- Weber el34 bias Spec sheets say that El34 in class-ab1 push-pull operation can run with a plate voltage anywhere from 350-780 Volts (max being somewhere around 800). It can connect somewhat lower than cathode. Put the first tube back into the tube socket. 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. i am using a weber bias rite, it is now arond 28-30 ma the plates around 480v . It is full wave bridge rectified with Schottky diodes. Is it too low? Is the EL34 self biased or fixed biased? Self bias voltage is subtracted from the voltage at the plate. Senior Member. Now, when you use the bias calculator on the Weber-site, they do make a difference between 6L6, 6L6GC and 6L6WGB and for the same plate voltage, they all have different max settings. I Hi all, i want to make a class A pp amp with fixed bias. Opinions on the advantages of this procedure are mixed. I don't think that Ampmaker It's very common for cathode biased amps to run at 100% of max plate dissipation. The little one is 16" x 16" with a 10" speaker, cathode bias 6V6's. The JJ E34Ls are a high transconductance (more reactive) tube and can easily spike to 200mA at clipping while the EH EL34 is a bit lower in transconductance and generally will spike lower (150mA) at clipping. 040 ( 40Ma) = 15. Note: This adapter will NOT test 7591 The one limiting factor when going from 6L6 to EL34 is the bias voltage range. The schematic you showed is for blending EL84's and 6V6's. EL34 tubes are typically idled hotter tha 6L6 tubes. Notice it has one more stage of filtration than the simple Fender bias system. -User Name-Password. If I owned any EL34 amps I would still use the cathode resistor method but I would also measure the voltage drop across the screen resistor in order to Definitely go with EL34's. So in my always cautious wisdom I figured maybe I needed to make the capped-off bias wire, a ground reference by connecting it to the chassis. I use one of those Weber Bias Rites and the 4 adapters are pretty tall and every other amp I've had needed to be removed from the headshell to bias. That said, the Weber Proluxe kit is more different than that. read it in a book by the guru Gerald Weber, of Trainwreck fame . A visit to the Weber Bias Calculator and the Tube Amp Bias Calculator both suggested a bias measurement of 38. I have used mine 3 times since I bought it several years ago and it paid for itself after the 2nd use. Requires multimeter for readout. the 100k connects between the 0. 36 So, 36mA is the bias per tube. Also IMHO you will probably want to have a switchable cathode resistor/bypass cap combination for switching from 6V6/6L6 mode to EL34 mode. 3v filament line. What exactly is Bias? The best analogy of bias adjustment that we can think of goes back to older cars that had carburetors. Buckeyedog Active member. Members; 3. 450 volts for KT66's and KT77's, and . M. Purchased this Weber bias meter (octal) a few years ago but used it only two times. 6, should be a fair trial cathode resistor. now there is some people that does a mod in the bias area, but that would be a little over your head. Is the EL34 in Pentode mode, Ultra Linear mode, or Triode wired? I put some different EL34's in my new 6534+ the other day and I thought I'd share my findings. It has a bias pot. 040 The current (measured at the cathode pin 8 is Plate and Screen combined so with that plate voltage 40 ma would be 70%. Thanks I'd try fresh GOOD brand EL34. 3mA, so I believe I had hit this sucker as close as I’d care How to Measure Bias. 00 and available in our online store and can be used with 6V6 - EL34 - Buy a weber bias rite and you can make sure your ok. Not with the 6534. EL-34's use more heater (filament) current than 6L6 types. are all octal tubes. This is only for the Single Rec's and Rectoverbs that are switchable from 6L6 to EL34 mode because the 6V6's should be run in the EL34 mode. These parameters usually include amplifier class, plate distribution, tube type and plate voltage. The local amp techs around here want to take 2 weeks and charge an insane amount to install and bias new tubes. Instead of 7591 I used EL34, and I play around it a lot especially on the bias where I learn a lot. If it is a Latino built with the VTA board there is a bias adjustment for each tube and with EL34's or 6L6's the bias should be . An Hoffman Amplifiers Tube Amp Forum, Cathode biasing a pair of EL34s. so between 30-40ma. If According to my Groove Tubes bias kit manual, that means 20-50 mV is the range, with a nominal set point of 37. 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 Help biasing an amp, PP EL34 I acquired bias probes and correctly connected them to my multimeter, but it always reads 0. Join Date: Jun 2018; Posts: 800; Share Tweet #35. 