Re Biasing A Tube Amp

The newest in the Bias amp series brings an abundance of different amps, cabinet simulations, pedals, and microphones, all extremely realistically representing the respective models that they’re imitating. The gain improvement is obtained at the cost of lower output swing. When a transistor amplifier has a shorted transistor or other problem, your speaker will blow unless their cables are fused. Increasing or decreasing that voltage by a small amount will affect the amount of current drawn by the anode. English/german operation manual. ) With the Bias-rite in place, I get a voltage reading, then hit the switch to get the current draw of the tube. To set the bias for the first output tube, you set the switch to 1 and use the first adjuster to bring the needle onto the red line. As long as you're using matched tubes, you'll just divide this value by 2 to get the actual bias current. When a vacuum tube is amplifying signals, the level of negativity on its control grid is important. FAQ Search Join Private Messages Profile Log in. In this lesson, musician and teacher Kennis Russell demonstrates how to safely bias a tube guitar amplifier using a millivolt reader with DC voltage. BIAS AMP 2 is the ultimate virtual amp designer, authentically recreating the tone and feel of real tube amplifiers, while allowing you to mix and match BIAS AMP 2 represents a revolution in virtual amplifier design, providing the tools to take your ultimate guitar tone with you anywhere, from the. This is known as the bias voltage. Posted: Oct Mon 13, 2014 1:26 am. All about matching power amplifier tubes, pre-amp tube selection, biasing and a JTM45 hand wired 30V DC is what you're looking for between PR1 and PR2 or PR1 and Chassi Ground. Re: Used Vibrolux Reverb: Tube biasing question If my memory serves me correct, which it rarely does, the bias resisitor is on one of the smaller boards, not the main board. Then you switch to 2 and repeat the adjustment for the second tube. Most class A amps are cathode biased,meaning self biasing. - The amp is very well built (I'm comparing it to the Peavey Classic 30 and a number of Fender amps I've had/used). I'm biasing the 6L6/6V6 tubes in a Vintage Sound Amp. If the amp was born with a pair of “hotter” tubes, the setting on the wheel will be far to the left. Biasing an amp is really just simple math. No need for triode matching as the bias is set manually. these will measure as a short on most continuity meters (i. The 741 Op Amp IC is a monolithic integrated circuit, comprising of a general purpose Operational Amplifier. 12: Tube Biasing (6. If you have any shiny aluminum tube covers, remove them by pushing up and turning counterclockwise. Plate voltage is right around 450V. The particular amp you are referring to looks like it may be fixed bias but it doesn't have a bias adjust pot. 95: Magnetic Components Inc. I personally use amp sims like BIAS FX for playing quietly at my apartment but I keep the amp for. anyone have any experience with chinese tube amps? wish i hadnt gotten rid of my pas 3/st 70 all those years ago, but probably will never be able to get. Post subject: Re: How to bias a 6v6gt tube amp that uses "Free DC" biasing. Ampeg SVT-CL Classic 300 Watt tube bass guitar amp head Road Worn Relic'd. As such, the audio transformers were unsuitable for high fidelity service, the amp was cathode biased and the phase inverter was not balanced. I usually have my amp biased around 34ma. I've actually been biasing my other tube amps for a while (and haven't given myself the Richard Simmons perm yet ), I'm just new to the Kendrick amp and was hoping someone was familiar with that amp, specifically. Cathode biased amps are often bias very hot and near Class A (tube amp rarely actually meet the standard for being true class a). Each channel of the hybrid amp requires a power supply capable of delivering 35+35 V DC/6A for the main amplifier, and a regulated 6. If they are biased incorrectly or if there is a fault in one of the biasing components, it can cause a number of power supply and output section problems. The new preamp tubes are all about headroom: The new 12BH7 and 12AY7 tubes put out more gain before distortion than normal 12AX7’s, so they’re often used in bass and hi-fi amplifier designs where being both loud AND clean is super important. V1-V3: 12AX7, V4-5: EHX EL34 (matched pair), V6: EHX 5U4GB. The circuit also applies negative bias to control grids, keeping the tube’s quiescent current at 200 mA (class AB). 40 Reisong A10 EL34 Hi-Fi Audio Stereo Tube Amplifier Single-end Class - A Amp 138. 53 shipping. To bias your 6100 you will need to do a few things. Low to medium power valve amplifiers for frequencies below the microwaves were largely replaced by solid state amplifiers in the 1960s and 1970s. Power tubes are cathode biased. If you have any shiny aluminum tube covers, remove them by pushing up and turning counterclockwise. A re-launch of my popular Special 6SN7 Line-Stage featuring many updates over the original while still maintaining the same sonic signature. Age: 5 years. It was built from organ parts. I had in the past designed some pretty amazing SS circuits that could do warm tubelike OD, but the clean aspect (depth and dimension) of my SS amps were noticeably lacking when A-B’d with a good well tweaked tube amp. 5 watts a tube. Fixed bias allows you to get maximum power before distortion. I suspect that it's auto biasing or more than likely you would have red plated a tube if your swapping tubes. The Bias King is a simple, effective, and accurate diagnostic tool designed to read the current flowing through the tube of an amplifier. Tube Complement: One 12AX7, two 12AT7s, four KT120s Hum and Noise: Better than 100 dB below 75 Watts, A-weighted. With Cathode bias, the tube voltage is the B+ minus the bias voltage, so the tube runs on lower voltage. The Class A amp has a fuller sound (my opinion) and breaks over. Master amp builder Bruce Collins has designed them from the ground up to to be the most exceptional and economical pro-level small and mid-sized harp amps on the planet. Individual tubes vary widely in the grid. One way is to use your multi-meter set to read ma's. Because of this, there are many versions by different manufacturers. In particular, biasing is adjusting the voltage on the grid of a tube so that the tube operates in the desired current range. 