6l6 bias voltage amp. For EL34 tubes, the factory .

6l6 bias voltage amp With 475V 70% =44ma. Biasing your amp doesn’t have to be difficult. My suggestions above are for a push pull style amp (2 x6L6 tubes) Oct 6, 2014 · So for the 6L6-GC in triode mode, max plate dissipation is 30 watts; 60% of that would be 18 watts. Does this sound right to Jul 4, 2011 · There are differences in anode dissipation, and the KT66 requires slightly different bias. So the biasing voltage in an AB amp Plate voltage: 510v Voltage from bias test points provided by peavey: 58v Bias test probe 1 in tube 1(from the left) set to 38. Fixed bias does not have the cathode voltage difference of 20v. Don’t forget that it’s not just the tube your running harder, because if you play the amp loud enough to have the power supply voltage start to sag then your also running a lot more average current thru the OT and it will Also the Bias for your power tubes would have to be changed to accommodate the 6L6 tubes. Cathode bias also looses power in the cathode resistor. Green is the baseline and blue is the max. The current thru the 6L6s increases just a bit, driving the bias voltage up. All readings are mA. And if the power tubes are a matched pair. instead of the 115/117 volts the amp were designed for. Here is s video to simplify the process. It's at that point i get jittery. The schematic shows 6L6GC power tubes. Joined 2003. How to Measure Bias. That amp with the 6l6's is like a cross between having that feel and using steve vai's legacy. If you increase the value of the 22K R to ground it will cause the dcv to go up. 5V). It has been I would rather not name my amps brand name but it has 2 - 5881/6L6WGC power tubes. But you could try a 470R screen resistor and a 470R cathode resistor. This forum is for talking about all kinds of Peavey guitar amplifiers. 15 volts. Safeguard your amplifier and tubes by Because of one 6L6 power tube that was red plateing I installed an old set of tubes to see if the problem was only the tube. Where the 6l6 might take -50 volts to bias at 35ma the el 34 would only want maybe -35 volts. I have read somewhere that to set the bias one can put a 1 ohm resistor from pin 8 to ground then measure the voltage across this resistor and that will be the direct bias reading. For EL34 tubes, the factory For 6L6gc(30w), you can run it pretty hot in cathode bias, but for now let's say you want to dissipate 25w(~85%): First, I usually try and find a schematic of a similar amp, with similar plate voltage, to find a "starting" cathode resistor value. 3V and then keeping a close watch on the Amps ; 6L6 bias range? 6L6 bias range? By The4thlast1 October 11, 2008 in Amps. 25 in (108 mm) Bias voltage: −18 V: Anode resistance: 5 kOhms: Typical class-AB amplifier operation The voltage and power ratings of the 6L6 series were gradually pushed upwards by such features as thicker plates, grids of larger diameter wire, grid Per the Onix SP3 WIKI, the bias voltage for the 5881 tubes is 1. If the amp doesn't have 1 ohm cathode resistors in the amp to measure cathode current as a voltage or you don't have a bias probe, best to leave biasing your amp to a qualified tech. Member. Using a 6L6GC in an amplifier with ECC83 driver and direct coupled cathode follower with 10dB negative feedback I managed 1% THD at 1W output. General discussion area for tube amps. So in this particular amp a variation of only 3 volts at the factory test points made an incredible 20mA difference in bias!! The grid cannot operate at zero volts. EL34 needs higher value until 5k6 for grid stoppers. (400-20 = 380 as above). ? Thank You. Members; lol. You could easily bring the plate voltage of the preamp tubes back in line by In Cathode bias we have an effective voltage of 400-20 or 380 v. 25? plate and screen voltages as applicable and the bias voltage required to satisfy those conditions at the target Douk Audio Nobsound Vacuum Tube Amp Amplifier Plate Bias Current Probe Tester 8 Pin Socket for EL34, KT88, 6L6, 6V6, 5881, 6550, KT66, KT100, KT120, 7027 (CT1-P, Plate Current) With its dual meters, it ensures precise I recently picked up a Harmon Kardon CA-35 PA amp. A 100W PT could obviously handle the current requirement for 4x6V6 (~40W), but the output voltage will be high for 6V6, and higher still due to the reduced current draw wrt 6L6. This can be done HI all, just curious what the proper voltage should be at the bias check point in a fender blues deluxe amp? I read on another website that the 6L6's int eh hot rod deluxe should be around 68mV. Variation in bias voltage at a given plate voltage really doesn’t have a