Best 6l6 bias adjustment chart amp View The amp is a pushpull of 6l6's ; the manual recommends to bias each tube at 35ma; I want to use 6L6 GC tubes instead; should I keep the same biasing or what is the optimized operating point per tube for a plate supply of approx 335V? As for the best 6L6, I prefer the winged C in my Mark 4. More Information. 30 in the video) that says 6V6's have a max diss of 14W (and not the 12W figure that I've read elsewhere) he even says that he likes to bias it 'towards Class A' and ended up setting it to 27mA, which for a Plate Voltage of 410 - 430V could mean he was Any work inside a tube amp is not "safe," so exercising due caution, this method would not be a threat to you. I'd like to be able to swap in 6L6/6CA7/EL34. Amps with bias-wobble-trem need to be biased a bit colder (let's say 55%) to Just set the plate voltage you have now (plate B+ minus current cathode voltage), the screen voltage (same, screen B+ minus cathode), and then adjust the bias voltage to 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 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. Boogies have set bias-you can't change the bias. However, when trying to check and adjust bias according to manual (2 bias adjustment knobs) something looks really strange. was a good experience for me and knowledge is power Great end results. No more weird fizz on the note trails just solid clear tone. And if the power tubes are a matched pair. Some people say that it can take two different set of power tubes, as it has two different bias points etc. This applies to all models containing the following circuit boards: DB-2, DB-3, DB-4, GP-1, GP-2, GP-3, GP-3A,GD-1,GD-2 AND GD-2A. T. 5, a Sovtek 6L6WXT rated 8. Three other previous made amplifiers of the same configuration were able to adjust the bias to the appropriate range without any problems. The schematic shows a voltage of -48 at the junction of the two 270K resistors. The resistor in there now 15. They must bias the tubes pretty cool to allow such a variance of tubes. The 5150III 50S 6L6 50-Watt Head is the perfect amp for players who want EVH signature touring tone, arena volume and performance in a compact package. Typically you set the bias voltage to the maximum and check the current. We’ll see why later. Metlupass2 Well-known member. Hit me with the comments of being a "noob" but, I am. PLEASE NOTE: you cannot use 6L6WGB power tubes in a 60 Watt, Hot Rod Deville. 00 and available in our online store and can be used with 6V6 - EL34 - Learn how to calculate bias with our online calculator. The Peavey 5150 has no adjustment for bias. Note: Some amps will act funny and develop horrible noises (parasitic oscillations) when a bias probe is in place while the amp is being played. This allows you Many tube amp owners are unaware of this simple regular service for their amp that will keep it sounding its absolute best. A. ) Hi kind folks. does that still need biasing? IMO, always at least test the bias when changing output tubes in a fixed-bias amp (that includes ones with and without bias adjustment pots, so don't get the term In this guide we'll highlight five of the best Victory amps and review the pros and cons of each to help you find which suits your style most. 435v, etc. The bias range for the Hot Rod Deville can go between 70mV-80mV. Bias test points and overall bias adjustment on rear panel; OPTIONS: None; RANGE OPTIONS: Kraken V4 amp pedal (£849), VX Kraken MKII compact head in wooden sleeve (£1,529), VX Kraken 100 head (£2,199). https://www. Voltage after Hello all! Recently bought this amp, it has yellow led inside I suspect it's old model. Adjust bias until crossover notch just In most Fender style amps with 6L6s I prefer 65% or lower so the low-end stays a bit tighter. The easiest way to make your Bass guitar amplifier work reliably and with long life . Follow the manufacturer’s 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. Do not increase the capacitance value of the electrolytic bias cap on this style of bias circuit, or you could draw excessive current in the output tubes before the bias voltage builds up. A Worry-Free Holiday. I would recommend installing the tubes with an initial bias setting close to your target and check them again after ten minutes in play mode with a final check and adjustment after twenty minutes. It doesn't work. like a mark iii or mark iv. Many earlier Fender tube amps used rectifier tubes. xtian Posts: 7108 Joined: Mon Apr 19, 2010 8:15 pm Location: Chico, CA. Do I connect pin 1 and 8 at the base or do I run pin 1 direct to its own ground. When I adjust bias for low power then check bias at high power I get different readings that are much higher. Without a good working knowledge of electronics you could blow your amp, or your tubes, and possibly kill yourself in the process. you are using for a pair of 6L6** running cathode biased. If you find that your bias adjustment does not run hot or cold enough bias circuit of the amp must be modified to change the range of bias voltage it can produce. Diezel einstein 100 watt. Someone on here or the gear page posted a pic of the amp with a meter on it. With 22nF couplers that's reduced to about 6ms and grid clamping is reduced. Adjustment is as follows: 1. It also has a bias adjustment pot as well. As to why the 6L6 tube family is not an optimum tube for use with UL operation; it has nothing to do with voltage or dissipation ratings, but can be traced back to