El84 Bias Voltage

Cathode Bias (Self Adjusting). Each EL84 has gain of about 18 and the two commoned cathodes are taken to a constant current sink, CCS, using MJE340. With the 16 Ohms in the emitter of the bottom transistor in teh CCS Bias Blocks you will get 40. If each tube has it's own bias screw, or if you have a PrimaLuna or Mystere amplifier with Adaptive Autobias, there is no need for matched tubes, though it certainly doesn't hurt. Output transformer - when needs must Components and Circuits. If you control those,the EL84's will live. Early models were set at 1. Improved voltage tolerance, plate dissipation, higher transconductance, more power and longer life than the less expensive EL84 The EL84 does have a warmer distortion where are EL84M is tighter and cleaner - Perfect for clean tones. Consider for example, the 2A3 triode, which requires 45V bias voltage. 1%, mainly 2H. 1mV, B 20mV, C 7. combinations. Figure 2 shows the ‘transfer function’ or ‘load line’ for this amplifier. 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. attempt an input voltage change. We specialize in the repair of electronic sound equipment and related products. as I understand it,musicman amps on high power run a plate voltage of 700vDC,this should fry any el84 in no time ,even the 360vDC at half power seems abit hard on that tube,the yellow jackets give these amps a kinda kool class A sound ,but it makes for a really heavy 15 watt amp,nice for studio work ,but kinda a pain for stage. an IF amplifier, so in effect, this can be used as a positive voltage source. ) will change optimum plate to plate load impedance. EL84s aren't used with fixed bias often because they need less bias voltage the effects of cathode biasing are reduced. For musician's use and to promote 'sag', the two output diodes may be replaced with a EZ80 or EZ81 rectifier valve, although you should also provide it with its own extra VT1036 heater transformer to avoid a large voltage difference between the cathode and heater (i. Measure the AC rms voltage with a digital meter between pins 6 and 5 of the Noval socket on the TV10 and adjust the LINE voltage control until it reads 5V +/- 0. 5, and a negative bias of -16 volts. So new coupling caps, and the problem went away. Anyway, it's good to see Osamu's test results. The high voltage 20-watt setting provides the ideal voltages for higher-power 6L6 or EL34 output tubes. The EL84's are being over run in these amps! Fender do the same but the over run margin is less. This code can beused to see what. As always biasing these tubes is a good idea for optimum tone. 9LE All tubes have a basing specification, or pin-out code. The grid will be at 1 V below the cathode so it will be running at 136V. There is also a "high voltage EL84" that was made by Reflector in ex-USSR states that is a military tube. 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. Furthermore, since the output voltage is 5V, approximately half the bias of the EL84 in this design, the resistor will perform half of the dissipation (approximately 250mW) leaving the remaining 1/4W to the. 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. 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. As the guitar signal causes the current flow through the cathode resistor to fluctuate so does the voltage drop across the cathode resistor (the bias voltage). Electro Harmonix EL34. The EL84 (6BQ5 or 7189) power tube. 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. Increasing or decreasing that voltage by a small amount will affect the amount of current drawn by the anode. An early direct coupled test circuit. The normal output of a '30 is 16 milliwatts, while with two such tubes in "push-push" an output of 1 watt is obtained - at a plate voltage of 157. Simply swapping the valves round will quickly show if the fault is in the valve itself or somewhere in the amp gubbins. If you are a metal fan , the Serbian made EI 6BQ5 sounds a bit more powerful, with ‘balls’ for rock music. And the voltage across the EL84 cathode resistor measures 15 volts giving a total EL84 operating point current of approx. Negative Bias Temperature Instability (NBTI) is a key reliability issue in MOSFETs. Amps with the cathode resistor you mentioned are cathode biased and generally run at a higher idle dissipation. Bias Tool testing probe for EL84 6BQ5 7189 amplifier 9 pin tube biasing USA MADE 5. Because, the output voltage is the reference voltage that will define and limit the current draw of each current sink, and thus each EL84. The yellow highlighted circuitry in Figure 6 illustrates the pair of output transformer taps that supply the bias voltage to the screen grids (pin 9) of the EL84 tubes in UL430 and UL730 amps. All tubes can be set to a fixed bias or