Marshall Amps. Even though we always state right on our customer invoices that the V4 phase inverter tube is the closest preamp tube to the power tubes, our inbox and message machine continue to overflow with the following question.
Because there is a cover on the tube farthest from the power tubes so that must be it! Yes, without a question of a doubt!!!
We are sure! V4 is closest to your power tubes!!!
The reason the V1 tube has an RF cover on it is to help shield it from noise and radio frequency interference because it is the most susceptible tube for these things.
We tube almost as many Marshall amps as we do Fender amps. These are hands down the best we have ever heard. They are very warm with a great clean tone and the breakup is raw, crunchy and gritty. They are simply a lot of fun to play. However, if power, headroom and ultimate thickness in overall tone is the mission then the JJ KT88's are it.
The only warning we have on the series amps is, always play one before you buy one! They are the most inconsistent Marshall's ever made. You can line up 10 of them no matter which model, and you will find 2 or 3 that sound amazing, then 2 or 3 that sound really flat and sterile with the rest of them sounding pretty good, but not amazing.
Good tubes and proper bias will help a few of the amps that fall in that middle ground but you will find that several will still sound mediocre at best even with good tubes and proper bias.
Buyer beware! The KT77's are also an option once again but because the 77's have more sizzle presence on the top end it's sometimes a bit too much if you're playing single coils so you will have to roll the presence back, with humbuckers the KT77's ROCK! They are BIG, warm and thick sounding. The ECC83S's do very well to tame the shrill high end and thicken up the mids and low end and a good balanced ECC83S in V4 for the phase inverter really helps these amps.
This does real well with humbuckers. The hand wired X84 amp is a nice addition but boutique pricey! These are biased real hot so cooler grades are necessary to get much tube life from them. We get LOTS of questions about biasing these amps and lots of players tell us they are going to take the amp in to get it biased. Our response is "don't waste your money! We use bias probes to bias these but the test points and a multimeter will do just fine. If after you read all the info below, you still don't get it or have the courage to bias the amp yourself then head on down to your local grade school and find a fourth grader to give you a hand, that's how easy it is!We are often asked how to determine when a tube is bad without access to a tube tester.
Well although not all tube problems can be found without a tester, many problems can be.
Is phase inverter a tough tube position?
But keep in mind the same issues will arise in hifi stereo tube amplifiers and preamplifiers so audiophiles will find this article useful too. There are a couple very obvious things to look for.
First, every tube will have a heater filament that, when working, will cast a nice warm orange glow. What matters is that it is glowing to some degree. There are some tubes that have their filaments well hidden making it nearly impossible to see. In these cases you can carefully check if the tube is hot or cold.
Be careful not to burn your skin. The tube must be heated in order to function. If the filament has failed the tube is useless. The second thing to look for is the condition of the getter.
This is the greyish coating usually found at the top of a tube, but can be on the sides, or both top and sides, depending upon the tube type. When a vacuum tube develops an air leak a small crack or bad seal by a pin for example this getter color will change to pure white.
Third, look for a purple glow that is very focused around specific elements inside the tube. Do not confuse this with blue glow that is often cloudy and near the glass. The purple glow around wires or other elements indicates leakage and a tube with this should be discarded. Perhaps the most obvious thing to look for is any loose parts that have broken off inside the bottle. You can gently shake the tube as well and listen for rattling. But there are times when a properly biased amp has a tube that begins to red-plate.
A tube like this should be replaced. If not, the amp will eventually blow a fuse or worse damage other parts. In the event your amplifier will not power on, it is almost certainly due to a blown fuse. Check and replace and blown fuse and try again. If the visual inspections mentioned earlier do not help locate a bad tube we recommend hiring a technician to inspect your amp. Problems with preamp tubes are often due to microphonics and noise issues.
A microphonic tube will ring and amplify any outside noises such as bumping the amp, tapping on the bottle, or even footsteps as you walk across the floor. All tubes will amplify tapping to some degree but an unusable tube will be very loud and often feedback or squeal. In a guitar amp with many preamp tubes it can be difficult to determine which one is microphonic. This is because tapping any tube near the bad tube appears to be bad as well. Rest assured it is very unlikely to find multiple bad tubes all at once.
We suggest you tap each tube gently with a pencil or chopstick something wooden or plastic, not conductive and often the culprit will be louder or noisier than the others. Replace that tube and likely all will be quiet. In a home stereo amp or preamp these same steps can be followed. However one more trick that is useful is to swap a suspect tube to the same position in the other channel.
In a stereo amp you would use this same procedure to find tubes with any noise issues. Tube noise such as sputtering, hissing, popping can be tougher to find in a guitar amplifier.In many cases, these tubes are interchangeable and can easily be swapped. We will take a look at why you might, or might not want to swap out the different types of tubes. The 12AX7 is by far the best known preamp tube among guitar players. It has a Gain output ofmaking it perfect for the preamp stage of an amplifier, allowing it to drive the power section harder, and enabling it to reach high levels of distortion.