5. If you think you find the problem , redd the negative voltage at the grid on each Output Power tube 's sockets before you plug tubes . Replacing a GZ34 tube rectifier with a solid state rectifier like the plug-n-play Weber WS1 Copper Cap will supply the amp with a little more voltage and current to I experimented with cathode biasing two EL34's in a 1987 model 6V6 Plexi. Just replaced all the electrolytics, have done the Heater Mod, have reseated all the other Molexes (Boy! aren't they crap!). Asking $95 or best offer I was watching clips of the new marshall 2525 mini jubilee amp which is 20 watt amp with EL34 tubes and it got me thinking about biasing. can you all reccommend one? Maybe one that checks the plate voltage as well. Please login or register. New posts Search forums. The author cames no responsibility for any information provided. So if the outer tubes are really operating in AB mode you are getting more than the 6 watts output that you found on the Weber site. If Ken Fischer and Gerald Weber think it's a good way to do it i want to know why. Hoffman Amplifiers Tube Amp Forum, Weber Bias-Rite "expectations"? Welcome To the Hoffman Amplifiers Forum January 31, 2024, 09:04:57 am: Welcome, Guest. Hi, I'm new to the forum. But that Weber layout has a true bias pot, and convenient test jacks. I'm confused about the correlation between voltage and current. -User Name-Password. I am using a weber bias probe for all 4 tubes and a eurotube that does 1 at a time. For amps with cathode bias resistors you can simply measure their voltage drop and use the Tube Dissipation Using Cathode Resistor Better bias system This is the bias system that I use on the Hoffman turret boards like the 5F6A Bassman and Plexi boards. I actually like the fact that you need a really thin screwdriver and have to be deliberately trying to get in there to make an adjustment but you might be looking for something else. Working on a 91 VL-502. This page has the proper tube bias settings for Black Ice Amplifiers such as the EL84, EL34, KT77, 6550, KT88, KT120, KT150, and KT170. It's not center tapped, but the bias winding is a separate 50vac pair of secondary wires. Tube amp Bias Calculator. Oct 3, 2024 A regular 80cm wide K40 with a 700-720mm tube can realistically output 32-35W. a 2xEL34 amp at 70% is actually a 35 watt amp not the 50 watts of the two 25 watt EL34 tubes. Home 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 I would not worry about a little less power output from self biasing, unless you have very in-efficient loudspeakers, or are trying to fill an auditorium. And a few tweaks here and there can go a long way. The resistor values for the EL34 bias circuit (except the 220k grid resistors) seem to be more appropriate for your extra "cold" 6550s as well. post id: 7822861484. So you choose the adapter based on the amp you plan to use it with and what type of tube that amp uses. Posted August 22 I’ve always read that to be safe, since Marshall transformers are designed for EL34 NOT 6550s, you should bias them as an EL34. tedweber. I even accidentally manage to run This mod allows wide range of adjustment to bias 6V6, 6L6, EL34, KT66, KT77 and KT88 power tubes. The plate voltage averages 472. Here's my Phoenix amp on the bench right now. 5W is 70% of that, so we are in the safe zone. but will not give you a very accurate reading of the actual bias (idle) current. Bias Section - Screen grid Resistors - One ohm cathode resistors - 100 ohm heater resistors Gerald Weber, Terry Oubre, Doug Hoffman, Bob Fieberts Old Tube amp shop photo: Top of page: In my amp I put a potentiometer in place of that resistor and can easily dial in the proper range for KT66's or EL34's, and then use the standard bias adjust pot to 'fine tune' the value. Anything above 60% dissipation a 6550 tends to lose its definition and low end detail. Well worth the investment. crabby New member. Member. The measured plate voltage was 456VDC. This may melt or freeze. 25K or 22K pots with 25K or 22K R's will work. I used the Weber Bias calculator on their website and was Home. I wont use it too much and dont need top of the line but i would like a good quality one. What's new. You can perfectly match the tube bias even if the tubes are not perfectly matched. When you slide it over to the EL34 position, it will throw another 47K resistor in parallel to the already existing 47K resistor. This is a Weber kit amp. Currently getting a reading of 39mV & 37mV using a Weber bias probe the basic one that plugs into your meter (mV on the meter Bias Settings For Safe Plate Dissipation - Class AB 70% Class A 90% Explain This: Class . The plate voltage of Diezels is 480V DC, so use the following calculation: (max. Other than that, it's just minor wiring changes plus re-biasing. 