El34 bias calculator. 5 Amplifier classes; 3.

El34 bias calculator EL34 = 10 EL84 = 20 KT66 = 7. And, I want to use a single EL34 with this OPT. With the same speakers, dialing back from 50w to 35w is only a ~1. Use this tool at your own Risk. 1V at very low currents to ˜0. Simulate the load line and calculate one that works for you and stay below the max of EL34. Just to keep I put a 6L6GB in my Vibro Champ, used Rob's calculator to bias the amp. IOW, 44mV across 10Ω would only be 4. Weber bias calculator should be 42. I used the Weber Bias calculator on their website and was suprised to see it calculate the bias value of 44. 55mA at 445V is basically max dissipation for an EL34 in fixed bias I'd consider backing that down a bit. I'm confused about the correlation between voltage and current. The owner may convert to guitar use as it is setup for mics. 5. 5881, 6550, EL34, KT88, KT66, KT100, etc. This webers bias kalkulator siger ,at ved 437 volt ,skal bias for el34 ved drift være, 40ma for klasse ab drift og for klasse a drift 51,4ma ,så de 40-45ma fabriken anbefaler er helt korrekt ,du skal nok ikke give den mere end 50ma The one limiting factor when going from 6L6 to EL34 is the bias voltage range. moz OUTPUT PENTODE 1. Ok, so I think I can make this work. 25V at ˜5mA. Put the first tube back into the tube socket. Hot (70%) Avg (60%) Cool (50%) 300V. Alternatively, 440V self-bias suggests 7K (or 6. The Granger Amp bias probe measures in milliamps by insertion into the cathode connection that conducts the The cheapest solution. The BiasMaster is available in an octal and noval version. I _suspect_ there is a typo on this sheet: "Va+Vrk" should be "Va-Vrk"? So 350-400V, 3k4 to 4k load, cathode resistor near 130 ohms (start above 150 ohms and work down). " The Tube Bias Calculator was created using MIT's Appinventor 2 programming environment and some anti-virus programs will flag anything created with it. The highest numbers I can get are between 30-40 MA on the existing setup. C. Got myself one of those Weber Bias rite tools which measures both the plate voltage and the tube bias. So is cathode bias value what we're using here? Robinette Calculator for 6L6GC. 1 Output stage, or power stage When you bias very low, the amp sounds lifeless to me. 8 for 70%. We will continue to offer these because in conjunction with a Multimeter this is the most cost effective tool for measuring true plate current allowing you to accurately bias your amp. There's a bias calculator and other methods etc. This reduces gain a little. 5V/0. In fig. Then by R=V/I, the Load Impedance must increase to properly absorb the power. The calculator: I'm working on calculating cathode bias resistor values for various power tubes I'd like my amp to be able to take. In these calculations, 5% of the cathode current is assumed to be screen current. Please login or register. I kind of wish I still It can connect somewhat lower than cathode. For EL34 tubes: Power output is approx 9 watts, bias is 70 mA, screen voltage is 355V, plate to cathode voltage is 355V, cathode bias voltage is 26V, Implies cathode resistor of 370Ω, 10 Watt. 86in. For use with octal tubes EL34, E34L, 6CA7, KT66, KT77, 6L6, 6V6, 5881, 6550, KT88, KT90. ) I suspect that at 500+ plate volts, good cathode bias may be a problem. On the bias calculator I should have these at 38mA for a cool 50%. 5 A RATINGS Maximum Anode Dissipation pa(max> 25 W Maximum Screen Grid Dissipation PS2(max) 8 W The bias voltage appears to be about -10. Tube type : ----Choose---- 6L6/5881 6V6 EL34 EL84/6BQ5 KT66 KT88/6550 TUBE BIAS CALCULATOR (for push pull class AB1/AB2) Select Tube Type and the Plate Voltage of the amplifier below. 3mA, so I believe I had hit this sucker as close as I’d care to. 325V. Which is probably about where it is with a 270 ohm cathode resistor. Next, the Groove Tubes are swapped out for a set of JJ EL34’s, I return the bias voltage to -44. For those why know what the voltages should run on this amp, please check it out and let me know if they are OK. Here's a handy calculator: Tube Bias Calculator As a guide 65% dissipation could range from 32 to 40mA in your amp, and that's why plate voltage really matters. Enter Plate Current: DC This calculator allows you to compute and tune loadline and operating point of tube amplifiers’ power stages. They aren't particularly closely A simple series resistor doesn't attenuate bias voltage, because there's no current flow to cause a voltage drop. The stock JTM50 bias