Best 6l6 bias adjustment chart I got a reply, but it was useless. Use this formula to find out what the bias range is: Max Dissipation of tube type / Plate Voltage * (. . The Bias Easy™ 800 allows you to monitor the bias setting safely and easily. When setting the bias pot to the coldest setting I'm getting about 25W with those tubes installed. Replace them with a matched set of tubes rated Sovtek Medium or an equivalent. If Vp is increased, Ip must DEcrease so the tubes don't melt. One more thing: some fixed/non-adjustable bias amps have a "bias switch" to select for a specific tube type. Repeat steps 4 & 5 for pin3 and until both pin1 and pin3 mV are the same. What to prepare; Steps to bias tube amp with bias probe Return the BIAS VOLTS control to the counter clockwise, zero volts, position. In this video, we'll show you how to bias your tube amp using the TAD BiasMaster. See my How to Bias a Tube Amp for more info. Jun 1, 2022 · Hello all! Recently bought this amp, it has yellow led inside I suspect it's old model. (% of max) x (max wattage/plate v) x 1000 =bias current. Aug 10, 2005 · Excellent info there, base on that chart where they have the mesa color system compare to the GT # system, that is why i have mesa's 6L6 STR 440 code green in the first and forth position and mesa's 6L6 STR 440 code blue in the second and third position on the power tube location on my mark 5. This mod also allows you enough adjustment range to bias 6V6, 6L6, EL34, KT66, KT77 and KT88 power tubes. Based on the chart, it states it can be biased up at 600V in a class A/B amplifier. In cathode biased amps we must change the cathode resistor value to change the cathode voltage to adjust the bias. 2 Adjust bias trim pot from the internal circuitry; Step-by-step to Bias Tube Amp With Bias Probe and Tube Bias Calculator. then turn standby off,make sure the meter is set to read DCV, and CLIP the neg . 4 to 1. that's great info!!!!! :wink: Feb 14, 2024 · Locate the bias adjustment points: Identify the bias adjustment points on the amplifier’s circuit board or by referring to the amplifier’s user manual or schematic diagram. 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. Setting Bias – Auto, Fast and Fixed Bias What exactly is Bias? The best analogy of bias adjustment that we can think of goes back to older cars that had carburetors. I also have a Carvin Belair, 4x El84 amp, also sounds a little bit colder. Fully assembled and ready to use. In AA964 there was just one common DC feed wire to the 6L6 grid resistors. If you have a tube tester with Bias and/or Line Voltage meters (539A/B/C), adjust them again when the tube is being tested. A modern DMM can be shunted with a 50k resistor to simulate the original meter used to make this measurement. The plate voltage should be measured from pin 3. com will make sure you get ones that work, in your mesa, without a bias adjustment. I e-mailed Randall USA because of the question how to bias an EL34 Randall RH50t/RG50TC. See full list on killerrig. com Jun 20, 2024 · The increase in bias voltage pushes the tube toward class B operation where no current flows at the zero-reference line of the signal. Are you looking for the very best 6L6 power tubes for your vacuum tube amplifier? This is the place to start. 6L6 Guitar Amp Valve Kits; EL34 Based Kits; Power Valves Menu Toggle. The primary modification necessary is to properly bias the amp. Unrated Tubes, a bias adjust, and you have a bias probe. The bias trimpots don't last forever and they need to be periodically replaced, best at the same time of a recap. Proper bias adjustment of tube amplifiers can be performed accurately using a bias tool which directly measures the cathode current of each output 6L6 power tube. These can be substituted with appropriate bias adjustment. 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 * . Grid bias adjustment: remove power and unplug tester from the mains before making any adjustment. Set the BIAS RANGE switch to the 10V position. EL34 tubes, however, tend to be more flexible, adaptable to both fixed and cathode bias setups, providing you with a wider tonal palette. The 6L6 is synonymous with the "American Tone" style of amplifier. BIAS CHART mV SETTINGS (pin1 and pin3) DSL50 45mV TSL60/1/2 80mV May 8, 2011 · Set the bias according to the directions on the Schematic or in the owner's manual. Aug 17, 2015 · How to Bias a Fender Bassman (AB165) The 6L6 amplifier I chose is a 1969 Fender Bassman head (AB165). More volts, less milliamps. Fender has never recommended any setting other than 60mV. This value is 25w for an EL34, and actually about 19w for a 6L6, so as you can see, even using 25w for a 6L6 is ambitious. The differences between the 5881 and 6L6GC are large enough that a bias change will be required. Same power transformer, and same bias circuit, but the total circuit load has changed, so I had to adjust one of the bias resistors to get the bias range right. You can measure them individually but the voltage goes across them both so you should find the average value for both. May 5, 2013 · Set bias adjust pot R82 to obtain a reading of +60mV at TP30. Here's another example. The Black Magic of Setting the Bias make your amp sound its best. Feb 15, 2021 · Just jump pins 1 and 8 and then go to your cathode resistor. There is also a test point under the chassis by this selection switch for checking the voltage. Adjust the BIAS VOLTS to - 25. Extract from schematic for Fender Hot Rod Deluxe showing notes which include bias setting. 