65 = ?. The webber calculator only goes up to 500v. Re: Help biasing an amp, PP EL34 « Reply #28 on: September 27, 2023, 12:14:45 pm » AlNewman I took your recommendation to dial it back a little, and aimed for 60% dissipation, to my surprise now, the amp sounds great even past 3 o'clock volume. If you want a little more life out of your EL34 tubes, then try increasing the individual 470 Ohm self bias resistors to 560 This is a great tool so that you can bias your own amp quickly and easily! My amp is cathode biased, so I no longer need this tool. This lets you milk the most performance out of your output transformers and you'll notice Our bias probe measures true bias current. For one, you have this freakin copper tube with a bunch of wires crammed in it with high voltage everywhere The amp I built is adjustible fixed bias with AC/DC balance pots and test points. Plate voltage is set from the factory. Note that if the plate voltage was still 460 volts for the 68. Next Last. C. 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. I simply want to understand the process and why some techs think this is the best way to bias an amp. Jump to Latest T. I also get tubes from suppliers who do a 24 hour burn in, so I don’t wait for the amp to warm up an hour before setting bias. Unique tone quality over the same two 12-inch speakers. Then that is followed by another "fixed" resistor which also sets the negative grid voltage. 050 X . Are they 70% of the full plate current capability? you can use the Weber bias calculator to calculate that too. 400 volts, . Source voltage is -57V and replace the 180K resistor value with 220K in the equations above. I think 5W 470R/25uF 63V will work fine for either a single 6V6 or a 6L6, but you will want probably around 5-10W 220R/100uF for the EL34. by directmetalmonster Sat Oct 23, 2021 3:34 pm When I went to bias I noticed the reading was quite Weber's bias calculator says my AB push and pull amp with 6L6's at a 395 volts on the plates, needs 51 mA to be at 70% dissipation. The output is filtered with a An EL34 can produce 25W (so 2 per channel gives 50W maximum). 72 watts. Cathode resistor bias is a compromise: good enough for most purposes, simple and cheap. 00 mA. I never did like the Mesa Blue angel myself. plate dissipation W* 600)/480V = current in mA. These days I have no problem using 50-55% dissipation. Check the next power tube and split the difference if they are off just a bit. I have not seen any A/B schematics to compare too. It uses fixed bias rather than cathode bias, which gets even more power (substantially more, like another ten watts or So I can get the bias reading with that and the cathode current reading. Welcome To the Hoffman Amplifiers Forum February 23, 2025, 01:45:35 pm: Welcome, Guest. Pure fixed bias regulates quiescent current and so is theoretically best. So bias the EL34 to get 33mA on 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. What would be a good bias setting for these voltages. Great little gadget. Use this formula to find out what the bias range is: Max Dissipation of tube type / Plate Voltage * (. 70 = . Also, your bias voltage is very low; it should be somewhere in the range of 35-55VDC or so. -User Name -Password. Forums. Octal plate pin 3 & cathode pin 8, 9-Pin plate pin 7 and Also, your bias voltage is very low; it should be somewhere in the range of 35-55VDC or so. You do have to buy the adapter (without shaft) to mount it through the chassis, but it works nicely. Any pair of real Mullard (UK) EL34 that matches (bias) will be fine. Thread starter amiller; Start date Jun 3, 2008; amiller New member. The 70% rating for an EL34 is 20 watts max so that value should be just fine. If you plan to roll Rectifier 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. (between pins 3 & 8 on the power tubes). Hoffman Amplifiers Tube Amp Forum, EL34 bias way too high. T In my amp I put a potentiometer in place of that resistor and can easily dial in the proper range for KT66's or EL34's, and then use the standard bias adjust pot to 'fine tune' the value. It will get louder set at -34 but then the plate voltage The amp is a push-pull EL34 with bias set by adjusting a pot near each tube. Home; Help I use the Weber Bias Calculator. Better, find on eBay these 4 position Octal digital bias meters, they have 4 octal plugs you put in the amp, in which you insert your EL34 tubes / 6CA7. You will measure millivolts across the 1 ohm resistor. Home; Help; Search; Bias refers to the high-frequency alternating current applied to a tape recorder to minimize distortion. Bias supply is 100k off the wiper of the 20k bias pot. Level 3; Posts: 1870; Cathode biasing EL34’s « on: May 06, 2022, 11:11:02 pm ATM-1 Biasing Hi this is not so elegant with this amp, what you need to do is measure over the OPT primaries! in which you insert your EL34 tubes / 6CA7. I am very ignorant to electrical work, but even I can use the Bias rite. The 2 half's of the 12AU7 are wired in parallel for more current/drive to the power tubes. Always double check plate voltage when adjusting bias as current increases/decreases the B+ voltage follows accordingly. Welcome To the Hoffman Amplifiers Forum February 17, 2025, 08:15:29 am: Welcome, Guest. If you would like this kit assembled for you by one of our techs, you can email your request HERE. S. But what I like about the Weber OT (aside from price and good tone), is that there is that 32(16) ohm tap available such that just like was said the bias is fixed. 