Cathode bias amps. Aug 26, 2006 · TYPES OF (FIXED) BIAS CIRCUITS.

Cathode bias amps. Fisher SA100 uses a Cathodyne design b.

1. Many amps which use "fixed" (negative grid) bias have provisions for adjusting the negative grid voltage upward or downward. With a properly biased amp, the amplifier will work more efficiently and will accurately amplify the sound of the guitar, pedals, and preamp. In this case, the setting is 95%. Cathode bias not only automatically sets bias Jan 7, 2014 · Not a real popular amp and not a "current production build", but my little PTP Beltone AP-22 is cathode biased. One of the critical factors influencing the sound of a tube amp is the biasing method used, … Cathode Bias vs. Stick with the 7591's. Sep 25, 2008 · "cathode", "automatic" and "self" bias are all synonyms, meaning the cathode is lifted from GND by some amount, using the cathode current to create a drop across a fixed resistor, thus making the control grid negative with respect to the cathode without the use of an external negative power supply ( hence the names "self" "cathode" and I just did the cathode/fixed bias switch and the low power switch on one of my V-Verb amps and I love it. the amp has about 20 hours max on it, and the bias was at 31. All preamp tubes are cathode biased which is why preamp tubes are plug and play. Jan 17, 2019 · These amps run about 150 volts to the 12AX plate, and use a 1500 ohm resistor for the cathode bias. Cathode Biased Tube Amps. If you used a paraphrase inverter (instead on an LTP), you could get quite a funky sounding blues amp. LTPI vs Cathodine needs to be decided and it can be either. Fixed Bias: How Does It Impact Cathode bias amps have more sustain and more compressed dynamics but sometime can be flabby or bassy. barely got the amp going, so I bumped it up to 45. Dec 31, 2009 · sepulchre Posts: 923 Joined: Mon Dec 28, 2009 1:43 am Location: Way out here (Logansport,In, USA) Jun 5, 2019 · I recently built the blue glow/Kegger SE KT88 amplifier. – make the cathode more positive than the grid (grid stays at 0 volts, called cathode bias or auto bias) – make the grid more negative than the cathode (cathode stays at 0 volts, called fixed bias) This predefined voltage difference between the grid and cathode is called the bias. Jul 15, 2013 · A Vox AC4, like many amps, is designed to make the power tube's cathode slightly positive—a state that is commonly referred to in the guitar universe as cathode biased. Some amplifiers don't have a bias-adjusting control (pot) but instead use a fixed resistor to set the voltage. Recommended Bias Point: Cathode Biased (no re-biasing necessary) KT 45 V1: NOS EF86, V2: Sovtek 12AX7LPS, V3/4: JJ E34L (matched pair), V5 Solid State plug in or Sovtek 5AR4 In cathode biased amps like the VOX they get a premium workout and will suffer some effects from heating and cooling. Fender: Deluxe, Bassbreaker 15, Bassbreaker 30R, Vaporizer, Champ, Champ 600, Vibro Champ XD and Excelsior. May 5, 2024 · I'm building a single channel amp, with a simple blackface preamp, 2*6v6 cathode biased power amp and a boost circuit (two triodes and a tone control) IN FRONT OF THE blackface preamp. We have a blog on Cathode Bias plus a list of the amps that are cathode biased in a different blog which you can access here. the normal cathode resistor on a champ/vibrochamp is 470 Ohms. Apr 21, 2012 · There are some tricks to deal with it or prevent it, like the "paul ruby" mod or putting a zener in parallel with Rk in order to prevent the voltage across Rk from getting too high. Some of this depends on the tubes being used. Making the grids LESS negative will cause MORE current to flow through the tubes. Jul 13, 2023 · Cathode-biased amps, on the other hand, which are often advertised as being “class A,” don’t need re-biasing when output tubes are replaced. That means they let a lot of cathode current flow compared to Class AB biased amps. Sep 21, 2018 · In this video we'll take a look at how to use Ohm's Law to calculate the bias on a cathode biased Fender Pro Amp. With over 400 volts on the plates, you might want to consider trying fixed bias Here is a list of some of the amplifiers that are cathode biased and therefore do not need biasing: Bugera: BC30, V5, V22 and 1990n Infinium. Anyway, first I measured the resistance of both halves of OT. ” This will be most familiar to guitarists as heard in the Vox AC30 and AC15, or other amps that follow those templates. Cathode bias is mostly used in low cost valve amps that function from a It can connect somewhat lower than cathode. I like that one; cathode bias at clean output but fixed bias at heavy overdrive. Jun 29, 2011 · All Tweeds through the 1954 schematics were cathode-biased. I was just hoping to get some of you to chime in about what cathode bias resistor value YOU are using, and any experience you have had with adjusting this resistor value. They are safe at 14W *if* you meter every unit Aug 9, 2005 · Cathode biased amps have a bit more compression than fixed bias amps because of the way the cathode resistor affects tube current. No re-biasing or modifications needed Includes a pair of Yellow Jackets converters and a pair of EL84 tubes Will not lower the output/wattage of your amplifier For use in lower wattage amps - 20 watts or less Comes with a ground wire for cathode biased amps. Oct 4, 2008 · Cathode biased amps run at max signal at idle, so with