El84 Cathode Bias

Special Order. EL84 Power Tubes provide 15/30W of Power in Class A modes. In this type of bias, the characteristic curve of the diode is shown in the fourth quadrant of the below figure. Using a matched set of properly biased tubes will yield a clear smooth sound that is fairly warm and transitions into a smooth breakup with that singing tone that EL84’s are known for. I'm staying away from UL for the EL84's because it came out so dark and sterile in a. Description Close reproduction of NOS EL84, Electro-Harmonix version sis contructed to withstand the heat better. As you hit a note the tube calls for more power and negative voltage on the cathode decreases briefly changing the tube's bias. welcome to the enginerd diy tube amp blog- a website dedicated to the do-it-yourself amp builder using a cost-effective approach to building vacuum tube guitar amps browse by topic on the. Comes in a Head, Combos are available in 1x12, 2X10 and 1X15. Their cathode K1 is connected to tag 6 (orange) and cathode K2 to tag 9 (violet). Tubes on the other hand now need to be biased properly for extreme performance, the tubes need to be perfectly matched. Super Goldtone is the next level – if you’re ready for it. 3) Choose a desired cathode bias voltage and divide by the cathode current for the resistor value. Grid 2 normally has its own node on the power supply, but in triode mode, it is connected to the anode. Everybody says it will, but I don't hear it, and I've tried it on probably 20 different amps…. CATHODE BIAS or Automatic Bias or Self Bias, call it what you will, is and always has been used as a safe, effective and somewhat automatic way of setting the bias point of output tubes, (or any tube for that matter), hence the name Automatic Bias. Signal waveforms also distort. Grounded Grid Tetrode General Example Let's assume we have a tube operating in AB1 with a grid-to-cathode bias voltage of -50 volts. A classic 50 peavey is to compete with fender hot rod deville using 6l6 bottles and 60 watt so maximum output from the 4 x El84 is wanted. Cathode Bias Resistor 150 Ohms (Now 160 Ohm) JJ EL84 Valves - 150 Ohm resistor now replaced with a 10 Ohm and 150 Ohm in series to obtain accurate biasing for 12W on the plate. 3 volts even after the warm-up, you should further investigate around the EL84 biasing. The data sheets seem to indicate that the 6sj7 remains fairly linear more or less to cutoff. Fit for EL84 6BQ5 6P147189 6P1 tube. Yep, that's definitely a cool feature in "fixed bias (aka, adjustable bias)" EL84 amps. Furthermore: When substituting old stock el84's for the modern Russian equivalents. In a properly biased amp, the plate current x plate voltage should be in the neighborhood of 70% of the max plate dissipation for an EL84, or 12W. Traynor ran their EL84/6BQ5's at 420v,but had lower current and dropped the screens down to sane levels. If you have not been trained to work with high voltage then have an amp technician adjust the amp's bias. Cathode Bias with a Constant Current Source A few years ago, I received many e-mails asking for help on how tube-based, push-pull amplifiers that used a constant-current source at the output tube's connected cathodes worked. The TELEFUNKEN ELTK is a perfect replacement for any EL84 / 6BQ5 tube offering a reliable and great sound. That extremely high plate voltage didn't seem to bother them. JJ EL84 PDF - Buy Used and Save: Buy a Used "JJ Electronics Amplifier Tube (T-ELJJ-MP)" and save 52% off the $ list price. The JJ tubes also sounded very good. 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). The EL84 has been one of our very favorite tubes for many years, extremely long lasting and reliable,. The tubes are AC heated as I think that DC heating make the amp sound too dull. It can accept a wide variety of tubes, including EL34, KT66 and KT88, etc. With cooler grades the dissipation is around 80 to 90% and the tone is still warm and juicy. Problem: What is the plate dissipation at idle?. 92 Likes, 4 Comments - Shyboy & Tex Repair Co. 05" to reflect a total current of 50 mA. I think Cathode Bias sounds good as well (300 ohm 5 watt resistor, 22 microfarad bypass), it adds a little grain and sparkle. Grounded Grid Tetrode General Example. Nice, warm tone in guitar amps, especially on cathode biased amps. In cathode biased amps, the grids will be held at ground, but for a fixed bias amp you should have -20 to -60 volts here, depending on what kind of output tubes the amp uses. The negative bias voltage is often designed to be adjustable by way of a bias pot. I like the 6V6 mod however. Tube Dissipation Using Cathode Resistor Voltage Drop