5Kohm grid resistors. By Stewart / 13 October 2015 . This is something that must be done no matter which tubes you are changing. 6. Step 2. (-40 vdc ±2V) . In the following part, we explain which options are available for this for amps. In fixed bias amps we adjust the grid voltage to set the bias. 2000 pF caps were introduced on 6L6 grids to filter out high frequencies, resulting in a cleaner sound. Then by R=V/I, the Load Impedance must increase to properly absorb the power. you could bias it way too high and blow another tube i guess, but you'd have to be pretty dumb. Often it is a switch that can select bias for EL34 tubes, or 6L6 tubes depending which is installed. Note: Some amps will act funny and develop horrible noises (parasitic oscillations) when a bias probe is in place while the Nov 17, 2022 · In all but a few cases, 6L6 and EL34 tubes are not interchangeable without modification. The 6L6 tubes are listed in the WIKI as suitable replacements for the 5881 with the following caveat: "These are not direct replacements for the stock Melody 5881 power tubes, as the bias voltage must be adjusted to compensate for the different tube specifications. It also changes as they warm up so let them get to operating temp before you do a fine adjustment. also I think the Mesa tubes sound great and no worries. 6 to . Then an adjustment will be required. While adjusting the bias control pot of your amp, the Bias Easy™ shows the actual current flowing through each of two power tubes. Adjust the BIAS VOLTS to - 5. Your amp's "best" bias setting is pretty subjective so play it while you adjust it. Hold “Gas 1” and press “Gas 2”. For 8-pin power tubes such as 6L6, 6V6, 5881, 6550, EL34, KT88, KT66, KT100, etc. May 11, 2023 · The best way for you to decide what setting is best for you is a combination of the reading on the meter and your ears! Using the bias control, set the bias to somewhere in the ranges given above (Fig. The bias voltage requirements for these tubes differ, affecting the overall amp design and tone. Set the bias to the suggested figure on the Schematic or in the owner's manual. But there is no chart. 00 volts as read on the DC voltmeter. Or, if a little less power is OK, then converting from: Adjustable Fixed Bias; To: Individual Self Bias resistors and individual bypass caps across each resistor. No, you don't use the absolute maximum values for biasing. Plate voltage will change a little when adjusting the bias so you may need to take another reading from pin 3 and adjust your equation accordingly and repeat steps 4 & 5. In fact, I bias 6L6s using 22w as a design center value. Change the BIAS RANGE switch to the 50V position. Jul 25, 2015 · I found this formula…. Due to superior performance, the more modern 6L6GC, which also features a glass envelope, remains the only type still manufactured. Oct 5, 2001 · The amp has the bias adjustment trim pots located on the back near the EL34/6L6 selection switch. 0 volts. Set the range to 3000. 2: If bias test point and bias trim pot are not accessible from outside the amp; Step 3. 8 times higher, 7K to 9K. And the reverse is true. 15 volts. On the electronics schematic, R82 is the bias adjustment wheel and TP30 is the location of the test point for your multimeter. In this video we go over step by step instructions on how to bias your vacuum tube amplifier. SO adjust it by ear, and if the tubes don't start red-plating, then whatever setting you wound up with is OK. These are still fixed/non-adjustable bias amps as there is no internal bias trimmer pot to fine tune. However, when trying to check and adjust bias according to manual (2 bias adjustment knobs) something looks really strange. 035V to 0. But this doesn’t mean that they don’t need a bias-setting adjustment. 