3 12/1/2015 Enter data in blue Maximum Safe Bias Select Tube Type 6V6GT 12 Max Dissipation is shown at right of tube type. If you are getting into tube amps grab one. Info for maintaining and tweaking your amp to perfection. Still, very tight, nothing like a tweed Deluxe, for instance. 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. Current visitors. The cheapest solution. Posted October 10, 2010. In a short accident with modern EL34 in 7027/6550 holes, nothing bad happened when I left pin 1 disconnected. 6l6's are 25 to 60, with a set point of 45 mA. 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). yes, you can use el34's, e34l's, kt77's, kt88's, 6v6's, kt66's and whatever regular guitar amp power tubes that fit in those sockets the fortin modified rd50h didn't require any bias adjustments and came stock with jj e34l's not sure if this one needs biasing better pm Mike my ex-fortin rd50h had a diezelish gain texture, Some Traynor guitar amplifiers had their EL34 suppressor grids connected to the negative grid bias, without any apparent ill effects. What bias current do I want for my 6L6GC power tubes with the Twin Rever? The Weber bias calculator*, at 445 measured plate volts, suggested 47 mA but my amp wont let me go above 45 mA. 85 percent but you will wear out the tubes quicker! 12 watts divided by "I suspect the difference is fixed bias (yours) vs cathode bias (mine). I measured several voltages: Voltage between pin 3 and pin 8: 470V Voltage between pin 3 and ground: 470V Voltage across the resistor connected to pin 8: 150V This page is a step by step guide on how to adjust Black Ice Fusion tube amplifier bias. The Ampeg schematics leave me yearning for more Info as so does Lee Jackson's one "Master Series" series video where Hey all, I'd like to be able to check the bias myself and as much as I'd like to think that I'm pretty good with electronics, I don't feel right poking around an amp with dmm probes. 6 posts • Page 1 of 1. This way it's done in no time. SKT-9G Tube Socket Spring type Tube Retainer for EL34 and 2. for an amp with B+ of 400dcv, 70%MPD would be 43mA in example #1 45mA would Refers to a bias obtained by means of cathode resistor(s) ( or diode(s) ) whose voltage drop makes the grid negative with respect to the cathode. Home; Help; Search; Login I've used the Weber locking pots with success, but if you'd like some other options, here's a digikey Re: Changing from 5881 to EL34? It's do-able, but not as easy as some tube swaps. 1. This reduces gain a little. If you bias them in the 50+ range like a typical 6550 you’re taking chances on stressing the transformer. Featured content New posts Latest activity. 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). So if you make a fixed-bias class AB amp that is lower wattage than the tubes used could produce do you still idle bias it to the 70% of the max dissipation of the tube? ps. As for the Mark IVb, the bias on the inner tubes is -52v and outer pair is -47v. The typical bias servo regulates average current and so forces quiescent current down when a signal is present - theoretically bad but some people use it OK. ) this unit allows you to bias it so you don't need to take it to a tech for biasing. This model is unique in that it has a full tone stack for both the clean and the overdrive sections, as well as gain and drive controls. 20 Add to cart. Enter plate voltage: Select output tube: EL84: 6v6: 6L6: 7027: KT66/EL34: 6L6GC: kt77: KT88: 6550: KT120: This information is for reference only. The max range i could get was -44MA. 1 ma bias point this would translate into an idle power of 31 watts which exceeds the maximum rating for the tube. you must have around -30 volts . Rated 0 out of 5 $ 1. Since 2006 we have offered a single octal bias probe for use with a Multimeter. Logged tdvt. mrwood200 Well-Known Member. Cathode Bias 85% Cool = DC milliamps 95% Average = 100 % Max Safe Dissipation = *Merlin Blencowe believes up to 85% is OK for Class AB Fixed Bias Amps. 035 Plus . Mullard 5-20 EL34 biasing Thread starter teemumm; Start date 2014-06-11 9:50 pm; Status Not open for further replies. Welcome To the Hoffman Amplifiers Forum March 06, 2025, 11:54:37 pm: Welcome, Guest. 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. The best I got from each EL34 was 21watts dissipation w/250ohm Resistor and the 5AR4, SS plugin 23 watts, (I was temped to use a 5Y3 but first filter was 50uf). It holds it's own with 45 watt newer Fenders. 