Please enter Tube Type and Plate-to-Cathode Voltage above before calculating Tube Dissipation. The EL34 has separate g3 (pin 1) and cathode (pin 8) terminations, whereas the EL36 does not; in the EL36 both g3 and cathode appear at pin 8, while pin 1 is “n/c”. In fact, they can't be biased as I just mentioned. For adjustable fixed bias amplifiers, the amp should be biased by a tech with experience. The output stage draws a high current compared to e. I needed some matched sets of EL84 tubes to install in two Crate Vintage Club combo amps equipped with non- adjustable fixed bias. If your amp comes with one of the common octal power-tube types (6L6, EL34, 6V6, 6550, 7027, or 7591), these converters allow you to plug cathode-biased EL84s in their place without bias adjustment. Just got the schematic last night and had a look. 6BQ5 / EL84 tube data Key: Rp=8k PP fixed bias. As such, fixed bias squeezes the most wattage from a pair of output tubes while also sounding punchy and tight in the process, relative to cathode biasing. Connect the voltmeter across the cathode resistor W36, 120. By TJIann, The amp is cathode biased which is a older approach to regulation and thusly a more classic tube sound. I've been tempted to build my own EL84 amp, though I will stay with single-ended, as I don't need more than a couple of watts with 99dB/W speakers. Yellow Jackets are a type of specialized adapter which permit the use of EL84/6BQ5 power tubes in place of 6V6, 6L6 and EL34 types, and converts any amp to Class-A operation. For triodes, like you mention, it suggest the same I k pot across the heaters on the valve base, but lifting the ground end of the cathode bypass cap and connectiing that to the wiper. External Locking Bias Trimmer and Test Points on back panel. The amp is fed between 300 - 310 volts (depending on the wall voltage) and idles at 155mA. Cathode Bias with a Constant Current Source A few years ago, I received many e-mails asking for help on how tube-based, push-pull amplifiers that used a constant-current source at the output tube's connected cathodes worked. The YJC is an adapter that permits the use of an EL84 power tube in place of a 6L6, EL34, or 6550 in cathode-biased amps. Plate Dissipation (Watts) Note: For calculating plate dissipation in cathode biased circuits, subtract the measured cathode voltage from the measured plate voltage and use that as the plate voltage in the calculator above. From the schematic, the EL84 only use -10V bias!!! I can tell you, I almost never see a low voltage like this causing the cap to leak and short out. 1x ECC83/12AX7 preamp/tremolo tube. Back in 2004, I asked a friend of mine to test the first prototype with his four Quad ESLs. The EL84 was developed to eliminate the need for a driver tube in radios, so it has rather more gain than is usual in a power pentode. The amplifier’s extreme touch-sensitivity alllows you. The Bassbreaker 007 has one EL84 in a single-ended, cathode-bias arrangement. EL84 is high transconductance pentode, used as class A1, AB1 and B in audio amplifier. 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. Miles's Taste Tests for 6BQ5 / EL84 Overview I got five new EL84/6BQ5 (the EL84 was the European designation; the 6BQ5 was the USA designation) type tubes from Lord Valve, Ned at Triode Electronics and Jim McShane. The cathode resistors for the output tube are of the new type in TO220-package (partly visible left of the octal socket). Used Telefunken EL84 Vacuum tubes for sale on + second hand hifi sites & shops. (In triode anode and cathode currents are equal). The quiescent current is set by R24, which is bypassed by C19 for extra gain. Although it is. Comes in a Head, Combos are available in 1x12, 2X10 and 1X15. Fixed bias means that bias is provided by a separate negative supply, not by the cathode resistor, commonly known as self-bias. If the anode voltage is too low, the phase splitter bias will be too high, and the stage will operate away from the linear position of the valve characteristics with a resulting increase in distortion. This circuit can output ~10 Watts in UL operation. Running a pair of these big bottles in a cathode-bias, Class-A configuration results in the very loud 35 watt power section of the original tube-rectified Supro Thunderbolt. The footswitchable trem effect is achieved by modulating the bias of the phase inverter, yielding a smooth musical effect that is not effected by the volume of the. Aye it's also the same pin out and another substitute you can try, although you'd have to be a little more careful and that nothings been anchored to pin 1, you need to check the pinout on most el84 amps