20 watts) or EL34 power tubes with a simple re-bias. Then you switch to 2 and repeat the adjustment for the second tube. Almost every AA165 Bassman has a tube chart inside the back of the cabinet that shows the AA864 circuit. You can then switch to DOWN (“ON”) to use the amp. Pre-amps and pickup components that are not seated well can also rattle. Fixed biased amps require biasing to change power tubes as well as periodic bias checks to ensure they are working properly. The whole purpose of biasing is to set the right amount of current passing through the power tubes when no signal is present. This will also be discussed shortly. Dude, That is one bEAUTIFUL AMP ! – man that sounds just as nice – if not better than a all tube SE amp with exceptional trannies! Your playing is as a real as it gets, what a treat. i've got heard solid issues approximately it. While adjusting the Bias control pot of your amp the BiasMaster(TM) does show the actual result. It is wise to go back and re-check the readings after doing all of the tubes, as sometimes ones previously biased can be effected by as much as 10-20%. While this is probably the case, most beginners can’t afford to shell out the $500-$1000 it costs to buy a good tube amp. The resistor value is determined based on design averages for plate voltage and current. It would be nice to have seperate EQ controls for both gain. The amp also excepts 6V6 (approx. Amps with a single EL84 output tube are probably class A and will run normally at around 100% max. Again, it depends on where the tube is biased on its operating curve not how it is biased. Wide bias range for EL34/6L6/6550/KT88 with the ultimate in power tube flexibility and selection. I marked the tubes and then tried to swap them with ones from the other channel, but the difference became even greater. In a tube-based guitar amplifier, the preamp is important for basic tone shaping, but it’s the power amp design that really defines the overall sonic signature and playing feel. This allows the meter to jump into the circuitry of the power amp without the need to disconnect any wires or components. Tube sockets cleaned and re-tensioned. There is a proper biased and signal test that always has to be done on a tube amp, it's not a Depending on how much you play, a tube swap (the amp equivalent of a car tune-up and oil re-tube using the specified EH from Electro-Harmonix tubes. GL Grid current in micro-amps. Thus, the 70% recommendation. The tube closest to the input jack is the first one in the chain, and it’s a great place to start if you’re experimenting with different tubes. Rattling and buzzing not unfamiliar with combo amps. Re-tubing of an amplifier can be a good choice (and fun too), if a tube of similar plate dissipation and operating characteristics can be found. Fixing the current draw of the tube with a simple circuit (LM317 + current setting resistor) allows a constant current draw regardless of the tube inserted. Make It Loud & Lasting!. Every tube amplifier has what is called a bias circuit that controls how the tube outputs eventually become sound. Some amps have an individual pot for each tube and some share a pot between both tubes in a push pull type amp. But, I saw somewhere that biasing a class AB amp at 90% will warm up the tone significantly, while only reducing the tube life by about 20%. When you bias your amp you will be rewarded with great sound, lots of power and long tube life. It may be a little more 35 ma or a little less 25 ma. How to bias a tube amp with a voltage multimeter. CAREFULLY measure the voltage to ground from pin 8 on each power tube, and adjust each bias pot to set the bias to 1. This test adaptor will have a couple of testleads hanging out through a hole in the side, for connection to your meter(s). BIAS AMP 2 is the ultimate virtual amp designer, authentically recreating the tone and feel of real tube amplifiers, while allowing you to mix and match components to create your ideal amp. And severely wrong bias settings can destroy tubes and possibly damage other components. I had the opportunity to test this amp with the power supply that I used to prototype the. I suspect that it's auto biasing or more than likely you would have red plated a tube if your swapping tubes. my question. FAQ Search Join Private Messages Profile Log in. Dial in your tone settings and crank your amp’s gain to play massively heavy chords! American 5153. What is bias? When should re-biasing my amplifier be considered? A power amp tube is generally biased using fixed bias because you don't want it to change that much(big changes in current going through it = big change is cathode bias) and you want as much gain as you can get(cause that's the. The more bias, the longer it stays in Class A. lift the ground connection on the cathode of the power tube(s), and insert a resistor, possibly bypassed by a capacitor. Recommended Bias Point: Cathode Biased (no re-biasing necessary). In Mesa/Boogie amps no such trim-pots are fitted but, contrary to. And now you can do much more in your DAWs: re-amping with BIAS amps, re-design and improve your amp models for all kinds of recordings, and use Amp Match to capture your tube amps. An amp can be A or A/B and fixed or cathode biased. Balanced, round,. But, it is common for these factory set bias supplies to drift so it is best to have it checked and set up by a good tech. Biasing your amp's tubes isn't just some sort of amplification function. It costs only about as much as a single output tube, doesn't requiring re-wiring or modifying your amp to use and is a huge enhancement in safety (think Life Insurance Policy) when working with 700Vdc! You don't need an expensive one with its own meter display. Although you can use this hardware/software combination to closely approximate the sound and experience of playing through a particular tube guitar amplifier, the real strength of Bias Amp Pro 2 is that it enables you to create an amp emulation tailored specifically to your requirements, and can load the result into the Bias Mini or your DAW software, making it incredibly versatile — and extremely convincing — whether live on stage or tweaking in the studio. I see too many DT series amps come across my bench because. Answer – set the amplifier bias adjustment for that set of tubes in that particular amplifier. It would be nice to have seperate EQ controls for both gain. Rattling and buzzing not unfamiliar with combo amps. We bias most major tube amps: Ampeg, Fender, Hiwatt, Marshall, Peavey, Vox, and more, using the “Groove Tube Bias Probe Method. 7 – Full cleaning of chassis and transformers. Thanks for the input, guys. Another major reason would be to extend the useful life of the power tubes through what I call periodic re-biasing - something not possible with non-adjustable biasing. Use a COTTON cloth to wrap around the tubes then gently rock / pull it one by one out of the socket. Marshall JCM 800 2203 Guitar Amp - Tube Swap and Re-Biasing Chris from Cornerstone joins us again for this Marshall re-biasing video. Amps with a single EL84 output tube are probably class A and will run normally at around 100% max. In the first instalment of a new column, Rift Amps mainman Chris Fantana dispenses expert advice on all things amplification. if your tube amp uses more than one brand of tubes (EL34, 6L6, etc) then when changing brands the amp needs to be rebiased. It was built from organ parts. Depending on the type of amp (Class A, B, AB etc) this can vary. Remember, tube amps can store up serious voltages, and messing with power supplies could shorten tube life. English/german operation manual. Please take note that the amp has HIGH voltages thus extra care should be taken. BTW, the screen resistors in SVT's should only be 1 watt, no matter the value; they're the "off switch" should an output tube fail. The Osprey is an amazingly capable stereo tube amplifier that drives speakers with all delicacy, attention to detail, and musicality of the Nighthawk and Blackhawk but, with even more power and authority. 