Tube Amp Bias Too High

To produce this power the Magma relies on three different tubes: the 6N1P-EV, the 6N30P-DR, and the Eimac 450TH. The 12Ω is probably a bit too high for load currents above 100mA, so you should experiment with it, or short it out altogether. The early (1997-2003) Marshall JCM2000 DSL50, DSL100, TSL100 en TSL122 amps are often troubled by an unstable bias (drifting bias). Dating Fender Tube Amps by Serial Number - Free download as PDF File (. Bias Adjustment Pot - Varies the amount of bias current applied to the power tubes. The Schiit Magni 3 which is a solid-state headphone amplifier retails for $99 so quite a bit cheaper. • 6L6—Used in classic American stage amps and some modern high-gain designs, the 6L6 output tube delivers high-headroom punch with a round and full midrange character. The bias voltage is generated using a voltage doubler circuit off the low voltage AC from the power transformer. Decrease bias. This parameter is highly reactive with the Drive and Master settings. The program also asks you for the DC bias voltage required. Bias is a negative voltage so to clarify If you increase the voltage in pin 5 of an octal based (EL-34, 6L6, etc) tube from say -48v to -50 volts the tube will run cooler and have lower idle dissapation noted, that is, on a bias tool you will see a drop from say 36mA to 32mA as an example. I drop it between 0 and 20%. When using the terms cathode or fixed bias we are discussing the power tubes of an amp (pre-amp tubes are nearly always cathode bias or grid-leak biased but that is a discussion for another time). One of two new designs birthed from a 2012 partnership with Mike Fortin, the Thrasher line is gourmet metal gear with the extreme gain. The Tube Screamer TS808 by Ibanez is the most famous overdrive guitar pedal. The idea behind automatic electronic bias is a reduction of quiescent current and heat in high power radio-frequency amplifiers. Grid bias for the 300B tubes is generated by a shunt-regulated bias supply PCB that I designed. 22nF will have limit frequency of 72Hz, which is too high for downtuned guitar (low E is 82Hz). I love working on amplifiers and have many of the best tools available for diagnosis and repair. The Last Word on Class A. Panor/Dynaco's most ambitious stereo tube amplifier was the Stereo 160, a 75 wpc, all-tube stereo power amplifier with switchable pentode/triode modes, adjustable tube bias potentiometers, and 6550 output tubes. - Click above for full resolution - This is essentially the Space Tone Reverb, a circuit based on the little 5W, Class A, single-ended 6V6'R that started it all, but with new found bottom, and just amazing breakup (in my. QUAD TUBE AMP Bias Meter 6L6 El34 KT88 Probe with PLATE VOLTAGE MEASUREMENT - $69. They may utilize strong loaded words (wording that attempts to influence an audience by using appeal to emotion or stereotypes), publish misleading reports and omit reporting of information that may damage liberal causes. "Bias meters are for *****" Oh my! Aren't we opinionated! I use the Bias King from The tube Store. If the bias is set too high for your new power tubes, you can destroy them in a matter of minutes. ) With the amp on in play mode, You’ll want to make small adjustments to the bias pot and observe the bias probe as you make the changes. The Best High-End Tube Amplifiers 2020. With the grids grounded directly to the chassis, the center tap of the filament transformer can be switched directly to the chassis to activate the amplifier. Posted: Oct Tue 14, 2014 9:40 pm. Again, the tubes will be very HOT at this time. Setting a higher % of max dissipation will make the bias 'hotter. It is obvious that an input step-up transformer 1:4 or 1:8 can resolve the voltage gain problem but in this case this amplifier should be driven by very low output impedance source near to 300-600ohm because the input capacity of the grid is multiplied two times for. The tube amp proudly sits as a cornerstone of many a home setup. In extreme circumstances, the amp could be on the verge of meltdown if you just plug in new tubes without biasing. Much like the idle in your car's engine, a tube amplifier needs to have the output tubes (power tubes) biased properly, for optimal performance. Like the output impedance of a tube amp. Matched tubes are tubes of the same, or close, rating. While the earliest AC-100 amps had a cathode or "self biasing" output circuit , the AC-100/2 had a fixed bias output circuit. The program also asks you for the DC bias voltage required. The real up side of Class A/B operation is its inherent efficiency. There is slightly less splatter or distortion. It sounds like Jefferson airplane type. Just like the idle of your car may need adjusting when a major change is done to the engine, new power tubes need their idle (the "bias") adjusted to make sure the amp sounds as good as possible. Another 10 years were to pass (1980s) before interest in valve amps began to re-emerge. Swap the offending pair of tubes with the tubes from the other side. This board gives the amp the bass definition that the ST70 original lacked. I also have two Tubelab SE amplifiers for comparison. In some cases it can be pretty easy to change up an amp's fundamental characteristics, too, just by changing tubes in some crucial positions—and the tube that affects the biggest sonic change in most amps is the one we call "V1" (for "valve number one"), the first preamp tube that your guitar's signal hits after entering the amp's input. A resistor accomplishes this task by being made of materials that are semiconductive. 3mA, so I believe I had hit this sucker as close as I'd care to. The noise is generated within the amp itself. "Unlike many tube headphone amps that exhibit the rolled off high frequencies and bottom end that a seeming majority of electrical engineers think is the “tube” sound, the Schiit Lyr 3 produces a true audiophile sound with extreme linearity in both the low bass extending into the subsonic and the upper registers, while retaining the. The Big Boy has silky smooth big warm lively tube sound packing a powerful tight punch. With preamp tubes, the bias is intended to put the plate current within the center of the linearity curve for minimal distortion. If the operating point is set too high, that is if the grid bias voltage is too high, as exemplified by the blue spot and range, then saturation would occur when the signal oscillation produces a grid voltage above 0V. Yes, overheating will sometimes cause unexpected noises in the tube for sure. X-Tube simulates a tube amplifier saturation effect. and if the current is set too high you may be risking the tubes to begin the melt-down process and take out the output transformer. 