the design of the tube itself -- specifically, as it relates to its perveance. If you’re in the market for a compact amp then the EL34 or 6L6 could be just what you’re looking for. This amp will handle all the higher dissipation members of the 6L6 family including the 6L6GC and the 5881. The best way to check bias is across the output transformer-but it is not for the casual user, pro only. slayer44 Well-known member. Takes a tough tube to put up with that. Do I need to bias my amp? Maybe, maybe not. The 7868 is only rated at 19 watts. Now without adjusting the bias control any further at this point, testing the various NEW out of the box matched set of JJ tubes I got 23. Tube Amp Doctor 6L6WGC-STR Adjusting the Bias. The best way is to observe the live current. Hope that helps! Stephen . Moreover, bias adjustment is also mandatory because the plate dissipation at 30Watts of the 6L6GC exceeds 25W of the KT66. So let me know what you think of the 6L6 “Spalted Alder EL 34s take a lower bias voltage than 6L6s. Jim's amp runs a quad of 6V6 at nearly 500V on the plates. 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. I think they still have a stash of them. The few that he made before he had to stop were some of the best 6L6's ever made and are highly sought after. These are both great 6L6 tubes. Nov 30, 2020 #8 Yep drop them in a bias up! Sounded brutal! I had mine at 28mv The Switchable Bias feature in Mesa amps allows the user to choose between 6L6 or EL-34 power tubes with just the flip of a switch (and once the corresponding tubes are installed). 3, 13, 11. I use a wooden coffee stirrer from a local coffee shop to turn the bias pot in my EC Twinolux in case I accidentally touch anything serious. 4 Responses. This is something that must be done no matter which tubes you are changing. Popularised by Fender, the 6L6 helped to establish what is known as the "American sound". This is a 30watt mono 6L6GC PP amp with 2 5814-A (12AU7) driver/tone control tubes. The newest version has an adjustable bias for just about any octal tube. All the later models have a single bias The BIAS pot, as labeled on the schematic goes from 0 to 12. Share Reply Quote. Some like to use 60% thinking it may extend the tube life. If he left the bias balance pot intact and added a bias adjust pot, you may have The 5150 III 50 watt is biased at 30mA or so. Requires separate digital volt-ohmmeter capable of reading current. It is recommended that this adjustment be done by a technician, but if you are handy with a Volt Meter you can check the voltage yourself. I used to run JJ There are many web sites that explain setting bias. Without any tools to read voltage, I just want to bias it as hotly as possible. Good thing #2 is, I've found the 6L6 version of the Mesa 50 cal to be the better one. Thanks in Advance Best Regards Rzenc Re: Svetlana 6L6 Bias BDRI It depends on the actual plate voltage of the specific amp. 035V to 0. And then you swap the probe from tube to tube to check the bias off all four tubes. 5. If you are going to be biasing a lot, spend the money and get a bias probe tool from Amp-Wares. This is another way to adjust bias on the amplifier successfully. While many early rockers Revisions to the original metal 6L6 such as increased power handling and glass envelopes yielded new designations such as 6L6G, 6L6GA, 6L6GB and finally 6L6GC (introduced by GE in the late 1950s). This will always be a little bit on the cold side, but perfectly adequate for a guitar amp. Reply. The 6L6, 7581A, 6V6, 6550, EL34, 5881, KT66, KT88, KT90, KT100, etc. Answer – set the amplifier bias adjustment for that set of tubes in that particular amplifier. I say test your tubes first, so you know if their good. you can easily find the manufacture year by looking at the tag inside the amp. 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. I set the bias adjustment low to see what readings I'd get. e. These were Sovtek 6l6wxt+, and I have a spare set of Ruby 6L6gcms. lettmusic New member. The Amp Garage. Also, I would suggest either TAD 6L6GCs or SED =C= 6L6GCs in that beast. 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. A great rule of thumb for a amp that uses 6l6 outputs with fixed bias is that before you put any of them in there socket, confirm that pin 5 has at least -52 vdc showing up. The purpose of this comparison is simply to provide guitar players with a frame of reference to help in finding the best current production 6L6GC for their needs. I have run original Tung Sol 5881s in my . The amp has the bias balance circuit in it. 1 others liked this Re: 6L6 Cathode biased advice / ideas. tele_player Posts: 311 Joined: Sat Sep 29, 2007 3:27 am. Here is s video to simplify the process. Moderators: pompeiisneaks, Colossal. 