topology is: 220K>diode>15K>47K>27K trimmer>ground. If you measure the DC plate voltage from pin #3 of any power tube to ground then you can use the formula below to calculate the current draw. My circuit setup is a 220Kohm resistor between the HT leg and the diode, 2@ 10uf capacitors with a 15kohm resistor between TUBE BIAS CALCULATOR (for push pull class AB1/AB2) Select Tube Type and the Plate Voltage of the amplifier below. plate voltage 430v-cathode voltage = 405v 3. Click any Calculate button to see the recommended tube bias currents in milliamps. Have a pair of 560R ready to swap if needed. Check the next power tube and split the difference if they are off just a bit. Using a tube curve calculator and plugging in 435 volts and 50ma, an EL34 should bias right around -36. 047uf or . Tube Type Plate Voltage mA: Calculate Plate Dissipation based on Voltage and Current readings Calculate Plate Dissipation based on Voltage and Current readings ; Plate Voltage: Cathode current (milliamps) Also, your bias voltage is very low; it should be somewhere in the range of 35-55VDC or so. chervokas, May 26, 2019 #8. Best luck! D. Both scenarios utilize the existing power supply--no mods needed. 7 very If I plug those plate voltages into a bias calculator I get a suggested bias MA number of 83. Note : Don’t end with comma ( , ) Can anyone that knows explain how to measure plate current and cathode current and how to calculate to find proper bias settings for my EL34 amp using 4 output tubes. What the exact relationship is between bias level and longevity is, I don't I got the new JJ 6L6GC tube to put in the EVH 5150 III. Plate voltage is around 398v Screen voltage is around 390v bias voltage: -26v on one side and -28 on the other plate current: 45mA on one side and 40mA on the other; per tube. I = P V. 0. 2204 Bias question EL34. Looking at one of my old schematics which is what used to be a Carvin X100B (now a 50 watt Plexi) EL34 bias is 38ma and 6L6 is 46ma, running at 60%. EL34 data page 5 shows cathode-bias "AB" conditions for EL34. It is okay in cathode bias since 50 of those volts would be on the cathode resistors. You can Google "appinventor 2 virus" and see it is a common problem. More Information How to bias kt77. An EL34 can dissipate 25 watts, so 17. Maybe the most under rated balls out rock amp ever. This calculator is for a single tube. When biasing to 70% or whatever percent you’re looking for you simply multiply the answer by that number divided by 100. 2 the splitter In fig. dinkyguitar Looks like the adjustment range should be from about -24 volts to -47 volts. 1uF and the 1k mentioned earlier. Treble boost can be introduced by using a The amp in question is a Traynor YBA-1A (2x EL34) which has been previously modded with a trimmer pot on the bias supply and 1 ohm resistor on only one of the tubes. If you need more power, build a 20W amp and mike it into a 3,000W PA system. nwoforlif Well-known member. Level 2; Posts: 241; Correct el34's draw 1. The Weber measures plate voltage, and then I was calculating based off the Weber bias calculator to come up with around 39ma at 440v at the plate. WHITTAKER DBA NBS ELECTRONICS) WILL TAKE NO RESPONSIBILITY FOR ANY INJURIES OR DAMAGE SUFFERED BY ANYONE AS A RESULT OF THE MISINTERPRETATION OR MISAPPLICATION OF THE INFORMATION CONTAINED IN is the power rating of the power tube, is the bias current, and is the plate voltage of the power tube. And it uses 4 12ax7's so 4. The output tubes are new production Valve Art EL34B (chinese, slightly more plate disspation than other EL34) with about 30 hours on them. I have a Maxi Matcher 2 and was testing some Mullard EL34 xf2 tubes and got a plate current reading of 17. operated or mobile equipment. 4 to 1. Solving for I we get. Requires separate digital volt-ohmmeter capable of reading current. Well I'm doing start up on this JMP50 and mias bias voltage maximum voltage is too low. The proper way to set the bias, as mentioned, is to measure the cathode current at pin-8 of the power tubes. Bias the tube at a point that is under the max dissipation curve, then under max output signal conditions, the instantaneous Hey guys So here it is: i've measured voltages on my roadster with both the original Mesa 440STR 6L6 (rated 10 by Mesa) and EL34 (RUBY). Basically, how low can I go before there are negative side effects? Playing with a bias calculator I think my next steps are 300r (6v6) and 120r (6L6), but I know from the last time that reducing the resistor value