EL84 Power Tubes provide 12W of Power in Class A mode. In the context of something like a bass preamplifier, for example, one would want a "clean" channel, perhaps with some heavy compression, in order to have a consistent signal (especially in the lower registers), as well as a "dirty" channel, with a high-passed signal having some distortion. External Bias Adjustment Take all the hassle out of replacing output valves with the Sheriff 44's external bias measurement points and adjustment. Introduction. All of the custom amplifiers you create with BIAS AMP 2 are automatically available in your BIAS FX, providing a foundation for your ideal finished tone. The Kingsley Barbican is a single channel fixed bias class AB hand wired tube amplifier, inspired by classic American designs. THIS IS NOT A COMMON PUSH-PULL! - very low feedback only 16dB - low distortion near to 0. Komet Amplification collaborated with Trainwreck Circuits designer Ken Fischer to build several amplifiers that Ken designed. Speaker- Celestion G12H30 8 Ohms. Changing the small preamp/driver tubes (like 12AX7, 12AT7, 6DJ8,etc) in your amp or preamp does not require making bias adjustments,only changing the power tubes (ones that drive the speakerlike 6L6, EL34, 6550, KT88). Use only recommended types (12AX7 and 12AU7). What's the best way to bias new power tubes in my amp? If you are new to biasing… carefully read and follow the manufacturers instructions. 5V I think you'll have issues. With brand new tubes, this should be done every two weeks for the first month, until they get burned in. diytubes) submitted 2 years ago by frosty1 So, I'm working on step 1 of my plan outlined here to improve the sound of my Blackheart Killer Ant amplifier (2 x 12ax7 tubes, 1/4W, Class A) by replacing the 12ax7 "power" tube (V2) with a 12au7 for more clean headroom. We make the setting under no-signal conditions. Deep, full, creamy Blues tone set. That said, some folks like hot or cold biasing, others like the opposite. Excellent: Raytheon 12AX7. 5751 I have a Cary V12 with 12BZ7 tubes in the input. It is used in the Push-Pull Phase inverter circuit so both sides of the phase inverter have EXACTLY the same gain. I have a Micro Cube that works great except for one odd problem. This 12AX7 based EQ / overdrive circuit is designed for the Hammond tone wheel console organs that have valve preamplifiers such as the B2, C2 , RT2 , B3 , C3 , RT3 , A100 series , D150 series etc. However there is a broad class of "good audio amplifiers". The 12AX7 double triode is connected as a differential amplifier (long-tailed pair). For phonostages, linestages & driver stages using ground cathode topologies, replacing cathode bias resistors will be much less complicted than O/P power stages. SUBSCRIPTS FOR MULTI-UNIT TUBES: b = Beam Power Unit. A full size Accutronics spring tank is transformer coupled to a USA manufacture 12AT7 for superior reverb performance. So I thought I would have a look at the bias, as some articles suggested this may help with the ice pick highs. Class AB operation eliminates this distortion by applying the correct bias so each active element will will share part of the output signal in the crossover region. (The 12AX7 has all the same less the shield, except the Chinese put in a shield without connecting it to anything, so you decide if that makes it a 12AX8. Price: $1,979. The eq knobs have push pull knobs to add options to shape the eq and it has reverb. This dual-channel, EL34-powered amp is all about classic British overdrive sounds. For compression problems, check the tube at the 6AQ5 marking, and the tube at the 12AX7 marking on the center-left side of the unit. (In our case, excursions of Source Voltage Vs run a little above ground. External Locking Bias Trimmer and Test Points on back panel. The same amp in fixed bias would be about 40 Watts. The 12AU7 makes a less ideal swap for the 12AX7 because other factors such as Bias come into play and the mismatch can cause the tube to sound unpredictable and very quiet. You may find the Telefunkens a bit bright True Telefunkens have a Diamond pattern molded in the bottom between the pins. I just ordered a set of Ruby 6L6GCs for a '65 bandmaster from the, will see how they are. Transformadores de Força. M180 Monoblock Amplifiers Power, Grace, and Precision -- when you are ready for the ultimate in vacuum tube amplification, look