cathode biased amps usually 90% is acceptable for real class A, and 80% to 85% for class AB1. Vintage-inspired modern Feb 4, 2015 · 425V B+ 6L6GC 4k center tapped ot Push pull class A Fixed bias TDSL says this for cathode bias: B+ 360 Vg2 270 Ia 50 Ig2 9. But don't chase your tail on obtaining the exact sound of your friend's amp. " V1A's bias voltage is set by cathode resistor R4 which is connected to V1A's cathode (pin 3). The optional Bypass capacitor boosts gain by acting as an electron reservoir. Just dial the voltage down and the amplifier’s maximum volume drops. The Bad Cat Hot Cat 30 has an EL34 push-pull power amp biased for Class A operation, a rarity for guitar amps. Between the bias system in your amp and the natural idle current of the tubes you use, you have the ability to tailor your sound. Mar 5, 2018 · The amp is cathode biased, you would need a drastic variation from regular EL34 to have an issue. Cathode biasing is also called self-bias where the way the circuit is set up BASICALLY allows the tube to draw what current it needs. Have folks experimented with using film capacitors of similar value in this application, or adding a small film cap in parallel with the electrolytic? May 28, 2010 · Therefore 2 output valves that are Cathode biased is described as Class A push pull. On Fender amps it often connects to 2-220K resistors. Cathode bias is a kind of self-bias circuit. Only they weren't matched. The amp will distort sooner with unmatched tubes in cathode bias. ) Some amplifiers such as cathode biased amps are generally good to go without any adjustments but many amplifiers have a fixed bias. As long as you know (or can test) the plate voltage in your amp, and have a way to measure the idle current, you can determine where to bias it, using our calculator. The LED simply replaces the resistor and its bypass capacitor. However, just as different tubes from different manufacturers will draw varying amounts of current in a fixed-bias amplifier, the same is true of a cathode-biased amplifier. Fixed bias when you want the punch,cathode biased when you want a little less with a bit of hair on the notes and 1/4 power for home,recording and small clubs. 5 Mv, and adjusted the tube balance to around 44. But swapping tubes like this should only be done by someone who really knows what they're doing, and has the ability to swap out the cathode resistor(s) to proper values if the tubes aren't running within spec. . Note that cathode biased does not automatically mean Class A, nor does fixed bias mean Class AB. 3″ 50. Recommended Bias Point: Cathode Biased (no re-biasing necessary) KT 45 V1: NOS EF86, V2: Sovtek 12AX7LPS, V3/4: JJ E34L (matched pair), V5 Solid State plug in or Sovtek 5AR4 Jan 4, 2008 · Most cathode biased amps, especially those that are somewhat based on the AC30, overbias the tubes. The cathode current does not decrease, neither does the cathode voltage. Fixed Bias. Vox AC15) have cathode-biased output tubes (EL84) and these amps don’t need biasing. However, with cathode-biased amps, the surges in bias voltage across the cathode temporarily bias the tube colder while cranking, and help keep things under a degree of control. In fact, we CAN’T bias them even if we wanted to. 6g3 Deluxe and 6g2 Princeton. All of the early Fender amps were cathode biased. I spent more than a year tweaking this thing, so I wanted to share the results Jan 11, 2024 · The desired sound of a Hi Fi Stereo amplifier is often very different than the desired sound of a guitar amplifier. SELF-biased amps, worked for "high" power, must be run at 90%, 99%, 110% of rating (AND loaded appropriately). These amps require a bias adjustment for the tubes to operate properly. And always use a meter to measure the bias point so that you don’t cause any damage to your tubes. If you were going to do anything though, I'd make sure the cathode bypass cap on the output stage (the power tubes) is good quality. In AC terms, the cathode is loaded by a constant-current source and whatever external load impedance is driven times two. Sep 22, 2020 · How about insuring that the 6V6 currents are close to each other. Some call a cathode biased amp a working man's amp. I don't know whether it was the Selmer or just the added complexity of VVR having to track bias voltage in it that made it less successful, but it didn't seem to work as well. Jul 15, 2013 · Cathode vs. Jul 9, 2022 · Amps with cathode-biased power-tube circuits are lower-output ones — 30 watts or less. Switchable fixed/cathode bias: SV1 + RBX. In DC terms, the result is that the two 10-ohm cathode resistors effectively double in value, acting as if a single 40-ohm cathode resistor were used to cathode-bias the triode. But it has a trim pot for the bias (page 2, on the right of schematic). These amps may be fixed biased or cathode biased. Don't forget that a hot biased amp will sound different than a cool biased amp and a cold biased amp can sound thin and sterile. It’s been successfully fitted to many amplifiers, from Champs, Deluxes, 18Wers, AC30s, etc. Dec 8, 2016 · There is an exception to all of this - cathode biased amps. Often it is a switch that can select bias for EL34 tubes, or 6L6 tubes depending which is installed. Select your tube type and amp class (Class A, Class AB Low, Class AB, or Class AB High) and enter your Plate Voltage or B+. On a cathode-biased amp, the value of the cathode