00 volts as read on the DC In order to optimally adjust the amplifier and get the best performance out of the equipment, the quiescent currents of the individual electron tubes should be matched to each other during the bias check. From 360-400 to 480V, the load should be 1. Nov 29, 2001 · 5. . Gas: Turn the Bias control to 100. Use this as a guide for setting your bias. The BiasMaster is available in an octal and noval version. The power dissipation of the amplifier as a whole can also be measured using the amplifier input line power using an AC power meter such as the P4400 Kill A Watt device. Buy a matched pair. Check out the following 6L6 tube reviews for guidance on getting the best tone out of your tube amp. Press and hold the “Gas 1” button and turn the Bias control to show 500 on the 3000 range. Messages 1, Ive found that the EH 6l6's were set about v. Mar 8, 2009 · the point of this negative voltage is to regulate the flow of electrons through the tube. Turn the bias pot until you get somewhere around 35 milliamps of current. We adjust the voltage difference between the cathode and control grid (bias voltage) to adjust the amount of electrons flowing from the cathode to the plate. Doesn’t this seem a little low?” “I bias my JJ’s in my ’59 Bassman clone at 48mA’s. Aug 16, 2009 · And remember if you are biasing 6L6 tubes in the 6l6 mode on the amp and the bias will not go above 35mA even with the trim pot turned all the way up, flip to the EL34 mode and bias it up from them. Apr 29, 2007 · i dont think so. The Best 6L6 / 6L6GC / 5881 Power Tubes - Reviews and Guide. There are several different 6L6 power tube types and it can get a little Nov 10, 2010 · The stock range is supposed to be limited anyway. Just note that the 6L6 family of Tubes biases in a good amount different then those others you will run so to get the best out of which ever you run you might want to use 2 separate cathode resistors and of course separate bypass caps that are selectable by means of a switch. Is rated 40-50 watts. The carburetor had an adjustment screw to set the fuel-air ratio. Mar 30, 2023 · Per the Onix SP3 WIKI, the bias voltage for the 5881 tubes is 1. 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. 0555 * . 60% is pretty high for these amps. Now I do have a vintage set of two RCA 6l6GC's that I ran in my D'lite and they also sounded better under 70%. He was kinda shocked about this and said that is WAY to high for 6L6 tubes and said to definitely keep them under 30mA. You have to buy matched tubes to get matched bias. Wait about 5 to 10 minutes with the amp in the play mode and do a final bias adjustment after the tubes are hot. > what to bias the 6L6's at "Bias" includes plate voltage. Measure the bias voltage: Connect a multimeter set to DC voltage mode to the bias adjustment points. EL34 tubes don’t draw quite as much power as 6L6 tubes. Does it only have to do with bias adjustment, or is there some other parameter that is critical? To make the 5F6A's bias adjustable you simply replace the bias circuit's 56k resistor (connected to 15k resistor and ground) with a mini-50k linear pot (or trim pot) and 27k resistor. A lean mixture would have less power, but give better mileage. The bias of the amp was set way too high when I bought it used and caused red plating in a TAD 6L6 WGC as it goes, plugged the bias master in, replaced with a pair of NOS Jan Philips and set bias near to the top end of what they recommend for this amp and now it sounds fantastic and I have the price of mind that everything is as it should be. Cheers, Dave O. Apr 28, 2018 · I also stated the 6L6 series, not the 6L6 GA, GB, or GC, or 5881's for that matter. 3) and play the amp. 6L6 Author: RCA Subject: FP-1999-02-28 Created Date: 2/24/2002 7:46:40 PM Dec 11, 2008 · Wow, great response here. The bonus is that with a cooler bias setting, your power tubes will last longer. To add adjustable bias to fixed bias amps with no bias pot you simply replace the bias circuit's second, larger resistor (connected to ground) with a mini-50k linear pot (or trim pot) and a resistor of about half the value of the original resistor. 65 = . 6L6 tubes are frequently used in fixed bias configurations, demanding a precise bias voltage for optimal operation. Cathode Bias (Self Adjusting) Apr 26, 2012 · Yes, the bias is set for both tubes together, not individually. The higher the voltage from -55 (as in towards -60) the lower the current will be. This is why fixed bias amplifiers - which don't experience the bias change relative to output level - can generally be set to idle at lower current, which promotes longer tube life. now, different tubes, even of the same brand, will require a different bias voltage in order to control the flow of electrons. Verify that the tester meter reads 5. 