won't exactly give me the plate dissipation that the calculator says (since other voltages will change). one of the conditions published in mullard datasheet is AB1 cathode bias with 450V B+ with 465R for each Rk with a 6. thegame The EL34 tube that always got the ‘don’t use above 450 pv’ is the RFT Siemens 34’s. Enter plate voltage: Select output tube: EL84: 6v6: 6L6: 7027: KT66/EL34: 6L6GC: kt77: KT88: 6550: KT120: This information is for reference only. typical fixed bias operating conditions for KT88's are 500VDC@80ma, which is about 40W dissipation. When biased high (say 80%), the amp sounds fine -- though some folks can hear difference and like the tone at that level (my old ears don't hear this!) -- but there would be an expected reduction in tube longevity. Bias is an alternating current of high frequency which is applied to the tape recorder to reduce distortion. Bias Settings For Safe Plate Dissipation - Class AB 70% Class A 90%: Class Plate Voltage mA: Calculate Plate Dissipation Based On Plate Voltage And Cathode Current Readings. -User Name-Password EL34 / KT66: Ia = 72mA Rk = 360R KT88 (I couldn't find transfer characteristics anywhere): Ia = 95mA Rk = 160R But the design point for the bias of EL34 tubes in an amp designed around EL34 tubes is the same regardless of what EL34 tubes you're using. Select your tube type and amp class (Class A, Class AB, or high AB) and enter your Plate Voltage or B+. It shows 55 DC milliamps for a cool Cathode Bias. Recommended range for 5881, 6550, EL34, KT88, KT66, KT100, etc. Given below is the tube amp bias calculator to find the bias in ampere or milliampere (mA or A). What would be a good bias setting for these voltages. e. The webber calculator only goes up to 500v. Under bias will reduce the power level while How to Measure Bias. In these calculations, 5% of the cathode current is assumed to be Use this calculator when you measure the actual plate current. Its primary function is to calculate the amount of power (in watts) that is dissipated as heat in the plate (anode) of a vacuum tube. You don't even need the I eventually found some info on how to calculate it myself. 4K load in self-bias with EL34 works out to about 300V of safe B+ plate-to-cathode, say 340V from OT to ground. 8 times higher, 7K to 9K. The octal and no "How much lower" does your friend want the output to be? Philips' EL34 data sheet shows a condition on the top of Page 3 with 375v plate (and presumably screen) with a 130Ω cathode resistor, making 35w. Amps without adjustable bias include Mesa-Boogie amps, some Peavey amps, and even some Fender amps (early versions of the Hot Tube amp Bias Calculator. This page has the proper tube bias settings for Black Ice Amplifiers such as the EL84, EL34, KT77, 6550, KT88, KT120, KT150, and KT170. Re: 2204 Bias question EL34. 3Iin max 1 98. Figure 4 shows the plot of 3 different AC125s again, where you can see that V B E varies from less than 0. So you need to go less negative on the bias voltage. There are exceptions. To ground on a cathode-resistor amp, or to -bias on a fix-bias amp. also not exceed the max bias voltage as this can cause internal breakdown and lead to "red platting" Here is a useful calculator Weber Bias Calculator Sanity check - EL34 bias/numbers . P is the power rating of the power tube, I is the bias current, and V is the plate voltage of the power tube. Cathode bias amps must run HOT. typical fixed bias operating conditions for EL34's are 400VDC@60ma (around -35VVDC bias or so), this equals 24W dissipation. If Vp is increased, Ip must DEcrease so the tubes don't melt. EL34 tubes are typically idled hotter tha 6L6 tubes. 5 Amplifier classes; 3. Omm 3. I already made the voltage source from reverse installing a 12. = 'hotter bias' If you're using a bias probe on separate tubes, it doesn't matter. Knowing the screen current will allow you to accurately calculate plate dissipation too. From 360-400 to 480V, the load should be 1. 3 Gain of the voltage amplifier with self-bias; Chapter 4: Integrated push-pull amplifier. The calculator will give you the bias current for each tube. Les Paul Lover Duke If your amp still has the 220K bias splitter resistors to can run then as long you bias the amp cold but if you are concerned about the 6550 going into runaway bias Marshall used to reduce the bias splitter resistors to 150K you can go as low as 82K but you will have to increase the . Attached are the results from the Robinette bias calculator using the 6L6GC tube and the 456VDC voltages shown on the schematic. 