resistor (stock 5E3, this is the 250Ω 5W from the 6V6 cathodes to ground, with a bypass cap across it in parallel) sets the bias point. Sep 21, 2005 · get a Digital Multi-Meter (can be a cheap radio shack one) - and buy a weber bias rite head - www. If you have a cathode biased amp and find that the sound is never clean enough, or too mushy, you can try using tubes that have lower idle Sep 21, 2013 · "Self-biased" usually refers to tubes configured with cathode biasing. The cathode follower bias point (i. Any of the fixed bias setups can be run using cathode bias instead. The easiest way to make your Bass guitar amplifier work reliably and with long life . Fisher SA100 uses a Cathodyne design b. so i had it replaced at the time. Many people actually refer to them as "self-biasing" for this reason. my first amps were cathode bias and I was buying "matched" sets from a vendor. [5] The power dissipated by the cathode bias resistor is the product of the square of the cathode current and the resistance in ohms. In our days of tubes of doubtful manufacture quality, fixed (i. Capacitor C6 is a cathode bypass cap that helps decrease local feedback and increase V2's gain. Cathode Bias vs. 2Mv. This extends tube life and helps make the tone difference between fixed-bias and cathode-bias a bit wider. Cathode-biased amps will safely run at 100% plate dissipation at idle. I would not be afraid to copy that schematic. The output signal of the common cathode amplifier is inverted with respect to the input signal. When a signal goes through a cathode bias amp and output watts increase a voltage drop across the cathode resistor goes up and limits the output power. You may find you prefer a cooler bias than the standard 70% target for push-pull amps. Converting to cathode bias in the blackface and silverface Bassman circuits, and other Fender amps with fixed bias, is very simple. Drop of max output power is not a problem. It is in fact so simple that we recommend everyone to try it. This reduces gain a little. The grid of cathode biased amps will be at 0 volts. Sep 28, 2007 · yes, a cathode biased amp has its bias point changed by changing the value of the cathode resistor. Fixed bias amps have a bias circuit that puts a negative voltage on the power tube grid. Note that each KT66 draws 1. is to purchase a very well matched Quad of 6L6 tubes (6L6GC is best for long life if the amplifier is driven hard into overload clipping the cathode to the plate. e. This is known as the grid bias of your amp – the correct bias level is vital to the operation and tone of the amplifier. on my multimeter it doesn't show Mv, but shows it under the Vdc range-200v=the milli volt setting. Most output valves in HiFi valve amps (40 Watt and less) are Cathode biased in the same way that pre-amp valves are biased. Just be sure to stay within the maximum ratings. Jan 27, 2015 · Going by the GEC KT66 data sheet, a cathode-biased non-UL version could be designed running ~450 on the plates and ~300 on the screens with a 2 separate 500R cathode resistors running into an 8kPP OT. Quite a few amps (e. Few questions regarding new setup. Cathode bias: SV2 + VCK. A cathode biased tube amp uses a resistor, connected to the cathode and then grounded. check the voltage referenced to ground on Pin 8 and see what you've got. The cathode resistor can also be bypassed by a bypass capacitor to reduce the negative feedback, introduced by the cathode resistor, and increasing gain. Would I like a do it all 40-50w head or combo well yes but the reliability, practicality needing to change a big number of tubes if it is a bigger amp, how heavy etc. The other common type of bias circuit is known as fixed bias, and will not apply to the 5E3. "Keen to build high-quality amps in the vein nominally referred to as 'Class A,' founder James Heidrich did his due diligence before starting up the company and, as he told me in the early 2000s, 'All roads seemed to lead to Mark [Sampson, founder of Matchless]. Jun 25, 2018 · Cathode biased means the output tubes are biased by a large power resistor that's permanently connected to the tubes' cathodes. May 11, 2023 · Using the bias control, set the bias to somewhere in the ranges given above (Fig. In general, this resolves to the following kit requirements: Fixed bias: SV1 + RBX. Note: Some amps will act funny and develop horrible noises (parasitic oscillations) when a bias probe is in place while the amp is being played. You can bias a Class A amp in two primary ways: cathode biasing or fixed biasing. The tube will reach a stable point of equilibrium and stay there. I think the CAZ is as well. 66 "On cathode-biased amp, the bias adjustment is not necessary beacuse there is a large resistor on the cathode of the tube (hence the name cathode-biased). Pilot SA232 uses a Paraphase design Each of my amps have been restored to stock form and they each sound very good but very different. The Grids are referenced to ground (chassis) by a 220k resistor. 