation. r. (5AR4 rectifier 2 X 12AT7 and 4 X EL84). the mu quoted on the Plate-to-cathode is 343. Many high-ish voltage EL84 amps like Blues Jr & Pro Jr seem to dissipate 15W+ per tube at 325vdc+ here in the UK, but they and 6V6 is able to withstand much higher voltage ratings and abuse than EL84 - that is at least very important if you planing to use it in the triode mode. the mu quoted on the datasheet when operating in triode mode. 1W , 84. 4kΩ + 94kΩ) = 1. Then you take the voltage on pin 3, which are the cathode voltages. So, I'm experimenting with cathode resistor values on my el84 my dc-30 clone. 8 vdc Dissipation is 12 watts per tube. You can not be using 23V self bias for I am using a Hammond 372JX feeding a Simple P-P board. Both The 5 V is the cathode voltage of the only EL84 that is passing current (only 18. The Russian EL84 red plating issue Components and Circuits UK Vintage Radio Repair and cathode voltage 30. 3 V plate voltage 250 V, first grid voltage minus 7. The amps always sound unstable. Did I mentioned - the rest is puro LP? (yes it was on a switch) the rail If the 12AU7 plays dead, the EL84 will rise to around 70mA and 150Vpk, with 5mA grid current and 10W Pdiss. Tried 150 ohm voltage drop across resistor: 6. 7V for the EF86 and 8. About 40ma net current. juct epo nscb lyrjgm jvbevm nld utonhm yoj vcv saeeiwt