1/2 WATT PRECISION METAL-FILM RESISTOR FOR INSTALLATION ON POWER TUBES FOR I don't often make any bias adjustment even though I've checked many times. When analyzing these tubes, we discovered that they have a particularly significant impact on the low-end of a guitar amplifier’s output. Though not all amps with The existing 10K and 56K resistors form a divider that puts ~85% of the rectified DC voltage at the junction of the 220K bias feed resistors. single ended != class a, you could have a class b single ended amp, but it would sound like <insert epithet here> single ended != cathode bias My first build was a G5, a French project that used an EL34 single-ended. Carvin T100 power amp. Stock, that amp has the dual-pot bias adjustment: one pot adjusts the actual bias voltage, the other one adjusts the balance. Does this sound right to I would like suggestions on what O. Reported plate voltages vary quite a bit from around 400v to 455 volts. Without a true bias adjustment pot I can't lower the bias of the tubes. Of course a good tube compliment and speaker change helped too. Adjust the bias: If necessary, make small adjustments to the bias potentiometer using a small screwdriver or a suitable tool. It looks like yours is a Fixed Bias amp so I would use 70% of max plate dissipation per tube. In some amps, there is no 'pot' so The test jacks on the back of the amp are used read the Bias Voltage, which can be tweaked using the Bias Adjust control located next to the power tubes. This is a variable potentiometer. Accept Cookies Some commercial amps claim with their cathode bias circuit that you can run just about any octal power tube in them. Use a bias probe and a calculator, and do it right. In the real world they would be different with the 6L6's generally biased a little higher. 95! Shipping Deadlines. there is no "bias tap". 60% is a nice plate dissipation number for the JJs. Best 6L6 Amps Fender ’65 Twin This is the grid bias we’ve been zoning in on, and the vast majority of tube guitar amps boast this type of bias. of 6L6GC's. In this Killer Rig article, we’ll take a look at some of the best 6l6 tubes on the market today and see how they compare. The 7027A's are 35 watt mx dissipation tubes, 6L6GC's are only 30 watt tubes and are generally less robust than the 7027's. So take it to some one that can safely measure the plate voltage of your specific amp. I did not change any resistor value in the bias voltage divider circuit, which may have been a mistake. B. Many run in the 460-480 range. mark v you have to run all el34 or all 6l6 power tubes. This amp, I leave it all together. The '66 Bandmasters used the AB763 circuit. Unless they have a trick in there. For your amp, I'd probably The term "fixed bias" is simply the way that the circuit "fixes" or "sets" the bias level, and many fixed bias amps will have an adjustment pot, and some only have a non adjustable resistor to set the bias level. These were almost always at If your amp comes with one of the common octal power-tube types (6L6, EL34, 6V6, 6550, 7027, or 7591), these converters allow you to plug cathode-biased EL84s in their place without bias adjustment. The cathode of any octal based amp (EL-34's, 6L6's, 6550's, 6V6's, KT-88's, 7027's) is on PIN 8. It has been Listen for the "sweet spot". More important than a bias adjustment is knowing the condition of the tubes you are using. YMMV Hoffman Amplifiers Tube Amp Forum, What is best way to have individual bias on 4 power tube amp? The 6L6 grids suck "ZERO" current. If you replace the 10K with a 5K in series with the element of a 10K bias pot, and take the bias voltage from the wiper of the pot, you will have a variable divider with a range of about 79% to 93% of the rectified DC voltage. RCA chart calls for 9Kohms plate to plate with 360V @ Plates and 270V @ G2. I'm using 6L6s so the whole range of the knob is supposedly safe to use. The amp as designed gets its tone from the preamp, the power amp is loud and strong, but the tubes run very cool. Unless you know what you are doing, never attempt to adjust the bias on your amp yourself. While the Triple XXX's bias pot allows for adjustment, my understanding is over the years of reading about this subject from various sources (including Peavey specifically) is that the range of adjustment with the bias switch in 6L6 mode is rather limited and probably is responsible for not getting the tubes up to "proper" bias. I have talked a lot about this tube and I think its the nicest 6L6 tube available today. Oct 23, 2008 #3 You have to mod the amp to add a bias adjustment to use non-Mesa tubes? Stephen . I have some detailed technical tests on my website, but there are also some comments on the G. This will idle tubes at 19 watts static plate dissipation per tube (about 40 mA per tube), which is about 60% of design center max value. Posts: 351 So far so good, I'm curious to try a better set of 6L6, apparantly the mesa ones aren't the best, but they're still better for recording than the E34L IMO. The 6L6 STR 441 power tubes provide everything we’ve come to expect from Mesa/Boogie – power, clarity, and an abundance of warmth. The differences between the 5881 and 6L6GC are large enough that a bias change will be required. For 8-pin power tubes such as 6L6, 6V6, 5881, 6550, EL34, KT88, KT66, KT100, etc. But why are 6L6 amp tubes used by these brands? They are known for their The cheapest solution. It also has 2 12AX7 mic drivers. One of the best ways to set a bias is to measure the cathode current, and that depends on the tube type and it's plate voltage for the most part, and Please see the chart below for some quick comparisons, and read on for more information on power-tube tone and development. When setting the bias pot to the coldest setting I'm getting about 25W with those tubes installed. The only way to adjust bias is to modify the bias supply. Measure the bias voltage: Connect a multimeter set to DC voltage mode to the bias adjustment points. They were built better, with the best materials, but also speced to run lower voltages. Tom Don't let that smoke out! Top. Most neutral new production are JJ's. You can go to their The TAD 6L6 that usually sounds good in my Randall MTS doesn't really quite work in the EVH, but I did find a Mesa Boogie 12AX7 works a bit better in the phase inverter than the JJ. So re-biasing is necessary. 