2 Mv. I've biased amps for years, but know little about cathode bias, and/or what, if any, difference a hotter tube would make, or if they could possibly be too hot. Aug 26, 2006 · TYPES OF (FIXED) BIAS CIRCUITS. For an ideal amplifier, at FULL power it shifts (as TS said) to 150mA one tube, zero in other. If an amp has a small number of knobs, then we will invent the knobs in a way that makes the most Jan 8, 2022 · Cathode biasing done to any amp that was fixed bias would 1) lower the output wattage of the amp some. It allows the Vette engine (see above) to draw what it needs to run right and discard the rest. I wanted to install 1 or 10 Ohm resistors to the cathode of each El34, but it would've been a mess 'cause of amps layout and printed board. And Madison's estimated 440V ain't very different from the Clubman running 430V. For cathode-biased amps, they take care of the adjustment themselves. We will disc Apr 26, 2019 · I don't think 1 dB less power out of an amp has ever killed anyone (a 10 Watt amplifier that only put out 7. One more thing: some fixed/non-adjustable bias amps have a "bias switch" to select for a specific tube type. 4 – 6N14N (NOS EL84, cathode biased 1 – 5879 1 – 12AX7 1 – 5AR4 tube rectifier: Volume, Master, Tone, Cut, 1/2 Power Switch: Post-Phase Inverter Master Volume: N/A: N/A: Tube-driven FX loop: Head 1×12 (with WGS Retro 30) NOS Pentode preamp, NOS mil-spec 6N14N power tubes: 4/8/16 Ohm: Z-28 Mk. To ground on a cathode-resistor amp, or to -bias on a fix-bias amp. My favorite Fisher tube integrated is cathode biased. Another way of putting it might be that we can virtually change the value of the cathode bias resistor in a cathode bias amp. Unless you are designing an amp. Jul 27, 2022 · Now, before assembling final variant, would like to get rid of fixed bias circuit and switch to cathode bias, with 490 - 500V B+ and 520 Ohm cathode resistor (2 x 5W metal film resistors, 300 + 220 = 520 Ohm total). Oct 10, 2005 · Yep, the LC30II is cathode biased. Use individual self bias. The above selection covers 99% of all guitar amps, but there are a few exceptions listed below: Jan 18, 2024 · I am just a musician, but usually with cathode biased amps you only see a resistor for the bias, not a trim pot. Assuming that you want more power output, I think it would be way better to switch to fixed bias. Sep 3, 2012 · The stiffness of the power supply can really affect that, and you can build a cathode bias amp that is stiffer than a fixed bias amp. Mar 9, 2017 · Most small cathode biased use pre-amp tube bias shifting trems but there is version that modulates the bias indirectly through the grid leak resistors of the power tubes. Without getting into too much technical detail/jargon, basically through a series of design characteristics - mainly a resistor - these amps balance themselves The bias control affects where the idling state of the tube is "located"; if it's hot or cold. measure the voltage at this point (say it's -32V) measure the current the tubes are drawing at idle using one of the ways to measure bias (say it's 44mA per Jul 9, 2014 · Some also have Mid control. It uses a cathode bias resistor with a bypass cap as the bias method. I read where Dennis Cornell's small 20 watt Plexi Jrs. Sep 23, 2023 · Tube amplifiers, often referred to as “valve amps,” have been a staple in the world of audio amplification for decades. 6V6 are safe at 12W if you do not meter every unit you build and ship (mass production). find the voltage supply that applies a negative voltage to the grid(s). The Grid controls the flow of electrons through the tube. That's called fixed bias, and it has a similar effect. IMHO, you may want to put down the slide-rule and the Smith chart and get on the bench and try it Oct 6, 2014 · The higher load impedance coupled with the presence of the resistor is why cathode biased designs always produce less power output than a corresponding fixed bias design does. This amp could be even class A in which case the measured current is low, but I'm pretty sure it's not unless the cathode resistor has been changed. Oct 22, 2007 · when i got the amp, the board under the 10 watt resistor was burned, could've been a tube or resistor failure, right. Cathode Bias Jul 14, 2020 · The Traynor Custom Valve 15 is a cathode bias amp, 2 x 6BQ5 (EL84) running parallel in class A. The 2 x 6V6 Tweed amps were cathode baised except for the 5G9 Tremolux, which was fixed. Being prone to mechanical noise in a combo amp, the EL84 is not recommended for amps with poor air circulation. In this system the cathode resistor self-regulates, allowing the tube to achieve bias automatically, depending on the level of signal it's receiving. Phase Inverter circuit design: a. These amps are cathode bias and therefore require no bias adjust. In building them, I've played around with a 'tone' control, feedback vs 'no' feedback, a bypass cap on the 12AX cathode resistor, and even changing coupling cap values. What I found was that the amps are biased too hot for the mesa tubes I was sold; one of them redplated with less than 4 hours of play time. Personally we prefer cathode bias in big, powerful amps with big transformers where you have more than enough power and attack. I haven't Apr 21, 2023 · My PSET 300B amp currently use electrolytics to shunt AC in the cathode bias circuits (both for the driver and 300Bs). This biasing method is known as ‘fixed bias’ and the valve’s cathode is connected directly to ground. Tubes like 12AX7 use cathode bias and do not need bias adjustment. This happens because the capacitor is now “giving” this current through its charge. I always recommend sampling the clean and overdrive tone and different volume levels each time a bias adjustment is made. Anything less leaves precious power un-sucked and thus un-delivered. However, I'm wondering if it might be a good idea to make the cathode bias adjustable? 