65) or even as high as 80% (multiplied by. The amp is, roughly, between 18-22 watts, Class AB and fixed bias. It onoly effects the power tubes. When the lamp is not lit (neither green nor red) it means that the bias setting is correct and is in the. Mine was factory set to 45 but I didn't check it after about 6-8 months into playing it and one of the tubes started failing, I set them to 35 after that but they were too cold for me and it made the Marshall growl disappear in my opinion so I set them at around 38-39 and I am happy with it. must be use high current for plate. an 200ohm load with about 30mA bias current, is perfect, the distortion is near 0. This happens because many amplifiers share a bias supply between more than one tube. Product Weakness: hard to find, parts getting scarce, loose bass in comparasion to the best, may be too laid back for some, too warm and rich for Vandersteens, Spendors, Sonus Fabers, and not enough control for old Magnepans. Grid bias for the 300B tubes is generated by a shunt-regulated bias supply PCB that I designed. * Never operate a tube amp without a load (speaker or resistor). exceeds this easily. It uses a single pentode as the driver (a 12HG7 video amp tube), and a solid-state power supply with a microprocessor controller. Incredibly touch sensitive and dynamic, it has those crisp cleans and crunchy punch & pop that only a good tube amp can provide - and that you expect. I save this amp as a new custom amp and then reload it and go to amp match it. That then goes to the cicuit that mixes the bias voltage and the signal voltage that gets applied to the power amp tube, the 12BH7 at the top of the page. I am replacing the tubes because one was microphonic. Guitar amp's generally come equipped with 12AX7 preamp tubes. Guitar tube amp design was nascent in the 60s and 70s and designers didn't fully understand the impact of overdriving tubes. Re: Bias too high on a 5E5A « Reply #6 on: May 11, 2010, 09:49:51 AM » 12av7, they are very similar in gain to a 12ay7, and are super cheap. By Rob Robinette. Use the provided screw driver in the slot and adjust up. Insert bias meter probes into the tube sockets of the amplifier. If the idle is too high, you will waste gas, cause premature engine wear, and early failure. The amp sounded killer when I got it, then for safety, I checked the bias one tube at. FFX - the top-of-the-line 2A3S, some considered it as the best compact stereo 2A3 SET amp available on the market, also our bestseller. Both too low and too high voltages can be bad for an amp. Normally, two stages of preamplification would be needed to achieve this. It worked well in both test amps and can be used to advantage if your amp has too much grind. You can use Amp Match to clone the tone of real hardware or a guitar track, or connect to the ToneCloud® to gain access to thousands of custom amps from. Turn the bias pot too high and the LED turned red. You never know if you are straining the power supply by setting the bias too high. (Aside: if the bias is way too high, the tubes will 'redplate' which means the anode will glow cherry red. As of early 2008, the B+ fuse value was changed FROM 0. and if the current is set too high you may be risking the tubes to begin the melt-down process and take out the output transformer. Probably because the owner wanted a more distorted sound and didn't care about tube life. You can also damage your amp. They are great sounding, New old stock is abundant and they are economical too!. Signal input: 2 V for max power. an 200ohm load with about 30mA bias current, is perfect, the distortion is near 0. These tubes take the signal voltage and bring it through the cap on top of the tube - a nice way to keep the fragile signal away from noisy power supplies. THE CHAMP CBA-20807 1000 Watt AMPLIFIER APRIL 2009 - PART 1 THE BEAST!! Hi Peoples. When the lamp is not lit (neither green nor red) it means that the bias setting is correct and is in the. Turn the bias pot until you get somewhere around 35 milliamps of current. Too low a plate load will cause the tube to draw much more current. If not set properly, the performance (tone) of your amp will suffer. So next I threw in a pair of fresh JJ 7591 tubes. The negative bias must be more than the largest positive swing of the signal. Only allow a seven minute window of adjustment. This causes choppy sounding audio and rotten splatter. Most books don’t say anything about “grid-leakage bias ” !!! If there is a value, use it. In general, I think it is best to set the bias at the recommended amount. This parameter is highly reactive with the Drive and Master settings. It takes 2 EL84 power tubes. But 10 years later solid-state technology took over and nearly all valve amp manufacturing came to a close. There are two gain (volume) controls each with a 3-way bright switch which is found below the gain controls. "Unconscious bias" is a. Final measurements that will be used as the published parameters for the 2m-8877: No RF drive: Bias=15. > looks like a servo tube. Bias scheme modifications, anything that changes the tube type, or the power transformer (dramatically) and anything that adds new bands. 12AT7 power drivers. All was left which could cause the problem was the tube. Insert bias meter probes into the tube sockets of the amplifier. For tube geeks and 'tweakers' (another Egnater model name, LOL) there are super-handy bias test point and adjustment pots on the back of the amp. When I stuck in a pair of Svetlanas, the amp was way too hot!. If too low, bring it up to close to the suggested value. Bias 2 completely resets that custom amp and uses a starting point that is much farther off. Too much current flowing (idle too high, wears parts and wastes fuel) and the amp runs hot and burns up tubes and transformers. For example, a tube requires -10V of bias to conduct 50mA, then the cathode can be raised to +10V with the grid at 0V. With 5 audio imputs, no less. Biasing an amp requires some knowledge of tube amp circuits and experience with high voltage. 5mv) than the prior set ("straddling" @ 24mv) but they JJs showed no signs of clipping on the oscilloscope and were pleasing to my ear. Some audiophile gear is butt-ugly, but gloriously competent at revealing the music. diodes are ice cold. If the amp uses a fixed voltage and only one tube is glowing, you would suspect a bad bias resistor. Center tapped heater winding, 50V bias tap, copper flux bands and internal hum shield brought out to a lead for grounding (ensures the quietest amp possible). If you want to use them as standalone applications, please set up your audio device first. I didn't include any individual tube bias or balance adjustments, so I am using matched pairs of 300B tubes. The former, called V1, is a battery-powered tube amp that's switchable between triode and pentode modes, while the latter, P1, is a mains-powered solid-state amp. problem with tube amp: crackling/buzzing after heating up Sign in to follow this short time. I would be suspicious of something in the power supply causing a. (In other words, rotate the bias trimmer until you obtain the highest negative voltage that the bias supply is capable of delivering. Along way to go. So much for premium 'matched' tubes. Charlie’s passion for true sound earned him the well deserved recognition in Time Magazine and the entertainment industry as the purveyor of custom high end, high performance audio systems. 