0 to 33K, passing zero current, is zero volts dropped. tube from a listening point of view that we I agree. have told this story several times, mine was glued wide open from the factory! Literally had to chip away the glue to adjust the bias pot. Dec 13, 2009 #12 Mesa/Boogie 6L6 STR 441 Power Tubes – Matched Duet Review. JJ Electronics is celebrated for creating performance-driven heavy-duty preamp vacuum tubes, and the T-6L6GC embodies JJ’s commitment to high-quality manufacturing. L. the amp sounds best to me. I would take it to a tech or get a bias probe to be sure, an adjustment of the bias may enhance the quality of your tone over the factory cool settings. How you adjust the fixed-bias voltage supplied to the control grid often varies from amp to amp and from brand to brand. Fender still uses 6L6s in the majority of its valve amplifiers, but brands like Mesa/Boogie, EVH and Morgan also use them extensively in their models. This is the best resource for these amps. It taps pin 3 for plate voltage and pin 8 (inserts a 1 ohm resister) for bias current (actually a bias Pretty sure I've seen pics of those amps with 6P3S-E's, which are basically 5881 equivalent. A big difference you'd notice is the bias excursion, though. So if you see a big resistor between pin 8 and ground, it's most likely the cathode resistor, meaning the amp is cathode biased. I. I use the amp with the front switch in the low power position. I recently picked up a Harmon Kardon CA-35 PA amp. B+ 440v. 4. My plate voltage is 455 V. Andy Le Blanc DIY Bias probe. Mine sounded best with the Sovtek 5881's, wafer bottoms like in an SLO. There's also high-power and low-power settings that affect the bias EL34s operate best with the taps at 33% using fixed bias, while the EL84 family works best with fixed bias and the taps placed at 25%. There are 2 main types of amps, as far as bias is concerned. 1/2 WATT PRECISION METAL-FILM RESISTOR FOR INSTALLATION ON POWER TUBES FOR Our 6L6 Tube Review Chart helps you find reviews and ratings of our best 6L6 and 5881 tubes. The octal and no Fender 6L6 Amp HELP!!! . What is the range value for the 6L6 tubes? more of 35mA? Thanks. JPP100 New member. 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). Some circuits have internal trim pots, while others may have adjustment controls on the rear panel. This means adjusting a preset control INSIDE the amp in the amplifier bias circuit. . Can In this video, we'll show you how to bias your tube amp using the TAD BiasMaster. Unrated Tubes, a bias adjust, and you have a bias probe. so, i dont see why the bias pot mod wouldnt work just fine. My point is simple, the technology to make tubes every bit as good as Note if the pot wiper ever does disconnect from the track, the bias voltage just swings down to its lowest (most negative) value allowed, as if the pot was turned all the way in that direction--the result being that the output tubes never totally lose bias and thus protect the tubes in the case of a bias pot failure. I added a 5U4 and brought it up slowly on a varaic. When the power tubes are clipping, with the 100nF caps there's about a 28. If your amp has fixed bias with a bias pot make small changes when adjusting the bias pot and measure the plate voltage and plate current again. It depends on your own amplifier and I would suggest you trust your ears. Use a wooden or plastic tool such as those commonly used to adjust inductor coils. The calculator will give you the bias current for Is there a formula or chart for finding the correct cathode resistor for biasing a 6l6 tube? According to my math I have 380v plate voltage running . say for example you buy a 6L6 amp. Should bias be adjusted for power output that I am using or what is the proper way to adjust bias. I've been on 110 lately, but the lower the voltage, the less the tubes seem to red plate - that could be I have the problem with my KT88 PP stereo integrated amp to set bias voltages of KT88 of which scheme as below; If I set Vk to the same value by adjusting the pots for both tubes, I have audible hum so I cannot set them to the same value but different values, I. Very, very few product amps use individual bias, you have one bias pot to bias all 4 tubes. When selecting new power tubes for your amplifier, there are many things to consider. May 26, 2014 #4 the other 20ma. Having said that, there's a video on Youtube with someone showing how to rebias a DRRI, and he uses a chart (at 3. I would recommend this to any rectifier user, it makes a great amplifier even better. Joined Jan 6, 2007 Messages 211. One of you kind fellows suggested that I use a 6L6 based amp for more Those rare amps simply require a bias adjustment, however the majority will likely require some physical modifications. I just looked at all the Dual Showman schematics and none of them have dual bias pots. So, if I recall: 30w/420v*50% = 36ma 30w/420v*70% = 50ma When I bias at 35 (max recommended for 6L6) it feels cold. Ended up taking the amp to a tech and after a scope check and bias down to the 73Mv range. These probes are $25. Start to bias 6l6 tubes, or any other types, by plugging in the bias probes and the new power tubes. They are NOT 6L6GC equivalent, so you need to dial back the idle dissipation if you're going to use them in a