anyway when valve rolling since the old and. Fit for ECC83 12AX7 ECC82 12AU7 ECC81 12AT7 12BH7 6CG7 ECC99 ECC88 6922 E288CC tube. This tube has under gone continuous improvements. Checking the bias current in a cathode biased amplifier is easy, just measure the voltage across the cathode resistor and divide by the resistance value to obtain the cathode current. Its screen voltage is taken off the cathode of the output tube which stabilizes the bias conditions for both tubes. EL84 Power Tube. For this new amplifier I have chosen to use 4 x EL84's as this is a logical progression from the ValveTone 10, which uses a pair of EL84's to deliver 10 watts. It is an inexpensive and easy method of generating a negative bias supply for an amplifier which uses a full-wave, center-tapped rectifier, either tube or solid-state. Reminiscent of vintage tweed-era warmth but with unique tonal qualities. The Cathode Follower An amplifier with the anode as the common terminal is called a cathode follower. Billy Rocker: 16-watt cathode-biased 6V6 or EL84 output tubes operating in class A push-pull with 5Y3, 12AY7, and 12AX7/7025 tubes. I have a cathode biased amp. Note that if the output tubes share a common cathode resistor, you must divide the current reading by the number of tubes sharing the resistor. el84 v5 el84 c r19 1k/ w c 7 8 6 r25 470 r30 47k r24 1m r26 1m c14 0. g1fest fixed grid bias 2) I g1+0,3 µA Limiting values: U a = 300 V W a =12 W U g2 = 300 V W g2 =2 W U g1 = -100 V I k = 65 mA R JJ EL84 Datasheet 2003 Created Date:. The negative bias voltage is often designed to be adjustable by way of a bias pot. Normally they are used in a very simple circuit that features no negative feedback and are run in the cathode biased mode which gets close to them being run in class A, which makes for a. Yellow Jacket® Converters not only rearrange the pin locations of the tubes, but also provide the necessary current limiting on the screens and cathode as well as blocking the amplifier's grid bias voltage, while configuring the EL84 in a Class-A, Self-adjusiting cathode-bias circuit. Plate current can be identical on two tubes (tubes are matched by plate current readings) while one tube is drawing more screen current; with this method, the readings will appear to indicate a mismatch when such is not actually the case. So to answer the original question, you can just replace the tubes without worrying about biasing the amp. This means putting the 1 ohm resistor in the anode circuit and not the cathode circuit. It seems that the modern ‘guru’, never at a lack for self-esteem, loves to bully people into feeling inferior with incomprehensible techno-babble if they should dare disagree with his repair methods. The negative grid voltage (bias voltage) required to get the tubes idling in an acceptable range ,will be ,well what it will be. Some amplifier are self biasing in that they use a fixed bias or a cathode bias which is not adjustable. There are very many cathode biased EL84 circuits around so would expect the KT88 to sound much the same but bigger. When a tube is fixed bias, though, it means there's a pot somewhere. This project is a bit of a departure for me. Problem: What's the expected cathode voltage? Solution: Ek =. Amps with the cathode resistor you mentioned are cathode biased and generally run at a higher idle dissipation. page 11Distortion for triode class AB. El84 Tubes are for good sound reproduction and this is paramount importance unless they do not last of fail quickly. Higher B+ (up to 380 to 400VDC) can be used, just reduce the plate current accordingly, to 30 mA or less. While the EL84 is capable of 15-20 watts the distortion goes up significantly when UL operation is not used. JJ EL84 tubes were the only EL84 tubes I found that were perfectly biased to these Crate amps. Cathode biased amps are self biasing as you know. Otherwise bias must shift between idle and full, i. And that's where the 'fixed' bit comes in. From what I learned you'd like a voltage rating for the caps that is 1/3 more than the actual voltage there for a 50% extension of life so an EL84 SE is typically 10 volts or less for the cathode bias so a 16 volt would be fine. The philes tell us that cathode bias is no where as good as fixed bias. When I noticed that I set it to the more normal -7v, but the stock design with 2. I find it currently alittle unpleasant - it has a harsh breakup even at lower gain levels. Yellow Jackets are a type of specialized adapter which permit the use of EL84/6BQ5 power tubes in place of 6V6, 6L6 and EL34 types, and converts any amp to Class-A operation. By Peter Stewart Gebbie. Although it is. The