56 volts DC across R20 in the center of rotation of P1 and P2. Pro Audio PA Hire for Band Party & Special Function. First it's completely cold, then left running. In a tube-based guitar amplifier, the preamp is important for basic tone shaping, but it’s the power amp design that really defines the overall sonic signature and playing feel. Remember: Tube sockets are not highly reliable connectors! If the sockets are dirty or not tight Many times, just the act of removing a tube and re-seating it, either in another position or back into its We always recommend biasing your amp to the setting specified in your amp's manual or maybe a little. In this method a current flow through the tube’s cathode to the ground (low voltage) is measured. Just like customizing real amps, you can swap out the tubes, preamp transformer, tone stacks, cab and mic of your virtual amp. When I re-tubed my Roland Bolt 60, I just installed the new tubes, turned the amp on in "standby" and left them to sit in the basement/studio overnite. Not finding what you're looking for? Save amp bias meter to get e-mail alerts and updates on your 2pc Tube amp bias probe for el34 6v6 6l6 kt88 6550 5881 7024 "mV. It is meant for use in lower power output amps (20W or less) when no power reduction is desired and you would prefer to use the amp's original cathode bias components. 111 107 просмотров. You measure pin 8 of the power tube socket and ground. The power valves. Now let the amplifier run, and check and re-adjust the bias for the next hour or so. Biasing a Diezel amp with no external fuses: Some early amps have the tube fault fuses inside on the PCB board. BIAS AMP 2 is the ultimate virtual amp designer, authentically recreating the tone and feel of real tube amplifiers, while allowing you to mix and match BIAS AMP 2 represents a revolution in virtual amplifier design, providing the tools to take your ultimate guitar tone with you anywhere, from the. Exception: if the one tube you are replacing has a sibling, in a connected tandem-way (for example push-pull) it is best to replace both tubes with a matching pair. New to Tube amp repair? Start by watching this video. All tubes must be biased (yes, even preamp tubes) and all tube amps have bias applied, weather fixed bias or cathode bias. These are the same as the tubes listed inthe power tube section below; they're fully burned in and If your amp has individually adjustable bias for each of its four power tubes you can use the pair and. Replace the PRE-AMP tubes and listen. The schematics for op-amp voltage follower for biasing is provided:. Most 6v6, 6l6, and el34 amps need biasing. The DC biasing arrangement is exactly the same as the common emitter amplifier we have previously described, in that the base is held sufficiently higher than the emitter that the transistor is. A "cold" bias means that the tubes are running much colder, the tone is cleaner and a bit more sterile, but the tubes last much longer. Connect the red lead to the CT of your output tranny and the black lead to the plate of one of the tubes. Tube biasing - posted in Effects, Amps and their Settings: What tools would I need to bias my tube amp, and would it be practical? I have no real knowledge of this stuff, but if I could figure out how to do repairs, upkeep, and modification, I could provide myself with hours of fun. As the “Original Boutique Builder”, we grew up (but didn’t sell out) and we can be pretty demanding!. Asking: $2000 for the pair including all tubes, cash only. The gain improvement is obtained at the cost of lower output swing. Cathode biased amps can safely run at 100% plate dissipation at idle. Design of the input stage is very straightforward (the loadline is seen in the left corner. In standard form, the Chicago amp is a 2x6L6, rated very conservatively at 32 watts in fixed bias and over 20 watts in cathode bias. If a guitar signal passes through the amp without a speaker connected this can cause the tubes to malfunction, and sometimes – if you’re really unlucky – even destroy the transformer. - Autio bias circuit to automatically optimize tube performance. 5 – Replacement of RCA jacks with original type. Biasing in mV or mA has been a great source of confusion to many new Hot Rod owners. Again, when it comes to getting an amp sim, it’s always a battle between Bias FX vs AmpliTube. Biasing is important because there is a lot of variation from one tube to the next. Your amp might need one or more new tubes if its volume, tone, or punch has gotten weaker. Typically, 70% of maximum tube dissipation at idle is what I work around. In some amps, there is no 'pot' so you need to swap out the fixed resistor to one with a different value to bias the amp correctly. Then you switch to 2 and repeat the adjustment for the second tube. This is where the screwdriver comes in handy. When you adjust this voltage to attain the optimum idle current of a specific type of power tube, you are biasing the amplifier. Fixed Bias is a confusing tube-industry term. This sets your output tube bias at the factory setting of 100 ma. These old amps were manufactured back in the 1970s my 2000/6 was made in 1976, my 80-10 jb2000 was made in. Bias set to 45% of dissipation limit (like Elekit). At its most basic, the idea is to set bias where it minimizes distortion, but not so high as to red plate the tubes. Asking: $2000 for the pair including all tubes, cash only. For adjustable fixed bias amplifiers, the amp should be biased by a tech with experience. Many people safely and. Don't focus on fine adjustment, just correct changes of 7% or more. The BIAS Amp 2 from Positive Grid is simply an amazing piece of kit for recording great guitar tones. The Preamp tubes are all JJ's??? why not JJ's on the power section? Ok. Dial in your tone settings and crank your amp’s gain to play massively heavy chords! American 5153. For amps UNDER 500vdc feel free to set up to 70%. To my knowledge (research) no AA165 amps exist with true AA165 tube charts. Re: Effect loop settings tube amp Bias FX mobile output settings Can someone help me figure out this? I'm using Bias FX Mobile, with a Laney lv200 amp and i want to know the recommended output settings for that, and where do i need to connect in the amp, in the amp front or in the effects loop. ' The power tube grid voltage is always negative on fixed bias amps and a hotter bias will have the grid voltage closer to zero. they are a spin-off of the 1982-87 concert series amps. It costs only about as much as a single output tube, doesn't requiring re-wiring or modifying your amp to use and is a huge enhancement in safety (think Life Insurance Policy) when working with 700Vdc! You don't need an expensive one with its own meter display. The bias of guitar amp tubes is the amount of electricity that each tube uses in relation to the other tubes in the amplifier. Notes: Completed 12/2019. I dig tube amps. All current production 6L6 tubes are great tubes. There are a few types of systems available on the market that will measure the “idle” or “bias” current of an output tube but for me that is only part of the. How to bias a tube amp with a voltage multimeter. * * * * * * * That said, you obviously don't want to go poking around a tube amp without knowing EVERY safety precaution to be taken. 