great effect on peak RMS power output. -User Name-Password. You also need to know what your plate voltage is to know what the maximum safe plate current value can be. SE 6L6GC Amp - dialing in the 12AT7 driver Bias. 8 times higher, 7K to 9K. At What should the bias be set at for a 6L6 amp? What should the pin 8 resistance be? I am running them in a st70 clone with adjustable pin 8 Home. Since its fixed bias and slightly higher rail voltage you may achieve some benefit by Hello, I'd like to accurately check the bias on my 6L6 amp. The entries at the top of the table demonstrate that the example operates near the maximum values for an "all-metal" 6L6, which is more limited that a modern Re: Svetlana 6L6 Bias BDRI It depends on the actual plate voltage of the specific amp. With the bias set to 45 volts at the factory test points the bias went way down to a very acceptable 37mA. The fact that it's uneven tells me something's not quite right. I have one that reads plate voltage and bias current I got cheap off fleabay, very handy so you can read plate voltage and not have to guess where the 60-70% bias I have not found a detailed factory procedure description on the factory bias test points on the back of the amp. That's ok for 6L6. I like 6L6GC at 70% and EL34's at 60%. As before, the plate voltage seems to be the major driver in maximum power output. I am watching with a scope and can see that the 2 grid inputs are tracking but what is the difference between having a lower than "normal" plate voltage for said tubes, and reducing the bias voltage. S/T (mode) - 355 to 375V(Plate voltage) - 12 mA(bias current) - 6L6 mode S/SD - 390 to 400 -18 The early tweed amps didn't generally use screen resistors. 5 250ohm shared impedance: 9,000 output power: 24w > what to bias the 6L6's at "Bias" includes plate voltage. Assuming that the amp is properly designed, unless the primary impedance is changed or the HT voltages raised, a 6L6 can't pass Old Fender amps have 1k5 grid stoppers on power amp. You could easily bring the plate voltage of the preamp tubes back in line by I'm repairing an old Peavey Classic VT (212). This webpage offers two ways to calculate tube bias and plate dissipation. for 400VDC on 6L6GCs in Class AB, RobRob's site says 45mA is 60% dissipation For 360VDC, Class AB, 50mA. Just pull the 6L6s out of the amp and measure the voltage on pin 5 of the empty sockets. Apr 16, 2022 · My info states that for a 6L6 and it’s 30 watt rating this should be observed. Then by R=V/I, the Load Impedance must increase to properly absorb the power. That's tipically due to the kind of power tubes you have. You would need to input your power tube’s details and the voltage you A common trick is to design the amp to take either a 6L6 and a EL34. When biasing cathode tubes, and knowing the current through the 1 ohm r, calculate the power using Plate - cathode voltage for V. This is for a 6L6GC tube typewith some common amp voltages and safe dissipation settings. pot. It also has 2 12AX7 mic drivers. 6K primary OT as long as its a hefty one and not a light 2 lb one. Tone Lizard Tales from the Tone Lounge. Like the early Canadian amps that wired G3 to Here are some ballpark areas of where the plate voltage is both bias modes with the amp's overall mode shown. For 8-pin power tubes such as 6L6, 6V6, 5881, 6550, EL34, KT88, KT66, KT100, etc. Welcome To the Hoffman Amplifiers Forum December 22, 2024, 09:41:42 pm: Welcome, Guest. it is true that using the bias voltage to bias an amp is not the best method ; However, I think it is a good place to start for a newbie - It involves measurements away from the power tube socket, helps to Plate voltage: 510v Voltage from bias test points provided by peavey: 58v Bias test probe 1 in tube 1(from the left) set to 38. This amperage is a part of the equation of simple ohms law There are differences in anode dissipation, and the KT66 requires slightly different bias. Forums. . The amp runs at 480 or so volts so 35ma would be 70%. You would need to input your power tube’s details and the voltage you Here's the resistive loadline for 560VDC plate and 400VDC screen-voltage, with the 5K6Ω OPT and using fixed-bias. That being said- after unplugging the unit, discharging all the caps with a 50 ohm resistor, and removing the tubes: 1) replace any old selenium diode rectifiers with a silicon diode 1n4007 etc 2) replace any burst or leaking electrolytic capacitors (replace all low voltage ones, high voltage A common trick is to design the amp to take either a 6L6 and a EL34. That being said- after unplugging the unit, discharging all the caps with a 50 ohm