no further than the Rogue Audio M-180 monoblocks. You can check. You might be better off sticking with a 5751 if you want less gain than a 12AX7. I do believe that biasing the amp is very easy besides the pain of getting to the adjustment. Choix des lampe de preampli 12AX7, 5751, 12AY7. This valve featured superb linearity, balanced sections, and extremely low noise. This is achieved by choosing a plate resistor of twice the internal plate resistance of the tube, which for a 12AX7 is approximately 50k requiring a plate resistor of 100k, then choosing a bias resistor so that plate voltage is 2/3 of B+. They have their greatest effect early in the preamp and less down the line. Set it higher, more electrons, more heat, til heat gets too much and the tube burns up. However once. Please check with Sales Staff if you do not see what you are looking for on website. It was common in early radio receivers when valves had directly heated cathodes (filaments), so cathode biasing couldn't be used. Try out various tubes (especially NOS) to find a tonality that suits your taste. This is in Parallel with 68K resistor that is in series with the bias pot, 5K and that is also in series with a 10K resistor that goes to ground. This is a great practice amp for guitar, and it is pure Chicago blues with a harmonica. The pumps that are used to evacuate tubes can typically get down to about 10-7 mm of mercury, or about 10-10 of atmospheric pressure. Modern amps are described as "auto biasing" but are they? Do they have a bias monitor that adjusts for tube bias changes?. Some amps do this automatically, but many do not - particularly in the world of guitar amps. Another tube that works well for this purpose is the Electro-Harmonix 12AY7EH/6072A. This is the "milspec" version of the 12AX7, but is also slightly different. The fixed bias technique requires a separate power supply that provides the wanted negative voltage. In this way the grid voltage is negative with respect to the cathode voltage. Can someone give a brief description of what to expect sonically when biasing tubes as hot as recommended and as cold as recommended? I've been told it is unsafe to bias too hot, is there any danger in biasing too cold. We make the setting under no-signal conditions. the Fisher 800C considered by many to be one of the best receivers ever made available. Eurotubes is a webpage for musicians by musicians. (example: 17. 4% - good damping factor near to transistorr amp. Most modern tube amps use a 12AX7 for pre-amplification, however, you can swap it for a variety of preamp tubes without the need for re-biasing for amp. The driver stage uses a high-gain 12AX7/ECC83 dual triode that operates as a grounded cathode amplifier. If your amp's bias is adjustable, it's a good idea to have the bias setting checked when replacing power tubes. 12AU7 will be in between 12AT7 and 12AU7. Tube manual data on the 12AX7 gives Amplification factor = 100 and plate resistance = 80 k ohms. First, determine if an amp is fixed bias (not adjustable) or cathode bias. It also uses pairs of 12AX7 preamp tubes and 12AT7 "driver" tubes. There are numerous output tube substitutions that will work in the Express, though the bias may have to be adjusted for best performance. M180 Monoblock Amplifiers Power, Grace, and Precision -- when you are ready for the ultimate in vacuum tube amplification, look no further than the Rogue Audio M-180 monoblocks. One of the most common recommendations is a JAN Philips 5751 in V1, and I can certainly see why, it sounded great. I ran across several articles about biasing tubes and swapping out the (V1 )12ax7 with a 12at7 to help with the volume. For reasonable tubes, for reasonable supply voltages, not using any obviously goofy values, Z(out) is 0. the Fisher 800C considered by many to be one of the best receivers ever made available. The LA-2A requires biasing if the V5 tube needs to be replaced. The heart of the matter - AST Head II Chassis with all tube circuitry - Click above for FULL view. 12AX7 6V6 Fig 2. In particular, I can't understand how the LM334 can switch on, where does it find the required voltage to sw. 12AX7 tubes. Introduction. Different Types of Amp Bias. tube #two[0] I tried different tubes. The 6DJ8 has to cathodes, two grids, two plates, one heater and one internal shield, for a total of eight elements. Likewise, the preamp section will accept 12AX7, 12AU7, 12AY7, 12AT7 and 5751 tubes which allows a variety of tone options with a simple tube change. In comparison, the 12AX7 would be 62. 