560 ohms is the planned cathode resistor, but what about changing that to, say, a 500 ohm resistor and 100 ohm pot in series? That would put the pot at roughly midpoint. all the schematics call for it as well. One side 74,2 Ohm and the other 73,9 Ohm. A higher value cathode resistor will cool the bias, a lower value will warm the bias. Nov 24, 2022 · With cathode biased amps the most common way of setting the bias is adjusting the value of the cathode resistor. A couple of channels sharing tone and reverb settings, built like a tank. Just install from cathode of tube to ground, with the LED's cathode connecting to ground (LED anode to tube's cathode). Feb 16, 2023 · 1. the voltage between the cathode and ground) should be ≈85v. II: 30 Watts: 2 – 5881, cathode biased) 1 Sep 26, 2018 · For the output stage of a power amp, amp manufactures will sometimes provide a user adjustable mechanism to set the output stage bias by allowing the voltage difference between cathode and control grid to be adjusted within a certain predetermined range, which once set, will automatically set the other values. Then I got a tube tester and checked my "matched" tubes. Most cathode biased amps are either deeply toward Class A, or completely to Class A. The tube's Cathode is the source of electrons. The 6V6 power valves in this amp are actually pentodes, but the explanation applies nevertheless. Bias circuit: a. The Cathode resistor generates the bias voltage between the cathode and grid. V1B's bias is set by R6. Is that a For a cathode-biased amplifier the total current should not change much from idle to full roar. If so, nothing else is required. The classic Vox AC30 combo is a great example of a cathode-biased amp. So the g1-k and g2-k voltages will be changing with signal level, hence throwing g3-k into the mix too is yet another variable. That has about 10vAC so I can wire up a bias circuit feeding about 14vDC tops). They don't ever seem to really be an issue. The cathode bias resistor value is found by dividing the absolute value of the operating point grid voltage by the operating point cathode current (plate current plus screen current). Cathode Bias (Self Adjusting) Nov 4, 2017 · In my forthcoming build cathode bias is the plan. Although I have not heard this directly from B*, I've heard from multiple sources that from the factory the HT20 bias is set to 11. Less tubes (depends) to change, cathode bias makes life a tiny bit easier and even mic'd you can use your amps potential more unlike a big 100w (but this is my opinion). So gives 9/56= 160mA total cathode current. Hot rod your tube amp with Yellow Jackets YJ20 tube converters. The first Fenders to go to fixed bias was, iirc, the 5E6 Bassman and the 5E amps listed above. I've greatly enjoyed the cathode bias 6L6 amps I've had and currently have. Biasing your amp doesn’t have to be difficult. A Harman Kardon 250 is supposed to be cathode biased, but I've never seen one up close. Feb 10, 2010 · One cathode biased amp I was recently worked on was designed for 90%, other amps are higher. The common-cathode amplifier configuration - fully bypassed cathode. should sound better If your amp has fixed bias without a bias pot (like the original 5F6A Bassman) you must either install a bias pot or replace bias resistors to adjust the bias. The earlier 5E5 Pro is a cathode biased amp. V2's bias is set by R8. 8 x 33 mm; Built height: 1. The gain bias (cathode to ground) should be in the neighborhood of 6V. Famous fixed-bias amps include larger tweed and blackface Fenders, Marshalls JTM45 and Plexi, most high-gain amps made today and many others. For the rare single-node fixed-biased output stage, add TBS Tracking Bias Supply and RBX Raw Bias Auxiliary Supply to SV84. Fisher SA100 is a Fixed Bias Amplifier b. Tube life isn't a problem, just like with the Traynors and Mesas where you expect the high voltage along with high-ish dissipation to kill the tubes but in reality they last quite well. Epiphone: BC30, Valve Junior. james, thanks for the info. 3A filament Jan 13, 2021 · The Marshall 2020 EL84 amp has a b+ of 400v and tube dissipation is 14w. com Or, just buy the bias rite that comes with the meter from the same site for a bit more (though it may be cheaper than meter + bias rite head) Or, take it to a tech, and have him set the bias - it shouldn't cost more than $35 Apr 10, 2010 · (Schematic attached below) Bias Calculation for EL84 tube A Cathode voltage: 12,8 V (measured from pin 3 to ground) Cathode resistor: 303 Ohms (measured in circuit) Cathode current: 12,8 V/303 Ohms = 0,04224 A Plate voltage: 395 V (measured from pin 7 to ground) Actual plate voltage: (395-12,8) V = 382,2 V Dissipated power: 382,2 V x 0,04224 A The current which the output tubes need to flow is dependent on the operating class. If your amplifier is cathode biased you must replace the cathode resistor to change the bias level. If your amp has fixed bias and you'd like to try cathode bias. The valve therefore operates literally as Practically all preamp tube circuits use cathode bias. These supplies are “single-node” and require a single, high-voltage regulator path. looks like i need another pair of tubes. WIth the amp I could adjust teh bias so no problem,, With a cathode biased amp like the 5e3, the 250 ohm resistor might fit some brands of 6v6 tubes where other would require a 330 ohm resistor to be biased correctly. Easy to build Biasing an amp requires some knowledge of tube amp circuits and experience with high voltage. My question is when you tube roll the amp, when you use kt88 tubes the cathode current is approx 76ma. You may want to look at the Brown era. SV84 is the choice for most of these amps, which tend to be <450V. Is having a shared cathode resistor a poor idea in my situation? I understand May 10, 2024 · You can even replace the bias resistors for adjusting the bias. The Amp Maker version is called VCB, and this version, VCB1, is for cathode biased amps. 5mV when measured May 16, 2023 · Hoffman Amplifiers Tube Amp Forum, Cathode bias amp variable resistor. VVR was designed and refined by Dana and Richie Hall of Hall Amplification. 