040V range and see how it sounds. This has its pros and cons. Tube type: ----Choose---- 6V6 EL84/6BQ5 5881 EL34 KT66 6L6GC KT88/6550 May 5, 2013 · Set bias adjust pot R82 to obtain a reading of +60mV at TP30. Right knob not responding at all, doesn't matter which tube is being checked. when you adjust the bias, you are changing the value of that negative voltage. The 5881 and 6L6 come from the same family of tubes. Fixed bias also minimizes warranty expenses (read: more profits). One slightly hotter and one slightly colder. Other variables needed are, fixed bias or cathode bias? Plate voltage on the output tubes? If cathode bias, what size resistor? It's a custom built amp can you go back to the builder for advice? Last edited: May 11, Thanks Guys, its a 1 ohm resister on the ground with a bias pot. just make sure you have the volumes down to zero- nothing plugged into it- and make sure you have it connected to a load(a cabinet or hotplate set to load),and turn the amp on,let it warm up on standby. I’ve heard that a lot of people bias them around 32-34ma…. You use the design center values. That would be about 35 ma to 40 ma total current flow through each power tube. The octal and no Feb 29, 2016 · Changing the bias trim changes bias of ALL the output tubes, and it can go way beyond the narrow range of appropriate bias, such that it can be rebiased for EL34. Put the first tube back into the tube socket. 65 = ?. The calculator will give you the bias current for each tube. This yields (34ma) / (30W / 440V) x 1000 = approximately 50% of maximum plate dissipation. I have a HRD that I rebuilt as a Tweed Pro (5E5A), and to get to 69% max plate dissipation, my cathode voltage reads about 108mV. Careful safety measures must be taken when working with internal Jan 6, 2025 · Step 3. The original 6L6 tube featured a metal envelope. Cathode bias amps must run HOT. Check the next power tube and split the difference if they are off just a bit. Jan 11, 2024 · is to purchase a very well matched Quad of 6L6 tubes (6L6GC is best for long life if the amplifier is driven hard into overload clipping). 1: Adjust bias trim pot according to the recommended values. A rich mixture would have more power, but would decrease gas mileage. The amp's tone is what really matters so don't just set a standard bias target like 70% for Class AB amps and forget it. I rewired the gawd-awful bias balance circuit into a true bias adjust circuit. An original RCA datasheet which I've taken the time to screenshot each page and highlight the limit as stated. Feb 16, 2010 · I attached a 6L6 bias chart if you don't feel like doing the math for the bias numbers. Not for 7591 tubes. Congratulations again! You have just biased your amp! The following info is for octal power tubes. Nov 29, 2005 · The JJ's are fine and Bob at eurotubes. Ensure the multimeter’s probes are correctly connected to the Nov 10, 2024 · The bias section in the amp is: 50v bias tap -> 1k resistor -> Rectifier Diode -> 10k Bias divider; 2x 10uF Bias Filters and then a 50k bias pot with a 22k resistor in series. Mar 27, 2013 · Assuming those test points are measuring across a 1 ohm resistor and you have typical 6L6 type plate voltages, you appear to be running the tubes way hot! Lower the bias adjustment until you get into the 0. The grid bias voltage is measured between pins 5 and 8 with the bias control at 100 and the TEST button is depressed. What exactly is Bias? The best analogy of bias adjustment that we can think of goes back to older cars that had carburetors. Forget the 30w figure. Jack Jan 11, 2024 · is to purchase a very well matched Quad of 6L6 tubes (6L6GC is best for long life if the amplifier is driven hard into overload clipping). Jun 23, 2007 · Do this on all power tubes and adjust the tube with the highest value to your desired bias voltage from step 4. Take amplifier off of STANDBY with no signal, adjust mini-pot (PR1) closest to pin that the positive lead from your DMM is connected to and set it to the mV voltage that is listed in the chart below. They found that selecting tubes for that "Sweet spot" and branding them "Mesa Boogie" eliminated the components for bias adjustment. You will notice as the voltage goes up, the bias current goes down. Try settings between the 50 and 60%. Grove tubes are fine and you get the warranty, also they will work fine in mesa with no biasing(use GT 4-5 #). Feb 15, 2006 · In my limited experience, with modern power tubes, I find a colder bias, depends on the amp but on my D clones around 60-65% seems to sound the best. One for the EL34 and one for the 6L6. I can't imagine how you would balance bias of 4 mismatched tubes, in any possible combination of mismatch, with a single bias control. 36 So, 36mA is the bias per tube. The total circuit load affects this, too. 10 KOhm resistors in bias circuits were introduced, as well as 100 KOhm resistors to the 6L6 grids before the 1. This mod allows wide range of adjustment to bias 6V6, 6L6, EL34, KT66, KT77 and KT88 power tubes. Turn the trim pot to adjust the plate current to the desired setting. Mar 8, 2006 · Also, it seems like there is still confusion on why the value of the grid resistor is crucial at 50k for a 6550, versus the 220k the D'Lite circuit uses for 6L6's. Those rare amps simply require a bias adjustment, however the majority will likely require some physical modifications. sjgb xqdeloo knnpxlel oaxgvipi ecfvr nye tbz apcnd uwshnq sud