The 12AX7 is also used in many audio preamps and in guitar effects pedals. There are many versions of the 12AX7 tube and many brands. The version of the 12AXY tube is a military version that is rugged and has a lower Gain of The 12AT7 is another very well known tube among guitar players. It has a much lower Gain output at 60, but what you lose in Gain you get back with more headroom, higher fidelity, and an increased current output.
Because of their high fidelity they are also used in many tube microphone preamps, compressors, and recording equipment. They are also used in many organs. Because of their higher current you sometimes see them driving effects such as Tube Driven Spring Reverb in many guitar amps.
Just like the 12AX7 tube, the 12AT7 has many different versions created for specific reasons, such as low noise and ruggedness. The version of the 12AT7 has a lower gain of The 12AU7 is the last tube on this list and it has the lowest Gain, with an amplification factor of This is used much less as a preamp tube because of the low Gain, and more as a driver for the Tube Driven Spring Reverb.
The 12AU7 is also used quite often in the Phase Inverter position of the amplifier because of the high fidelity and great headroom that it provides. The 12AU7 is used in many hi fidelity audio systems and recording equipment, and the Current from the tube is enough to drive a pair of headphones or a guitar speaker. Because of this, it is used in many different headphone amps, several small one-tube guitar amplifiers, and in many home hobby projects.
The 12AU7 is also heavily used in all stages of organs. There are also many different versions of this tube that have been created for specific reasons, such as low noise, military grade and ruggedness.
As you look at each tube, you might notice that as the amount of Gain decreases, the amount of Current increases.Phase Inverter Preamp Tube Comparison / Shootout: JJ ECC83s & ECC803s, Tung Sol, Telefunken
As the Gain decreases, the amount of headroom increases, and fidelity is improved. Noise is also reduced with lower gain tubes. 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 need to look into your guitar wiring to get the proper resistance load necessary to use a 12AU7 in place of a 12AX7.
There are dozens of varieties of each of these tubes that span more than 60 years, and the sound that each creates will change over the course of its life.
One of the most fun aspects of tube amps is the never-ending quest for the perfect tone — that perfect tube. I encourage you to try out as many tubes as you can and to listen to the subtle differences, even in the same type of tubes, as this will inform you in ways that words and even sound samples cannot.
All About Audio Amplifiers.
If there are many tubes in the preamp section of your amplifier the first one will always be the one that has the largest impact on your sound, so start there. This will usually be a 12AX7 but you can swap it for a 12AT7.
Next, if you have tube-driven effects on your amp, try a 12AU7 or a 12AT7 and see if you prefer the results to a 12AX7 tube in this part of the amp. Now you can think about any other tubes between the first one and the PI. Just keep experimenting until you have YOUR sound, and….
Your email address will not be published. Skip to content Let's take a look at the less glamorous, but certainly important type of amplifier tube - the preamp tube.For a look at the cathodyne from a hi-fi persepctive, see my web exclusive book chapter here.
The cathodyne phase inverter is a cross between a gain stage and a cathode follower, because the total load resistance is divided into two parts and shared between the anode and cathode. It has been used in many popular guitar amps including the Fender push-pull Princeton, most Orange amps and several Ampegs. It is also known as the 'split load' or 'concertina inverter'.
However, it has received criticism from some quarters, though not always fairly. It is true that without due care and attention the cathodyne can produce some fairly ugly overdrive tones, but this is avoidable with a simple ValveWizard trick.
When the input signal swings negative the valve will reduce its conduction, so current through it falls. The voltage drops across the two load resistors therefore also fall, meaning the cathode voltage must fall while the anode voltage rises. When the input signal swings positive the opposite happens.
The output from the anode is inverted, while from the cathode it is not. Since the same current flows through both loads, the signals generated across them will be identical but degrees out of phase assuming we use equal loads. This might be seen as a disadvantage, but remember, we only need one triode, unlike a long-tailed pair.
This usually leaves you with an extra triode which can be used as a gain stage -the combination then provides about twice the gain of a long-tailed pair using the same two triodes. The cathodyne usually provides better balance too. Load Lines Any triode could make a good cathodyne. Valves with small internal resistance like the ECC82 can acheive greater swing into heavier loads, and are also easier to DC couple to the previous stage.
When choosing a load we are really only concerned with output signal swing. If you need to overdrive bigger bottles like EL34s then you might want to push this closer to k. For example, the blue load line in the image represents a total load of 94k with a V HT. In other words, the anode and cathode resistors are both 47k. The green line is an AC load line and represnts the effect of choosing a 1.
The valve sees two of these, or 64k. You can see from the green load line that the total output signal swing is about Vpp. However, this is shared between the anode and cathode, so we will actually get a maximum of 75pp from each output.Welcome, Guest. Please login or register. Home Help Search Login Register. The most important tube in your amp?
Author Topic: The Phase inverter! Read times. I have a Pignose! I hope someone can get some use out of them. Take care, Love, PeaceMaker. I actually use a 12BH7 in my phase inverter to get a sweet clean amp that takes pedals extremely well. I've tried all the tubes and a 12AX7 makes my little amp grind like a bastard,but it's got no clean headroom. Good for small clubs where I just do blues or classic rock but not so good at the medium sized clubs.