5 volt range, a 260 would provide a 50K shunt resistance load which would upset the operation and measurement of a control grid with a 10 meg grid "leak". Dynaco Power Amplifier Output Tube Bias Operation & Troubleshooting Page 1 Rev 0 Introduction Other than finding and eliminating system "hum", the most frequent question found on our Dynaco-Doctor forum how to solve output tube bias issues (too low, too high or unstable). But 10 years later solid-state technology took over and nearly all valve amp manufacturing came to a close. Enjoy the music;. Tremade likes this. With 5 audio imputs, no less. The basic idea is when RF drops to a very low level, large amounts of quiescent current are not necessary. Not really intended for first timer builders, but manageable for those who do their homework. If too much current flows through a tube, the tube may run red hot and fail prematurely. must be use high current for plate. After you have completed checking the bias on your output tubes turn your amplifier off and allow it to cool down. Bias that is set too low can make the amp sound thin or veiled, while running the bias too high may shorten the life of your tubes, and in some cases may damage the tube or the amp. 10 Things You Didn't Know You Could Do With String. Here we use the Focusrite Scarlett 2i2 interface as an example. Amps of the 50s and 60s often featured at tremolo circuit driven by power tubes that was the last. 5 to even 3. With preamp tubes, the bias is intended to put the plate current within the center of the linearity curve for minimal distortion. (As shown on the picture). 5 mA and nowhere else to go but upw. Adjustable bias is necessity in a fixed bias tube amp. This is easy to do with a voltmeter: 1. Initially, after 6 years of service, my 6550 showed a DC offset of 826/234 mV on L/R channels, both extremely high values, totally unacceptable. Tube Amp Building - Tweaks By "bias voltage too high" do you mean too negative, as in its -57 at the moment as opposed to -38 or so that I should be shooting for. If you end up purchasing, I suggest you purchase as well a step down transformer to 110v, so you can use them safely at a bit of lower voltage. A KT88 tube has a recommended bias at around 380mv-420mv. The bias mod is installing a bias potmeter (so that the bias current can be adjusted) and one or more bias measurement resistors so that the bias current can actually be measured. I've picked up for a great price a somewhat older tube amp from the 70's that hasn't seen much use that's in great condition. high quality output transformer from Ogonowski, made of very fine German steel. The Big Boy has silky smooth big warm lively tube sound packing a powerful tight punch. Next, adjust the bias control until you have MAX NEGATIVE voltage on pin FIVE. txt) or read online for free. Bias these tubes hot for best results. If the operating current is set too high, the tube will draw excessive current, which will shorten the life of the tubes. Put the amp back on. Grid bias for the 300B tubes is generated by a shunt-regulated bias supply PCB that I designed. It's either the AC ripple in the DC supply, the power transformer too close to the output x-former (not much I can do there), inadequate shielding around the preamp tube (hard to imagine since it's housed inside an aluminum sleeve), any combination of the three, or something else I haven't thought of. The original McIntosh MC275 tube amp made its debut in 1961 and gave audio fans a lush, detailed and powerful soundstage still cherished by audiophiles to this day. 6CA7-Z and KT88-Z were released over 10 years ago to the market as the very first high end upgrade tubes. There are a few common mistakes that come up occasionally:. Every device has an amperage rating that indicates what current strength it can handle. The HeadAmp GS-X does both insanely well. Setting the idle current doesn´t mean the tube can´t go way too high when the amp is cranked. With such high Eg2, the Eg1 bias must be a highly negative voltage and is difficult to set correctly for PL509. This will increase the plate dissipation, unless you choose to operator the tube at a lower bias point. I like to lower the amp's Bias (and Bias X which basically "locks in" my low Bias setting). It picks an entirely different amp, the power tube type is wrong, the cab type is something way different than my cab, etc. The idea behind automatic electronic bias is a reduction of quiescent current and heat in high power radio-frequency amplifiers. The former, called V1, is a battery-powered tube amp that's switchable between triode and pentode modes, while the latter, P1, is a mains-powered solid-state amp. Since I was not sure how the 6C33C tube was going to behave, I installed meters to monitor the bias voltage which for this amp was supposed to be -80 volts. DANGER! HIGH VOLTAGE!. I am not familiar with Mystere products, nor an expert on tube hifi (although familiar with tube guitar amps which operate on the same principles) I would call the manufacturer, talk on the phone. Using a classic all-valve design with contemporary features including a Celestion Eight-15 8” speaker this amp is unmistakeably Marshall. Just pick a zener that will break. But that is for the biasing page. And for those who feel this amp is too loud, we have a very nice alternative available: the Tube-Town PX18 with tamed 18 watts, but the full Plexi sound. One normally thinks tube amps with EL84's are wimpy, but definitely not so with these gems. This happens because many amplifiers share a bias supply between more than one tube. BE A SMART CONSUMER Those products made in China might be cheaper, but the LED type meter display used a lot of power. That alone can cause premature tube failure, since one or two can become the ‘weak link’ and draw more current than the others in attempting to achieve a ‘balance. So we aim to adjust tube bias somewhere in the middle - a compromise between long life and good tone. Tubes should last 5000 hours if manufactured. Defining Implicit Bias Also known as implicit social cognition, implicit bias refers to the attitudes or stereotypes that affect our understanding, actions, and decisions in an unconscious manner. bias is high voltage, low current and impedance is high like from 5K to 3. First I was afraid I needed Rx // to the choke because the gain of a penthode is the slope ( mA/v ) multiplied by Rl, since the choke is not a linear Resistance but a. If you have the bias setting turned up too high (technically the negative bias is too low, causing your meter to read a higher number), it may let the tubes get away from you once the amp is on. If the operating current is set too high, the tube will draw excessive current, which will shorten the life of the tubes. 12AT7 power drivers. If it is biased hotter the output stage will be too hot, adding some power stage distortion, and running the tube closer to the max. According to forums and a call to a guitar technician 90% chance it was bad end-tubes. Dating Fender Tube Amps by Serial Number - Free download as PDF File (. A friend suggested this tubeI tried it. X-Tube simulates a tube amplifier saturation effect. The bias is set by putting a DC volt meter between the Imon1 terminal and ground. if would like to use low voltage like a 250V. I bias by ear on the cabinet I'm using, then check the current w/ a bias probe meter to make sure the current isn't too high. Too much bias either way can introduce unpleasant levels of distortion. We recommend setting the bias current to 45 milliamps. Until I learned to do this, I didn't realize how bad vacuum tube amps could sound if the power tubes are not getting the appropriate voltage (or how you can fry the tubes if set too high). Also, this is what many consider a pseudo-tube amp since the tube itself does very little of the amplification and is largely used a pre-amp stage for coloring/warming the sound. Since the amp is transformer coupled on the input, Class A2 operation is possible. 