4 Nos Nib Tube's Matched Set El84 6bq5 12ax7 7025 Ecc83 Vintage Sylvania New. If you have not been trained to work with high voltage then have an amp technician adjust the amp's bias. The 260 is a two channel amp, each channel using a 12AX7 gain stage followed by "volume", "treble", and "bass" controls in a Baxandall arrangement. OK to eliminate cathode bias resistor? (1/2) > >> Hi, I'm trying to fix up an old Heathkit Twoer. (4) To force the bias-point, the correct self-biasing cathode resistor is chosen, or better, several tubes are set up in a rig, and the resistor is selected by experiment to put the bias-point in the best compromise position between the acceptable range of tube samples. Analyzing Amplifier Stages. The distinctions have evaporated and some tubes with several names are all the same tube now. In the two years since the Fetzer Valve was first published in the midst of our adaptation of tube amps for use as distortion pedals, the circuit has enjoyed popularity as a standalone booster and as a building block in larger circuits. hx = Hexode Unit. Originally Posted by Ferbose I have a Cayin HA-1A and which uses 12AX7, 12AU7 and two EL84. The preamp is typically implemeted with 12AX7 triode devices. The differences in tube and MOSFET biasing make this configuration not work. The gain of a 12AX7 is 5 times higher and the bias is different too. I have a Micro Cube that works great except for one odd problem. 12BZ7/12AX7 vs. Driver tubes are cathode biased with a 1. Tune up your tube amplifier. From the plate, the signal is now strong enough to drive the voltage doubling rectifier. In simplest terms, this bias voltage starts the flow of electrons from the cathode to the plate, providing amplification. Tube Bias Settings. Far Corners finds Hot Treasures: Svecheniye 12AX7 Vacuum Tubes Posted on August 21, 2016 by Modest I. When you install new tubes in a fixed bias amp, you need to make sure that the amp is biased right. External Locking Bias Trimmer and Test Points on back panel. This is true in some cases but not in all cases. There is a 100uF cap going to ground. Tune up your tube amplifier. If the bias is wrong for the tube, you simply will shift the center point of the curve, so you could get a non-linear output. Most tube guitar amps employ this tube and the remaining tube manufacturers all produce a 12AX7 model. I started replacing electrolytic capacitors and noticed a big drop in the hum when I replaced the 25 uf cathode bypass electrolytic on the 12AX7 audio amplifier. ” Lately, however, the smaller Princeton has finagled its way into that position. It has quite a few names. But pre-amplifier manufacturers assume that any tube of the correct type (12ax7, 6922, whatever the designer has decided to use) will allow the unit to run at a voltage and a current that are “close enough” to what the designer intended. Note for users who only want a deeper knowledge : In the 60’s already appeared some auto-bias (using a resistor and capacitor below the cathode). The Acoustic Guitar Forum > General Acoustic Guitar and Amplification Discussion > Electric Guitars: Looking for a good (low price) practice amp. PRE ANALYSIS / DESIGN A. It also uses pairs of 12AX7 preamp tubes and 12AT7 "driver" tubes. They did this by using a shorter plate structure (with the grid pitch and distances adjusted to keep the same electrical specs) which allowed stiffer cathodes and grids. It is used in 99% of all guitar amplifiers. Current Production 12AX7 Tubes Click on this image for a larger image I have been promising a current test of some of the current production 12AX7 / ECC83 offerings and have just completed my testing. Anyone for class C?, otherwise known as fuzztone?:D Or you may require the absolute maximum p-p signal swing before clipping. Now there is an exception, the 5751 was designed to have a mu of 70, and a plate resistance identical to a AX, the 5751 tube was specifically designed to be a lower-gain, plug-in replacement for the 12AX7. pin # Electrode name. 12AX7 tubes. Vox AC-100 MkII "Fixed Bias" Amp Head, Black Control Panel - 1968 Cabinet Serial #1948 - Chassis Serial # 1858 - A Look Under the Hood. If cathode bias signifies anything then it's a lower-power