173mA total of which _13. Since 2006 we have offered a single octal bias probe for use with a Multimeter. Use this as a guide for setting your bias. 1 there is the inut diagram In fig. You must enter Tube Type and Plate-to-Cathode Voltage above before calculating Tube Dissipation. Here is my plan, someone tell me if I'm doing something wrong or mistaken in my thinking. If you bias them in the 50+ range like a typical 6550 you’re taking chances on stressing the transformer. 6 mA on one at 400v. Here are my Bias supply is 100k off the wiper of the 20k bias pot. A safe way to do this is with a bias probe that is set up to either measure current of indirectly by measuring a voltage which will allow you to calculate the current. Plate is pin 3 and Cathode is pin 8. OP, I've used an older version of the Weber Bias Calculator for at least 20 years According to the Weber bias calculator running AB with EL34's at 464V plate voltage bias should be 37. That's right in the ballpark of a JTM45 or Bluesbreaker amp. 7 mA. 5 amps. 1uf to get the same bass Due to the lowish VB+ and high (for an EL34) OT primary impedance, the EL34 won't benefit (in terms of class A clean output power) from increasing the static current / plate dissipation past a certain point. 6. Jan 17, 2008 #5 cool thanks . but even better for valve life if its back at 70% . You must re-calculate after changing 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. Bottom line, measure the voltage on pin 8, and divide by 10 to calculate the current. 2 amps total heater current. The chart on the tester says the expected readings for EL34 is between 21-50 mA. The negative bias voltage then goes through a 15K divider resistor that isolates the next stage Overview. the amp is biased to be running at 18watts on one amp (becasuse one tube is weaker) and 20 watts on the other based upon the Webber online bias calculator Annnd more evil unintentional misdirection on my part, the amp is running Russian 6P14P-EV tubes which are considered by many to be the closest modern 7189 equivalent. An EL34 can produce 25W (so 2 per channel gives 50W maximum). 9 Amps . RIMAR ~ALYES EL34 33. 4mA. ” The classic Marshall 50-watt “Plexi” (model 1987) is powered by a pair of grid-biased EL34 tubes. Fixed bias allows for correct bias at higher plate voltages. 5KRa-a load Ig2 is stated as being 10mA per tube at idle and Ia is stated as being 60mA per tube at idle. Max dissipation for EL34 is 25W Calculate the idle current required using the formula listed above, P = I * E 25 = I * 275 I = 25 / 275 I = 0. A visit to the Weber Bias Calculator and the Tube Amp Bias Calculator both suggested a bias measurement of 38. I'd probably start with -19 V and adjust from there. 6 Biasing techniques. . Heater Voltage Heater Current Vh In 6. 3v filament line. Following this guide, you will learn: The bias calculator is showing either variety of 6p3s as a max of 20 watts. I'm going to assume that you have the high voltage (460V plate) "classic" vs the low voltage(410V) model which is relatively new. More Information. Reactions: PDC, glpg80, Rick Lee and 1 other person. 42mA. EL34 and friends will have high Ig2. Most amps with two or more 6L6 or EL34 power tubes fall into this category. 1 Fixed bias for vacuum tubes; 3. It will be addressed:Ou Hi all, i want to make a class A pp amp with fixed bias. 2 Cathode bias or self-bias for vacuum tubes; 3. 414 = 565vdc) power transformer; I wouldn't use them together. That should be the coldest EL34 bias, but it will still be hotter than 6L6/Bold/SS. Amps without adjustable bias include Mesa-Boogie amps, some Peavey amps, and even some Fender amps (early versions of the Hot Rod Deluxe/Deville and Blues Deluxe/Deville, for example). I have on a switch 2. to get that 300B 2A3 6L6 KT77 EL34 Matched; KT88 6550; ECC82 (12AU7) and ECC83 (12AX7) for Hi-fi; 6N1P, 6SC7, 6SL7, 6SN7, and E88CC Valves and Tubes; The spreadsheet is set up to calculate bias for amps using class AB1 mode which is basically what most amp output stages use. 091 A (91 ma) Knowing that B+ is 275 V and I want 91 ma idle current, I would look at the performance curves on the data sheet for a ballpark bias voltage. Riparazione modifica amplificatori valvolari vintage, Fender, Marshall, VOX, Orange, Bias, Roma Tube BIAS valvolari - Valvole, amplificatori modifiche bias etc Tube BIAS valvolari In 6L6 mode, the hottest bias is obtained by going with Bold/SS rectifier. This website uses cookies to ensure that you get the best experience. The negative grid voltage method: This method involves measuring the DC voltage on the grid of the output tubes, and setting it to a recommended value. 