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. Adjustable bias is necessity in a fixed bias tube amp. It delivers a warm and rich tone via its full vacuum tube amplification. I compared the sound of EAR509 to a normal UL 50W amp with 2 x KT88 and with fewer input tubes and only17dB GNFB. Very soon the tube will die. In some amps, this can result in a burnt fuse. This voltage is also known as the ‘bias’. Dial the master volume to zero and the power up. If its within range, its ok, tone is subjective. I also have a Mojo bias meter that still works fine after 5 years. This is a typical amp of Henry quality, sorta. If you have the bias setting turned up too high (technically the negative bias is too low, causing your meter to read a higher number), it may let the tubes get away from you once the amp is on. This EL 34 loaded stereo amp runs in pure Class A 100% of the time, operates in push pull tetrode, has auto bias, and has dual volume controls. Big tube power amps that can really give 100W or so tend to be overweight, cumbersome and demanding: high-maintenance creatures that produce a lot of heat. The bias on an amplifier can be adjusted by a technician to allow more or less current to flow. All-in-all, the GAV19T is like other Chandler products - full of fat, vintage tone! CONTROLS. The ALO Studio Six is a Class-A single-ended triode circuit design with zero feedback. But 10 years later solid-state technology took over and nearly all valve amp manufacturing came to a close. If you lack experience working on tube amps, I suggest you take the amp to a guitar tube amp tech for the bias adjustment and voltage measurements. You can run the tube as high as 85% but you will wear them out quite a bit quicker. Call 800-472-6274 for expert advice. (Remember that the triode’s grid actually sees a slightly different DC voltage, as the coupling capacitor is biased through a large-valued resistor. Though the heat sinks are massive they still get to 50c and can only be touch briefly. The amp had a loud 60 hertz hum with nothing plugged in, so my first thought is the filter caps are the problem area. It really seems to tweak the "feel" of the amp the most, and not necessarily the sound, although it depends on where the voltage is at. This prevents damage to the tube when plate voltage is first applied. However, there is no easy way to adjust the bias current level without changing the fixed resistor in the circuit. The amp also features zero negative feedback, delayed warm-up circuit that extends tube life as well as a automatic power protection circuit. Bias also allows you to optimize your tube life, since running them with a hot bias will blow through power tubes faster than you can scream "High Voltage" à la Bon Scott. Ohm's Law tells us that V=I*R, so 300V/0. The EL34 versus the KT88 family, for instance. Couple that with my unique, old-school, grid-bias tremolo that pulses with that "Hypnotic Slam Effect" and you have a highly portable 14 Watt combo amp perfect for Indie, blues, country, pop, and. Another 10 years were to pass (1980s) before interest in valve amps began to re-emerge. If there is a bias control, it’s possible to set this incorrectly and you will observe this overheating problem. Newer set of KT 120 (4) tubes (about 500 hrs), with the original set included too. The use of Class AB1 mode essentially doubles our output power, compared to the KT-92 design; where the KT-92 barely achieves 2 watts before exhibiting noticeable flattening of the input waveform, the "Li'l 4x4" puts out a. This EL 34 loaded stereo amp runs in pure Class A 100% of the time, operates in push pull tetrode, has auto bias, and has dual volume controls. About a month later the amp is really blatty and farty (like crappy blocking distortion) when the master volume is turned up a little beyond bedroom. 35ma is a Generic bias setting, set your bias accordingly 10. All current production 6L6 tubes are great tubes. An electronic bias switch is more than fast enough to keep up with modern high speed RF relays. Sometimes the amp can function ok while red plating but it’s not recommended to use it. Biasing an amp requires some knowledge of tube amp circuits and experience with high voltage. 3) *Be very careful on this step (high voltages)*. They may utilize strong loaded words (wording that attempts to influence an audience by using appeal to emotion or stereotypes), publish misleading reports and omit reporting of information that may damage liberal causes. I drop it between 0 and 20%. Improper usage including using in an amp not suitable for the tube or set bias too high or too low, input power spikes etc will result in tube failure prematurely - such incidence will not be covered by tube manufacturer's warranty. Not really intended for first timer builders, but manageable for those who do their homework. Some sources in this category may. When the grid conducts it shifts the bias point and in those old amps it can shift so much that the tube goes into cutoff prematurely. Another advantage in tube amplifiers is linearity generally is a bit better with slight over-coupling. bias is high voltage, low current and impedance is high like from 5K to 3. These are the other two models rounding out my present-day sampling of Fisher's popular receivers. what you observed when set at 4 mA, the factory setting for the 12AU7. I've used the Ameritron AL-1200 linear amplifier for several years (since the end of 1997). There's a typical non-tube, high end "gritty" sound to virtually everything it does, whether through speakers or headphones. Biasing is important too. Newer set of KT 120 (4) tubes (about 500 hrs), with the original set included too. To push the amp to turbo the idle current is raised to 1. "Unconscious bias" is a. Each tube sample used for comparison was chosen because it measured in the middle range of idle plate current draw at. How to bias a tube amp with a voltage multimeter. I've gotten used amps that had the bias set way too high. I’m biasing the 6L6/6V6 tubes in a Vintage Sound Amp. I ran each tube from 250 volts to 400 volts (the max of my power supply) in 50 volt steps with several different output transformers. 