amplifier and the typical guitar amp transition from cathode to fixed bias was the 40W to 60W step. Get a bias meter and learn how to bias. The bias is set at the factory on these amps to run their particular type of power tube so generally speaking. Because the VickyVerb is a single ended, single power tube design, there’s never a requirement for “matched” tubes, making the use of NOS tube types attractive and affordable. Also this is a general statement. With new production tubes al this means nothing. The distribution of current is called “bias. Les meilleures offres pour 12AX7B préampli Electron Tube à vide 9 broches double Triode 12AX7 ECC83 M6Z8 sont sur eBay Comparez les prix et les spécificités des produits neufs et d'occasion Pleins d'articles en livraison gratuite!. No re-biasing is ever necessary. Vox AC-100 MkII "Fixed Bias" Amp Head, Black Control Panel - 1968 Cabinet Serial #1948 - Chassis Serial # 1858 - A Look Under the Hood. Initial impressions on the Treasure 12ax7-LS in the critical phono preamp application are positive (George Wright's WPP200C, 2 x 12ax7 per channel, 60db gain MC). The 5751 Windmills and the 12AX7 black plates whether they Raytheon or RCA,along with the 12AX7 smooth plate Telefunkens are the best sounding 12AX7s ever made IMHO. If the bias is wrong for the tube, you simply will shift the center point of the curve, so you could get a non-linear output. The pumps that are used to evacuate tubes can typically get down to about 10-7 mm of mercury, or about 10-10 of atmospheric pressure. The tubes are thoroughly screened, and power tubes are matched closely to extract the most classic Fender sound out of your amp. The good news, is that once this is done, you should be able to replace your power tubes with Groove Tubes of the same type and rating without bias adjustment. all tubes are 16yrs old. Harp (harmonica) players may get a kick out of using a 12DW7 , also known as an ECC832 , in V3. 12AX7A: This version can be used in series or parallel filament circuits. Tube Biasing One of the key factors which affects the tone of your amplifier and its long-term health is something called the bias setting. EL84s have a tight and focused sound, and most converters will produce a substantial maximum power reduction making it easier to find that sweet. If you have any other 12AX7 in your possession then I would suggest swapping those out one at a time to determine if that is the source of your problems. Today, it is by far the most common preamp tube used for electric guitar amplification and there is an almost overwhelming supply of current production options to choose from. All the EL84 cathodes are tied together. You will hear the big improvements here. Can I use these 12AX7's from Mesa and directly replace the ECC83 in the Marshall, I read on the web they are the same and the preamp tubes don't need to be matched. A 12AX7 triode will bias with the cathode about 1V more positive than the preceding plate; a big MOSFET like an IRF820 will bias with the source about 2V more negative than the preceding plate - the 3V difference is utterly inconsequential. (In our case, excursions of Source Voltage Vs run a little above ground. I switched test leads still the same. I keep seeing 15-25mv mentioned; is this for solid state phase inverter version? The tech paper lists. Unlike most standard variable-bias designs, which use the bias of a single tube for compression, Iron uses a dual circuit topology. My problem is as follows: With twin bias probes (precision 1 ohm resistor reading current through pin 8 of power tubes )I do not get close to balanced idle currents. If a 12ax7 acts as a power tube, a fixed bias would give more headroom and we could use a 12au7 to get more headroom out of it, in order to use it as the 1 st preamp tube, taking advantage of it's particular tone. diytubes) submitted 2 years ago by frosty1 So, I'm working on step 1 of my plan outlined here to improve the sound of my Blackheart Killer Ant amplifier (2 x 12ax7 tubes, 1/4W, Class A) by replacing the 12ax7 "power" tube (V2) with a 12au7 for more clean headroom. pin # Electrode name. The Pro reverb has a smaller OT than other 6L6 BF/SF amps like Super Reverb and Vibroverb. The 12AU7 makes a less ideal swap for the 12AX7 because other factors such as Bias come into play and the mismatch can cause the tube to sound unpredictable and very