fixed bias amp. 99. THE BOTTOM LINE With its new independent gain and volume controls for channels 1 and 2 and The large 6L6 cathode capacitor is an attempt to go nearer a fixed bias condition under normal music signal circumstances, in which case slightly increased and more linear output peaks can be expected. The possibility to adjust the bias on these amps seems like the way too go to make them alive. These power tubes will be operated far below their limits but will provide good performance and long life. This website uses cookies to ensure that you get the best experience. The bias supply is a part of the power supply circuit that supplies a bias voltage to the output tubes in order to set their “idle” current. For fixed bias amps without a bias adjust pot, the resistor can be changed to a different value, or a pot can be added in order to 6L6 valves have been used in guitar amplifiers since the '50s. 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. Skip to content. Drive it with a 1 to 2 kHz signal to just below the point of clipping. The 5F2A is the tweed Princeton amp. 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 The 6L6 tubes in the power amp section provide the same thick, dynamic tones of the original version. And that's all the 70% number is - "safe". ) With a time constant of about 0,2 Hz you should find very little increase in bias voltage on there. Post by xtian » Sat Mar 18, 2023 4:15 pm. Where the 6l6 might take -50 volts to bias at 35ma the el 34 would only want maybe -35 volts. This is the amount of current the tube consumes before beginning to amplify the signal. ampegv4. The best speaker I found for this configuration was a 10" 30W greenback. 49k Plate voltage measured 415V at 37. In the blackface circuit, the same voltage was sent to all four output tubes, and was adjustable using the bias potentiometer, which enabled a ^ This BIAS has to be adjusted. HELP 1-877 Tube Amp Doctor 6L6GC (discontinued) 5. I have balanced the two 6L6GC tubes using the bias resistor that was in the amp. Discover how to address gender bias with the gender bias calculator and bias amp calculator. The primary modification necessary is to properly bias the amp. They are fine with the plate voltages in the amp and can handle 30W. So it had quite a range f B+ voltages from around 320 to 420V. Conclusion: The Best KT66 Tube Is Choosing a new tube for your amp is a very personal choice. That alone could be the source of the problem. but, you cant run el34 tubes on each end and 6l6 tubes in the middle. The JJ Electronics’ T-6L6GC-JJ-MP amplifier tubes find widespread application in guitar amps serve as the yardstick for all 6L6 tubes. and P. A recent customer comment: That went smoothly. Posted in 6L6 / 5881 Tubes. True 5881 tube are about 23-24 watt max. the plate leads on their way to pin 3 are also connected to pin 1. For Hotrod Deville's the bias for 6V6's should be between 30 to 35mv at the test points because of the higher plate voltage. There's certainly parts of the chart that don't apply, and out of whack. Thank you for the suggestions and for the excellent article! I've run the amp at wall voltage (about 120-122 typically), 117 and 110. :mrgreen: Jim made his amps late 70's - early 80's and he's back at it now, working in conjunction with John Suhr, and both are TAG members. Since 2006 we have offered a single octal bias probe for use with a Multimeter. For best tone and amp On another note, Bob at eurotubes will send you 6L6's that can be run in the EL34 mode and brings the bias up to where a normal 6L6 should be. I think they are cheaper than buying from Mesa online. If your Mesa amp has this option and Get the best sound from a tube amp while extending its life! This lesson demonstrates the process of biasing a 6L6 Class A amp for optimal performance. 1x12 extension cabinets start at £619, 2x12 cabs sell from £899, full-fat 4x12 is £1,299; CONTACT: Victory Amplification But when I bias them between 30-35 (recommended for this amp and 6L6s) they seem cold and harsh. 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 Set the bias according to the directions on the Schematic or in the owner's manual. Carefully remove the old, worn out tubes from the amplifier. You can still get it by Christmas for only $29. New orders processed the same day! Boost and Bright Switches, Internal Variable Bias The Groove Tubes 6L6GE tube is now shipping but is in short supply. I've seen mention on the forum of biasing the 6V6s at 39mV - I presume that's for both tubes? I have set the amp up that way, but I still can't get any real breakup on the clean channel, 2. Each manufacturer’s tube will achieve its best performance for this desired result at different bias current Revisit™ Bias Checker Kit by Hoffman Amps The Revisit Bias Checker Kit by Hoffman Amps is the best of both worlds when it comes to ease of assembly and cost effectiveness. I put the bias pots so I can adjust them from the top of the chassis. Post by tele_player » Fri Jan 18, 2008 8:20 pm. Adjust bias until crossover notch just disappears. First, you Hey guys, Just trying to confirm pin 1 and 8 in my build. I've greatly enjoyed the cathode bias 6L6 amps I've had and currently have. I have my 1971 Fender Vibrolux Reverb on the bench today. I will tell you now I have had this along side another 2 channel rect with normal tubes set a little warmer, and the amp with the normal tubes sounded better, same thing when I switched the tubes, which