ground wire is used to bypass the amp's original cathode bias components so that the Yellow Jacket® converter's internal bias components are used instead. The tubes were running at 13 watts or more and we could hear a 'tick' in the speaker. To do this set your multimeter for DC Volt measurement, clip the black probe to a chassis ground (so you can use just one hand to do the measurement) and put the red probe on the tube socket cathode pin 8. That means the cathode can charge 63% of the way to some new value in ~20ms. The improvement is measurable on the bench as increased power output and reduced distortion. In a properly biased amp, the plate current x plate voltage should be in the neighborhood of 70% of the max plate dissipation for an EL84, or 12W. Medium numbers are the most versatile, will drop into most amps and be very close to most factories bias settings, and are the best general choice for most players wanting a versatile well rounded amp. Because these Philips OPT's do not have an airgap, the EL84's are to be biased exact symmetrically. If you not sure of your amp compatibility with our tubes, please check with us before placing order. The grid-reference resistor (Rg1) can be found by consulting the data sheet for the maximum allowable value in cathode bias, which will usually be less for a power valve than a preamp valve. Current through both EL84's was increased to 56mA per side for optimal interaction with the Philips OPT's. EL84 Power Tube. All amps will have their bias checked and adjusted if necessary fixed or variable or cathode will all be check on our TAD bias master Any 15 watt amp (2 x EL84 ) £69 Any 30 watt amp (4 x EL84 ) £89 Any 50 watt amp ( 2 x EL34 ) £89 Any 50 watt amp ( 2 x 6L6GC ) £89 Any 100 watt amp ( 4 x EL34 ) £119 Any 100 watt amp ( 4 x 6L6GC ) £119 If. It's a good idea to check the bias on these units every now and thenmore so than on your 400. With fixed grid bias on the EL84 also the bypass capacitor required in case of cathode bias can be ommited. This kit includes all the parts to build a single octal socket TubeDepot Bias Scout. It utilizes two EL84 output tubes in a push-pull configuration, and has switchable fixed- and cathode-bias on the power tubes, and an ultralinear / pentode switch on the output transformer. This is actually a method of calculating plate dissipation in watts of a Cathode biased amp by using just a voltmeter, not how to bias as the title suggests. The JJ tubes also sounded very good. More specifically, the design of this vacuum tube amplifier is described in details in " Chapter 6: Step by step design of a push-pull tube amplifier. Meticulously assembled with only the best sounding and most reliable parts. We also know that using a cathode resistor drops the power output. Now the two cathode windings are used, while resistors R21 and R22 function as well, enabling you to measure the quiescent currents. Maybe 90W/pair allowing for bias-shift. They should build an adjustable bias system that can't be adjusted far enough to really fry the amp, with a user-accessible knob and meter calibrated for cathode current in green, yellow and red zones, so on tube changes the user can quickly adjust to the same idle current he had with the old tubes, without needing the services of a tech. 5V and the cathode resistor is 390ohm. If you are trying to get the maxium power out of a EL84 tube fixed bias, controlled by a 10 turn screwdriver adjustable pot is the way to go. I find it currently alittle unpleasant - it has a harsh breakup even at lower gain levels. That extremely high plate voltage didn't seem to bother them. I guess that, when the grid bias falls toward zero, even the sound decreases. EL34 Power Tubes provide 25W of Power in Class A mode and 50W of Power in Class A/B mode. More negative bias can be generated by reducing the value of the 68K resistor hooked to the 6X5GT cathode. Problem: What is the plate dissipation at idle?. Effective cathode resistance. The cathode resistor is an energy. Includes a pair of Yellow Jackets converters and a pair of EL84 tubes 50% to 70% drop in output power Perfect for getting killer power tube break up at lower volumes or taming amps that are too loud For use with amp that range from 20 to 100 watts Comes with a ground wire for cathode-biased amps. When the Skylark is set to full power, the attenuator is taken completely out of the circuit. Super Goldtone is the next level – if you’re ready for it. Note that EL84EH tends to bias 'hot' and may not work well in fixed bias amps like Peavey Classic 30. Yellow Jacket Converters not only rearrange the pin locations of the tubes, but also provide the