with mod, an auto bias of sorts. Come and download the tube amp absolutely for free. BTW - the transformers come from an old Traynor. Unfortunately, the design is a bit difficult to incorporate in higher powered amps, which is one reason for the limited use in tube amps. For a typical output stage working from a 3l0V HT supply and using EL84 valves, the rise in cathode current -and thus in cathode bias voltage- with a sinusoidal signal voltage is about 40% at full drive. What you really want to know is the plate voltage, and then set current draw of the tubes by adjusting the bias voltage. Selects from high and low gain Specifications: 30 watts output Zero negative feedback Selectable Preamp Gain Response. TrANsfer ChArACTerisTiCs pLATe ChArACTerisTiCs A. The negative bias voltage is often designed to be adjustable by way of a bias pot. Bias current accuracy 1%25. 6 product ratings - Bias Tool testing probe for EL84 6BQ5 7189 amplifier 9 pin tube biasing USA MADE. 7V VON Negative Output Voltage Swing RL = 150 100 150 mV RL = 1k (EL8202,EL8203) 25 50 mV RL = 1k (EL8403) 50 100 mV IOUT Linear Output Current 65 mA ISC (source) Short Circuit Current RL = 10 60 80 mA ISC (sink) Short Circuit Current RL = 10 120 150 mA POWER SUPPLY. as I understand it,musicman amps on high power run a plate voltage of 700vDC,this should fry any el84 in no time ,even the 360vDC at half power seems abit hard on that tube,the yellow jackets give these amps a kinda kool class A sound ,but it makes for a really heavy 15 watt amp,nice for studio work ,but kinda a pain for stage. Self-biasing (or cathode biased) circuit is a very common power amp design. These tubes lasted only about 10-12 playing hours. By employing a higher voltage, over-biasing can also lead to early signal distortion. This is a monophonic setup the left and right channels are added via resistors before the input. That's the. If you are in doubt, look on your Peters amplifier for the bias test points and bias pot opening; if it has these provisions, then the biasing instructions here apply to it. I noticed that Fender runs the screen voltage on the EL84 of the Blue Jr a good 22VDC below the anode voltage (X tap versus B+). It uses fixed bias and low feedback. [2] SPEAKER OUTPUT JACKS: Provided for connection of speaker(s) or speaker cabinet(s) with a. This circuit can output ~10 Watts in UL operation. In these calculations, 5% of the cathode current is assumed to be screen current. It is fixed in the sense that the bias voltage is always constant, regardless of the music signal applied to the circuit. The plate and the grid #2 voltage are fixed, non-changeable values, while the so-called bias voltage at grid #1, which is negative, can be varied (only by a qualified person!). I've read up on a lot of mods, all of which involve reducing the negative voltage to the control grid from the existing -11vdc to about -14vdc. Pulling the power tubes and measuring the voltage from the grid to ground showed a positive voltage. View our Tube Biasing Tutorial online. Amps with a single EL84 output tube are probably class A and will run normally at around 100% max. 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. Bias resistor on Q1 is 1Mohm Q2 bias is the voltage divider plus 50K pot and Q3 has been replaced with a 10K pot. They are the only folks I know making this. 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. A quick tutorial on how to set the bias on a guitar tube amp, specifically the Fender Hot Rod Deluxe. We specialize in the repair of electronic sound equipment and related products. pair, quad, sextet, etc. From this you can see how the grid bias point necessary for proper bias ties into gain and drive power. Also using only NOS ef86 is a must - current production ef86 sound terrible and do the amp no justice! thanks for your help. Notes: (a) The bias control only applies to the push-pull option. HM = Heater Tap. We work out the trending price by crunching the data on the product’s sale price over the last 90 days. panel, a special voltage range switch provides the proper voltages for 6V6 or EL84 output tubes (in 12-watt low-voltage/low-power mode). OUTPUT TUBE BIAS Tube bias refers to the idle current of the output tube (power tube). The Mullard used the ef86-el84 combination, with much lower voltage and current on the plate of the ef86. V5 is the output valve, driving output transformer T1. 