ever one had the It is fixed bias but doesn't appear to have adjustable bias. It might not be the best sounding bias point for the guitar amp but the tubes will last a long time; longer than the 6L6 GE bias setting in old fender amp? Thread starter JPP100; Start date Dec 8, 2009; Dec 8, 2009 #1 J. I wouldn't use that chart at all. Hmm. Obviously there is a variable pot between the plates, but doesn't that just adjust the balance between the two There is only one source of bias voltage, so the voltage at every tube's grid will be the same (it better be!). A few years ago Mesa amps came with all Chinese tubes from the factory, my Maverick had them. A colder bias will make the amp play cleaner with more headroom, but OTOH it may make the amp sound a bit sterile. but from what i have heard so far JJ's are the best for this amp . The front of amp has a high power 100watt and low power 25watt switch. 6l6gc's are 30 watts max plate dissipation per tube. This is The desired sound of a Hi Fi Stereo amplifier is often very different than the desired sound of a guitar amplifier. Most amps sound best biased a bit on the hotter side - warmer tone, earlier breakup. Best 6L6 Tubes. As long as the best tone is within 10-20 of max plate dissipation you're safe. what do you guys like to set your bias at in old super reverb and concerts (blackface) at with 6L6 ouput tubes? That's the starting point, best to use your ears after that for fine tuning. I installed new B+ caps, bias caps, and cathode caps. . It I have a bad tube in my amp, so I need to replace them. FAQ; Board index. It will likely be fairly low. Victory Kraken Guitar Amps External bias test The hum adjust procedure is in there. These amps were 40 watts, fixed bias with a bias adjustment pot, and the tubes were 4 x 7025, 2 x 12AX7, 2 x 5881 with a solidstate rectifier. Fender Frontman 10G Electric Guitar Amplifier - Midnight Blue Austin Bazaar-7%. Requires separate ampgeek wrote: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 problem is that my tubes now balance out at 58mA which is way to high for safe operation. It depends on the plate voltage, but in most cases, The chart that came with the bias tool has a list of plate voltages but does it mean the 8/3 pin readings or 3 to ground? If the plate voltage is such that excessive dissipation would result in 'near' class A operation, then best to reduce plate voltage somehow or give up on cathode biasing. At least on paper. you always purchase the EXACT same pack of tubes from the EXACT same store. The earlier amps were being sent out biased 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. At about 40mV, things started smoothing out, and at 45 the amp sounded very What exactly is Bias? The best analogy of bias adjustment that we can think of goes back to older cars that had carburetors. (this is why it came with 6L6s in stock Using the bias control, set the bias to somewhere in the ranges given above (Fig. General discussion area for tube amps. I still use it as What exactly is Bias? The best analogy of bias adjustment that we can think of goes back to older cars that had carburetors. Sit back and enjoy those amazing guitar riffs without worrying much about your amp’s lifespan. are common guitar amplifier power tubes, and are all easily biased with this method. Fender 6L6 Amp HELP!!! Thread starter mjarve Bias adjust for each 6L6GC tube and even gain on 12AT7 I just finished modifying my Fender Twin 135RMS and it sounds better than the day I bought it in 1976. I later converted that to 6L6. Adjust to maximum negative bias. Better than Amazon. The BiasMaster is available in an octal and noval version. 074ma I should have a Hook a scope across the output. I like the warmer lead tone out of the 34's and the deeper bottom end out of the 6L6. Right knob not responding at all, doesn't matter which tube is being checked. com Also for parts check https: 7027A are a 6l6 family tube that’s true, and functionally they’re the same plus two internal pins, but a true 7027A has a plate max of 600V compared to 500V for a 6L6GC. S. I rewired the gawd-awful bias balance circuit into a true bias adjust circuit. If this is the case, you’ll need to remove the bias probe each time you play the amp. About the Author John Templeton. Biasing the amp isn't hard to do, the hard part is pulling the chassis out of the head cabinet. Parts arrived on time, now installed and working fine. A missing 5AR4 rectifier. 5k, but even turned all the way down, there is still some slight red plating. 5. so basically, you are using the same branded 6L6 tubes. and someone else might confirm this, the Ampeg V2 from 1975 does not have a Bias adjustment does it? All I see is a hum balance. jimipage Posts: 189 Joined: Fri Apr 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. Because once you are aware where the plate voltage likes to sit, you can pretty much bias the amp without pulling the chassis or plugging in sockets and such. They are good tubes thou, but maybe not as plentiful as they once were. I would never suggest running 6L6's at 600v and dont know many amps that require it. Replace them with a matched set of tubes rated Sovtek Medium or an How to Measure Bias. If you have an amp which uses power tubes which are not listed above, you will need to consult a spec Music Man Amplifiers SERVICE BULLETIN #1 _____ Section I DRIVER TRANSISTOR BIAS CALIBRATION PROCEDURE A. The beefiest PT I have at this time is a Hammond 273BX (350-0-350, DC Very simple to use but very effective, literally just plug in, turn on and adjust bias if necessary. Single ended 6V6. E. Here is a good read and explanation of how to measure and set bias in a Tube amp. 0. 