1 of 2 Go to page. They aren't particularly closely Advice on purchase of bias tool for 6L6, EL34, 6BQ5. This device reads cathode current. Post Cancel. Each 7591 has it's own 27ohm resistor to ground at each of the four test points. The EL34 will also want 5W min (or even a 10W) screen grid resistor Bias Measuring Equipment for Guitar Amps. Because they draw differently they need to have that sophisticated switching/cathode cap arrangement to prevent the tubes from being too hot. On my LS I had to run the el34's on the 6l6's setting to get the tubes even close to where they should be. the weber lets you plug the tubes into it, then you plug the tubes into the amp. My PT, 325-0-325 with a 5AR4, is around 400v B+. On the dual -bias if the wiper fails then the safety R will still give -bias to the power tube grid. 50 watt circuit with clean and overdrive channels, switchable with a footswitch. that is the maximum you should use, I like 65% for EL34s. for a build quote. After the diode there is a 10uf/100v filter cap. Go. Cabinet is small box, same as 6M45. New production 6550s I would bias in el34 range as 25w tubes. It’s a copy of a Marshall JCM800. 1uF and the 1k mentioned earlier. The 1 ohm resistor is The Vishay 43P family of trimmer pots has worked well for me in a couple of builds. 6 volt filament trans wired to the 6. StratLou Member. Yes, we have sent so many of our customers to Weber over the years that after talking with Ted we decided to take on Weber Bias Probes, Attenuators and select models of Weber Speakers. ) The EF86 can sound different than a 12AX7, more grit. Usually in the pass I was told, forgetting plate voltage for a monument, that 6L6's should be biased around 30 to 35 mA for about 70% dissipation (estimate). The Duncan Weber sells a copper cap SS rectifier with sag as well which is a good choice for durability, but if you fine a Bendix 6106 NOS which is the same as a 5y3, it will last longer than people usually have amps. I was running SED 6L6GCs and after testing them, they turned out to be pretty much death after only 6 months of usage so I guess he was right that 42mA is to high Bias Rite Instructions; Chassis Dimensions; Cabinet Dimensions; Cabinet Covering Swatches (Includes Handle Pics) socket with bright blue anodized shield. 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 PT is the Twin Reverb job from Weber. You must enter Tube Type and Plate-to-Cathode Voltage above before calculating Tube Dissipation. 10 You can buy a Weber Bias Rite (www. Welcome To the Hoffman Amplifiers Forum February 16, 2025, 02:47:46 pm: Welcome, Guest. per output tube. Joined 2014. 5 mA for El34's. It uses an eyelette board and the bias circuit is kinda funky, but it works and sounds damn good for the ST70 el34 bias low. The Granger Amp bias probe measures in milliamps by insertion into the cathode connection that conducts the current to the plate (anode) of the tube. I see different voltages listed on bias adjustments From what I understand I need to figure out the plate current, then plug that into the handy weber bias calculator, then adjust the bias to the suggested value and see how I've been using Weber's Bias Calculator and when you plug in the numbers from the Clubman schematic it shows those figures. Weber BR-AH experiences with EL34 bias procedure. Everything before that EF86 is the preamp. You can push them over 40W, but the tube won't last long. Not bad Hoffman Amplifiers Tube Amp Forum, Bias settings for common power tubes. In heavy abuse with pin 1 connected to cathode via 470K, I could not measure any G3 (pin 1) current. You can do it easy adjustable to a point. on cold bias amps like 5150 and mesa boogie 50/50 I recommend replacing the output tubes before touring. Keep in mind when this switch is changed, power valve bias adjustment is needed. Tube Dissipation Using Cathode Resistor Voltage Drop. directmetalmonster Posts: 9 Join date: 2021-02-15. The formula for biasing is the plate dissipation of the tube (12 watts for standard EL84’s or 9 watts for the JJ EL844’s) divided by the plate voltage (let’s use 350 for this example) times . On the -bias/balance if the wiper on either pot fails then it will give full/max -bias to the power tubes grid. A K40 has more power than a 20W blue-light diode and the wavelength of CO2 lasers is more convenient in most cases. Just take the top grille off Hoffman Amplifiers Tube Amp Forum, 25k ,50k locking potentiometers for bias. directmetalmonster. It currently has Groove Tube EL34's and previously it had 6550's which is what it came with. You will need 2 voltmeters to balance out one channel. I've seen amps that have a switch to change the bias point for 6L6-to-EL34, but they mostly seem to let the plates stay the same (around 450V). The correct bias for an EL34 running at 470VDC is 32mA-37mA when using the 60-70 percent max dissipation formula. I warm the amp up for 15 minutes, then set the bias for 40mA, if I check again 10 minutes later it I would back them off a bit, most knowledgeable techs recommend