'course, I ain't gonna be changing tubes every 3-6 months either. Welcome To the Hoffman Amplifiers Forum August 16, 2024, 02:57:36 am : Welcome, Guest May 6, 2014 · in cathode bias it does matter. Typical examples of cathode biased amps include all the tweed Fender Deluxe models, the Vox AC10, AC15 and AC30, and Marshall 18 Watt. You can always check the voltage across the 500 Ohm resistors, when the tubes are first put in, and later as they age. Dec 11, 2015 · I figured out the problem. In most common guitar amp circuits, cathode biased amps will self regulate plate current, in many cases plate current will drop when the amp is at full power. Nov 10, 2021 · Cathode-bypass capacitors (“caps” for short) are found connected in parallel to the cathode-bias resistors in many preamp stages and some output stages, and to many beginner and novice amp enthusiasts they may well be the most mysterious of all three capacitor usages within the guitar-amp circuit. They aren't like an el84 in any way or like a 6v6. 25 and 35 volt work but their life is reduced by 50% and using a 10 volt at 10 volts is at the caps rated life. This is why you do not see bias adjustment on single-ended amps like SET audio amps or Fender Champ. By comparison a common target for fixed biased amps is 70% or less. It is a 5C5 circuit from 1953. Another reason is that the tubes see only the difference between the cathode and plate voltages. Other amps, instead, put a negative charge on the power tube's grid. Quick answers: Installing an LED for cathode bias is as simple as it gets. Running hot may be part of the magic. 3) and play the amp. Mar 29, 2017 · I've tried Hall VVR on cathode biased amps and a fixed bias Selmer Treble 'n' Bass 50. The output tubes are plate current matched using a wee bit of fixed bias and operate in class A using the classic 2A3 SE operating point. Additionally, single-ended power amplifiers are mostly cathode biased also. If this is the case, you’ll need to remove the bias probe each time you play the amp. I have seen a neat adjustable cathode biased system that used a 350 ohm resistor together with a 100 ohm 5W pot. In a short accident with modern EL34 in 7027/6550 holes, nothing bad happened when I left pin 1 disconnected. 2--45. If you are uncertain that you are experienced enough to work on a live high voltage amp, please take your amp to a professional to get it biased. Aug 5, 2024 · The total draw on the power supply should be ≈22mA with two channels. Mar 17, 2010 · For those of you who want to try a cathode-biased Express-type amp with 6V6s and Deluxe iron, here's a schematic that might give you some ideas to play around with - there are about 30 of these floating around now, and everyone seems pretty happy. Oct 21, 2005 · I assume since it is using 7591's, it is an older Jet. One 6V6 amp, a 6L6GC amp and one with a GZ34 and EL34s with some subtle Plexi type tweaks, and I used the Dale 50 watt extruded aluminum resistors for the cathode biasing resistors 'cause they looked cool and price was no object! Mar 13, 2007 · While I'm OK to go down this route since the VC30 is also a cathode biased design, I'm curious if I can make the new amp a fixed bias type since the transformer had a secondary that used to power the transistor driven fx loop and reverb on the VC 30. It sounds really good for the cost, but since it came with no manual or schema attached, i was wondering if it's a fixed bias or cathode/auto-bias one. the normal cathode voltage across the resistor is about 20-21 VDC. tedweber. Dec 21, 2016 · just biased my JTM 60 with output transformer resistance/voltage method. In heavy abuse with pin 1 connected to cathode via 470K, I could not measure any G3 (pin 1) current. Mar 15, 2014 · Cathode biased amps are more forgiving of bias differences, so it's more likely you won't have to re-bias for new tubes. You will get unpredictable results from one set to the next for that reason. Have you checked circuit voltages? Check the bias voltages on the gain and CF stages. Musicians and audiophiles alike have long admired the warm and harmonically rich tones produced by these vintage electronics. Jan 28, 2009 · From what I learned you'd like a voltage rating for the caps that is 1/3 more than the actual voltage there for a 50% extension of life so an EL84 SE is typically 10 volts or less for the cathode bias so a 16 volt would be fine. Since we tend to cathode bias amps really hot, many actually have LESS sag/compression than some of the classic bluesy fixed biased amps such as a deluxe reverb, fender bassman etc Jan 31, 2023 · Plate Voltage is low in the 