quiet. Stock tube in the cathode follower position is best. 1 Fixed bias; 3. Different Types of Amp Bias. Both tubes are darker than the stock 12AX7. The pair of 6V6GT power tubes remained the same, although the bias structure was changed from cathode to fixed biasing, bringing the output power up to around 20 watts. I used EL84 power vacuum tubes and 12AX7 vacuum tubes as input and phase split. Price: $1,979. The reissue Genalex Gold Lion ECC83/B759 features gold plated pins and has been carefully engineered to recreate all of the attributes of the original. Bias the amp after it's warmed up and follow their directions. The Acoustic Guitar Forum > General Acoustic Guitar and Amplification Discussion > Electric Guitars: Looking for a good (low price) practice amp. A “Class A Amplifier” operation is one where the transistors Base terminal is biased in such a way as to forward bias the Base-emitter junction. There is a 100uF cap going to ground. I do believe that biasing the amp is very easy besides the pain of getting to the adjustment. I personally would not push it beyond 40 millivolts. AMPLIFIER CLASSES OF OPERATION. Just remember to respect Yaqin's power tubes' bias limits. > How to calculate tube ( valve ) ouput impedance Whatever you want it to be. Butler used an op amp stage to create the overdrive/distortion, which was followed by a 12AX7 pre amp tube stage to filter the sound. If you have any other 12AX7 in your possession then I would suggest swapping those out one at a time to determine if that is the source of your problems. Red Amp Series All our Red Amps have an “American sound” with 6L6/6V6 power tubes, some negative feedback, and fixed bias supplies. BTW, there is no specified maximum for 12AX7 grid resistance. The ECC83 MG is a "Mid Gain" 12AX7 type tube. Differentes lampes pour plus de basse, plus de gain, plus de précision. It's data from JJ803S [ 12AX7 equivalent ] - data from a sampling of remaining old stock Mullards will also have variation. This 12AX7 based EQ / overdrive circuit is designed for the Hammond tone wheel console organs that have valve preamplifiers such as the B2, C2 , RT2 , B3 , C3 , RT3 , A100 series , D150 series etc. Its MU of 70 puts it closer to a 5751. The asymmetric clipping will give a different distortion characteristic. Remove one power tube for 2-watts output. Grid of 2: under fixed bias, Mohm, not more. The result is that the transistor is always operating halfway between its cut-off and saturation regions, thereby allowing the transistor amplifier to accurately reproduce the positive and negative halves of any AC input signal superimposed upon this DC biasing voltage. 1uf 22k feedback on off note 4 3. The Pro reverb has a smaller OT than other 6L6 BF/SF amps like Super Reverb and Vibroverb. The U45B's I've seen have two 12AX7's for preamps, while the U60's have had either two or one 12AX7. RCA engineers developed it around 1946 and released it for sale as the 12AX7 shortly after. Get a bias meter and learn how to bias. For your Fender Twin to sound and perform at its best, the tubes must all draw an equal amount of current. Biasing an amp requires some knowledge of tube amp circuits and experience with high voltage. INTRODUCTION. Biasing This is a standard cathode-biased Class A setup. Loud enough for almost any venue, the EL34 driven 40-watt all-tube design makes the IronHorse a true tone monster that delivers maximum versatility at club and concert volume. Features (2) 12AX7's, (1) 5AR4 rectifier, and (2) OD3 Regulator tubes. Set it higher, more electrons, more heat, til heat gets too much and the tube burns up. Example: a cathode bias Tweed Bassman type amp with two 6L6’s would be about 25 Watts. guitarman on Ted Weber's Amp Board 10/8/2003 Part 1 External Modifications Tube Replacement, Bias, Speaker Replacement I just finished modifying a Fender 65' Deluxe Reverb reissue amp, and had promised to share the details. Power Output: 8 watts max into 8 or 16 ohm load. The JJ Electronic 12AX7 / ECC83 has quickly become a modern classic in preamp tubes. Best new production tubes for this socket are Electro Harmonix , JJ ECC803S , Sovtek 12AX7LPS. Get the guaranteed best price on Tube Guitar Amplifier Heads like the Bugera T5 5W Tube Guitar Amplifier Head at Musician's Friend. For your Fender Twin to sound and perform at its best, the tubes must all draw an equal amount of