76 ampere Heater Warm-up Time (Average) 11 seconds Peak Heater-Cathode Voltage Heater negative with respect to cathode 100 max volts Heater positive with respect to cathode 100 max Direct Interelectrode Capacitance Grid No. 2 2 VBIAS Input Bias Voltage for powering all circuitry on the regulator with the exception of the output power device. (Sorry if this is a. roughly 1/3 on each. Selects from high and low gain Specifications: 30 watts output Zero negative feedback Selectable Preamp Gain Response. As this is a cathode biased output stage, there is no adjustment for the bias voltage so no need to go probing just yet. Definitely changing the cathode bias bypass cap from 220uf to 22uf will not make the amp so wooly and choke up at higher gain levels. So, we apply a BIAS voltage to the grid. Red tube mainly due to the filtering cap on the negative bias leaks and short out the negative voltage. The EL84EH is a remarkable reproduction of a vintage tube that is capable of maintaining its sweet and musical tone under any voltage conditions. Maybe, this is why they need to run the EL84 bias so hot. Unfortunately, the design is a bit difficult to incorporate in higher powered amps, which is one reason for the limited use in tube amps. Physically, parts were designed to look similar to original factory units (where possible). The negative voltage is essential for the proper operation of the audio output tube(s). 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,. 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. Bias current accuracy 1%25. An El84 is an 11 watt tube(DC dissipation). The Bias Voltage setting on the Power Valves is too LOW compounded by Fender supplying all Amps in the UK with a Mains Voltage setting of 230vac. But in circuits intended for the 12AX7 family, the shield will be connected to one side of the filament line. Compare this to JMI schematic OS/114 in Figure 5 where the screen grids are connected to the B+ power supply. The feedback ratio is about 56, which sets the voltage gain of the amplifier, by the usual rule. Use a series voltage divider as a minimum load across the B+ at the second choke, allow about 10 to 20ma, tap down to provide B+ to preamp/inverter, add a 33 to 66 mf cap that source. variable voltage supply can be used (and was successfully in the "Sussex" valve tester design), I was looking for a simpler solution. 4 Watts (70% max). And the voltage across the EL84 cathode resistor measures 15 volts giving a total EL84 operating point current of approx. SInce the amp is fixed bias i thought that with the right power transformer i could add more voltage on the plates and then adjust bias so tubes are operating around 70% dissipation on idle (8. Dual Bias Current Probes Tester Meter for EL34 KT88 6L6 6V6 6550 Vacuum Tube Amp. Sovtek EL84's are available in platinum matched sets. We can plot plate current as a function of grid voltage at various plate voltage levels. Tapping the heaters may be important since the heater filaments can act like a diode if the cathod is some volts above heater potential (which is the case most of the time with auto bias) and induce AC hum in you beloved signal. Looking at the circuit above… An EL84 has a mu of 20 and in this implementation the screen voltage is 350, which gives us 17. ECONOMICAL VALVE BASED AUDIO POWER AMPLIFIER. When the HV supply is solid state and plate voltages are up around the 800 volts plus range, the typical modulator idling current will be around 70 mA, but not more. over the cathode resistor. Key Point: if you have a 'fixed bias amp' you can adjust the bias voltage (usually with a pot, or by swapping out a fixed resistor). Customer ” Joe” puts his four brand new matched Tung Sol 6L6GC-STR into his amp and he checks the bias on each of the valves. 6) After setting the bias you will need to go back to step 2 and recheck the voltage on the plates to see if it has changed. An early direct coupled test circuit. If you keep the feedback/biasing network from this amp, I think the ef86 would bias somewhere between. The BiasMaster(TM) allows to monitor the bias current savely and easily. Bias Tool testing probe for EL84 6BQ5 7189 amplifier 9 pin tube biasing USA MADE 5. With multiple tubes sharing the same cathode resistor, this calculator assumes the tubes are fairly well matched. A self-biasing amplifier, also know as a cathode bias amplifier, has a cathode resistor that sets the bias current of the tube. Physically, parts were designed to look similar to original factory units (where possible). ECONOMICAL VALVE BASED AUDIO POWER AMPLIFIER. Bias tool probe plate voltage tester for EL84 tube amp amplifier NEW MADE IN USA. Customer ” Joe” puts his four brand new matched Tung Sol 6L6GC-STR into his amp and he checks the bias on each of the valves. - the cathode of V1 is LED biased. If your amp is adjustable bias like the Marshall 201 and 401 or Bugera V22, Jet City or Carvin then because the EL844's dissipate 9 watts these must biased 25% lower than standard EL84's. I chose this mode because I wanted very low distortion. This is also related to the matching of the valves. 