6L6: 6V6: 5881 : 6550 but doesn't really offer full bias adjustment. As mentioned, looks like the 5F6/6-A Bassman ran them around 425v or so. Cole This is one of the amps that derives its bias voltage directly off the high voltage secondary of the power transformer i. For 6L6 valves then yes you would be around the 70mV range. Ensure the multimeter’s probes are correctly connected to the amplifier’s bias points. It will also handle the KT88 and 6550 tubes without modification. Top. $16 per 12ax/at7 and $42 for matched set of 6L6's. It looks like my Tungsten Sol 6L6GC-STR has 30w max plate dissipation. I have not found a detailed factory procedure description on the factory bias test points on the back of the amp. smallest, with the mighty V130 Super Countess being the largest and loudest. (Infinite capacitor = fixed bias. 3) and play the amp. This webpage offers two ways to calculate tube bias and plate dissipation. Recently I had a 1960's 2x 6L6 cathode biased amp in for some work. As you turn up the bias and flow more current through the power tube the demand on the power Run it into a load bank. There is a bias chart and calculator on Webers site (click on Bias Rite) that will help you figure out the numbers in the future. The 5881 and 6L6 come from the same family of tubes. This kit is easy to build, and comes with assembly instructions in the link below. I get the second amp, put JJ EL34's (not matched, i need to get a matched quad)and JJ12ax7's matched quad 803s series. Set plate voltage at 450V. Most Marshall™ amps with 8-pin output tubes offered This mod allows wide range of adjustment to bias 6V6, 6L6, EL34, KT66, KT77 and KT88 power tubes. Other than that, it is real easy and I would suggest doing it. I just use the same bias probe and technique I used with my Soldano, nothing different. Use fixed bias, with -42V bias delivered to grids. So many frequencies, so little time It's strange that a 6L6 amp has the same bias setting as an EL34 amp. The voltage chart looks something like this. but running cathode bias. Hook a scope across the output. Re: current bias for 6L6. I measured the plate voltage off both 6L6 sockets at 420v. Connect output stage in pentode mode, with 400V on screens. The schematic shows 6L6GC power tubes. The If you replace the tubes with 6L6 type tubes be sure to make sure the bias is correct for those tubes. LOAD IMPEDANCE: Selects amp output Other brands of 6L6's like the chinese tad tubes and sovtek, grade and sometimes these will top out at 75 to 80mv but if its headroom you're after then that is a good place to bias the amp. How to Bias a 6L6 Class A Tube Amp. The amp is cathode biased. 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. Here's a chart from 300guitars. The power dissipation of the amplifier as a whole can also be measured using the With that amp I had to take the chassis out of the headshell and turn it upside down. All readings are mA. Using the best soldering gun is much Use a matched quad of 6L6-GC tubes configured in push pull, class AB1. Series effects loop. i think if 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. (Approximate numbers). Forums. If you want to bias the amp properly, you will need either a bias probe, 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+. 8 millisecond recovery time for the bias. I wanna build a standard AB763 - no vib no verb - preamp + P. 9 posts • Page 1 of 1. A tube amp builder's community. If you have for example a 250 ohm cathode resistor for cathode bias, adding a 1 ohm resistor in series with that won;t change the bias to the tube How to Bias a Fender Bassman (AB165) The 6L6 amplifier I chose is a 1969 Fender Bassman head (AB165). Again, there is a gut shot out there showing it 6L6 fixed bias/PT question. You have to date by the small silver Fitment issues may be possible because KT66 is wider than 6L6. does, the overdrive is gorgeously smooth, supple, organic and balanced. Turn the amplifier to "ON" with the HI / LO Standby switch in the HI There is a great YouTube video on how to bias Hot Rod style amps, by the guys at the "TubeDepot": "How To Bias a Deville Amplifier" It is the same procedure for Hot Rod Deluxe or a Blues Deluxe (except the early 90's Blues Deluxe amps do not have a bias trim adjuster). 5 mA Some bias charts suggest that biasing a valve for 60-70% of the maximum plate dissipation at idle results in the valve anode dissipating much less when running at full power; however, it is rarely the case, when using your amplifier at a gig or rehearsal, that you would play your amplifier as loudly as possible all of the time so biasing for cooler operation and longer life is our approach. They have powerful deep bass and a clear, airy top end. 410v and 0. I bought another JSX to put EL34's in versus the 6L6 tubes. The short version: What's your favorite 6L6 Bass Amp Circuit? The long version: I recently asked for some help on a couple of circuits that I found for 6V6 - based amps. and the plate voltage is close to the same. Such as 6V6, 6L6, KT66, etc. 2, and one sovtek rated 9. 