necessary current limiting on the screens and cathode as well as blocking the amplifier's grid bias voltage, while configuring the EL84 in a Class-A, Self-adjusiting cathode-bias circuit. I said they wern't intended to be ran in cathode bias not that they wern't mostly used like that. Cathode biased amps are self biasing as you know. With cooler grades the dissipation is around 80 to 90% and the tone is still warm and juicy. Sachant que le courant de cathode est la somme du courant d'anode et du courant de la grille écran. EL84 Voltages: Bias Resistor: Cathode Current: Volts DC Ohms mA Watts AC Mains: El84 6V6 Pin 9 Pin 4 Pins 4&5 2&7 - Power Cord Jack - Pins 4,5 - 9 1000. Working chassis to fit in your Blues Junior cabinet $1099. V1: JJ ECC83, V2: Tung Sol 12AX7, V3/4 JJ EL84 (matched pair), V5: 5Y3. Fender Champ, Fender Tweed Deluxe, and VOX AC-30 are common examples of cathode-biased amplifiers. Anyway, it's good to see Osamu's test results. This is what bias does, either by applying a negative voltage to the grid (fixed bias), or by putting a positive voltage on the cathode (cathode bias). I've used EL84 in triode for. It utilizes two EL84 output tubes in a push-pull configuration, and has switchable fixed- and cathode-bias on the power tubes, and an ultralinear / pentode switch on the output transformer. EL86 is another tube like EL84, but triode Ra is 1k4, µ = 11, and it likes lower Ea than EL84, so its a fabulous input/driver/whatever tube IMHO. in this kind of amp, the bias is generally set with a cathode resistor yes, it's fixed, but it makes the tubes self bias. I find it currently alittle unpleasant - it has a harsh breakup even at lower gain levels. Buy Telefunken EL84-TK Black Diamond Series Vacuum Tubes (Matched Pair) featuring Pentode Output Tubes, Ideal for Guitar Amps & Hi-Fi Gear, Ideal Replacement for EL84/6BQ5, Distinctive Chiming & Articulate Sound, Delivers up to 17W of Output Power, Characteristic "British" Tone. The negative grid voltage (bias voltage) required to get the tubes idling in an acceptable range ,will be ,well what it will be. EL84 Single Ended AmplifierD. even Mullard EL84 old tube if you can get too. As per usual when putting in new, properly spec'ed (i. These tubes are run as cathode followers, directly coupled to the grids of the KT90′s. In (b) , the bias resistances are replaced by their parallel equivalent Rg. Here's a collection of Bias-modulating "Tremolo" circuits which I use for retro-fitting common class-AB guitar amplifiers, circuits which are mostly based around the high gain 12ax7 dual Triode. Fixed bias amplifiers can be either adjustable or non-adjustable. Amps with the cathode resistor you mentioned are cathode biased and generally run at a higher idle dissipation. Hi Joe - there are a few ways to bias the tubes and currently the most popular is fixed bias where you can adjust the voltage, some use cathode bias (which is more common than one thinks) and then we have auto bias. The Traynor circuit was a pretty close copy of a BF Fender, but they used EL84's and SS rectifier. How Vacuum Tubes Work by Eric Barbour - [Inside a Tube] - [Why are Tubes Still Used] - [Using Tubes] The BASICS. It is a thermionic valve of the power pentode type. In the diagram, the cathode bias resistors values did not give the required anode current measuring resistor values need to determine, because of the same brand same model light of the lamps even bias notices, were left stranded on the EL84 instead 6bq5, 6p34p, 6p1p, 6p14 as equivalent wear what happens if you would think about it,. Id like to see where the various bias values that people use relate to the 70% etc rule. Buy Yellow Jacket Cathode Biased Tube Converter For 6L6 / EL34 / 6V6 / 6550, Single: Tubes - Amazon. Unfortunately, the design is a bit difficult to incorporate in higher powered amps, which is one reason for the limited use in tube amps. Comes in a Head, Combos are available in 1x12, 2X10 and 1X15. The result is the "Fatboy" 300B amp - named as such because, like me, it is a tad overweight. Running a pair of these big bottles in a cathode-bias, Class-A configuration results in the very loud 35 watt power section of the original tube-rectified Supro Thunderbolt. page 11Distortion for triode class AB. EL84 SE – The Small One. Add a 150 kOhm/1W resistor tied from the plate of 12AX7A to the plate of 12BY7A. Unfortunately, while the design is very effective with these applications, it's harder to incorporate with higher powered amps, hence its limited usage in tube amps overall. The TAD ToneBone improves the amp sonically, its sensitivity and reduces the overall loudness so you can crank it up at reasonable volume. With cooler grades the dissipation is around 80 to 90% and the tone is still warm and juicy. Your amp has cathode bias. tOutput power and dt are measured at fixed bias and therefore fepresent the power ouput available during the reproduction of speech and music. Clear and clean sound. • 2x6V6 12W Class A cathode biased power amp • JJ ECC83s single triode 1. I have never found cathode biasing to rob all that much power from an amp. 5 watts Total harmonic distor tion at 16. 