7 volts RMS drive voltage, instead of 35 volts, at the same 1 ampere RMS. 6V heaters – the cathode follower needs it. WARNING: A tube amplifier chassis contains lethal high voltage--sometimes over 700 volts AC and 500 volts DC. The bias Voltage is. BTW when I mentioned 33. El84 Tubes are for good sound reproduction and this is paramount importance unless they do not last of fail quickly. I've read up on a lot of mods, all of which involve reducing the negative voltage to the control grid from the existing -11vdc to about -14vdc. max current max voltage. 7 of the peak voltage, and the peak is approx 1. I would not recommend substitution of a standard El84, as it is only rated for a maximum dissipation of 12 watts. 9 PIN SOCKET Saver EL84, 12AX7 etc. They are the only folks I know making this. The EL84's are being over run in these amps! Fender do the same but the over run margin is less. Re: Bias voltage for EL84? Post by romberg » Sun Apr 08, 2018 7:21 am Merlin has a nice page which describes how one can calculate the required bias voltage from the screen to plate voltage and the mu of the tube in question:. The bias is a NEGATIVE voltage applied to the control grid of each valve. This is referred to as fixed bias, though it is usually adjustable, and is more usually used for fairly high power push-pull output stages. I'd like to bias my amp using a bias probe, I'm picking one up on eBay. 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. Re: Bias voltage for EL84? Post by romberg » Sun Apr 08, 2018 7:21 am Merlin has a nice page which describes how one can calculate the required bias voltage from the screen to plate voltage and the mu of the tube in question:. This would be somewhat the same as testing at 500 plate volts and a -28 volt bias all things being equal. The bias is different, but it is a 9 pin output tube of about the same output power. These tubes lasted only about 10-12 playing hours. Cathode-biased amps have a bias voltage that varies as the amp is being used, so it's not a fixed voltage. Electro Harmonix EL34. Welcome to my tube amp biasing page. We specialize in the repair of electronic sound equipment and related products. I have one fixed bias EL84 amp with separate 1K screen resistors. K = Cathode. were kept as close as possible to the original part to preserve the stock "tone". The biasing voltage applied to the transistors would now be equal to the forward voltage drop of these diodes. The bias is different, but it is a 9 pin output tube of about the same output power. 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 Mullard used the ef86-el84 combination, with much lower voltage and current on the plate of the ef86. The EL34BHT is sweet on top with a perfectly balanced mid-range and focused low end. And it has this cool internal shield to separate the two halves. roughly 1/3 on each. grid resistance (fixed bias) grid resistance (self bias) typical operating conditions character istics class al amplifier single tube 5 148 4 350 250 -18 18 200 000 53 2. Use this tool at your own Risk. Heater voltage Vf 6,3 (V) Heater current If 760 (mA) FAX: +381 18 550 806. 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. This runs the tube at full rated plate and screen voltage, and plots the curves at 10 different grid bias levels. View from above: Tube type. 6 product ratings - Bias Tool testing probe for EL84 6BQ5 7189 amplifier 9 pin tube biasing USA MADE. This behaviour allows for variations in the grid voltage to appear at the anode. I believe the confusion arises since the grid applied bias strategy is frequently referred to as "fixed bias". 375V, hence 34mA per tube at the cathode. 4 Watts (70% max). Installed between the output tube and the amplifier tube socket, this device connects directly to any multi-meter using the industry standard banana plugs. If you have not been trained to work with high voltage then have an amp technician adjust the amp's bias. Compare this to JMI schematic OS/114 in Figure 5 where the screen grids are connected to the B+ power supply. But the web provides such an accessable and immense resource for such a purpose. Great manufacturers like Dynaco, Scott, Leak, Loyez just to name a few, sold thousands of amplifiers using this cute little pentode and for many serious listeners of that time these amps were by far superior for music reproduction to their more powerfull. BE A SMART CONSUMER Those products made in China might be cheaper, but its poor workmanship might damage your tube power amplifier. If your numbers for plate and screen grid current are low, bias it a bit hotter. Amps with a single EL84 output tube are probably class A and will run normally at around 100% max. If you are uncertain that you are experienced enough to work on a live high voltage amp, please take your amp to a professional to get it biased. 