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. Joined Dec 12, 2005 Messages 107 Reaction score 0 Location New Orleans. Your meter should be set to Adjust the bias to obtain the best tone, while keeping the tubes within specifications. If you just stick in tubes and don't know their quality, you're only guessing and a bias adjustment isn't getting you much. Gear Addict Joined: May 2008. Are these ok to use, since Home. Quick links. There is a bias adjustment pot on the circuit board. Or, you could ask the vendor for something with a higher or lower It's a good idea to at least check the bias on any fixed bias amp when changing power tubes, you may or may not need to change/adjust the bias. A bias setting between 30 to 45 is best for the JJ 6V6's. See more How exactly can I fine tune the bias of the 6l6 output stages. On a 6L6 this won;t matter, but the EL34 needs pin 1 to be grounded, or at least I dig mine because it has a kill mode but also does a lot of nice clean tones and takes pedals well. Can anyone shed some light on what the solution to this This article presents line power measurements for the vintage reissue Fender '65 Twin Reverb guitar amplifier model AB 763. I like the JJ tubes as well If you want to try 6V6s in a 6L6 amp, plate voltage and bias must be adjusted and a suitable output transformer should also be installed. Then an adjustment will be required. With respect, 10thtx. These features should only be used by an authorized service technician to adjust the bias of the amplifier tubes. Peavey XXX amps have a "fixed bias" and a bias adjustment knob. Permalink. 1, 9, and on older tubes Fender Groove tube 17. I have a couple of questions relating to biasing the amp and getting the best out of it. RESONANCE: Adjusts power amp low-frequency response. fixed bias One of the best know is the old Sylvania 6L6 tall bottles with the designation STR387. Many tubes are run over specs in guitar amps but it sounds like a real 6L6 has more stamina than a real 5881 regarding higher voltages. The best-sounding configuration to my ear for the 6L6 had the plates running at abut 320V, screens about 280, and a 220R cathode resistor. Should the knob be turned all the way to the right (clockwise) or to the left (counter-clockwise)? Having it set too hot may sound nice at low volumes, but Looking for 6L6 Guitar Combo Amps? Sweetwater has Easy Payments, FREE Shipping, and FREE Sweetwater Support for Guitar Combo Amps! Call in for the best savings! (800) 222-4700. That would be about 35 ma to 40 ma total current flow through each power tube. I checked the online Weber bias chart for these 6L6s and proceeded to gradually increase the bias current as I played the amp. Yes, the actual adjustment is the grid-cathode voltage (-). And I love the amp. 29mV and 475V respectively. Sylvania, Sovtek and Jan Phillips) but the Ruby Tubes 6L6GCMSTR has the best tone in my Fender Hot Rod Deluxe and this was without FINAL AMP KIT SALE Take 10 off Amp Kits till Monday 12/23 with coupon code FINAL I have had a Bias Adjustment kit fitted to my Fender Blues Deluxe and I am now running JJ 6V6 power tubes. The rest of the amplifier was ‘stock’. popvulture. This is for a 6L6GC tube typewith some common amp voltages and safe dissipation settings. A lesson with D-Lab Amps. For amps with cathode bias resistors you can simply measure their voltage drop and use the Tube Dissipation Using Cathode Resistor What exactly is Bias? The best analogy of bias adjustment that we can think of goes back to older cars that had carburetors. Very easy to do. The AB763 has a single bias adjust pot. You have to measure the voltage each time because the voltage and current will change with a bias pot change. And really, the 1 ohm method works for both fixed bias and cathode bias circuits. jeff In fixed bias amps you have more options. Some amps have individual bias adjustment for each power tube-- if your amp doesn't but uses fixed (not cathode) bias, it might be a reasonably simple mod to add individual bias. which can be tweaked using the Bias Adjust control located next to the power tubes. So you've virtually not changed the frequency response of the amp audibly whatsoever. These amps were 40 watts, fixed bias nonadjustable, and the tubes were 5 x 7025, 2 x 6L6GC with a solidstate rectifier. I love the 2203/2204 platform, but hate the bright cap and treble peaker--these only sound If I were servicing your amp and you had chosen tubes that would enable it to produce the maximum power and clean headroom, I would more than likely bias your amplifier in the 20–35mA range, based on the performance of the tube. So, you use the probe with one tube, dial in the necessary voltage on the bias pot. 040V range and see how it sounds. I used the Sovtek 5881's and biased it properly and the amp just crushed. In the description of the amp diezel does state the ability to bias together 6L6 and EL34. Note the 5 volt 3 amp heater current requirements for some of the tubes. com showing the different rectifier voltage drops: The 5Y3's current rating of only 125 milliamps would strangle a 5F6A but the 5R4 will work nicely. 30th July 2008 | Show parent #9. Post by Andy Le Blanc » Tue Jan 12, 2010 11:59 pm. The bias methods of amplifiers fall into three basic categories: Non-Adjustable Fixed Bias amplifiers Pre amp: 12AX7A; Power: 2 x 6L6; Bias: Fixed with adjustment pot Rectifier: Solid the Vibro-Kings were one of the amps that flew under the radar, and s/n dating for these amps are a guess at best. But this doesn’t mean that they don’t need a bias-setting adjustment. greg October 18, 2015 at 4:45 am. $89. zdgctj ysntu eqvj xywx bsjgrx jjz csqn alrfh pvfbsw imgrn