current. - no electrolytic capacitors started on March 10 st, 2012. The Input Network The input to the amplifier uses a resistive gamma network. Biasing a guitar amp 12AX7 - does it even matter? Well, of course it matters. Each will give reduced gain and a different tone. The Acoustic Guitar Forum > General Acoustic Guitar and Amplification Discussion > Electric Guitars: Looking for a good (low price) practice amp. Most modern tube amps use a 12AX7 for pre-amplification, however, you can swap it for a variety of preamp tubes without the need for re-biasing for amp. Large red amp: ZR50LV. Has more gain than a 12AT7 and is closer to the 12AX7 characteristic just lower gain. Victoria Vicky Verb The new Victoria "VickyVerb" combines the elegant simplicity of the narrow panel Champ style amp with the lush all tube reverb that Victoria is known for. Due to the protective bias scheme in the Valiant, I have come up with a compromise usubf part fixed bias and part grid leak bias. One of Magnatone's preimum amplifiers of the late 1950's (the only thing bigger was the 280). It is used in 99% of all guitar amplifiers. With 12AX7, the plate resistance = 70k, tube gain = 100. Cathode bias / Negative bias Placing a resistor in series with the Cathode to bias a valve is described as "Cathode bias". Original metal case. Re-Bias Pre-amp tubes? Quick question If I where to replace my 12AX7 preamp tube in my V1 position with a 12AT7 tube do I have to have someone re-bias them, or is that only for power tubes? Share Quote. Suggest a 12AX7 with high gain and reasonable quality, though very low noise or hum is not required. In other words if your amp is designed for a 7025 you can't go down to a 12AX7. The book said set the 12ax7 up for low bias (0. 3 VAC 340 VAC 340 VAC 4 8 2 6 7 2 V2 4 9 5 V3 V4 Line voltage is 120 VAC 7 4 2 9 5 V1 4 9 5 V5 V6 SS-5R4 2 1 3 2 AMP SLO BLO POWER LINE NEUTRAL GROUND Fisher 610 PT # T-686-115A E-50V 100Ω 100Ω 220K 5 VAC. I want to try more options at the 12AU7 position. 6V supply or in parallel from a 6. Groove Tubes used to sell that tube as the 12AX7R3. Now there is an exception, the 5751 was designed to have a mu of 70, and a plate resistance identical to a AX, the 5751 tube was specifically designed to be a lower-gain, plug-in replacement for the 12AX7. Butler used an op amp stage to create the overdrive/distortion, which was followed by a 12AX7 pre amp tube stage to filter the sound. The ECC83 / 12AX7 has a '9A' pinout, which has three connections to the two heaters. 12AX7 6V6 Fig 2. Using these value in the above formula, the calculated gain is 51. Tube # 2 Plate 526 Bias 0. The balanced tone of the JJ 12AX7 works well in any amp. Instead, the 12AX7 input differential pair provides implicit phase inversion by having the input applied to one side and the negative feedback applied to the other side of its input. The U45B’s I’ve seen have two 12AX7’s for preamps, while the U60’s have had either two or one 12AX7. Some amps are self-biasing. Large red amp: ZR50LV. It's catching on somewhat as of late and like Steve said,try it and let us know. Your amp has cathode bias. 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. Butler used an op amp stage to create the overdrive/distortion, which was followed by a 12AX7 pre amp tube stage to filter the sound. The eq knobs have push pull knobs to add options to shape the eq and it has reverb. It was common in early radio receivers when valves had directly heated cathodes (filaments), so cathode biasing couldn't be used. The 5751 Windmills and the 12AX7 black plates whether they Raytheon or RCA,along with the 12AX7 smooth plate Telefunkens are the best sounding 12AX7s ever made IMHO. Anyway , the Twinaxioms are a little screechy with the tone controls flat , and " loudness contour " switched off , that is , with the stock compliment of valves installed - Phonostage - 1x 12ax7 per channel. Now there is an exception, the 5751 was designed to have a mu of 70, and a plate resistance identical to a AX, the 5751 tube was specifically designed to be a lower-gain, plug-in replacement for the 12AX7. A full size Accutronics spring tank is transformer coupled to a USA manufacture 12AT7 for superior reverb performance. It also uses pairs of 12AX7 preamp tubes and 12AT7 "driver" tubes. With-out negative feedback, this type of cir-cuit has very high gain (around 80) and distortion, and high output impedance. Tremolo doesn't work Replace the fifth tube from the right (forth on a Princeton, second on a Vibro-Champ, third on a non reverb amp) looking from the back (12AX7). With 180 Watts of pure tube power, these monoblocks stunningly accomplish the impossible. For your Fender Twin to sound and perform at its best, the tubes must all draw an equal amount of current. 