95 pair/duet A military-spec version of the standard Sovtek EL84. By Rob Robinette. If you are trying to get the maxium power out of a EL84 tube fixed bias, controlled by a 10 turn screwdriver adjustable pot is the way to go. I have read not to use these el84 in cathode bias amps just like many new production tubes and 12ax7 made today also do not last a week in cathode follower positions in preamps !. The EL84 is normally a pentode, which means it has 5 elements inside the tube: anode, cathode, and three grids in between. This cuts the power, and makes the amp darker. Cathode bias, however, is problematic from an overload point of view. Yellow Jacket Converters not only rearrange the pin locations of the tubes, but also provide the necessary current limiting on the screens and cathode as well as blocking the amplifier's grid bias voltage, while configuring the EL84 in a Class-A, Self-adjusiting cathode-bias circuit. I guess that, when the grid bias falls toward zero, even the sound decreases. Buy with confidence as the condition of. 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. Close reproduction of NOS EL84, Electro-Harmonix version sis contructed to withstand the heat better. Used Telefunken EL84 Vacuum tubes for sale on + second hand hifi sites & shops. The cathode current is composed of the plate current *plus* the screen current. The subject of output tube biasing has many otherwise rational men arguing amongst themselves like little school children. Best AUDIO TUBES listed at: 6BQ5 = EL84 / 7189 PENTODE TO BUY 6BQ5=EL84 TO BUY 7189 and 7189A 6BQ5/EL84 Near Equivalent = 6CH6/EL821 It is NOT a plug in equivalent for the 6BQ5, but a near equivalent in specs. The Fender 5F6A Bassman and most Marshall amps are fixed bias Class AB amps. The 70% figure refers to fixed bias amps. If one of the 12AX7's has a heater failure, it can alter the bias of your output tubes. 6BQ5 / EL84 tube data Key: Rp=8k PP fixed bias. I also have a stock jet city jca20H (LTP, fixed bias, cathode follower before tone controls, master volume, positive feedback a very different amp) and it's a lot louder than this one (even the cleans are quite loud with my stock telecaster); but I. The TAD ToneBone improves the amp sonically, its sensitivity and reduces the overall loudness so you can crank it up at reasonable volume. The data sheets seem to indicate that the 6sj7 remains fairly linear more or less to cutoff. Happy playingand good luck on setting the bias in your amp! remember you are dealing with high voltages so take extreme caution!! As always just email us or phone us with any questions. on the pluck, and that's distressing. These cute little guys produce around 40 watts RMS in Ultra-Linear mode or around 20 watts in TRIODE from a quartet of EL84 / 6BQ5 tubes driven by a 6414 dual triode driver and a 12AT7EH input dual triode. Let's assume we have a tube operating in AB1 with a grid-to-cathode bias voltage of -50 volts. Bias current is measured by attaching an external ammeter to a set of test jacks, and activating the each tube, in turn, with a bias activation switch (shown at left). This bias is due to the tiny current that flows out of the grid through this resistor. In cathode bias a small value resistor is placed between the cathode and the ground so it develops negative voltage on the cathode thus achieving bias. Biasing an amp requires some knowledge of tube amp circuits and experience with high voltage. the mu quoted on the datasheet when operating in triode mode. values of Va and Vg2 are 250V and that of Wa is 9W. By owning a bias probe you’re not at the mercy of a tech anymore and you are now in control of your tone. Special Order. Finally, the step-by-step biasing of a single-ended cathode biased amplifier is demonstrated using a nice, original 1960 Gretsch Model 6150 amp. Triode type for most cathode-biased 6V6, 6L6 and EL34 amps. Recapping Guitar Amps. Insert tube in the socket of the probe. gain stage • JJ ECC83s 2. 