5 – Replacement of RCA jacks with original type. There are a number of ways to do this. First you'll need to find out how many amps the tube will handle and do some calculations. At some point, you won't be able to adjust the bias to. Fixed Bias Amplifier $100. This means adjusting a preset control INSIDE the amp in the amplifier bias circuit. A quick tutorial on how to set the bias on a guitar tube amp, specifically the Fender Hot Rod Deluxe. Tube values can vary greatly from one amp to the next. Turn master volumes to 0. hughes-and-kettner. Recently, I was tasked with the complete re-design of a disaster of a DiY tube amp that a customer had brought me. Biasing an amplifier is like adjusting the inflation level of your tires on your car. Currently using EI KT90's and would like to try out some Mitsubishi EL34's. The CFA was invented by David Nelson at Comlinear Corporation, and first sold in 1982 as a hybrid amplifier, the CLC103. I need to install a 50 amp spa panel for a new hot tub. conrad-johnson tube amplifiers feature a unique, easy to use bias circuit. What is a "tube bias probe"? Link? I've been in the service business for more than 40 years (servicing valve and SS equipment). That’s why solid state amps are actually a good buy in some cases. Each power tube needs a certain bias current to keep it operating at the point where the amount and type of distortion under normal conditions is well controlled. The way a bias supply is connected to a tube is akin to a dead end road, it just trails off to nowhere without really completing a circuit. Since the grid is negative relative to the cathode thus bias is achieved. 12: Tube Biasing (6. dissipation. The Sovtek 7591XYZ Octal Base tube is provided with a resistor that is required when the tube is used in an amplifier designed for 7591 tubes. The reverb is lame I'll say that much for it. As the 7591XYZ is NOT a real 7591 tube, but is a re-based 5881/6L6, if you drop this into a socket that is expecting a 7591 and don't use the resistor provided, damage will occur. Shop our selection today!. Fixing the current draw of the tube with a simple circuit (LM317 + current setting resistor) allows a constant current draw regardless of the tube inserted. In any other case, you should always have a qualified amp tech reset your amp’s bias whenever changing your tube type or rating number. Individual tubes vary widely in the grid. There doesn't seem to be much between the 6AS7G/6080WA (10 watts) and the 810 (600 watts. Turn it on normal position and let it run for one day, check the bias every hour and readjust when needed. It can be configured other ways (see the schematic and PCB picture) but I use this to generate three voltages, a plate voltage, a screen voltage, and a negative bias voltage from a center-tapped winding plus a floating bias winding. The amp itself had only a swing of 10-28 volts for the negative bias, so my first move was to change this for a 0-55 volts swing through two 20 turn pots; one for each tube. - The amp sounds superb - The Class A design has "self-biasing circuitry" according to the manual, and doesn't require biasing. All of them failed. For amps UNDER 500vdc feel free to set up to 70%. There is a possibility to compensate aging drift on power tubes. Almost every AA165 Bassman has a tube chart inside the back of the cabinet that shows the AA864 circuit. Eiclone Amp. It simply needs some knowledge and some basic equipment like a voltmeter. Choice of driver tube also makes a difference, but not much. Finally, adjust the bias pot so that the current reading is the appropriate value for the type of tube your amp uses, (see the list below). 95: Triode USA Dynaco Mk3 Tube DIY Amp Kit $689. Amps with the cathode resistor you mentioned are cathode biased and generally run at a higher idle dissipation. Recently, I was tasked with the complete re-design of a disaster of a DiY tube amp that a customer had brought me. fender added an extra switchable gain stage on channel two, on the super pro series. Biasing your amp's tubes isn't just some sort of amplification function. 7 to do this. Only a handful of vintage H. Two 6V6GT power tubes operating in class AB push/pull mode, 5Y3 tube rectifier and 12AY7 and 12AX7 in the preamp section. All tubes must be biased (yes, even preamp tubes) and all tube amps have bias applied, weather fixed bias or cathode bias. Tube equipment has added hassles that you don't get. This needs 2-2. In any other case, you should always have a qualified amp tech reset your amp’s bias whenever changing your tube type or rating number. I decided to up it to 35mA. The following post addresses this topic thoroughly. I've read about this bias mod. The output swing will be less than 20VPP and with 200V B+, a 20K load gives 6-7mA of idle current. So assuming that your description of your amp is accurate, then your amp is a rather rare exception, not the rule. Amps with adjustable bias and a way to measure current make these variations unimportant. Dual tester worked great, biasing a new set of 6L6GC tubes. The new preamp tubes are all about headroom: The new 12BH7 and 12AY7 tubes put out more gain before distortion than normal 12AX7’s, so they’re often used in bass and hi-fi. First, biasing is simply setting the output of the power tubes in your tube amp. I'm biasing the 6L6/6V6 tubes in a Vintage Sound Amp. You measure pin 8 of the power tube socket and ground. Connect the red lead to the CT of your output tranny and the black lead to the plate of one of the tubes. Cathode biasing means that the amp shouldn't explode even with an unoptimal bias, while an amp with a fixed bias with a way off bias will fry the tubes and possibly the transformer. Biasing in mV or mA has been a great source of confusion to many new Hot Rod owners. As such, the audio transformers were unsuitable for high fidelity service, the amp was cathode biased and the phase inverter was not balanced. Again, it depends on where the tube is biased on its operating curve not how it is biased. Those are a generic production tube (my 5 year old Valveking 100 had them in it new). To calculate this resistor, use Ohm's law: R=-32V / 0. The Preamp tubes are all JJ's??? why not JJ's on the power section? Ok. Eiclone Amp. With power amp valves you will notice very quickly when one or more have gone. For this reason a fixed voltage cannot be used as a reference for biasing the output tubes. See S-TBM4-EL84 for noval version. These tone stacks are the perfect match when you’re dishing out insane preamp distortion for harmonically rich leads and overdriven rock chords. The 752A has the ability to test the older and newer tubes, including compactrons. No negative feedback loop in the power amp section. Underside of the amplifier section itself, showing the pre-amp, phase splitter, and push-pull driver stages. Order below or call us at 318-703-4542. The YJM offers the perfect balance of vintage tone and looks alongside modern features, which makes the amplifier the perfect players™ tool for. A re-launch of my popular Special 6SN7 Line-Stage featuring many updates over the original while still maintaining the same sonic signature. I find this page handy for tube biasing. For the purposes of troubleshooting, you can install a new set without re-biasing the amp, but if they are indeed the cause of the noise then you should definitely. 