414 * the RMS. 5 6 30 2 250 250 14 14 100 000 75 4. This is a steady NEGATIVE voltage, more negative than the cathode. Jensen pure silver. This would be somewhat the same as testing at 500 plate volts and a -28 volt bias all things being equal. Here is a small gallery on the Small One :. These values shouldn't be viewed as written in stone, as the voltage from the wall can vary from region to region and from day to day. The normal output of a '30 is 16 milliwatts, while with two such tubes in "push-push" an output of 1 watt is obtained - at a plate voltage of 157. Joe Albano put Bias Amp 2 to the test. Unsoldering the ends of the caps and measuring the voltage at this point across a 1M resistor to ground showed 3 volts of DC--there should be 0 volts. By contrast, an EL84 running at 300V would need only: 300/20 = 15V negative. More commonly found is a pair of EL34s running class AB1 in push–pull around 375–450 V plate voltage and producing 50 watts output (if fixed bias is used), while a quad of EL34s running class AB1 in push–pull typically run anywhere from 425 to 500 V plate voltage and produces 100 watts output. EL84 Push Pull amplifier, the little giant The EL84 is NOT a DHT, but still a fascinating tube for many triodes lovers (I belong to this group) who recognize its sonic qualities. So, we apply a BIAS voltage to the grid. By contrast, an EL84 running at 300V would need only: 300/20 = 15V negative. El84 Tubes are for good sound reproduction and this is paramount importance unless they do not last of fail quickly. 1mV corresponds to 1mA of bias current. 1 to Plate 0. Now days tubes melt in this design. It means the voltage to the output tubes' grids (in DCV) is "fixed" by sending it a specific voltage, so it does not vary (practically speaking) while the amp is in use. The tube amplifies the voltage and the transformer changes this voltage into a current. Try biasing some Chinese 6L6's with 500VDC on the plates at 40mA. Many examples existed for triode mode or pentode mode, and using grid bias. Self biasing, no AC or DC balance to adjust. Where this is not given, use the. There is talk of setting the bias "cool" or "hot" and the effects on output valve life. If you control those,the EL84's will live. Tri-lam plate material and selected screen wire increase thermal dissipation. In fixed bias amps, when the output tubes are changed (always for a matched set of course), you readjust the bias until it is correct. Output transformer - when needs must Components and Circuits. Selects from high and low gain Specifications: 30 watts output Zero negative feedback Selectable Preamp Gain Response. How to Install a Fender Blues Junior Bias Trimpot Without Drilling Holes in the Board Where Fender Blues Junior mods are concerned, Bill M of billmaudio. There is a little-known method of generating a bias voltage which is called "back-biasing". See item #4152010 Bias Master EL84 Adapter. The TELEFUNKEN EL84-TK is a perfect replacement for any EL84 / 6BQ5 tube offering a reliable and great sound. Consult with an experienced technician. So, I simply adjust the bias of my amp such that the voltage across R reads “0. Furthermore, since the output voltage is 5V, approximately half the bias of the EL84 in this design, the resistor will perform half of the dissipation (approximately 250mW) leaving the remaining 1/4W to the. Because, the output voltage is the reference voltage that will define and limit the current draw of each current sink, and thus each EL84. com is truly a player on the world stage (see my previous appreciation of him and his mods here ). In most amplifiers the HT voltage is not regulated -it is free to rise and sag in accordance with load current and mains voltage fluctuations. Bias current accuracy 1%25. Hughes & Kettner Home - Since 1984, the name Hughes & Kettner has become synonymous worldwide with guitar amps of the highest quality. Here is a plot of plate current versus grid voltage for an EF86 pentode. Save on Tube Tester Meter today. It is a thermionic valve of the power pentode type. EL84s aren't used with fixed bias often because they need less bias voltage the effects of cathode biasing are reduced. Setting the Bias. pair, quad, sextet, etc. Selects from high and low gain Specifications: 30 watts output Zero negative feedback Selectable Preamp Gain Response. Where this is not given, use the. With a gold -plated molybdenum alloy grid and carbon -coated screen grid, the Svetlana EL34 is the finest power tube of its type being manufactured today. So don't mess inside your guitar amplifier unless you know what you are doing. Vd would be around 63V. dissipation. The maximum anode voltage for a EL84 is 300 volts, so let's say you can drive it safely (meaning faster burn-out) at 350 volts; so even if you pull out the octal sockets and put 9-pin in there and make a couple of other changes you will have extremely short tube life, at more than 100V over design maximum. I installed the tubes after performing the mods in the amp and testing the operation with the stock Sovtek EL84 power tubes. See item #4152010 Bias Master EL84 Adapter. The output stage draws a high current compared to e. 