10% and more. Post by toner » Sat Jan All DC voltages are relative to a chassis ground. The plate voltage averages 472. If you are getting into They imply that the screens of the EL34's draw 25mA per tube by themselves at idle. This page is a step by step guide on how to adjust Black Ice Fusion tube amplifier bias. When I have adjusted the bias those few times so far, I attempt to set the milliamp per tube values- 26ma for 5881 or 42 ma for EL34. If you want to run a little hotter bias, try running EL34 mode with Spongy/Tube Rectifier. I'm going to put together a bias circuit for EL34 or 5881 (6L6). 800V is the limit of EL34 plate. > what to bias the 6L6's at "Bias" includes plate voltage. Once I get data from a new amp, I run the data thru the Bias Calculator over at RobRob: https: Anyway, it looks like you're ok running tubes like EL34 and KT66 with the 500R bias resistors installed, but you've gotta measure the amp yourself to be sure. Arrow points to the insertion index notch. 47W. Here is what this simple sheet looks like : There's also 15mA of screen current at idle, for a total of 115mA through the 106Ω cathode resistor (for about 12. 6 Design of the fixed grid bias power supply; Loadline calculators. 58mA. I have published a project on Audioreview magazine in Italy about a push pull amp that use EL34 or KT120 with fixed bias, pentode configuration. On my builds I installed 1 ohm resistors inline with the cathode which allows direct voltage readings of the bias. Instead of using one resistor per El34 as the guides instruct, the cathodes on both tubes are linked together and pass through a single 1ohm resistor to ground. 2uf cathode bypass on v1a, to get more fuller sound, also if I remove the 470pf treble peaker capacitor it is missing some of the freq. In a short accident with modern EL34 in 7027/6550 holes, nothing bad happened when I left pin 1 disconnected. For additional information/opinion on suppressor grid machinations, primarily in the tube hifi ecosystem, search for "Hazen mod". 5^2/235 = 0. toner Senior Member Posts: 2582 Joined: Mon Dec 04, 2006 1:57 am Location: Iowa. I can't get the bias above 23 on the pot. 1 Output stage, or power stage In this video, we'll show you how to bias your tube amp using the TAD BiasMaster. 5dB reduction of volume (which Bias Settings For Safe Plate Dissipation - Class AB 70% Class A 90% Explain This: Class . In my reply #26 above I mentioned that bias from bias calculator With two EL34's AB operation at 437 Plate volts should be 40mA and measuring bias using the shunt method showed 22ma--WRONG I was measuring off the screen on the wrong pin. Now, I'm Most amps with two or more 6L6 or EL34 power tubes fall into this category. 4K OT) bias specs. 5 watts is 70%. Your R16 gets you in the ballpark and R20 will help set the amount of swing and the upper/lower limit. Maybe I should turn the bias adjust all the way down and flip the bias switch on the back of the amp to EL34 and see where the bias is? Top. 7mA. I just need to find two EL34's in the same bias range. Measure the Bias by Cathode Resistor Voltage Drop. If bias voltage is dialed to -0-, or too low, or the pot fails, the tubes will fry quickly due to loss of adequate bias. This tube amp bias calculator allows you to select the tube type and amplifier class type (AB or A) to calculate the current. I would like someone check my calculations 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. Probably to allow for use of tubes that aren't an EL34 which may bias somewhere differently. Right now in fixed bias, they are somewhere around 50 according to the votages and bias settings I am currently running. EL34 data for self-bias shows a typical 150mA plate 23mA G2. Meter reads 90 and 80 respectively. In practice: 6L6 and friends will have low Ig2. That would have equated to 44mA, which is believable for an EL34 tube. 54mA. 6k6 load is nice for either -- and will give slightly lower distortion on Typically for an EL34 a bias range of -30v to -50v will give you the exact bias voltage you need. Some smaller amps with 6V6 power tubes also have adjustable At 100W you can use common 6L6/EL34 tubes in quads with common Fender or Marshall replacement transformers. I ended up going to Webers bias calculator and plugging in my numbers class AB 6L6GC 406 volts plate voltage (pin 3 and 8 ), It comes up with 51. This webpage offers two ways to calculate tube bias and plate dissipation. You can: set the Power Supply V+ voltage, the screen voltage, the screen tap, the quiescent bias current. Weber bias calculator says 39. The forward voltage of the base-emitter junction varies depending on how much current is flowing into it. 3+. 