50+ videos Play all Mix - Troubleshooting Your Tube Amplifier YouTube; Roy Blankenship Amp Repair Shop - 1 - Duration: 51:02. In fact, it is driving a 4" wide range speaker and a 1/2" dome tweeter in an 0. An EL34 tube has a recommended bias at around 320mv-350mv. Center tapped heater winding, 50V bias tap, copper flux bands and internal hum shield brought out to a lead for grounding (ensures the quietest amp possible). By Rob Robinette. Turn the amp off. It is about the same power and is aimed at the same budget tube amp market. Since the amp is transformer coupled on the input, Class A2 operation is possible. Setting the bias correctly will give the best sound and longest tube life. Thanks Steve. Signal input: 2 V for max power. In fact, in terms of sheer enjoyment, I can say that the Super Amp equals my Lamm ML2 monoblocks, which do sound better in all the broad and small ways but are also priced out of reach for most audiophiles. This will allow you to bias where you like it best, usually between 65% (multiplied by. This can be difficult to diagnose correctly when the amp is on the repair bench as it can take half an hour or more of testing and/or playing before this bias drift manifests itself. Watch the LED bias levels on the output tubes and after stabilization adjust them all too equal intensity = 50 ma, matching as close as possible to prevent core saturation due to current offsets. The 4-1000A is an especially low gain grounded grid tube for a given anode voltage, because it has low µ and that causes a high cathode drive impedance. Our RBX Raw Bias Auxiliary Supply Kit provides a high-voltage, low-impedance raw bias supply when such a supply is not readily available in the amp. The model is the Vintage 15 which does not require me to open the chassis to adjust the bias. If we set the bias too high, too much current flows from anode to cathode and one or more valves will start to red plate. The first filter cap on this amp is a discrete one and the other 3 in the power supply are in a mulit-cap can. 1) When using the cathode resistor method, do I need an input signal? 2) Also, I've heard that I have to add 5 or 10 mA to the bias current to make up for leakage. I use four separate windings of 4 Volt that after rectification allow me to regulate the bias of four tube-halves separately. To act quickly, and hopefully degas the tube, you would remove the high voltage on the plate, and allow the tube to heat up by applying the filament power, and let it sit and "cook" for several hours. The plate would re-absorb the little gas by "cooking" this tube as described. When we calculated the bias point for Preamp Stage 1, we knew that the grid is at V2B. Most amp issues are sinply a bad tube, so a tube swap may be our first line of defense before sending the amp off for repair. Matched tubes are tubes of the same, or close, rating. These amps are "expecting" to see tubes of a certain parameter when setting bias. These are the other two models rounding out my present-day sampling of Fisher's popular receivers. The first and foremost is not to set the bias current so high as to exceed plate dissipation at any portion of the tubes operation, as indicated by that nice warm red glow of melting plates and the sound of a cash register ringing up a new set of tubes. For Stax headphones that can accept a high bias voltage, adjust the pot for 560V. The front of amp has a high power 100watt and low power 25watt switch. Bias 2 completely resets that custom amp and uses a starting point that is much farther off. Tubes in line level components last really long, dont need re-biasing, and is a very affordable way to give the tube flavor to the sound, yet still have the best attributes of the amps that you have. Launch the software you'd like to use, click the settings icon and then "Audio Settings. The op-amp must be one that operates on 3 volts or less and must have a very high input impedance. If the bias is set too high, I assume the tube's lifespan can be greatly shortened. Most Silverface Models • Convert to a better bias adjustment circuit for improved tone and longer power tube life for your silverface Fender amp? This is included in the "blackfacing" conversion or can be done to many other amps as a separate mod. 7 amps of 6. One of two new designs birthed from a 2012 partnership with Mike Fortin, the Thrasher line is gourmet metal gear with the extreme gain. It's power-on sequence is fairly complicated. It really seems to tweak the "feel" of the amp the most, and not necessarily the sound, although it depends on where the voltage is at. I've used the Ameritron AL-1200 linear amplifier for several years (since the end of 1997). In many ways it's the normal two tube GG amp with 3-400 tubes. In other words, we raise it by twice the bias voltage for A1 or twice plus a bit for A2. Thanks! Thanks to various folks on the www. Many OEM companies set the bias way too low (cold) resulting in poor tone. Normally, two stages of preamplification would be needed to achieve this. Too cold/low and your amp will sound lifeless, too hot/high and you'll get a more out-of-control sound but the tubes will burn up a lot faster. Here is the schematic, first off. Easy to use and operate. Example: Design the DC fixed bias conditions for the simple class A common emitter amplifier shown in Fig. There, the amp loses its poke, and harmonics and overtones will most likely suffer. When measuring voltages or setting bias potentiometers inside powered tube amps observe the following safety guideline. They may utilize strong loaded words (wording that attempts to influence an audience by using appeal to emotion or stereotypes), publish misleading reports and omit reporting of information that may damage liberal causes. Vintage 47 amps come with a 30 day trial period. So we aim to adjust tube bias somewhere in the middle - a compromise between long life and good tone. Hoffman Amplifiers Tube Amp Forum, Biasing a Fender Twin Reverb ultralinear 135 By "bias voltage too high" do you mean too negative, as in its -57 at the moment as opposed to -38 or so that I should be shooting for? Biasing a Fender Twin Reverb ultralinear 135. You never know if you are straining the power supply by setting the bias too high. If you want to use them as standalone applications, please set up your audio device first. Each tube in this comparison was installed in the same custom-built, fixed-bias single-ended guitar amplifier in order to obtain the voltage gain measurements and conduct listening tests. A tube socket was replaced with new high quality QQQ Japanese one. In some cases the available bias voltage is too low and the bias supply circuit must be redesigned. Measure the resistance from grid socket pin to bias supply point in fixed bias amps or to ground in cathode biased amps and make sure that both (all) output tubes have the same nominal resistance - usually 100K to 220K. The reasons for its popularity are obvious: This was (and still is) a simply lovely-sounding amp—sweet, bloomy. The amp that ‘started it all’, the Fender Bassman was loaded with a duet of of 5881s. It delivers a warm and rich tone via its full vacuum tube amplification. the 4uF and the 20uF caps before and after are the original value. The LM386 does not need a high-level input so placing this amp/buffer before it, improves the sound quality. Another 10 years were to pass (1980s) before interest in valve amps began to re-emerge. Again, the tubes will be very HOT at this time. You should be sure that your amp's power transformer has the capacity to handle the extra current draw. I measured 345V on the plates (and 310V for Vg2) of the EL84. 