biasing between 60 to 70% of max plate dissipation based on B+ voltage and don't forget to account for screen What are the collective experiences with using this product to measure and set EL34 bias (withstanding resister values)? Here is the product, you insert into tube socket, then You could try to adjust the bias until the EL34 plate dissipates its rated 25W but the power supply will likely overheat and fail well before that point. I have known about the effect on the bias voltage for a long time but had never even thought to check the B+. EL34, KT88, KT66, KT100, etc. The numbers from the Weber calculator are milliamps. EL34/6CA7 30mV to 38mV E34Ls 35mV to 45mV 6550 35mV to 45mV . This means you can set the bias voltage to zero. Mullard 5-20 EL34 biasing. mdc1 Senior Member Posts: 99 Joined: Sat Jun 17, 2006 3:43 pm. Logged TIMBO. 6 to . Sometimes, you have to add an extra little 6-volt filament transformer to power the EL34 heaters. You can see that the bias voltage nearly doubles and the B+ only drops to about 60V. " Actually, mine are cathode biased. • View Cab Covering options • Hello, greetings from the UK, I'm new to the forum, which looks very interesting. Casey4s. 6k6 load is nice for either -- and will give slightly lower distortion on Introduction to Bias Calculator: After collecting the above information, you enter the required parameters into the bias calculator. 2014-06-11 9:50 pm #1 2014-06-11 9:50 pm #1 I'm doing LTSpice simulations for Mullard 5-20 (which I'm Hello, greetings from the UK, I'm new to the forum, which looks very interesting. As already was mentioned bias check in is compulsory demands when replace the power tubes, even you replace with the same product. Jun 3, 2008 Go to the Weber Bias Calculator and plug your figures into the formula for cathode biased amps. Jan 17, 2008 #5 cool thanks . dude. Tubes like EL84 are 9 pin. It uses an eyelette board and the bias circuit is kinda funky, but it works and sounds damn good for the Having two bias pots is a good thing because it allows you to set the bias individually for each tube. I had one of them feeding the bias circuit & the other one capped off. Here are my 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. It did jump to 117v but that shouldnt 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. Due to major a backlog (since late Dec 2024) and inefficiencies at the Indianapolis IN United States Postal Hub, our shipments have been delayed beyond reasonable time frames. Runs off a 9 volt battery. That will be way more Marshall than the 5881's. So any setting between 60mA and 70mA for EL34 or 6L6 will work, all a matter of taste. Welcome to the EL34 World Tube Amp library of information. A balanced option may help you to keep the noise to minimum level. 500 volts for KT88's or 6550's. Adjust B+ or Rl until in ballpark. 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. teemumm. The owner may convert to guitar use as it is setup for mics. If your amp has four octal power tubes (6L6, EL34, etc. You can experiment with 70% dissipation and see if you In the Weber schemo, the 12AU7, that feeds the power tubes, is the PI (phase inverter). It’s pretty normal for amps to run one side of the output section harder than the other when pushed into clipping but it seemed excessive in this case. Jul 16, 2012 #3 bias range is calculated by the b+ of the given amp. Through Yes. The bias pot is inside requiring removal of the chassis. Enter Number Due to major a backlog (since late Dec 2024) and inefficiencies at the Indianapolis IN United States Postal Hub, our shipments have been delayed beyond reasonable time frames. Requires separate digital volt-ohmmeter capable of reading current. Financial Bias: In finance, bias can refer to behavioral biases in investment decisions, such as overconfidence or loss aversion, which can impact portfolio performance and risk management. Moderator: VelvetGeorge. The effects on B+ and bias voltages are shown on the schematic. Eventually I My amp has 2 EL34 power tubes. DOES NOT FIT WEBER CHASSIS. typical fixed bias operating conditions for KT88's are 500VDC@80ma, which is about 40W dissipation. I just want to check the bias to get use to doing it. If (Today I suspect both 6L6GC and EL34 may be the same plate-stamping; historically EL34 was worked well past the "25W" number, into 6L6GC turf, and why make different parts?) Load impedance, divided by Mu(g2), then times 0. B. Re: Amp bias range and running tubes hot I think you will be safe at 40mA with the EH tubes. Then, just cycle through the 4 switch positions while adjusting the bias. Tube Type Plate Voltage mA: Calculate Plate Dissipation based on Voltage and Current readings I've done biasing before. Where you might need -48Vdc with a KT66, you'd need only about -38 Vdc with EL34's. The fixed over saturated the OT when turn up too loud but at a loud enough volume just to Turn the