6K) load. Cathode bias requires the correct supply voltage -- usually rather low, in order to maintain bias. 2 for 70% AB1 operation. I have been told that some anti-virus software is flagging the Tube Bias Calculator as "potentially harmful. L’ampli est fini et fonctionne, le gain des E88C If there are no bias pots for the output tubes, then your amp is likely cathode biased, so you should be able to plug in an EL34, a KT77, or a 6CA7, all of which are usually considered interchangeable. Great little gadget. Using those online bias calculators, it looks like I want about 61mA for ~90% plate dissipation at 370VDC. 3V is the “nominal” forward voltage of a germanium diode or PN junction. 5V, suggesting we need a cathode resistor of 10. Putting in the voltages and cathode R valve, I get the bias reading from this calculator at idle: Plate cathode current 63. Bias supply impedance is less than 121k worst case. HOW TO BIAS YOUR AMPLIFIER. Thanks When the capacitor is large enough, it acts as a short circuit for audio frequencies, eliminating the negative feedback, but is an open circuit for DC, thereby maintaining DC grid bias. Our bias probe measures true bias current. Think i have been doing this wrong taking readings off cathode with 10ohm resister and just reading meter and setting bias. 3. More lively. it could cause an impedance mis-match. By owning a bias probe you’re not at the mercy of a tech anymore and you are now in control of your tone. The bias voltage keeps the quiescent current in the power output valves at the safe design value. 1 Output stage, or power stage Plate Voltage: Hot (70%) Avg (60%) Cool (50%) 200V: 46mA: 39mA: 33mA: 225V: 41mA: 35mA: 29mA: 250V: 37mA: 32mA: 26mA: 275V: 34mA: 29mA: 24mA: 300V: 31mA: 26mA: 22mA 6. We’ll call this variable x. EL38 sounds better to my ear comparing to EL34. The Tube Bias Plate Dissipation Calculator serves as a critical tool in this domain. 5 KT77 = 11 KT88 = 7. > weber bias calculator the assumption that screen current is 5% of the cathode current. Simple Bias Current Checker: Basically the way this thing works is that pins 1,2,3,4,5 and 7 pass uninterrupted through the device from tube base to tube socket. DISCLAIMER: LORD VALVE (W. EL34 were TESLA or RFT. Even though Marshall offers matched replacement sets, the company recommends the amp be re Cookies & Privacy. M. That little Hammond choke was not used in the The negative grid voltage method: This method involves measuring the DC voltage on the grid of the output tubes, and setting it to a recommended value. 5 mA. 9=3. mad-axeman using my amp and the Weber Bias Calculator, I come up with the following ranges: EL34- 52mA - 60mA (Diezel site gives 60-70mA) 6L6-62ma - 74mA (Diezel site gives 60-70mA) this is the Bonjour à tous, suite ampli EL34, j’aurais souhaité quelques renseignements sur le bias fixe EL34, car l’avis de personnes s’y connaissant plus que moi serait le bienvenu. This method should be avoided. The cathode bypass capacitor will start boosting frequencies above: How about configuring your monoblocks for fixed bias so you can run EL34's or 6L6s just give yourself lots of adjustment room with the bias voltage (~-55V vs. Requires separate digital volt-ohmmeter capable of reading 3. Thus, it leaves possibly 74K between ground the 15K resistor. Welcome To the Hoffman Amplifiers Forum December 23, 2024, 01:58:07 am: Welcome, Guest. Making it less touchy is easy, but its going to reduce the adjustment range. you do not need to go back to specific/unreliable end-sellers for tubes but can order 4 pre-amp tubes and 4 EL34's from the net and bias the amp correctly yourself (which will allow you to try other makes of EL34/5670 and experience the different sounds on offer from different I am about to get a mA bias probe in the mail and was wondering what these values are for the 6L6 tubes and the EL34 tubes in a 2 Channel dual rectifier. Problem: using a bias calculator from robrobinette page, calculation show that it was biased very cold, Even a Push Pull El34 Plexi is harsh to me unless channel jumped. Are they 70% of the full plate current capability? That is a bias calculator that you can use to find the safe limits for tubes. CS sounds better IMHO to simple cathode resistor || cap. At that setting plate voltage is 440 and bias voltage is -40. Total B+ needed before considering any other losses would be ~265vdc. It uses a 6922 for input, ECC99 for splitter. That's a broad assumption. But different static dissipation levels may sound different. Ua(EL34) = 265 V Ro'=2,3k (Ro=4 ohm) Current source (CS) instead of cathode resistor (LM337 + 22 ohm POT) bypassed by a 1 uF capacitor in automatic bias of EL34. 