resistor, and removing the tubes: 1) replace any old selenium diode rectifiers with a silicon diode 1n4007 etc 2) replace any burst or leaking electrolytic capacitors (replace all low voltage ones, high voltage Carefully remove the old, worn out tubes from the amplifier. The bias setting for any amp depends on the actual voltage the amp runs at. on cold bias amps like 5150 and mesa boogie 50/50 I recommend replacing the output the bias voltage is a negative voltage that is applied to the control grid inside the tube. I. It depends on your own amplifier and I would suggest you trust your ears. tying the suppressor grid to a negative voltage (bias voltage) in a fixed bias amp. PaisleyTube Posts: 208 Joined: Fri Feb 24, 2006 11:29 am Location: Vleuten, The Netherlands Very correct. It looks like the goal is -35mA as a good bias for 6L6GC's. Moderators: pompeiisneaks, Colossal. A missing 5AR4 rectifier. Is there a bias voltage and is it adjustable? If so are each 4 tubes independant for biasing? Normally there's a small resistor (10-15 ohm) on the cathode of the tube, you measure Class-A amplifier, class-B amplifier, class-AB amplifier, (audio amplifiers) Height: 4. See more The conversion requires some knowledge of the B+ voltage, and of the grid bias voltage of the original circuit (Ask, it can be answered). 4 to 1. Feb 28, 2009 · HI all, just curious what the proper voltage should be at the bias check point in a fender blues deluxe amp? I read on another website that the 6L6's int eh hot rod deluxe should be around 68mV. But tubes were much more robust back then and fairly cheap so I guess most people didn't care. So, today I took my multimeter to my practice space and May 31, 2014 · The 6L6 plate and screen is at 315v and 6L6 is cathode biased at 77ma There is 20v across my 270ohm cathode resistor. By LordRiffenstein November 4, 2005 in Amps. 8mA for my efforts. The output stage uses Grid biasing which is apparently factory set fairly cold so that any matched pair of 6L6 valves should work fine. Pin 5 voltage will tell you nothing. Class-A amplifier, class-B amplifier, class-AB amplifier, (audio amplifiers) Height: 4. B+ 440v. Andy Le Blanc cranking little 6v6 amp, about right for 6l6, 6l6-g, 6l6-gb, and cold for 6l6GC and 6ca7 . I'd like to be able to swap in 6L6/6CA7/EL34. A 6L6 would only stress the 6V6 amp's OT primary / PT HT winding if it was idled hotter than would be appropriate for a 6V6; an amp's signal power output is mainly determined by the OT primary impedance and HT voltage. PRR wrote: Plotting loadlines is only ground. e. the clipping starts. Tone Lizard / Workbench / Bassman Bias. (Approximate numbers). The best way is to observe the live current. I added a 5U4 and brought it up slowly on a varaic. Use the cathode voltage and resistance to get the cathode current. Select your tube type and amp class (Class A, Class AB Low, Class AB, or Class AB High) and enter your Plate Voltage or B+. I am running the 6L6 at about 75% bias. At 330 volts drop across the tube, plate current would be roughly 18W/330V = 54 mA. From 360-400 to 480V, the load should be 1. Again - bias voltage maxed. diyAudio The intersection of these perspectives puts the screen voltage in the vicinity of 300V with a 200Ω "self-bias resistor," which is included as an example design in an RCA 6L6 data sheet. Amp is a recently aquired Ampeg Reverberocket reissue 50watt 2x12 combo. Please login or register. 16 Ohms goes to 8, 8 goes to 4) to double the primary impedance. 25 in (108 mm) Bias voltage: −18 V: Anode resistance: 5 kOhms: Typical class-AB amplifier operation The voltage and power ratings of the 6L6 series were gradually pushed upwards by such features as thicker plates, grids of larger diameter wire, grid 6L6 fixed bias/PT question. End result: The JJ 6l6 gc's I should turn my bias dial pot UP to reach 82Mv. Take into account this amp ships with 6L6GC 30w tubes and uses 100ohm screen resistors. Fender schematics with 6l6 show bias points 15 -20 Volts either side of 45 . Bias voltage is like a control valve that regulates the current through the power tubes. The Amazon. 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 Anyone know how or why i would get two different bias voltage readings on a 6l6 push pull quad?? For example the one pair will will read bias sweep from -59 to -48 and the other end from -59 to -30. The bias voltage on any two-6L6 Fender I don't think is ever above 40V and usually closer to 30V for the typical 350-450V B+ amp. 9 posts • Page Post by jimipage » Sat Nov 08, 2008 11:17 pm. The 7868 is only rated at 19 watts. Top. These jacks are used read the Bias Voltage, which can be tweaked using the Bias Adjust control located next to the power tubes. 