5V Chinese/Russian valves 15 V Golden Dragon and NOS After modification BTW a new Doge 6210 is coming out which will use a circuit board instead of point to point wiring. Working chassis to fit in your Blues Junior cabinet $1099. Vox AC15) have cathode biased output tubes (EL84. In other words, wave peaks are flattened and valleys are deepened. com Make of Guitar Tube amplifier kits Our Pcb based kits are the fastest way to built your amp We have. If you are trying to get the maxium power out of a EL84 tube fixed bias, controlled by a 10 turn screwdriver adjustable pot is the way to go. You may wish to have certain fixed bias amps (such as Mesa Boogie®) modified by a technician to provide for bias adjustment. It's really nice sounding. Boost Footswitch for Channel 1 that disables the Treble and Bass controls and provides gain and volume boost and front panel LED indication. Raising the 100 ohm cathode resistor to 120 or 150 ohm would probably help with today's higher line voltages from the wall, where the 100 ohm R might run the 6BQ5's a bit hard. The amp has 4 x EL84, cathode biased with bias current for all four together determined by measuring voltage across a 10 Ohm resistor. Victoria Regal A combo amp featuring reverb and tremolo, The Regal is a pure, single-ended class A design that utilizes a new ‘Adaptive Transformer Technology’ that allows for the use of one or two power tubes at the same time. Immediately following are equations for calculating cathode voltages, currents and resistances. The Bassbreaker 007 has one EL84 in a single-ended, cathode-bias arrangement. Here's a collection of Bias-modulating "Tremolo" circuits which I use for retro-fitting common class-AB guitar amplifiers, circuits which are mostly based around the high gain 12ax7 dual Triode. I have never found cathode biasing to rob all that much power from an amp. The ground wire connects to the chassis-ground for cathode-biased sl84. The cathode biased quartet EL84 output section is responsible for a beautiful natural compression that supports the player. It's likely running somewhat cold, or hot, and your amp is apparently equipped with 2 12AX7 tubes, and 1 EL84. Your amp has cathode bias. Introduction to Triode vacuum tubes and calculating cathode bias resistor www. values of V a and V g2 are 250V and that of W a is 9W. I have a cathode biased amp. This is why you never have to bias them. I've been tempted to build my own EL84 amp, though I will stay with single-ended, as I don't need more than a couple of watts with 99dB/W speakers. In fact, I make this mod to all of the SE amps I build. However, it is always best to check that the idle power of these tubes does not exceed the maximum rating (12watts) in your amp. The high transconductance factor simplifies the design of driver stages and offers convenient self-biasing (cathode biased) operation. Cathode bias amplifiers use a cathode resistor to generate a positive bias voltage on the cathode while the grid is grounded through a 'grid leak' resistor. The cathode resistors for the output tube are of the new type in TO220-package (partly visible left of the octal socket). Remove the cathode capacitor, I read C61 but not sure, 100uF. Either way, this preference saw the Princeton upgraded to fixed-bias, and other than the single-ended Champ there was no longer a cathode-biased amp in the Fender line. Here's a collection of Bias-modulating "Tremolo" circuits which I use for retro-fitting common class-AB guitar amplifiers, circuits which are mostly based around the high gain 12ax7 dual Triode. It is an inexpensive and easy method of generating a negative bias supply for an amplifier which uses a full-wave, center-tapped rectifier, either tube or solid-state. The ground wire of the YJC is used to bypass the amp’s cathode bias components so the Yellow Jacket® converter’s internal bias components are used instead. The JJ tubes also sounded very good. Gambino pdf. EL84 cathode resistors are 150ω for about 48mA anode current giving near class AB1 type operation. In case you build according to the schematic shown below, depending on which side connects to the cathode of the EL84 via the electrolitic and which one to ground, the circuit is either an excellent amplifier or a powerfull oscillator. 