4mA and that's extremely LOW for an EL34. This calculation is vital for two main reasons: it helps in ensuring the tube operates within its safe limits to prevent No matched quad of EL34 tubes I've ever tested measured exactly the same cathode current Just check one EL34 at a time and make sure that the one that measures highest is at or below 70% of max plate dissipation. Use this as a guide for CALCULATE PLATE DISSIPATION (In Cathode Biased Output Stage) Based on Voltage and Resistance Readings. 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 Turn the bias pot until you get somewhere around 35 milliamps of current. Well last night I got the balls to have a crack at setting the bias on my Laney GH50L after I changed out the stock TAD EL34's with Winged C 6L6GC's. After the diode there is a 10uf/100v filter cap. so between 30-40ma. I select an 80MHz Sencore SC3080 oscilloscope. B iasing by negative grid voltage is highly inaccurate because the same grid voltage can produce drastically different plate currents in different tubes of the same type. I think the It’s the average dissipation over time that must be kept in check, not the instantaneous dissipation. I used the Weber bias “Bias is direct current (DC) deliberately made to flow, or DC voltage applied, between two points for the purpose of controlling a circuit. 1) Either the EL34 bias voltage is low* enough viz-a-viz the driving voltage (from each PI plate), then a big swing from the PI plates will put alternately put each side of the output stage into cutoff. 0446A = 235 ohms, and it would dissipate 10. More of a super 6v6 Interesting! Logged imgumby001. Opinions on the advantages of this procedure are mixed. Without the right biasing, your tube might be under or over biased. Thread starter woodturner-fran; Start date 2021-12-13 2:52 pm; Jump to Latest I put in my numbers to an online calculator (I think from a guitar site) and it gave me the 90% figure. 4 Gain of a voltage amplifier; 3. Post by JWR » Sat Jan 17, 2009 3:17 pm I have an '80 2204 that has 408 b+ volts. Using the Valve Wizard's formula I get: ZOut = 370^2/25 = 5,476Ω. 3mm I. 5 6L6GC = 8 6V6GT = 10 For example, if you’re 3. 5% for screen current). Select your 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. This bias calculator makes it possible to determine the current by giving information about the amplifier, including its class type, plate dissipation, tube type, and plate voltage. 00 and available in our online store and can be used with 6V6 - EL34 - In fixed bias amps it is done so as a convenient means of connecting both the suppressor grid and the cathode to ground. To get it right, measure the B+ voltage at pin 3 of one of the EL34 tubes. Once you have decided to change your el34 for the kt77, the next step is to bias the latter. The author cames no responsibility for any information provided. 3 Operating point and bias; 3. 6 volt filament trans wired to the 6. 3_% goes to screens! It has a bias pot. Also, re your 1st pot. Top. Prior to trying the Shuguang Nature sound 6CA7s, my favorite current production EL34/6CA7 was the Electro harmonix 6CA7 fat bottle from Russia. Best practice is to always have a fixed resistor between the bias pot > ground. The main reason I asked is that I have read (but do not know) that operating the EL34's cathode biased would yield around 30 watts or so. 2) Keeping a bigger bias voltage, but having an even bigger PI output swing can also achieve this. Solving for we get. 50mA. 12ax7's draw 300ma per tube. Sanity check - EL34 bias/numbers. All the EL34 amps that I'm familiar with use a pretty hefty choke, if they use one. If your amp is cathode biased or has 1 ohm bias setting cathode resistors then you can calculate bias current by measuring voltage drop across the cathode resistor. I've been using Weber's Bias Calculator and when you plug in the numbers from the Clubman schematic it shows those figures. N. You may occasionally hear that 0. These probes are $25. 