12AX7 Svetlana. Balancing this was a slightly more harmonically rich tone, with a lot of chimey Vox clean, although it quickly gets into ice-pick territory when you start to attack the strings (more so than any of the other tubes I tried). Based on the statement that the distortion is increased with a cathode bias would a grid bias give less distortion and no. 022uf 15k 9 b 1k/5w 1Ω bias bias com rk 150/5w ck 250uf 1Ω bias mode f cathode fixed 5k lin presence 0. Tube Driver / Real Tube Overdrive (BK Butler / Chandler) - The original, classic 4 knob Tube Driver, made from 1985 to 1987, with the iconic case color and graphics. I'm trying to get a good circuit using a 12ax7 to work as a distortion/overdrive, ive just done a basic circuit to get it woking but the problem i have at the moment is that it is sounding like a really badly biased jfet. hp = Heptode Unit. The fixed bias technique requires a separate power supply that provides the wanted negative voltage. The new model of the Blackbird tube preamp is fitted with a ‘PRESENCE’ toggle switch on the rear panel. The LA-2A requires biasing if the V5 tube needs to be replaced. The fixed bias supply in serial AC-100 #C2290 was unlike that installed in prior AC-100 amps. The Pro reverb has a smaller OT than other 6L6 BF/SF amps like Super Reverb and Vibroverb. The grid bias is now a combination of grid leak and fixed bias. The higher I turned the volume knob, the higher the bias climbed. Start by replacing the 12AX7 tube. 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. When I test the output tubes they match for bias and transconductance. BTW, there is no specified maximum for 12AX7 grid resistance. The elegant understated appearance works well with virtually any system and the small form factor makes the Fusion 1102 a great bookshelf amp. Bias NFB Output Stage. While they are the same pinout, the tubes are very different with regards to internal plate resistance, bias current, gain, etc. I've been offered some Raytheon 5755 tubes which I've been told are excellent sounding, at a ridiculous price,too low to tell, but this tube has a different pin out than standard 12AX7 so it would need a pin out socket converter or make a modification of the sockets pin out on my Phono preamp, and that's something I'm not definetely doing. An entire chapter is devoted to sculpting the dynamics of overdrive and harmonic distortion. If you have any other 12AX7 in your possession then I would suggest swapping those out one at a time to determine if that is the source of your problems. Fisher 800C Receiver Today were featuring a very special tube receiver. They are straightforward (follow the cable unhook recs). A few years ago I built a Tube guitar amp / pedal / preamp with a 12ax7 tube (and some other pin compatible tubes). Don't know what tubes sound good (pre/post), how to bias. 12AX7 as phase inverer tube will give the most effect out of this mod. The preamp tube complement was changed to a trio of 12AX7 tubes, and the rectifier was changed to the more efficient GZ34 tube. The output impedance of the 1st gain stage is equal to the plate load resistor paralleled with the plate resistance, so in my case it is about 51k, which is a bit high to drive a real load. 1 - Grid Leak Biasing A method for biasing (mainly high mu triodes or small signal pentodes) that used to be common is 'grid leak' or 'contact' (aka 'contact potential') biasing. With a correct setting, we can amplify the signal a lot before the amplifier clips. This is a hybrid tube that has the gain of a 12AX7 on one side and the gain of a 12AU7 on the other. The LM-845 Premium uses Shuguang 300B tubes in drivers, the 310A for amplifier and Shuguang 12AX7 in pre-amplification. In the two years since the Fetzer Valve was first published in the midst of our adaptation of tube amps for use as distortion pedals, the circuit has enjoyed popularity as a standalone booster and as a building block in larger circuits. After drawing the curtains aside on a soundstage