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. 5 Divided by 420Vdc = 41. Please The 50K pot with the 22K tail R form a voltage divider. Level 3; Posts: 952; I love Tube amps; NOT a SELF biased amp fixed bias is the VOLTAGE at the control grid (G1) that I plug these numbers into Weber's bias calculator (the voltage/resistor calculator method) and I get 10 watts per tube and 26ma plate current per tube . 450V 47ma = 70%, 40ma=60%, 33ma = 50%. D. Seriously though, they are killer to have. After playing a bit the sound cuts out and I'm measuring -120ish(!) volts on pin 1 of the 6L6's and the plates drop to about 285V. I was running SED 6L6GCs and after testing them, they turned out to be pretty The plate voltage on the 6L6 was about 490V and was biased a little bit on the cold side. 6L6 heaters draw 0. The Then take the 6L6 plate voltage and subtract the cathode voltage for your plate dissipation formula. 66mA per tube for 70 % bias keep adjusting till you get 70% at what ever plate voltage you end up with. All readings (initially) seem reasonable (6L6 344V plates, Bias at 43mA). Members; LordRiffenstein. A PP 6L6 amp using a floating paraphase phase splitter, a 6SN7. 6mA - adjusted by me upon installation via the provided bias adj. com: Nobsound 8-Pin Dual Bias Current Probes Tester Meter for EL34 KT88 6L6 6V6 6550 Vacuum Tube Amp Amplifier (2*Meter + 2*CT1-C, Cathode Current) : Industrial & Scientific. The Fender bias circuit is simpler than your Marshall circuit and it will provide enough bias voltage for 6L6 tubes. Reactions: assimaki. My wall voltage is 116v I never measured how much the voltages are dipping at maximum wattage but I will check it when I get the amp back from the studio. HOW TO BIAS YOUR AMPLIFIER. How to calculate the bias ? The amp is a pushpull of 6l6's ; the manual recommends to bias each tube at 35ma Search. (no offense intended to the primates) I have put it together from scrap, used parts, and junk box parts. Take note of the voltage displayed in the multimeter. There's also high-power and low-power settings that affect the bias voltage, so make sure that Some thoughts. Your 6v6 tubes probably have a 6. And the Ruby's currently using are good to go where at now For 6L6 valves then yes you would be around the 70mV range. This won't work with a single 4 Ohm speaker using a 6V6 (unless you happen to have a 2 Ohm tap) but this is the quick Carefully remove the old, worn out tubes from the amplifier. It was certainly running higher voltages than originally intended, maybe by 40-50V due to higher mains voltages, and In Cathode bias we have an effective voltage of 400-20 or 380 v. Search titles only By: Search Advanced search Search titles only Since its fixed bias and slightly higher rail voltage you may achieve some benefit by increasing bias per tube to say 40mA. 2 ohms. Don't, for example, put 6l6's of any kind into a Quad II, unless you change the cathode bias resistor. It doesn't work. 70% X 25 watts = 17. the point of this negative voltage is to regulate the flow of electrons through the tube. If you carry a high bias voltage, depending on the plate voltage, you will hit the tube cutoff voltage (-) before you get the (+) signal up to the bias voltage. I run my Ruby Found limited data on 6L6GC in class A PP BUT for: The tube bias current should be 36mA per tube. I was quite intrigued with the tone I was getting. They tend to vary a lot on the Devilles that is on one amplifier I have gone around the 70mV mark, on others I have gone a lot closer to 78mV or so. Recently I had a 1960's 2x 6L6 cathode biased amp in for some work. Stock, that amp has the dual-pot bias adjustment: one pot adjusts the actual bias voltage, the other one adjusts the balance. 5A, so a pair of tubes will add an additional 1. The Voltage will change everytime you change the current setting so it will take around 3 times and be very careful!!!!! Hoffman Amplifiers Tube Amp Forum, 6l6 bias pot value question. 