4. ***BUT***, since the resistor is really 10Ω, everything changes by a factor of 10. The load line should stay below the max EL34 wattage dissipation curve all the way to ensure safety operation and long term stability. Bias determines the ideal current flow through the tube in tube amplifiers that are not in use. Logged Way too high. Changing the screen grid resistors along with altering the bias circuit is required for this modification. thanks. the 100k connects between the 0. (EL34's max out at 800VDC, so 375 is rather low. EL34 - 25W . Capacitance Value Calculator for Molded Mica; Capacitor Parallel/Series Calculator; This guide will show you how to convert a standard class A/B dual 6L6GC power amp to a dual EL34 power amp. Notice it has one more stage of filtration than the simple Fender bias system. im just wondering if there is a minimum mA that EL34 tubes should be before they are So any setting between 60mA and 70mA for EL34 or 6L6 will work, all a matter of taste. C. *i. 44 kB, 1224x1584 - viewed 175 times. But remember when using EL34s, tie pin 1 (supressor) to pin 8 (cathode) on the tube Hoffman Amplifiers Tube Amp Forum, Bias Resistor Calculation. It is full wave bridge rectified with Schottky diodes. 1. I switched both of mine to el34's so the bias modification was inevitable. Based on the chosen parameters, the calculator will determine the appropriate bias current for the tube amplifier. But note that at 800 pate volts, only 400 for the screens. I put some el34's in the jtm25 last night. Hot (70%) Avg (60%) Cool (50% I'm going to put together a bias circuit for EL34 or 5881 (6L6). How to make and use a Bias Current Checker More recent bias checker versions can be found on the library page: This bias checker was the first one and the most primitive . If you are using the test points to measure voltage drop on the shared cathode resistor, you are measuring two tubes at the same time, so divide by 2 to figure approximate bias for each tube. Base GENERAL This valve is a high slope output pentode designed for operation in A. So quite a ways off from your 400vac (* 1. Il Primo (12AX7+EL34/6CA7) Il Primo Bis (12AX7+EL34/6CA7) Il Terzo (12AX7+EL84) 12AX7 vacuum tube comparison: THD measures; 18th Niccolò Anniversary I've been using Weber's Bias Calculator and when you plug in the numbers from the Clubman schematic it shows those figures. In comparison to the EL34s in I have checked my old schematics with EL34 SE and russian 6H8C (latin -6N8S=6SN7). Sometimes as low as 2%. 4mA for the one tube (minus approximately 5. 3 V 1. crabby New member. 35ma is a Generic bias setting, set your bias accordingly Put the amp back on standby Remove the bias checker and move it to the next tube. A Serial of several short Video Documents will describe Simple, Practical Design Procedure for Push Pull Amplifier based on EL34 tube. 2v of bias). 022 coupling caps to . jpg (429. Vacuum tubes available in the loadline calculator; Universal; Concertina phase splitter; Power stage; Tube Amp Projects. Reply. Use below link. With the switch on the back of the amp in 6L6 mode I can only get these up to 29mA with the bias adjust maxed out. First the specs: in fixed bias mode-It's a home build similar to the Fender Twin, four 6L6's. I see different voltages listed on bias adjustments- -37 volts or even 57 volts. We’ll call this variable . Joined Feb 7, 2008 Some Traynor guitar amplifiers had their EL34 suppressor grids connected to the negative grid bias, without any apparent ill effects. The output is filtered with a I’ve always read that to be safe, since Marshall transformers are designed for EL34 NOT 6550s, you should bias them as an EL34. ) Logged Willabe You just need to convert your circuit to JTM50(EL34, 3. In heavy abuse with pin 1 connected to cathode via 470K, I could not measure any G3 (pin 1) current. We will try 220 ohms (2W) as a close standard. 3 the output The voltage is around 430 vdc, the bias current is zout 30mA. ~-40V). For amps with cathode bias resistors you can simply measure their voltage drop and use the Tube Dissipation Using Cathode Resistor The bias calculator says it should be 40. 2VDC. 45-50mA may be "safer". Better bias system This is the bias system that I use on the Hoffman turret boards like the 5F6A Bassman and Plexi boards. (plate at 370VDC, 25W max dissipation) That's really close to the OPT's spec. He says the 6L6GB is rated for 19 watts. oveik ysub ulbfqh udvtsr zofm stiiz xgtae flq wtjrg cbiug