2009) I have been able to bring it to an end. Some years ago a co-worker put JJ's in a small Mesa amp. There is no bias adjustment on these amplifiers. The Granger Amp bias probe measures in milliamps by insertion into the cathode connection that conducts the current to the plates of the tube. Current through both EL84's was increased to 56mA per side for optimal interaction with the Philips OPT's. Cathode Bias Resistor 150 Ohms (Now 160 Ohm) JJ EL84 Valves - 150 Ohm resistor now replaced with a 10 Ohm and 150 Ohm in series to obtain accurate biasing for 12W on the plate. Back in 2004, I asked a friend of mine to test the first prototype with his four Quad ESLs. THD Yellow Jacket Converter with EL84 Duet Tube Single. RE: First impression of Kenwood KW-55 receiver upgrade EL84 cathode bias is a mess. What is Back-Biasing? General. Plug into the AC20 and instantly notice the familiar chime and compression of the cathode biased Class A EL84 driven output section. Some amps have cathode biased output tubes (EL84) and unlike fixed bias amps, these amps don’t need biasing. ANd EL84 needs less voltage compared to larger bottles. Hi Joe - there are a few ways to bias the tubes and currently the most popular is fixed bias where you can adjust the voltage, some use cathode bias (which is more common than one thinks) and then we have auto bias. The EL84 has been one of our very favorite tubes for many years, extremely long lasting and reliable,. 22, Peavey's amps, Marshall 20/20 rack power amp, amongst others). 048 * 140 = 6. The Bias Rite Cathode Current Monitor is a self contained unit designed to allow the user to set the desired idle cathode current value with the G1 bias control. The negative bias voltage is often designed to be adjustable by way of a bias pot. 6BQ5 / EL84 tube data Key: Rp=8k PP fixed bias. Clear and clean sound. The operating conditions for the EL84 are taken more or less from the data sheets. Working chassis to fit in your Blues Junior cabinet $1099. That's easy: just take the screen-to-cathode voltage and divide this by the triode mu of the valve, i. hun » Sat Oct 06, 2012 11:05 am Les Paul Lover wrote: So if I understand correctly, a cathode bias amp is a bit miskeading?. Cathode biased power tubes will have a resistor and bypass capacitor connected in parallel from their cathode to ground, as seen with most preamp 12AX7 triodes. Traynor ran their EL84/6BQ5's at 420v,but had lower current and dropped the screens down to sane levels. Buy Yellow Jacket Cathode Biased Tube Converter For 6L6 / EL34 / 6V6 / 6550, Single: Tubes - Amazon. Consider an output stage driven beyond its means for a few seconds (my goodness, those kettledrums were loud!). This sets the grid voltage negative in relation to the cathode and establishes the proper operating current. Ik = Ek / Rk cathode current equals cathode voltage divided by cathode resistor value (Remember to convert milliamps (ma) to amps (A) by dividing ma by 1000. Contains the following capacitors, used as main filters, decoupling filters, bias filter, footswitch suppression, and cathode bypass capacitors in the Fender `65 Twin Reverb Reissue amp, produced from 1991 to the present and the Fender `68 Custom Twin Reverb amp, produced from 2009 to the present. Note that EL84EH tends to bias 'hot' and may not work well in fixed bias amps like Peavey Classic 30. A very popular choice for the studio or small club (or any venue when using a microphone). Cathode bias, however, is problematic from an overload point of view. I had to search a bit to find an example or two of the output stage I had in mind; EL84 Class AB1 push-pull in ultralinear mode, with cathode (self) bias. As the wave goes more positive, more bias is created, lowering the tube's gain. GA-30RVH • 30 watts • Class A • Four EL84 tubes • 100% Tube Signal Path • Two independent channels, each with boost and separate. EH EL84 is very good tone has. It's really nice sounding. 53 ma flowing through the cathode resistor is the sum of the anode and the screen grid currents together. The negative bias voltage is often designed to be adjustable by way of a bias pot. Cathode Bias Resistor 150 Ohms (Now 160 Ohm) JJ EL84 Valves - 150 Ohm resistor now replaced with a 10 Ohm and 150 Ohm in series to obtain accurate biasing for 12W on the plate. Circa ’63 is reminiscent of the Blackface Fender amps of yesteryear. I build quite a few cathode biased amps and I was wondering about the bypass cap on the power tubes. EL84 Voltages: Bias Resistor: Cathode Current: Volts DC Ohms mA Watts AC Mains: El84 6V6 Pin 9 Pin 4 Pins 4&5 2&7 - Power Cord Jack - Pins 4,5 - 9 1000. 9 watts I would bump it up to a 3 to 5 watt resistor. If the tube is protective biased, it has to be biased at a safe dissipation but must not be near cutoff. If your amplifier features cathode biased output tubes also, then you don’t need to bias that amp – ever. The Traynor circuit was a pretty close copy of a BF Fender, but they used EL84's and SS rectifier. The EL84 Class-A cathode biased circuit can be set to either 6 or 12 watts. For these reasons, cathode bypass capacitors can be important. Immediately following are equations for calculating cathode voltages, currents and resistances.