9A each whereas EL34 heaters draw 1. But Hot Rods tend to leave the factory with their bias set somewhere between 60mV-70mV. Start new topic; Recommended Posts. I have measured with the tubes removed and they are then equal in measurement sweeping from -59 to -30. Sounds fair to me but if you are using EL34 you need to upgrade the screen resistors and check the Power Transformer. It was like 48mV from the store, Hoffman Amplifiers Tube Amp Forum, Correct OT impedance for a 2 6L6 cathode biased amp? Welcome To the Hoffman Amplifiers Forum December 20, 2024, 08:44:40 pm The conclusion is that the 6L6GC data sheet operating conditions don't point the user to the plate/screen voltage, bias and load which yield the max power available from the tube Peavey JSX biasing 6l6GC. What i would like to know is, firstly is this There are many web sites that explain setting bias. It helps to shape the response of that power stage for that "classic" Fender sound (clean and dirty). Search for a biasing tube amplifier calculator online. Posted November 4, 2005. checking the filament voltage to make sure it doesn't sag down below 6. Reported plate voltages vary quite a bit from around 400v to 455 volts. I've done biasing before. Lots of headroom and didn't clip unnecessarily. Search. Heater voltage will be high too, since 6V6 use less than half the heater current of 6L6. Compatibility with Multiple Tube Models: Our tester is compatible with a wide range of power tubes, including 5881, 6550, KT66, KT100, KT120, and 7027, making it a versatile tool for various vacuum tube amplifiers. The bias range for the Hot Rod Deville can go between 70mV-80mV. acerv12340 New Member Bias voltage in tube amps is called negative grid bias because they use a negative voltage to set the amount of amperage the tube draws. Let's say 350r and using Ohm's Law: Check the voltage drop across the resistor. Its got that hollow but sweet high end and darker Gah, be damn careful, there might be upwards of 400VDC inside that amp. Just pointing out to the effect of the power amp bias. When you want to use a 6V6, you just move the speaker jack down one impedance setting (i. I have a customer who wants an amp with an output along the lines of a Bassman/Super -- basically a pair of fixed bias 6L6's. Home; Contents What did I end up with? A bias voltage of -41VDC, a Plate voltage of 419, and an idle Plate current of 44. If just using tubes with a separate G3, wiring them separately will give more options. ? If the tube is dissipating 15 watts, is there an advantage of plate voltage over plate current. I just got 4 JJ 6L6GCs for my Twin Reverb. It uses two 6L6GC's for power tubes, fyi. Either needs a resistor connected between grid and B+ to form a fixed bias voltage divider or needs to be bootstrapped to the cathode by adding a 47K resistor between the junction of R2 and Because of one 6L6 power tube that was red plateing I installed an old set of tubes to see if the problem was only the tube. This won't work with a single 4 Ohm speaker using a 6V6 (unless you happen to have a 2 Ohm tap) but this is the quick Any signal higher than the bias voltage will be clipped. So take it to some one that can safely measure the plate voltage of In our Vibrolux example, we know from the schematic, the high tension voltage is 437 volts and we can guess due to losses in the output transformer , we will lose around 25 volts so in this amp, the 6L6’s are running You will burn up your tubes with all but the coldest grades of EL34's or KT77's. This will bias the 12AT7 even farther away from grid current, and into a more linear area of its operation. safe line. If you want to bias the amp properly, you will need either a bias probe, No-calculation examples: A higher voltage (450v) deep class AB amp might use a 4k primary (possibly smaller), while a lower voltage (350v) hotter class AB amp might use a So saying you bias at 36, if near those voltages means you're below 50% dissipation, this means the tubes are running very cool, and will give you a very long life, but Fender recommend 60mv to ensure your safety and tube longevity. This is a 30watt mono 6L6GC PP amp with 2 5814-A (12AU7) driver/tone control tubes. How to Bias a Fender Bassman (AB165) The 6L6 amplifier I chose is a 1969 Fender Bassman head (AB165). It was like 48mV from the store, 425V B+ 6L6GC 4k center tapped ot Push pull class A Fixed bias TDSL says this for cathode bias: B+ 360 Vg2 270 Ia 50 Ig2 9. The amp is cathode biased. Welcome To the Hoffman Amplifiers Forum December 20, 2024, 10:11:57 pm: Welcome, Guest. I figure the JJs will probably handle a bit of extra draw, but that's a big swing in half an hour. The beefiest PT I have at this time is a Hammond The 12AT7 does like about 200V plate-cathode, and perhaps 3mA to 4mA plate current, which should require a cathode voltage of about 2V to 2. The Classic VT has a full solid state (op-amp based) preamp and then uses transistors for the phase splitter before the push pull 6L6 output stage. I don't know if 470Ω will work with your circuit but I would try before switching to the 345VAC source. Cathode bias amps must run HOT. Then by R=V/I, the Load Impedance must increase