35ma is a Generic bias setting, set your bias accordingly 10. There are a few common mistakes that come up occasionally: Always have speakers hooked up when checking the amp. The power transformer has three secondaries: 720V at 120mA center-tapped for the plate and screen supplies, 6. but the OPT by the look should easily handle ~40W or power, and it's also ice cold. The 6GH8A was one of the most common T. Decrease gain. It was THE voltage-regulator pass-tube. These are the most credible media sources. diodes are ice cold. Since the amp is transformer coupled on the input, Class A2 operation is possible. Some amps do this automatically, but many do not - particularly in the world of guitar amps. Not only are they expensive when compared to a standard magnetic cartridge, but they require either an impedance matching transformer or a head amp which must be inserted into the reproducing chain between the cartridge and the RIAA. This prevents damage to the tube when plate voltage is first applied. > looks like a servo tube. So we aim to adjust tube bias somewhere in the middle - a compromise between long life and good tone. With the power tubes removed, power up the amp and measure the power tube grid voltages on all the tube sockets. Set high for more tube compression. If the amp uses a fixed voltage and only one tube is glowing, you would suspect a bad bias resistor. All was left which could cause the problem was the tube. Tube EQ, you use a good tube paramteric, and you get the tube flavor, without any of the hassle of tube amps. The Dynaco Stereo 70 is an example of a very common audio amplifier with a fixed bias, class AB output stage. I save this amp as a new custom amp and then reload it and go to amp match it. Before adjusting the bias let your amp warm up for a few minutes. Panor/Dynaco's most ambitious stereo tube amplifier was the Stereo 160, a 75 wpc, all-tube stereo power amplifier with switchable pentode/triode modes, adjustable tube bias potentiometers, and 6550 output tubes. The bigger OT really opens up the amp with better lows and highs and more response. One of the biggest differences between a tube amplifier and a transistor amplifier is that an audio output transformer is almost always required in a tube amplifier (this is because the output impedance of a tube circuit is far too high to properly interface directly to a low impedance loudspeaker). Insert bias meter probes into the tube sockets of the amplifier. The 5K trimmer should be adjusted so that the eye tube display closes completely when the amp is played at maximum power. I had a spare tube which has been in my amp for years, I installed the tube in the Amp tuned it and got full output again. While the promised amp was obviously to be an RH type, when I finally decided to design it I was already over the “old” type schematics, but the relatively low anode voltage at which it would operate as compared to the relatively high bias required (i. Others have a fixed bias resisitor. Right now, 0. After that, check the bias every month or so, and adjust if necessary. DANGER! HIGH VOLTAGE!. An EL34 tube has a recommended bias at around 320mv-350mv. If the bias is set too high, the negative power supply fuse will blow without damaging the circuit. 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´. 5w/ch, late version, 35db gain from only 2 stages, high-nickel xfmrs, 8+4 Ohm, metered bias, soft-start increases life of tubes. diodes are ice cold. Bias X is a bit like Sag, except it controls change in a tube’s operating point due to change in the tube bias when the amp is driven hard. This is a single-ended triode amp that I built using the 813 transmitting pentode, connected as a triode. (As shown on the picture). There's a bias range, but you would need to find it by knowing the plate voltage of the amp and the max dissipation rate for the tube. There might be times when, say, you're going through a bunch of quality power tubes using Bias grades (numbered by re-sellers) and you find there's no point trying to decide which Bias Grade sounds best in the amp without carefully adjusting the bias for each set. Hybrid amps use both a Valve and Solid-State circuits. The tube amp that spawned a thousand successors. For those new to the hobby, before Cavalli Audio made high-end amps Alex was known for his DIY designs. > looks like a servo tube. Defining Implicit Bias Also known as implicit social cognition, implicit bias refers to the attitudes or stereotypes that affect our understanding, actions, and decisions in an unconscious manner. In most cases when replacing aged tubes with new ones, you will need to turn down bias value. The load line intersects the current axis at about 2. You just want your bias to be in the center of the max and min voltage. So, how good is the Broskie auto-bias circuit? As it stands, not too bad. If the bias is too high the stage will be completely in cut-off, giving a raw, cold, spongy distortion. If the bias is set too high, I assume the tube's lifespan can be greatly shortened. Bias should be adjusted when tubes are replaced. what you observed when set at 4 mA, the factory setting for the 12AU7. The beam tetrode type. Here's why: The amplifier tube's anode capacitance normally provides most of the tune capacitance during 10m operation. 5W 2A3 hardly needs a slew rate of 1V/us – vinyl has a maximum rate of change of half a volt per uS. If the operating point is set too high, that is if the grid bias voltage is too high, as exemplified by the blue spot and range, then saturation would occur when the signal oscillation produces a grid voltage above 0V. The clean channel rules! The Spring Reverb is all Tube power too. These are the best tubes I heard yet in my modded Glow Audio Two amplifier. The tube will distort sooner, but will have a warmer, fat distortion quality and nice harmonics. Sounds amazing. Example: Design the DC fixed bias conditions for the simple class A common emitter amplifier shown in Fig. 6550 tubes may be used in place of the EL34's, but only if the amplifier is cathode biased, under fixed bias condition the value of the 240K grid resistors is too high for a 6550 or other beam-tetrode tubes. Too much current flowing (idle too high, wears parts and wastes fuel) and the amp runs hot and burns up tubes and transformers. 2K in the hot rod deluxe which is a little too low. I will ccs load this tube with 25-30 ma at 220v plate voltage parafeed to an Edcor 10k:15k interstage driving 845. Lowering the ripple on the rectified voltage will not, however, bring a 1:1 improvement on Vout because the ripple on Vref will start to dominate. It is discontinued but seems to have retailed for US $450 (replaced with Schiit Lyr 2). If you have a 100-watt tube amp, it's probably going to make more noise than a 15-watt tube amp. I didn't include any individual tube bias or balance adjustments, so I am using matched pairs of 300B tubes. For those new to the hobby, before Cavalli Audio made high-end amps Alex was known for his DIY designs. The amp is, roughly, between 18-22 watts, Class AB and fixed bias. In this post, you will discover the Bias-Variance Trade-Off and how to use it to better understand machine learning algorithms and get b. However, that won't help when I am running without NFB, so I am looking at the 120pF cap over/between the anodes of the P. Turn the newly added bias pot until you get -51 volts with the bias switch in 6L6 mode, or -39 volts in EL34 mode. Nick's amp Wednesday, 3 August 2011. Only allow a seven minute window of adjustment. Because the gain of the 6SL7 is too high for this design. Simplicity in design and function creates the purest and most musical bass tones made available yet. Another advantage in tube amplifiers is linearity generally is a bit better with slight over-coupling. It really seems to tweak the "feel" of the amp the most, and not necessarily the sound, although it depends on where the voltage is at. All was working fine again. It ensures the tubes are fed the correct voltage according the valves resistance rating. 