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 voltage you will be measuring across cathode resistor (R) is usually no more than 2 volts. Biasing an amp requires some knowledge of tube amp circuits and experience with high voltage. 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. Unfollow el84 tube amp to stop getting updates on your eBay Feed. Each tube sample was installed in the same custom built, fixed bias single-ended guitar amplifier (see schematic) with a Fender black face style preamp circuit. Bias Tool testing probe for EL84 6BQ5 7189 amplifier 9 pin tube biasing USA MADE 5. Each amplifier is beautifully hand assembled and tested. 4 ohm and 8 ohm terminals. BIASING: :EL84 max bias current is 48mA as measured in plate lead, or approximately 53mA as measured across R15 in cathode lead. 6 product ratings - Bias Tool testing probe for EL84 6BQ5 7189 amplifier 9 pin tube biasing USA MADE. El84 Tubes are for good sound reproduction and this is paramount importance unless they do not last of fail quickly. (b) The plate load resistance is shown as plate to plate resistance in push-pull. How you operate the tubes (push-pull, push-pull parallel, ultra-linear, class, B+, bias, operating points, etc. Plate Current. NC = No Internal Connection. Tri-lam plate material and selected screen wire increase thermal dissipation. It's also common for cathode biased EL84 amps to run at 100% plate dissipation. It's not a set number, just as you mentioned about biasing by ear, it's a preference of tone within the tubes design parameters. Material used & design specs. The EL84 tube has a snarly sound (bright with midrange punch), and is usually found in smaller wattage amplifiers. Only a few of the most popular tubes are shown. If each tube has it's own bias screw, or if you have a PrimaLuna or Mystere amplifier with Adaptive Autobias, there is no need for matched tubes, though it certainly doesn't hurt. 0 out of 5 stars. If you are uncertain that you are experienced enough to work on a live high voltage amp, please take your amp to a professional to get it biased. 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. Originally designed for the output stages of audio frequency amplifiers, the EL84 can deliver up to 1 7 watts. I got away from tubes for a while and forgot a couple of thingslike the Siemens EL84/6BQ5 I put in there wasn't robust enough for the 222c plate voltage. Based [1] Floyd, Electronic Devices 7th ed [2] Cook, [2] en. Various things can cause this but, like most things, it's best to check for the simple stuff first. 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. You know the EL84 is a 12 watt tube. S = Metal Shell. In this video I explain the principles of amplifier output tube biasing in very basic language. It has an international octal base (indicated by the '3' in the part number) and is found mainly in the final output stages of audio amplification circuits and was designed to be suitable as a series regulator by virtue of its high permissible voltage between heater and cathode and other parameters. This latest Inspire EL84 "Hot-Rod" version just leaped forward in performance. Output Stage The output stage consists of two output pentodes, type EL84, in a cathode-biased, push-pull circuit. Here is a small gallery on the Small One :. If you are a metal fan , the Serbian made EI 6BQ5 sounds a bit more powerful, with 'balls' for rock music. Remember to add the drop across the cathode resistor to the anode voltage to find the supply voltage if you do use cathode biassing. TERMINAL ABBREVIATIONS: H = Heater End (Unpolarized). NC = No Internal Connection. It takes the bias voltage from the right side of the circuit board and loops to every pin one and then goes back to the circuit board completing the circuit. In most amps, valves can be heated with AC or DC. These values shouldn't be viewed as written in stone, as the voltage from the wall can vary from region to region and from day to day. Electro Harmonix EL34. VOS Offset Voltage -6 -0. If you want to bias tube amplifiers just be aware that there are lethal voltages inside the chassis. Output transformer - when needs must Components and Circuits. Furthermore, since the output voltage is 5V, approximately half the bias of the EL84 in this design, the resistor will perform half of the dissipation (approximately 