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. Lineout w/ Level Control: $175. At some point, you won't be able to adjust the bias to. Amps with a single EL84 output tube are probably class A and will run normally at around 100% max. But, I saw somewhere that biasing a class AB amp at 90% will warm up the tone significantly, while only reducing the tube life by about 20%. When you bias your amp you will be rewarded with great sound, lots of power and long tube life. What we do The minimum requirement for electrical restoration itemized below, will produce a safe and quiet tube amp regaining that great tube tone. The 741 Op Amp IC is a monolithic integrated circuit, comprising of a general purpose Operational Amplifier. We bias most major tube amps: Ampeg, Fender, Hiwatt, Marshall, Peavey, Vox, and more, using the “Groove Tube Bias Probe Method. Dynaco™ replacement parts & vacuum tube audio amplifier kits. Then read about/research biasing. You can't use the EH bias spec on other tubes. The bias of guitar amp tubes is the amount of electricity that each tube uses in relation to the other tubes in the amplifier. As such, the audio transformers were unsuitable for high fidelity service, the amp was cathode biased and the phase inverter was not balanced. For the purposes of troubleshooting, you can install a new set without re-biasing the amp, but if they are indeed the cause of the noise then you should definitely. 5 watts/459v =. This amp (the 5E3) is my very 1st tube amp so forgive me if I am a little bit of a newbie. Careful adjustment of distance from the ground (bias) and position of the balance of the see-saw board (bias balance) can make for a wonderful result. When you adjust this voltage to attain the optimum idle current of a specific type of power tube, you are biasing the amplifier. Guitar Amp Re-Valve And Biasing Marshall JVM. If your amp has fixed bias and you'd like to try cathode bias. There is one hidden risk though: since all the heaters are in series and they're on ground potential, the upper 6N8S cathode follower will have its Vhk. The KT90's are biased at 400Mv, however, when I. (No need for you. After an absence of several years, Pacific Audio Regenesis has re-emerged on the vacuum tube audio scene. In a ’fixed bias’ amplifier the cathode is grounded and a separate negative voltage is applied to the grid of the output valve. Considerations need to be given to filament voltage, input signal feed, biasing, tube cooling and tube mounting. Available in Midnight Charcoal with Silver trim. When a car’s idle is set correctly, the engine doesn’t stall or rev up wildly when you’re not moving. You turn the volume switch, located on the top of the amp, all the way down,. All this doesn't just apply to non-NOS tubes and Garnet amps either, it's a generally useful thing to have variable bias for that purpose alone. Nick Bowcott determined to set the record straight in guitarist NOTE: There are some tube amps with self-biasing circuits for the power tubes, too. USB connection for BIAS Amp app for Windows and Mac; Bluetooth connectivity for BIAS Amp app for iPad and iPhone; Comes with BIAS Amp plugin (VST/AU/RTAS/AAX) and standalone app ; Dimensions: 3. Turn master volumes to 0. Tube Amp Bias is an electronic process that ensures the power amp tubes in your valve amp run at their optimimum capacity so that you can get the best possible guitar tone out of them. That’s why solid state amps are actually a good buy in some cases. Tube sockets cleaned and re-tensioned. To ensure long tube life, first power the unit on with the STANDBY toggle switch in UP position for approximately 30 seconds. There is a lot of misunderstanding among guitarists regarding exactly how Class A, Class A/B, cathode-bias and fixed-bias amps operate and differ from one another. volts as if they were EH tubes. Then it is turned back until the LED just turns off. If you dont know how to discharge the capacitors you are not going to be able to work on a tunbe amp safely. 5 Best High-End Tube Amps in 2020. The big ones. TUBE AMP DOCTOR – OCTAL PROBES – FOR BIAS MASTER (2) $ 179. First it is important to clarify the fundamentals of how a guitar tube (valve) actually operates. I’ve been messing with building amps, especially tweakin em and really end up liking split bias (even though the Fender Silverfaces caused it to get a bad. Tube socket springs loosen over time. There doesn't seem to be much between the 6AS7G/6080WA (10 watts) and the 810 (600 watts. Biasing an Audio Research VT100 Tube Amplifier. Re: First time biasing an amp - is this procedure correct? Just bought a multimeter. Simple tube failure. This is for Push-Pull amps. Your amp might need one or more new tubes if its volume, tone, or punch has gotten weaker. I hope you enjoy the journey through the rebuilding of this tube amplifier as much as I enjoyed writing it. If the amplifier is a single stage amplifier, provided the RE is not required for your biasing scheme your gain wil. Hardware tightened. Bias current affects this distortion, but not much. Now let the amplifier run, and check and re-adjust the bias for the next hour or so. You can't use the EH bias spec on other tubes. The Bias setting has a dramatic impact on the amp’s response, break-up and dynamic character. In Mesa/Boogie amps no such trim-pots are fitted but, contrary to. Do a lot of reading/researching on the safety rules for working on tube amps. Includes tube amp bias, cleaning potentiometers, cleaning and re-tensioning tube sockets, diagnose and advise on general operation, specifications, condition of all tubes, power supply and failed or missing components. Biasing an amplifier so that the operating point is at the center of the linear part of the transistor´s characteristic curves is called ´Class A bias´. Your author has had good luck with the JJ brand 6V6S spiral filament tubes running at a bias of 19mA. Re Biasing A Tube Amp. Generally, the bias should be set so that the tubes don't become too warm when there is no signal going through them. How to bias a tube amp with a voltage multimeter. Every tube has an optimum bias point, but as tubes age you have to readjust the bias. They’re versatile enough, so musicians who love experimenting will surely be amazed by the endless potential they’ll have. For example, the 202 uses EL34 power tubes - 2 per channel. 7 ohms Color: Sparkle Burgundy Red. I switched tubes' positions and the low bias still stays at V5. This is known as the bias voltage. Police find no bias, Focal Arche Amplifier Transforms Over-Ear Headphones Into High-Fidelity Sound Machines SPY 5 Things To Do When You're Stressing Over The 'COVID 15' HuffPost. It's so good that you can A quick tutorial on how to set the bias on a guitar tube amp, specifically the Fender Hot Rod Deluxe. The tube is not produced any more. Each power tube needs a certain bias current to keep it operating at the point where the amount and type of distortion under normal conditions is well controlled. A tube amp, even an unplugged tube amp, stores enough electrical energy in it's capacitors to kill you! Replacing with a 2 Meg POT, or moving the volume control to the preamp are other options for punching up the power stage. First it's completely cold, then left running. I have a Laney AOR Pro-Tube 100 and am going to re-tube the output tubes. Biasing an amp requires some knowledge of tube amp circuits and experience with high voltage. Lineout w/ Level Control: $175. Bias set to 45% of dissipation limit (like Elekit). do i just unplug the old ones and put in the new ones? or is there a special way of going about it like rebiasing?. Here's what I got Bias voltage: -48. Before re-biasing, the plate side of the output transformer should be tested with an ohm meter. There is a possibility to