8) When playing the amp the bias current will jump wildly as the tubes work and you may see the meter signal “OL” which stands for “Overload”. Tube complement for this amp are: 2 matched pairs (4) of 6CA7/EL34 power output; 2 pcs. The use of fixed bias does *not* automatically make an amp operate in class B. I would aim to bias the tube at about 120V on the plate 5V of bias, and 1. Compare the amp’s power ratings with the speakers and subwoofers. amp factor 2, Ip=125 ma. It's a fairly powerful SE amp that works very well. Choose a link from the Hoffman Amplifiers parts catalog: Mobile Device. If both are too low, it's rather a low emission tube. Bias these tubes hot for best results. X-Tube simulates a tube amplifier saturation effect. Willsenton R8 is an integrated Amplifier, it is a Power Amplifier too (there is a group Power amp input), it is a Headphones amp too. If you're a serious guitarist and own several tube amps like me, you'll want to learn how to bias your amps. Different Types of Amp Bias. No struggle at all for a TO-220 mosfet. Some amps do this automatically, but many do not - particularly in the world of guitar amps. When the grid conducts it shifts the bias point and in those old amps it can shift so much that the tube goes into cutoff prematurely. At last select also your tube according the amplification class you desire. This can be difficult to diagnose correctly when the amp is on the repair bench as it can take half an hour or more of testing and/or playing before this bias drift manifests itself. (A further danger of too much bias is the transistor going into thermal runaway as it heats up. If the current demands of your load are too high, the loadline will get too steep. To get the power amp tubes to break up you have to push them pretty hard and, as a consequence, the volume will usually be too high, even in a 15 watt amp - definitely too high for the bedroom. a lot of impulses are on offer out there but they still havent quite got it. The measured plate current was 31mA for one tube, and 33mA for the other tube. This means that a matched pair of tubes with a reading of 35mA from one distributor using a high-voltage setting of 450Vdc and a bias voltage of 40Vdc could bias differently in your amp than another distributor's pair of 35mA tubes using a high-voltage setting of 425Vdc and a bias voltage of 42Vdc. I turned it off! But it made me wonder if I liked the HOT setting and that's what made the amp stand out to me. One of the biggest issues was blocking distortion which is excessive bias excursion. If your particular unit uses 6CA7 output tubes, use the 12AX7 (these will work with the EL34 as well). Post subject: Re: How to bias a 6v6gt tube amp that uses "Free DC" biasing. Amp can be used with a 5AR4/GZ34 tube rectifier or solid state diode plug-in unit (sold separately), or just wire some diodes to the socket. Overall, we rate Reuters Least Biased based on objective reporting and Very High for factual reporting due to. Resistively derived bias supplies can have this range, but will lack the current needed for a bias regulator. Supervised machine learning algorithms can best be understood through the lens of the bias-variance trade-off. If the current demands of your load are too high, the loadline will get too steep. The most obvious approach is to use an input follower as seen in Figure 1. 2 Integrated SET, 12. 4A (4/10th Amp or 400mA) TO 0. Select cathode resistors that would yield about 1. If you're a serious guitarist and own several tube amps like me, you'll want to learn how to bias your amps. must be use high current for plate. (In other words, rotate the bias trimmer until you obtain the highest negative voltage that the bias supply is capable of delivering. 6L6GC Comparison of Current Made Tubes. It's a fairly powerful SE amp that works very well. This is a semi-integrated amplifier with two or three line-level inputs, an input selector and a volume control with loads of gain; you don't need a separate control amplifier or preamplifier unless you need more inputs (use a selector) or are stuck in the 1950s and need tape head or raw phono. As requested. For the 6922 types, the current was set for 5 mA and for the 12AU7, 4 mA. FENDER AMP MODIFICATIONS. Ringing in at 80 Watts of glorious tube power, our TTHP delivers the famous tones. With the Tesla tubes that came in it, the amp was biased too cold. Tubes that are biased too cold may not. All this pertains to my Hughes and Kettner Tube 50 combo. Turn the amp off. 65) or even as high as 80% (multiplied by. Dynaco ST-70 Sold as diy kits or factory-assembled, this very affordable, highly-tweakable, 35Wpc, EL34-based stereo tube amp from David Hafler is the best-selling audio component of all time with over 300,000 manufactured. Front driver tube will 76 ccs loaded and cap or direct coupled to 6AH4GT. I am not familiar with Mystere products, nor an expert on tube hifi (although familiar with tube guitar amps which operate on the same principles) I would call the manufacturer, talk on the phone. While I was still in high school, a friend of mine came into possession of a Leak Stereo 50 tube power amp, with a matching ‘Point One’ pre-amp, from the late 50’s. Tube Bias Knowledgebase. Making those impedances equal makes the offset voltage at each input equal, and so the non-zero bias currents will have no impact on the difference between the two inputs. Just right and it's a harmonic pleasure dome. You mount the back panel on the amp and fire it up again. I measured the power and distortion in triode and UL mode. Set the voltmeter to volts DC or millivolts DC (0. The cable has been replaced with a new run of LMR-400 with new N-connectors (loss=0. If we set the bias too high, too much current flows from anode to cathode and one or more valves will start to red plate. This is not normally a good practice as obviously the pots can then turn the bias off completely to the said tube(s), but…. If the bias is set too low (often referred to as running cold) the amp can sound thinner and less dynamic, and generally won't be performing at its best. Too high and the valve gets all embarrassed and glows red. If you have a poorly implemented power supply, it can add a little AC ripple to what you're hearing. I changed R52 with a 100k variable resistor (I think a 50k would have done the job, but I had a 100k in my spare box …) EL84 max Pa is 12W. 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. One of these should calm things down a bit. The design differs from most tube amps in that it uses high quality toroidal transformers for the. Best meter I've ever used. A great advantage of the relatively simple circuits and generally high quality construction used in many tube amps is the. Amplifier Bias. ) At the other extreme, reducing RB1 may limit the maximum output swing. Set high for more tube compression. The specs on this tube are very similar to the 25-watt originals. Atarashi originally built this amplifier as the fixed bias EL34 Class B Push-Pull monaural amplifier featured on the January 2003 Issue of the "High-Fidelity Audio: Radio Technology". If the problem follows the tubes to the other side indicates probable bad tube. It would be interesting to see what you think of the sound when set at 5 mA vs. Amp Repair and Modification. Call 800-472-6274 for expert advice. The amp sounded killer when I got it, then for safety, I checked the bias one tube at. They are perfect for what I need out of my Diezel VH4. 