250-ish range, and the bias reading was a crazy cold 45-50% dissipation. On the other hand, cathode bias shows a more smooth amp - biased on the hot side ~ 100mA's per tube @ 430V on plates Sep 25, 2006 · Normally in a fixed biased amp, 80% to 90% would result in the tubes running too hot when cranked. I have a 6550 p-p amp (my fav big bad tube) with ability to switch from fixed to cathode bias and although they behave differently, in fixed bias mode there seems to be a kinda punch which is not present on cathode bias mode. Cathode-biased amps, on the other hand, which are often billed as "Class A amps," have a bias level that is set at the factory with a fixed resistor. No negative feedback means there's no feedback loop from the output of the stage back to the beginning of the stage at the entry to the phase inverter, something used to tighten up and clean up many other types of amplifiers, most notably many Class AB designs, but Jan 14, 2009 · Confusingly enough, "fixed bias" amps are the ones that generally have adjustable bias levels that need to be checked and reset when you change tubes. Without getting into too much technical detail/jargon, basically through a series of design characteristics - mainly a resistor - these amps balance themselves Mar 25, 2021 · Also the cathode voltage isn’t fixed, with a typical hot AB cathode biased amp it’s going to bounce around a bit according to signal level. non-cathode-biased) amps new power tubes require at least checking the bias to see if it is good. Mar 2, 2008 · I'm simply talking about properly biasing cathode biased amps. I am considering a 300-390 ohm cathode bias resistor. But 300B does not have G2, so a beam power tube could fit the bill. Oct 27, 2013 · The issue is that successful cathode bias p-p amps generally operate close to class A. I would be more worried if you have low screen resistors on the tubes, but it looks like you have already replaced them. You get slightly less power and a "warmer" sound due to the lower voltages. Traynor also build 40 and 50 watt units that are auto-biasing. If I were to use say a 6l6gc or el34 this amount of bias current would be to much and cook the tubes. Jul 6, 2018 · I know this is covered in many previous threads and articles, as well as a few books. But an amp with fixed G1 bias, and driving signal to G2 does sound very interesting. The bias of an amplifier refers to the adjustment of current flowing through the output tubes when there’s no audio signal. If I can set up cathode biased 6V6 amps for correct power tube dissipation with amps that have B+ voltages ranging from 340V to 410V by changing the cathode resistor, so can anyone else. Apr 1, 2010 · I just finished building three versions of a cathode biased 5F6A head for a pro player. With respect, 10thtx Jan 22, 2021 · Such biasing is usually achieved in class-A amps, as well as amps that are purportedly class A, by a method known as “cathode biasing. If you are committed to using cathode bias, then it would be best to stick to a class A design so that the effects of the cathode bias resistor can be effectively discounted. In cathode bias mode, tubes can be run at close to 100 per cent of their power potential. g. Although it may be fine as-is, it's still best to check. So peak voltage swing is 280V. Nov 16, 2005 · Plug-and-play mostly is the case with cathode-biased circuits. 9 Watt). Following is a schematic of a typical common-cathode amplifier stage with a bypassed cathode resistor: Capacitor Ci is the input coupling capacitor. For a cathode biased amp, it's quite common to bias them on the hot side. EL84s are a very common tube in such designs, 6V6s are, too. 5 watts amps with a 12bh7 in the power amp. When current comes through this resistor, a voltage develops on the cathode. 3) give the amp a touch more overall sustain. A cathode biased El-84 is pretty firm while a 6L6GC is more compressed. It freely accepts EL34, 6CA7 or KT77. There are several ways to do this. . Aug 31, 2012 · The input signal is driving the grid to -1V. Apr 29, 2019 · My amp is push-pull 6B4G. Pilot SA232 is a Cathode Bias Amplifier 2. A higher value cathode resistor cools the bias, a lower value will actually warm the bias. Apr 2, 2012 · When a cathode biased amp starts to run out of steam, it asks too much of the power supply, limiting the available low end and distorting the high end. Mesa claims that if you buy their mesa tested and branded tubes they will be biased within a safe range intended for the amp. Jan 7, 2014 · The Fender 5F4 Super and its stablemates the 5E5A Pro, 5E7 Bandmaster, and 5E8A Twin are fixed bias amps. For this reason, the bias should always be checked, even with cathode-biased amplifiers. 