bias pot until you get somewhere around 35 milliamps of current. I tried several resistors and did the math. - Own Opinions Only - Comment. That's fine for an EL34. I thought there must be some sort of bias problem. I need to replace the power transformer in my Weber Mywatt 200, which is shorted and red coated. Also two of the four red JJ EL34 labels were blackened. You find various bias voltages, and a few commercial amps with a 34/L6 switch. To ground on a cathode-resistor amp, or to -bias on a fix-bias amp. I would say that Laney makes a fine amp,very British. Works perfectly. The EF86 is the PI driver. Sep 28, 2024 #5 I loaded my Bassman cab with one alnico magnet Weber and one ceramic magnet Celestron. So to adjust the bias, and maybe it won't need it, would the two 220K resistors be changed to get the bias to read -55VDC, or would it be done by changing the 8uf/150V(is that what it is?) electrolytic cap? Maybe I'll be lucky and it will have the pot installed to adjust. So far, I have not been able to determine the brand and specification of the power transformer. You tweak the balance so that you get zero sum DC current through the OPT primaries. TESLA_EL34 Orange Master Posts: 1129 Joined: Switch that allows you to drive the unit at 140watt or 70watt. for an amp with a B+ of 480dcv, 70%MPD would be 36mA 2. I'm going to put together a bias circuit for EL34 or 5881 (6L6). > I have EL34's in a '60's Fender Bassman Marshall started by building the Bassman in the UK, using UK parts, including EL34 because it was cheaper there than 6L6/KT66. The correct bias for an EL34 running at 470VDC is 32mA An El34's max dissipation is quoted as 25W, and 17. I almost got a weber bias rite but i have not heard good things about them. I w Here's what I got back from Phil at Matchless when asking about biasing a Matchless: Matchless are FIXED self biasing amps wired in Class "A". You get longevity and the 6550 tubes run cooler plus keep their composure. 7) = bias in mA So, for an EL34 (25w) with Plate Voltage of 450VDC running at 65% Max Dissipation (you can use anything from 60%-70% 25/450 * . posted: 2025-01-31 08:53. I settled on 435 VDC plate and -42 grid VDC. For use with octal tubes EL34, E34L, 6CA7, KT66, KT77, 6L6, 6V6, 5881, 6550, KT88, KT90. yes, you will have to re-bias the EL34's and will have to likely modify the bias circuit to change the range of the bias voltage. If you follow the above procedure, 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 Re: Amp bias range and running tubes hot I think you will be safe at 40mA with the EH tubes. Tube Max Dissipation 12 watts Plate-to-Cathode Voltage 338 DC volts Voltage measured between the plate and cathode. im not sure about the negative voltage on pin 5. The output tubes are new production Valve Art EL34B (chinese, slightly more plate disspation than other EL34) with about 30 hours on them. By inputting the amplifier’s class type, plate dissipation, tube type, and plate voltage into this bias calculator, you can My experience with 6550's is they do not like a hot bias unlike an EL34. I prefer to always use individual self biasing, and matched tubes. Marshall's recommendations (in newer amps like the JVM and others that have the bias probes on them) If you are using a Weber Bias Rite each reading is . For additional information/opinion on suppressor grid machinations, primarily in the tube hifi ecosystem, search for "Hazen mod". I have amps with 6l6, el34, kt66, 6v6, el84 and i am lookin for a bias probe. Don't wait to Marcus , first , don't plug any Output Power tubes before you fix bias circuit . Here’s another gain banger. The negative bias voltage then goes through a 15K divider resistor that isolates the next stage Knowing that to have both the Bias versions on the amp is possible and ispiring to the Weber 6d30 Kit, we have think to have both options as to be able to have different tone responses I put the switch in a Plexi 6V6 with EL34’s with a 30 watt OT. All 6ca7 I used shows extended reponse in bottom end (don't say better or not) relative to el34. com), put the adaptors between the sockets and the tubes, master=0 and turn the bias pot(s) until you get the correct reading per tube. With maintenance and service in mind, bias test points and adjustment points are installed on the back of the chassis, which permits a safe, easy Single channel 100 watt head with full Tone Stack, Tone Drive Selector, Presence, and dual pot MV. 65 = . updated: 2025-01-31 08:56. Level 4; Posts: 2833; Blues Forever; Re: Bias setting?? « Reply #3 on: November 10, 2015, 02:07:59 am First off, the EL34/6L6 bias switch basically allows throws 1 - 47K resistor in the bias circuit for the 6L6GC bias mode. plate voltage 430v-cathode voltage = 405v 270 My bias resistor was 56K with a 220K in parallel. It says -42 to -48 on the schematic. 