250mW) leaving the remaining 1/4W to the. Easiest way to start will be to plot the 2 points where Plate Current is zero and Plate Voltage is zero. We specialize in the repair of electronic sound equipment and related products. By employing a higher voltage, over-biasing can also lead to early signal distortion. The cap bypassing the current regulator needs to be at least twice the "bias" value (voltage drop from cathode to ground): for an EL84 22V is a good starting point among standard values. The yellow highlighted circuitry in Figure 6 illustrates the pair of output transformer taps that supply the bias voltage to the screen grids (pin 9) of the EL84 tubes in UL430 and UL730 amps. SInce the amp is fixed bias i thought that with the right power transformer i could add more voltage on the plates and then adjust bias so tubes are operating around 70% dissipation on idle (8. Each tube sample was installed in the same custom built, fixed bias single-ended guitar amplifier (see schematic) with a Fender black face style preamp circuit. !! It is well known that the original Mullard 10W amp requires 2x 10V rms to EL84 grids. What you really want to know is the plate voltage, and then set current draw of the tubes by adjusting the bias voltage. 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. How you operate the tubes (push-pull, push-pull parallel, ultra-linear, class, B+, bias, operating points, etc. Yellow Jacket converters not only re-arrange the pin locations of the tubes but also provide the necessary current limiting on the screens and cathode. Are you using fixed bias to copy the sound of a particular EL84 amp? If so, copy that amp. As you adjust the bias potentiometer (‘bias pot’ for short), shown on the left side in the schematic above, you are imposing a DC voltage on G1. Basically I am wondering has anyone have any experience with the Variable Bias option that is shown on the site? I have this set up at the moment and I am having issues with the voltage on my pin 8 of my output tube. Another method of biasing is to ground the cathode and use a separate negative voltage supply to give the grid a negative voltage level. Anyway, from what you say, I could safely bias upwards of 50 mV? With the measured bias voltage high or low, do I have this right?. If desired to use fixed bias for the 6V6 it can be derived from the center-tap of the power transformer, reposition that 2nd choke to the CT, place suitable. Remember to add the drop across the cathode resistor to the anode voltage to find the supply voltage if you do use cathode biassing. Under the influence of a bias voltage these carriers move through the material and induce a current in the external circuit. 05” to reflect a total current of 50 mA. If you are a metal fan , the Serbian made EI 6BQ5 sounds a bit more powerful, with 'balls' for rock music. 500V DC- which is an instant killer. Biasing Your Peters Amplifier. Now it can be bias colder/hotter as one wishes, but following the chart found on weber’s bias calculator page, with plate voltage of around 350vdc(340vdc in this Blues Jr) then avg% of 21mA per tube(AB EL84/6V6). iJJ EL844 in Carvin Vintage 16 This is a technical review of the JJ EL844 tubes as installed into a Carvin Vintage 16 amp with hasserl mods. 3 amps of heater current. These two diodes are generally called Biasing Diodes or Compensating Diodes and are chosen to match the characteristics of the matching transistors. What you really want to know is the plate voltage, and then set current draw of the tubes by adjusting the bias voltage. Just 1 volt difference in the bias voltage can make a difference of 10 or even more ma, of anode current. DIY All DC coupled EL84 SE Amplifier The two stages of the Aikido driver are DC coupled and I thought it would be nice to have the final stage DC coupled as well. You may want to consider splitting the cathode resistors, ie, use one 250Ω (or 300Ω) for each cathode. An EF86 Push-Pull Power Amp The EF86 is a small pentode commonly used in preamp stages. Use this bias calculator to calculate the current based on the amplifier class type, plate dissipation, tube type and plate voltage. This low cap value lets the cathode-bias voltage swing freely, so that the amp biases itself progressively colder as it works harder. ClassicTone # 40-18107, Project / Fender Style 40W Deluxe Power Transformer, 100/120/200/220/240V This is a great, multi-purpose power transformer for use in higher wattage project versions of Fender Deluxe **and Deluxe Reverb** style amps. He got a set of Sovtek's from Mesa and the amp was happy. This amplifier requires no adjustments or maintenance other than changing tubes every couple of years. This behaviour allows for variations in the grid voltage to appear at the anode.