500 Ohm for each cathode, and 47uF to bypass each cathode. Late in that year, the 5E5A PRo went to fixed-bias also. I was curious if a hotter pair would bump that to 60-70%, or stay the same. Too far from class A and there will be excessive bias shift with signal, resulting in yucky tone. However, there is a bias adjust pot on the HT20 and it's there for a reason. I am currently using a shared cathode resistor. Design Concerns-Bias shifting trem in fixed bias amps that vary power tube bias have several issues: 1. These where fairly matched. This includes amps based on the Marshall “18-watter,” Vox AC15 and AC30, and Fender tweed Deluxe templates, as well as plenty of larger designs such as the Matchless Chieftain, which uses the Cathode bias amps are the least work intensive, as they do not really require biasing at all in a general sense. But stranger things have happened. Cathode biased amps typically have a warmer sound with more gradually introduced distortion. i just popped a The 5F1's V1 and V2 use "common cathode biasing", also referred to as "self biasing" or just "cathode biased. The Fender 5F6A Bassman and most Marshall amps are fixed bias Class AB amps. There are other factors too, such as the grid return resistor to ground but I'd leave that one alone. All these extra knobs. By computing the resistor value, according to the wanted bias current, the cathode voltage is elevated so that the grid has the correct negative bias voltage. The Fender 5E3 Deluxe is a cathode biased Class AB amp. Sep 25, 2017 · Fortunately, most tubes can be biased in most amps without any issues. For sure it's excessive for many amps and especially those that use tiny power transformers for cost reduction. These are still fixed/non-adjustable bias amps as there is no internal bias trimmer pot to fine tune. The first selection parameter is how the amplifier is biased: cathode bias or fixed bias. Aug 6, 2013 · I am planing on using more than 250 ohms for the 6V6 cathode bias power resistors. Apr 28, 2016 · As such, fixed bias squeezes the most wattage from a pair of output tubes while also sounding punchy and tight in the process, relative to cathode biasing. Dec 20, 2022 · Having said that, checking the bias is never a bad idea given the cost of tubes these days. As quote on page. By varying the negative grid bias the technician can correctly set up your amp for maximum performance, thus ensuring that the valve is operating correctly. Those two Matchless amps are the only examples of cathode biased EL34 amps that I've seen. 70% is for fixed-bias amps. Aug 25, 2009 · Supposedly there are tonal differences. The tube has 330V to work with but can only pull-down to maybe 50V. 2) soften the attack as the availabile power supply current started to level off. Oct 30, 2008 · The bias shift that happens when a push-pull cathode-biased amp is driven hard has a time constant that determines how fast it recovers, typically a fraction of a second. The bias must be set correctly on the power tubes for the effect to work. There are a lot of factors that determine the sound. The 6L6 amps went to fixed biased in '55 with the exception of the 5E5 PRo. Just erase the trem sections, assuming you don't want trem, ground the junction of the output grid leaks and use cathode Jan 16, 2021 · Hi all! i recently acquired a little nice chinese amp, it's an ultralinear single ended EL34 integrated amp. in essence it is a 'big' 5E3 Deluxe. 5 250ohm shared impedance: 9,000 output power: 24w If i were to ha e 425V at the plate and fixed bias I'm guessing 60-75ma per tube and maybe 30 watts? Just a rough In class A, 80% is recommended and is pretty much the average. 4) dump more heat into the chassis since you would need close to a 20 watt cathode resistor . Fixed Bias A Vox AC4, like many amps, is designed to make the power tube's cathode slightly positive—a state that is commonly referred to in the guitar universe as cathode biased. In short – the cathode bypass capacitor “handles” any variations in the cathode current preventing the cathode voltage to vary as well. SV2 + our VCK Voltage Clamp Kit comprise the Power Scaling solution for 99% of all cathode-biased amps: For cathode-bias only; up to 750V plate (Va) up to 750V screen (Vs) Power range: 100% down to zero; Loudness range: unusably loud to unusably quiet; PCB size: 2″ x 1. (Clones of Marshall's 20 watt Lead and Bass amps) used separate cathode bias on the EL84s to get a bigger sound - whatever that means. -Zach Omega The Fender 5F1 Champ is a Class A cathode biased amp. ' Sampson had just left Jul 18, 2007 · Bias range - depending on how the amp is set up, a cathode biased amp *may* be able to take a different tube type without overworking it. Mar 17, 2023 · In fact, I think someone would be hard pressed to do a blind fold A/B listening (using different guitars and A/B testing each one thru the amp) and tell which is cathode or fixed biased with any consistency at all. Genz Benz: Black Pearl. Fixed Biased amps have a firmer feel but less compression and sustain. I'm pretty sure EL34L are a straight drop in too. Apr 30, 2021 · Cathode bias amps are the least work intensive, as they do not really require biasing at all in a general sense. IMPORTANT: Screen stops should be a minimum of 1k-1W flame-proof for all tubes and this is especially important in cathode-biased amps. If the amp is cathode-biased, you should replace the cathode resistor for changing the bias level. It's got 9 volts on the EL84 cathodes across a shared 56 ohm resistor. 3″ 33mm; Controls included: Power Aug 29, 2021 · All of the el84 designs are in addition to the Therapy, z-Plus, Jetta, Z-Lux, Cure and Z80, for sure. and the bias checker tool that does 2 tubes at once worked perfectly. This can make cathode-biased amps sound "woozy" when handling large signals. But this amp is similar to other cathode bias amps, i. Plus an FX loop and footswitches for boost and loop. i've done work on my other amps, but none of them are cathode biased. dword eypg rwzayh rrj kfahyao uil zdeyf flwep obnfl netess
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