compensate aging drift on power tubes. I received email from a person who tried 32 mA with EL 34's with no ill effects. $3 Tube Amp BIAS PROBE Made in UNDER 30 MINUTES! This video supports part of the Frequently Asked Questions section of the Victory website. these will measure as a short on most continuity meters (i. A lot of guitarists, however, prefer the tube amp due to the tube amp’s analog sensitivity, which they claim makes tube amps sound better. When the input stops, the coupling capacitor slowly discharges allowing the power tube bias to recover. The JJ E34L can be biased hotter than the standard EL34. This humungous monster is pushing 1015 watts RMS!!. Master amp builder Bruce Collins has designed them from the ground up to to be the most exceptional and economical pro-level small and mid-sized harp amps on the planet. If they are biased incorrectly or if there is a fault in one of the biasing components, it can cause a number of power supply and output section problems. I hope you enjoy the journey through the rebuilding of this tube amplifier as much as I enjoyed writing it. If the amp was born with a pair of “hotter” tubes, the setting on the wheel will be far to the left. If your amp is a fixed bias amp, you will need to bias it. Here is my single triode vacuum tube amplifier circuit I understand there needs to be a bias on the grid otherwise the signal will be rectified -not amplified. Bias current affects this distortion, but not much. , 1978) AC50. In an average room one solid-state amplifier (Class AB or Class D or other "switching" amps) will sound indistinguishable from another, assuming you're not driving them to distortion. There is the 811A but that's a zero bias triode so even a class A amplifier using this tube would have to draw grid current. Tube Set for Marshall JTM45 2245 Re-Issue. The bias determines when the amp switches from Class A to Class AB. Nick Bowcott determined to set the record straight in guitarist NOTE: There are some tube amps with self-biasing circuits for the power tubes, too. 7 to do this. The JJ E34L can be biased hotter than the standard EL34. Tube amps can kill you, even when they're not plugged in. Once you’ve removed the grille, you’ll see the bias prongs. Found 71 records in Search of Tubes Asylum. Most EL84 amps are the same way because they are cathode biased. 6 – Replacement of speaker barrier strips with original type. 1010 W 17th Street, Costa Mesa, CA 92627, United. The issue could be the tubes currently in the amp are getting too aged; it could also be that the amp needs a re-conditioning in case resistor / capacitor are out of spec from aging. My amp in particular uses 440 plate volts. Some folks who've used EL34's in these amps say they get better tone out of them by installing a variable bias control (the stock bias voltage on most Ampegs that use 7027, is a bit lean for EL34's), and by changing the screen resistors to 1,000 ohms instead of 470 ohms. Tube Amp Bias is an electronic process that ensures the power amp tubes in your valve amp run at their optimimum capacity so that you can get the best possible guitar tone out of them. TentLabs Negative Bias Supply Designed in co-operation with Menno Vanderveen, we are proud to announce a new module When using fixed bias in your amps, the currents need constant re-adjustment to compensate for mains variations and tube aging. If your amplifier does not have the bias points and trim pots accessible there will be a bit more work needed. So this is the only amp they sell that is a pure tube amplifier. Grip the base of. It ensures the tubes are fed the correct voltage according the valves resistance rating. We'll bring you right back here when you're done. Thus, the positive half-wave of the output is clipped. hello fluro and welcome to the forum! here's the power section of the amp so that we can see what we're talking about if you'll notice right there in the middle, r107 and r108 are 2 watt 1 ohm resistors from the pin 8 cathode (and technically also the pin 1 suppressor grid, but we can leave that out if this discussion) the ground. You should re-bias the amp whenever you change power tubes or modify the power amp circuits. Hardware tightened. Lineout w/ Level Control: $175. Bad Cat Amps. The Bias fuse is used to protect the Bias potentiometer if incorrect settings are made for the tube being tested. So I am very pleased with this probe. The gain improvement is obtained at the cost of lower output swing. Over-biasing, on the other hand, can shorten your tube amp's life through overheating. TUBE AMP DOCTOR – OCTAL PROBES – FOR BIAS MASTER (2) $ 179. Description. Recently, I was tasked with the complete re-design of a disaster of a DiY tube amp that a customer had brought me. TentLabs Negative Bias Supply Designed in co-operation with Menno Vanderveen, we are proud to announce a new module When using fixed bias in your amps, the currents need constant re-adjustment to compensate for mains variations and tube aging. But, it is common for these factory set bias supplies to drift so it is best to have it checked and set up by a good tech. 1×12″ speaker, originally Jensen P12r or P12q. Turn master volumes to 0. Tube amps can kill you, even when they're not plugged in. In Mesa/Boogie amps no such trim-pots are fitted but, contrary to. Each power tube needs a certain bias current to keep it operating at the point where the amount and type of distortion under normal conditions is well controlled. These may have an adjustment pot or a fixed resistor for the bias voltage setting, but either way they are called a fixed bias amplifier when there is no cathode resistor on the output tubes. If the ad is up, they're still available. away with the same kind of tube swapping like we used to do back. * * * * * * * That said, you obviously don't want to go poking around a tube amp without knowing EVERY safety precaution to be taken. These old amps were manufactured back in the 1970s my 2000/6 was made in 1976, my 80-10 jb2000 was made in. Recommended Bias Point: Cathode Biased (no re-biasing necessary). Turn the brass head of the blue pot until the reading is 350 mV. Fixed Bias Amplifier $100. Since the grid is negative relative to the cathode thus bias is achieved. The big ones. Mesa claims are mostly BS and so are GT claims as well when it comes dow to the need (or the lack of it ) for re-biasing after a tube change, if that's what You're wondering. An updated power supply section, Mogami shielded signal wire, TKD input control, Neutrik RCA connections and a solid hard-wood enclosure present some of the changes made to this preamplifier!. The sweetest overall tone and longevity of guitar amp tubes is attained when all of the tubes in the amplifier are drawing the same amount of current or electricity. ) because we want our amp to sound its best. Matched tubes are essential in vacuum tube power amps. The best time to re-check the bias is at the end of a listening session, before the amp is turned off. You will still need to manually obtain cathode-plate voltage and calculate conversion formula (included); Unit AB switch allows single multimeter use providing mV conversion of current draw, so you can determine your optimal bias point. Amps with a single EL84 output tube are probably class A and will run normally at around 100% max. To ensure long tube life, first power the unit on with the STANDBY toggle switch in UP position for approximately 30 seconds. They’re versatile enough, so musicians who love experimenting will surely be amazed by the endless potential they’ll have. The idea was often to maximize power. You might also need a new tube if you occasionally hear feedback from your amp for no reason. Plate voltage is right around 450V. Receiving tubes Edit Cathodes in small "receiving" tubes are coated with a mixture of barium oxide and strontium oxide , sometimes with addition of calcium oxide or aluminium oxide. Make sure the chassis doesn't get to hot, upside down. The people who designed and sold tubes made a ton of beam power pentodes but almost no power triodes. Turn OFF the amp 2. 