of full height, width,. Before adjusting the bias let your amp warm up for a few minutes. This type of transistor biasing arrangement is also beta dependent biasing as the steady-state condition of operation is a function of the transistors beta β value, so the biasing point will vary over a wide range for transistors of the same type as the characteristics of the transistors will not be exactly the same. That draws more current thru the tube, technically wearing it out sooner? Raising the cathode resistor value brings the heater-to-cathode voltage limit into play also. Biasing a guitar amp 12AX7 - does it even matter? Well, of course it matters. I have been using this phono circuit since the early 90s starting with a PAS chassis with Telefunken ECC83/12AX7. Start by replacing the 12AX7 tube. I read an article last night that suggest that the 5751 is interchangeable, just with less gain, and that it sounds significantly better. tube #two[0] I tried different tubes. For a selection of reasons both business and private, the expansion and recognition of individuals turning into involved in do-it-yourself or (DIY) woodworking projects has increased dramatically during the last variety of years. Common-cathode amplifier design ideas Although not that popular, the common-cathode amplifier is one of my favorite tube circuits—with good cause, as it offers low input capacitance, low distortion, no phase inversion, and two inputs, the second of which can readily accept feedback from the output or a sampling of power supply noise, to null the noise at the output. Calculating Cathode Bias Resistor. These were made for the equally rare Blue Voodoo 150 and 300-watt heads, like those played by Marty Friedman and John 5. Power output: 17 watts per channel into 8Ω (stereo) Valve complement: 4 x 12AX7, 2 x 6BL8, 4 x 7189, 1 x 5AR4. what tubes do you recommend, and does the amp need re-biasing?would also like to replace preamp tubes(12ax7). It is preferable to have total grid leak bias for best modulation linearity. One tube is a 12AX7/ECC83 and the other a 12AU7/ECC82. This makes the device unsuitable for most output drive stages without some form of buffer. I've been offered some Raytheon 5755 tubes which I've been told are excellent sounding, at a ridiculous price,too low to tell, but this tube has a different pin out than standard 12AX7 so it would need a pin out socket converter or make a modification of the sockets pin out on my Phono preamp, and that's something I'm not definetely doing. RCA and Sylvania first introduced the 12AX7 to the world in the late 1940s. I switched test leads still the same. The design is exactly the same as the 12AX7 preamp, it is a single gain stage triode tube with cathode follower. i thought i would replace the power tubes(6l6gc) in my vintage fender princeton silverface amp. That said, some folks like hot or cold biasing, others like the opposite. what tubes do you recommend, and does the amp need re-biasing?would also like to replace preamp tubes(12ax7). The 12AX7 is all about voltage gain whereas a 12AT7 is about current. No biasing or adjustments are necessary, just plug in and play. Power valves KT88s etc require -30V to -90V Bias which is supplied from a separate -V supply through the Grid resistor, described as "Negative bias" Gain A 12AX7 is a high gain triode (approx 30:1). Thanks again for the basic idea and for pointing out that a 12AX7 is essentially two 6AV6 triode sections in one envelope. Gibson es-125 from 1948? There is no label nor number on the guitar. I would check the bias once a month although many wait longer. Had it for 3 mths nowim thinking of replacing the stock tubes with JJ brand (1) T-12AX7-S-JJ (1) T-EL84-JJ. Any 12AX7 or 7025 is usable here--it need not be low-noise or low-hum, nor does it need to be tested for microphony. For your Fender Twin to sound and perform at its best, the tubes must all draw an equal amount of current. High grade is a measuring system used by Magic Parts, which basically means the tube is better suited for amps that need more quiet tubes. The Pro reverb has a smaller OT than other 6L6 BF/SF amps like Super Reverb and Vibroverb. Tube # 2 Plate 526 Bias 0. Carmen Ghia. 12AX7 Svetlana. The book said set the 12ax7 up for low bias (0. A 12AX7 has a plate load resistor, Rb, of 220 k ohms and the grid resistor of the following stage, Rcf, is 470 k ohms.