005 = . I can hear a difference and the way the amp attacks with EL34's between 150K and 220K for grid leak resistors but have to see what happens with 6550 going from 220k to 150K. However, Weber's bias pots are connected directly to ground. • View Cab Covering options • Hi all, i want to make a class A pp amp with fixed bias. 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 Due to major a backlog (since late Dec 2024) and inefficiencies at the Indianapolis IN United States Postal Hub, our shipments have been delayed beyond reasonable time frames. This webpage offers two ways to calculate tube bias and plate dissipation. . ~-40V). Greg_L. I already made the voltage source from reverse installing a 12. Jul 16, 2012 #2 rockstah New member. However, if we just used idle current and went to another EL34 amp (with a PV of 500V) and simply biased it using the same idle current, we would get a power dissipated of 500V x 0. Post n°1; ST70 el34 bias low. Will calculate and display plate power dissipation and approximate plate current per tube. Fits 7/8″ chassis holes with 1-1/8″ mounting ear spacing. Weber Power Tube Bias Probe - $20 (Campbell River) Can be used for 6V6 - EL34 - EL34II - E34L - KT77 - 6CA7 - 6L6 - 6L6GC - KT66 - 6550 and KT88 tubes Simple to use. it reads ma and platevoltage. 7 will just get you out of crossover distortion and you can go as high as . Get the Bias Rite. One would almost think you could run EL34 without using the bias switch set for EL34. It plugs into the power tube socket, and then the power tube plugs into it, you take your reading and your safe. 9k I used to actually build Bias Rites for Weber, and I thought at the time that it was a horrible, and even potentially unsafe, design. The orig Williamson used a nice cathode bias network with two pots - one to set the DC bias and another to set the bias balance. These 2 -bias adjust circuits will NOT work with bias very tremolo. 050A, which equals 25W, which is 100% if the max dissipation of an If your plate voltage is 393 and your current reading is 40Ma the power formula is: 393 x . Simply change the tube type. BIAS - 6L6GC vs. ♥ best of . These probes are $25. My amp is a Weber 6M45 kit (JTM45/5F6-A circuit). Top. If I'm doing this right, then: 27/. External bias=Refers to a negative control grid bias that is coming from an external source ( usually PT tap--->reverse biased diode---> filter cap, with or without an adjustment pot ) Introduction to Bias Calculator: After collecting the above information, you enter the required parameters into the bias calculator. 0555 * . Calculator Tube Bias Calculator By Rob Robinette V1. Members. That away you have a fresh 1000 hours of output tubes. Dave. typical fixed bias operating conditions for EL34's are 400VDC@60ma (around -35VVDC bias or so), this equals 24W dissipation. The output is filtered with a The advantages of using 6L6 rather than 6V6 in a tweed deluxe circuit, as I see it first, a bit more power. Second, a LOT more variety in tone from tube-swapping. (And tone stack recovery. Use this tool at your own Risk. Max Plate Dissipation for EL34 25W / Plate Voltage (500 VDC} 25W/500Vdc = . 9. Thread starter Bill11; Start date Jan 6, 2008; Help Support The Boogie Board: Guys just to seek your opinion of EL34 measured from pin 3 & 8 having a plate voltage of 290V biased at 46mA. Bias supply impedance is less than 121k worst case. Ampeg VL-502 EL34 bias voltage 06-08-2016, 06:51 PM. Got myself one of those Weber Bias rite tools which measures both the plate voltage and the tube bias. 1; 2; Next. Tubes like EL34's, 6L6's, 6550 etc. OP, I've used an older version of the Weber Bias Calculator for at least 20 years Author Topic: Cathode biasing EL34’s (Read 4495 times) 0 Members and 1 Guest are viewing this topic. Even though the Laney has the external bias switch you should have the bias checked after you swap tubes. Why Use a Bias Calculator? Output Transformer Shunt Method which I read about in the Gerald Weber book from Train Wreck and the Duncan amp page. However I would not recommend this. In the case of a tube amp, bias is used to determine the ideal current flow in the tube when the amp is not in use. My post said 116 wall voltage. 9=30ma. My test amp is my 1980 50 watt Marshall JMP MKII 2204 Lead head. A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. It has 2 adapters that plug into the tube sockets between your amp and the octal tube (6v6, EL34, 6L6) and will give you the values of the plate volate and cathode current, so you can set the bias accordingly. 6L6 and EL34. Members; Casey4s. Single channel 100 watt head with full Tone Stack, Tone Drive Selector, Presence, and dual pot MV. If PRS recommends 30 mA for 6l6's, their recommendation for El34's must be around 25. Home; Help; Search; Login; Register; Hoffman Amplifiers Tube Amplifier Forum EL34 data page 5 shows cathode-bias "AB" conditions for EL34. hgjhn fqckgx iriclv aie lsuh ibl babv hdqyz qdwourw epvmz ougaebb zwf hadhczd cmbuak xobeh