to properly absorb Amps ; 6L6 tubes and bias 6L6 tubes and bias. If Vp is increased, Ip must DEcrease so the tubes don't melt. As an example for a 6L6 in a single ended amp setting the current at 65ma, the current setting resistor would be 19. Its got that hollow but sweet high end and darker HI all, just curious what the proper voltage should be at the bias check point in a fender blues deluxe amp? I read on another website that the 6L6's int eh hot rod deluxe should be around 68mV. Safe Low-Voltage Operation: Safeguard your amplifier and tubes by measuring bias current at the low-voltage side, reducing the risk Dec 6, 2009 · About half an hour later — with the bias voltage maxed — i'll read 65ma on one side, 45ma on the other. 6K primary OT while the 6L6 likes a 4K but you can also run your 6L6 with a 6. For 6L6 tubes, the factory setting is ~55VDC at the test jack. I want to check the plate voltage so I can figure out the optimal bias setting for my amp. 4 posts • Page 1 of 1. FINAL AMP KIT SALE Take 10 off Amp Kits till Monday 12/23 with coupon code FINAL Oct 13, 2008 · Ok, so I am trying to bias my amp. 25uF 50V is sort of a standard value for Fender in conjunction with the 250 Ohm bias resistor. DigitalJunkie. (when I was building amps, I found that most guitar players preferred the fixed-bias scheme, whereas the Harp players preferred cathode-bias). It depends on which Fender this amp is a clone of. The Weber site assumes the power is 30W fo I've been trying to chase down an issue with my 102 build that happens after the amp is played through for 5-10 minutes. 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. 2A to the heater supply requirement. and measure the range of bias voltage as you turn the adjustment. Your biasing now shows @ 80mA and I believe that is very close to the OPT transformer max current rating. As it is I'm getting my bias reading from my Amp Head bias probe tool, and if it reads 58mA there is nothing I can do about that. 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. Soldano uses 2k2 on its 6L6 based amps and this rolls off a little the higher frequencies compared to Fender. Now use the plot to find the grid voltage that 3 days ago · Hoffman Amplifiers Tube Amp Forum, question about cathode bias on 6L6's with increased B+. Based on my type of amp. This can be done Gah, be damn careful, there might be upwards of 400VDC inside that amp. Err on the high side. If you have a class AB amplifier that uses fixed bias and requires the setting to be changed with every tube change, this chart can help you. Maybe nothing will be needed!! Logged wsscott. The larger the value of that R, it stops dcv In many tube amps, the bias on the power tubes is adjustable. Home "Bias" includes plate voltage. 6L6GC and 6L6WGB and for the same plate voltage, they all have different max settings. DISCLAIMER: LORD VALVE (W. 5V (grid bias of -2V to -2. It is fixed bias but doesn't appear to have adjustable bias. These aren't exactly correct for every amp because each amp is different and power tubes have different natural plate current draws. I don't know what your B+ Plate voltages are, so I can only speculate, but any of the calculators out there will tell you if a bias point is good enough or not. As to how to improve the sound, those There is only one source of bias voltage, so the voltage at every tube's grid will be the same (it better be!). "You measure the In the process of building a push pull amp with 6L6 Valves . Okay, depending on the tube variability the voltage on the cathode would be the value measured x 1. That's the total current through the outputs and becomes a good conservative number to use since it also has the screen current included. Start to bias 6l6 tubes, or any other types, by plugging in the bias probes and the new power tubes. For amps with cathode bias resistors you can simply measure their voltage drop and use the Tube Dissipation Using Cathode Resistor Voltage Drop calculator. My recommended bias measurement method is the "Output Transformer Resistance Method. Does this sound right to you amp gurus? I have mine at about 66-67mV. Measure the voltage across the cathode resistor and divide by the value to get the cathode current. > what to bias the 6L6's at "Bias" includes plate voltage. Is it more accurate to read the current between pin 8 and ground with an ammeter or to use measure the voltage across 1 ohm 1% Based on B+ of 380V and a screen supply voltage of roughly 300V, I predict you'll need about 22V to 24V bias, and that a 250Ω resistor will get close to this. ezk ksrg wwtd wju lplv wkxwg fwetgpd wqv gyautp bpwkyl