40 Reisong A10 EL34 Hi-Fi Audio Stereo Tube Amplifier Single-end Class - A Amp 138. Remember: Tube sockets are not highly reliable connectors! If the sockets are dirty or not tight Many times, just the act of removing a tube and re-seating it, either in another position or back into its We always recommend biasing your amp to the setting specified in your amp's manual or maybe a little. I peg it to be squarely between a Marshall and a Mesa in terms of sound output. series amps is not good for JJ's, Mesa's and Groove tubes. As such, the audio transformers were unsuitable for high fidelity service, the amp was cathode biased and the phase inverter was not balanced. This is the original amplifier. Bogner says set the bias to 25ma. An amplifier that is biased part-way between Class B and Class A operation is said to operate in Class AB mode. Ideally no, but You should always check the bias in any case and adjust if necessary when changing power tubes. Order below or call us at 318-703-4542. One way is to use your multi-meter set to read ma's. The single stage common emitter amplifier circuit shown above uses what is commonly called “Voltage Divider Biasing”. Using the tool supplied one turns the adjustment until the point at which the LED lights up. Jun 7, 2019 Will the ZOTL Ultralinear amplifier pair well with my speakers? Tubes Jun 7, 2019 What kind of tubes do you use in your amps? Jun 7, 2019 Do I have to adjust or bias my tubes? Jun 7, 2019 Do LTA tube amps generate a lot of heat?. If they are biased incorrectly or if there is a fault in one of the biasing components, it can cause a number of power supply and output section problems. Safer for Speakers. The world’s first large tube amp equipped with a Nutube in both the pre-amp and power amp sections. 77) Posted by tweakman on 2005-09-03, 20:36:43 (219. 5 volts, and a fresh 5670/396A/2C51 would take 4 volts bias. One of the most powerful and versatile Fender bass amps ever made, it's a stadium-level 300-watt tube head designed for the biggest shows and the largest stages, with enormous Fender bass sound and sparkling vintage-style Fender looks. Grid-leak biased stages will distort easily and cannot handle large input signals because so don't hookup a Fuzzface a grid-leak bias amp. With a "fixed bias" amp - which is actually not fixed in the same sense a cathode biased amp is - the grid current is controlling bias of the tubes, so because that current fluctuates considerably, you need more head room. I see too many DT series amps come across my bench because. Re: Cayin A88t - Biasing I owned previously a A88T amp below are the biasing procedures. I'm biasing the 6L6/6V6 tubes in a Vintage Sound Amp. The YJM offers the perfect balance of vintage tone and looks alongside modern features, which makes the amplifier the perfect players™ tool for. Often it is a switch that can select bias for EL34 tubes, or 6L6 tubes depending which is installed. A failed biasing component that lets the grid assume the same voltage. There are a number of ways to do this. Instant Power Amp Re-Voicing. With the toggle switch in the UP position, the amp is in STANDBY mode. - The amp is very well built (I'm comparing it to the Peavey Classic 30 and a number of Fender amps I've had/used). 58) Thanks for all of your information. " Martin Kloos "I felt like hearing my bass for the first time. When a vacuum tube is amplifying signals, the level of negativity on its control grid is important. "amp should be connected to your preamp but volume is turned fully down ( NO signal applied to the amp ). The resistor value is determined based on design averages for plate voltage and current. 5 – Replacement of RCA jacks with original type. 95: Magnetic Components Inc. All amps can be biased or re-biased or biased to point that the end user desires unless for some rare reason you simply can not get to the parts to unsolder them. It should be stable once it's broken in. Background music used for. Class A is a terminolgy about the relationship between voltage and the bias point. " Bertrand Sikes "Ah, finally a zero-maintenance tube amp!" Micheal van Diesen "A modern take, with classical elements" Kees Brandsma "It sounds beautiful. Q: So why the heck did we use voltage in the "Biasing for Dummies" section?!. When the input stops, the coupling capacitor slowly discharges allowing the power tube bias to recover. If your amp is a fixed bias amp, you will need to bias it. what does it mean to re-bias an amp? and whats internal variable bias control. Grip the base of. If you're wondering what a Univalve sounds like on low-power mode - this circuit captures a lot of the same tones. The bias is a NEGATIVE voltage applied to the control grid of each valve. The BIASTOOL testing probe works with most tube amplifiers, including Marshall, Fender, Ampeg, Hiwatt, Peavey, Soldano, and many others, measuring the amount of current which actually flows through your power tubes, using your volt/ohm meter, which can be purchased separately for as little as $24. In real life that is tough on tubes as it makes them run very hot. Even playing it clean it's too loud just feathering the gain These are all valid options, they're just expensive. The power valves. It is a pain when you have to troubleshoot bad tubes, rattling in the amp, or other issues. You turn the volume switch, located on the top of the amp, all the way down,. To my knowledge (research) no AA165 amps exist with true AA165 tube charts. How to Replace Tubes in a Guitar Amp. amplifier is operated in Class A biasing, both tubes are actively amplifying during the entire signal cycle. This means adjusting a preset control INSIDE the amp in the amplifier bias circuit. I don't think I'd go over 50mA per tube for EL34. After March at some point the AB165 circuit was manufactured and most of the early AB165 amps actually show the AA165 tube chart. I've read about this bias mod. As such, the audio transformers were unsuitable for high fidelity service, the amp was cathode biased and the phase inverter was not balanced. It was built from organ parts. 251) I am new to tube amps, have in mind the ming-da mc88c. amps, I've ever played on. Tube bias also affects the tonal qualities of the sound that's being produced. 