5W Class A • Single-Ended • 6V6/6L6 Tube Rectification • Pure Tone Goodness This is the amp that started it all. 2A3 was used before, but it has a fairly high plate drop for a given current. With the 50 watt and above valve amps, you would have to be playing a stadium before you could push the power amp tubes to distortion. I set the amp to 35. C1 = 1/(2 * PI * 0. While the promised amp was obviously to be an RH type, when I finally decided to design it I was already over the “old” type schematics, but the relatively low anode voltage at which it would operate as compared to the relatively high bias required (i. Another thing to look at are the plate load resistors. I tried, "Tube Bias". But 10 years later solid-state technology took over and nearly all valve amp manufacturing came to a close. If your amplifier has bias tremolo you need to sample the tremolo after you adjust the bias. My current amp that runs 6V6's I think is biased upward of 75% to 80% of design center max plate dissipation. The clean channel rules! The Spring Reverb is all Tube power too. These usually result in an un-maintainable amp, or causes unexpected/degraded behavior, or even “It’s dead, Jim” syndrome. The bass was more powerful and detailed. But over years, the factory’s lack of quality screening has flooded market with mixed quality. Even though tube amps are relatively easy to bias (a small flat head screwdriver and voltmeter are really all that's needed), manufacturers nowadays can insist you send them the amp for biasing. One normally thinks tube amps with EL84's are wimpy, but definitely not so with these gems. There are two gain (volume) controls each with a 3-way bright switch which is found below the gain controls. Bias that is set too low can make the amp sound thin or veiled, while running the bias too high may shorten the life of your tubes, and in some cases may damage the tube or the amp. If not set properly, the performance (tone) of your amp will suffer. In this post, you will discover the Bias-Variance Trade-Off and how to use it to better understand machine learning algorithms and get b. Use the provided screw driver in the slot and adjust up. If you have not been trained to work with high voltage then have an amp technician adjust the amp's bias. THE CHAMP CBA-20807 1000 Watt AMPLIFIER APRIL 2009 - PART 1 THE BEAST!! Hi Peoples. Setting a higher % of max dissipation will make the bias 'hotter. Here a small N channel Mosfet is biased up to served as a Source follower, presenting a very high input impedance, and a fairly low output impedance while. Tube Screamer Analysis. This parameter is highly reactive with the Drive and Master settings. The bias is adjusted when the amp is not playing (no signal), and the idle is adjusted when the car is not moving (no motion). I didn't include any individual tube bias or balance adjustments, so I am using matched pairs of 300B tubes. When using the terms cathode or fixed bias we are discussing the power tubes of an amp (pre-amp tubes are nearly always cathode bias or grid-leak biased but that is a discussion for another time). Due to the dangerous high voltages encountered in tube amplifiers in addition to the knowledge. In some cases the available bias voltage is too low and the bias supply circuit must be redesigned. The tone and attack in tube amps are unique, one amp will never capture everything. I compared the sound of EAR509 to a normal UL 50W amp with 2 x KT88 and with fewer input tubes and only17dB GNFB. Until now, there have been two ways to bias tubes "Cathode Bias" is commonly used, cheap to make, and often found in guitar amps. If the bias current is too low, the tube is said to be running "cold" and is not dissipating much power. So their fathers will buy amps too!. The biasing circuit in the stock AA-270 amp sends a differential bias voltage from that pot to each power tube in order to "balance" the idle current of the tube as a set. Major overhaul: A classic old Fender, Marshall, Vox, London City (etc. The measured plate voltage was 456VDC. It's rather like revving the engine to 8k R. It outputs nominally -72V for each pair of tubes. Positive Grid is proud to announce the release of BIAS FX 2, the next generation of its acclaimed BIAS FX guitar amp and effects software. Enjoy our 45-day return policy. A DC bias is required so that the amplifier can amplify the input signal over its entire cycle with the bias “Q-point” set as near to the middle of the load line as possible. You can also use off-board reservoir capacitors and/or chokes. Although designed for the AM avaiation band just over the FM broadcast band, superregens can slope-detect broadband FM and the circuit could be easily "slid down" to 100 MHz by adding another turn to the coil. The bias needs to be adjusted whenever the fixed-bias pair of 6V6s (inner pair of power tubes) are changed. Ringing in at 80 Watts of glorious tube power, our TTHP delivers the famous tones. "Unconscious bias" is a. There are only two things to worry about in biasing a guitar amp. Setting the bias correctly will give the best sound and longest tube life. Just pick a zener that will break. Setting the idle current doesn´t mean the tube can´t go way too high when the amp is cranked. Biasing to a high voltage and low. I also have a Mojo bias meter that still works fine after 5 years. 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. When the lamp is not lit (neither green nor red) it means that the bias setting is correct and is in the range of 74 to 87 millivolts, (measured across each 2 ohm output tube current sensing resistor - R20, 21, 120, or 121). Some amplifiers don't have a bias-adjusting control (pot) but instead use a fixed resistor to set the voltage. After about a year a friend convinced me to experiment with fixed bias. For a transistor, the collector impedance is considered theoretically too high to bother, and the emitter resistance too low to care. This VST plugin can be used in Microsoft Windows 32/64bit (XP SP2 or later, Windows 7) OS with any VST DAW. if would like to use low voltage like a 250V. Amp can be used with a 5AR4/GZ34 tube rectifier or solid state diode plug-in unit (sold separately), or just wire some diodes to the socket. At last select also your tube according the amplification class you desire. Extending the bandwidth too high increases its susceptibility to RF interference. Massdrop worked with Alex Cavalli to resuscitate a classic design from the Cavalli portfolio. If the amp fails to power up entirely, the problem is located in the power section of the amp. "Unlike many tube headphone amps that exhibit the rolled off high frequencies and bottom end that a seeming majority of electrical engineers think is the “tube” sound, the Schiit Lyr 3 produces a true audiophile sound with extreme linearity in both the low bass extending into the subsonic and the upper registers, while retaining the.