7v as noted in the schematic). Not all tube amps have adjustable bias, but most larger tube amps do (output power of 40 watts or greater, typically). You might quickly find the problem tube. my question. Mesa claims are mostly BS and so are GT claims as well when it comes dow to the need (or the lack of it ) for re-biasing after a tube change, if that's what You're wondering. The 752A has the ability to test the older and newer tubes, including compactrons. Now let the amplifier run, and check and re-adjust the bias for the next hour or so. Individual tubes vary widely in the grid. As the 7591XYZ is NOT a real 7591 tube, but is a re-based 5881/6L6, if you drop this into a socket that is expecting a 7591 and don't use the resistor provided, damage will occur. Receiving tubes Edit Cathodes in small "receiving" tubes are coated with a mixture of barium oxide and strontium oxide , sometimes with addition of calcium oxide or aluminium oxide. So in order for out amplifier to work properly, we have to make sure the power tubes are not under biased or, over biased. There are a few types of systems available on the market that will measure the “idle” or “bias” current of an output tube but for me that is only part of the. Simple tube failure. Bias automatically set to 45% of dissipation limit. Biasing a Diezel amp with no external fuses: Some early amps have the tube fault fuses inside on the PCB board. '63 Re-issue Vibroverb (1990–1995) As demand for vintage Fender tube amplifiers had increased, several re-issue models were introduced in 1990, beginning with the tweed '59 Bassman amplifier, the brownface '63 Reverb unit and the brownface '63 Vibroverb. After the amp has cooled down, remove the back panel if needed. Thus, the 70% recommendation. I usually have my amp biased around 34ma. Fixed bias applies a negative voltage to your grid, forcing it below the cathode. Amps with the cathode resistor you mentioned are cathode biased and generally run at a higher idle dissipation. Skip to main content Skip to footer site5116445261 site5116445261 Used 116445261 Positive Grid Bias 600w Tube Guitar Amp Head site5116445261 false. 79) Posted by smitlar on 2007-05-11, 18:06:30 (71. It simply needs some knowledge and some basic equipment like a voltmeter. Just like customizing real amps, you can swap out the tubes, preamp transformer, tone stacks, cab and mic of your virtual amp. In standard form, the Chicago amp is a 2x6L6, rated very conservatively at 32 watts in fixed bias and over 20 watts in cathode bias. Voltage Follower Biasing: This method is exactly the same as the voltage divider biasing, except it uses an op-amp (or transistor) to buffer the bias voltage, so choosing small resistor values is no longer necessary. A tribe of 12AX7 preamp tubes. Self Biasing/Cathode Bias: As the name suggests, these amplifiers are essentially 'plug-and-play' and will not need to be tinkered with if tubes are being replaced. You can't adjust the bias to less than 2. (organ crescendo) mill-eee-volts! After all when we bias an amp we're setting the idle current. The DC biasing arrangement is exactly the same as the common emitter amplifier we have previously described, in that the base is held sufficiently higher than the emitter that the transistor is. Re: Cayin A88t - Biasing I owned previously a A88T amp below are the biasing procedures. Q: So why the heck did we use voltage in the "Biasing for Dummies" section?!. While playing through a tube amplifier, it is important to make sure that the speakers are connected to the output of the amplifier before turning the amp on. The Yngwie Malmsteen Signature YJM100 100W Tube Guitar Amp Head is a 100-watt, valve head that was developed in close conjunction with the legendary Swedish six-string shredder, Yngwie Malmsteen. But biasing isn't hard or complicated. This calculator uses the power equation P = I × V. They use regular transistors like any other for output stage power. This lets you set and evaluate all reasonable biasing range your amp and tubes offers to find and set your personal perfect choice. A lot of guitarists, however, prefer the tube amp due to the tube amp’s analog sensitivity, which they claim makes tube amps sound better. com/tube-safety-control-preventing-amp-related-apocalypse/. Tolerate any tube-to-tube variance of 10% from the lowest current draw to the highest and set the maximum For BIG amps with OVER 500vdc to the plates I observe a 50% bias setting. For those looking to make the most of their JTM 45 reissue amplifier heads, ensuring that a good quality set of tubes that are properly biased will take these amps a long way. Output tubes handle probably 85% of all the power used by your guitar amp. The second tube is all over the map with readings as low as 19ma and as high as 32ma without any adjustment to the bias trimpot. Turn the brass head of the blue pot until the reading is 350 mV. There's probably more misunderstanding and opinions about how to properly bias a tube amp than any other area of tube lore. Re Triode RF Amplifier Biasing « on: September 21, 2009, 02:15:58 AM. The bias must be set correctly for the effect to work. 2), or for any situation where the power transformer does not have a bias winding. Again, the "sweet spot" in between is where most techs set the bias. When biasing to 70% or whatever percent you're looking for you simply multiply the answer by that number divided by 100. This allows a cathode-biased amplifier to be given the option of fixed-bias, using the bias switching methods shown in TUT2 (The Ultimate Tone vol. A valve amplifier or tube amplifier is a type of electronic amplifier that uses vacuum tubes to increase the amplitude or power of a signal. These amps were developed prior humbuckers, hot pickups and fx pedals so they were far more acceptable sounding with low output single coils. Recommended Bias Point: Cathode Biased (no re-biasing necessary). Individual tubes vary widely in the grid. The tube sounds a bit dynamically constrained compared to 71% bias. You merely turn the individual trimmers to set each tube. It may be a little more 35 ma or a little less 25 ma. Master amp builder Bruce Collins has designed them from the ground up to to be the most exceptional and economical pro-level small and mid-sized harp amps on the planet. In many PP amps I have used fixed bias, and in 100W ULAB amp with 6 x EL34 I have used 6 adjust pots. The two pots are labeled "Bias" on the chasis, and are 100ohms connecting pin-3 of the two 7189's in each channel (0. Example: Design the DC fixed bias conditions for the simple class A common emitter amplifier shown in Fig. 5A 250V SLO 1. From one tube ampoholic to another. The first thing you’ll have to do is remove the back metal grille. I avoid putting them into my amps and my customer's amps. When we 'bias' we're setting the working condition of our tubes. STANDBY applies high voltage to the vacuum tube anodes (and screen grids) during use of the amp. I lent this amp to a mate at work (he's very knowledgeable with tube amps) and he said he loved it, as did my brother-in-law, I love it as well, its awesome, I think I'll have it in another 5 decades. It ensures the tubes are fed the correct voltage according the valves resistance rating. Biasing an Audio Research VT100 Tube Amplifier. With Cathode bias, the tube voltage is the B+ minus the bias voltage, so the tube runs on lower voltage. As well, as your tube life degrades, it doesn't hurt to have the bias checked and adjusted periodically to make sure your amp is running properly, maybe every 4-6 months depending on how much tube life you get (which is directly dependent on how much use your amp is getting, of course). Pro Audio PA Hire for Band Party & Special Function. 12: Tube Biasing (6. The plate voltage can vary a lot from amp to amp.