I prefer changing the PI tube rather than V1 cause V1 alters the tone too much for my liking on this amp anyway. Quote from: PeaceMaker on August 17,pm. Build problems? Read this first. Our front end is going into distortion. If there's no master volume, which stage distorts first depends on the design of the particular amp. Most maybe all of the classic amps were designed to have the output tubes distort first, so that you got every watt you paid for especially since output tubes then, as now, were the most expensive tubes in the amp.
Keeping this simple, it means it takes a lot less input signal for a given output signal. So here's where he dropped the ball: Most of the classic amps use feedback around the output stage, from speaker to the phase inverter or the stage ahead of the inverter in a split-load circuit. The feedback acts to linearize the output stage and reduce audible variations with different tubes, as well as due to the tube aging.
If your amp doesn't have output stage feedback, you will hear more variation with different tubes and will notice the effects of a tube aging and wearing out more readily. Unless the output stage is run class AB2 or class B or B2the phase inverter wasn't designed to deliver current to the output tubes, so reference to "current output specs" is meaningless. When the output tube grids approach 0v and are driven positive, they no longer look like an infinite input impedance and begin drawing grid current.
Because the phase inverter was not designed to deliver this grid current, the phase inverter sees a much heavier load when the output tubes distort. Because the 12AT7 has a lower internal impedance, it is better able to cope with the lowering impedance of the output tube grids when they distort.
However, at some point, the apparent input impedance of the output tube grids will drop low enough to drag down the 12AT7 too. We can't draw any general conclusions that apply to every ampbut it is fair to say that lower mu tubes with lower internal impedance are more likely to maintain their gain and output as the output tubes distort and draw grid current. Whether that is "good" or "bad" depends on your perspective I suppose.
Quote from: DummyLoad on August 18,am. John Level 3 Posts: Just reading the parts that HBP quoted, I'm thinking maybe the author was aiming at guitarists who aren't builders really, just giving them some very basic info about swapping tubes? True, but the amplifier blueprinting notion is geared towards individuals who are often novice technicians. What I mean is it originally put forth the notion that an amp could be fixed if all resistors, caps and voltages were within a gnat's-ass of the schematic values.
Welcome To the Hoffman Amplifiers Forum
I realized that my earlier posts sound like I'm trying to put him down, and honestly I'm not. In fact, as I mentioned, I agree with his overall observations.
I just wanted to clarify what really caused the results he describes, and try to correct some misleading information. I learned a lot of my earliest amp knowledge from a series of books that, well, had as much marketing as true info. I was somewhat frustrated to find out I had a fair amount of false or incomplete knowledge to un-learn as a result.Tube amps: build, repair, modify. Search this site. Navigation Home. Visit my blog. I've run across 7 names for different phase inverter circuits, but have only found 4 in the guitar amp schematics that I've looked at.
The purpose of a phase inverter is to provide 2 signals that are degrees out of phase with each other. These signals drive each half of a push-pull power tube pair. Longtail pair. This one had me going for a minute. V5A is a split load phase inverter, and V6A and V6B are amplifier stages to provide more drive to the power tubes. This is the first circuit that I've come across that has a gain stage after the PI.
This provides some possibilities if you consider adding a master volume. Longtail pair The long-tailed pair is perhaps the most common, and was used in many Fender, Marshall, and Vox models.
It uses 2 tube sections, and can provide gain. Randall Aiken has two great articles on in the Tech Info-Advanced section of his site if you want a thorough description and info on design. Some notes on the above diagram--it's a silverface Fender design.
I've got a bit on the difference from a blackface design. The difference is an attempt to balance the outputs of both halves. Negative feedback can be part of this circuit, as well as a presence control.
It's probably the second most common PI I've found.
It's used in Fender Princetons and some Gibson amp models. Others say the tolerance of the resistors is a bigger factor, don't bother. I haven't tried this to have an opinion. Gibson amp style Gibson amps commonly used this circuit, although I don't know its name. It's one of the easier ones to understand how it works. A voltage divider K and 6.
This makes the output of V2's plate out of phase with V1's signal. Gibson amps are reputed to sound good, although this circuit is not supposed to be one of the better ones from what I've read.
12AX7 COMPARISONS ~ Best and Worst
I don't think I'd use this in one of my homebrews. Transformer Interstage transformers can be used to invert the phase. I've read that the cost of the transformer and a phasing problem when negative feedback is used are reasons it's not too common.Log in or Sign up.
The Gear Page. Is phase inverter a tough tube position? Jul 12, 1. Messages: 4, Mesa rectoverb crapped out yesterday. Anyway I was swapping one tube at a time to see if I might get lucky, and v5 phase inverter 12ax7 the amp works correctly again. The tube in the amp was an Electro-H tube, the only non-mesa so I figure its happened before. Other amps I've had the same. Is the phase inverter tube pushed harder, do you just buy cheapos or will top shelf tubes perform any better?
Do you check those tubes in for instance a v1 position to make sure they are quiet or just stick whatever you can get in there, forget about it, and it either works or not? Jul 12, 2. Messages: 17, Tubes, especially modern tubes, can die or get noisy at any time I even worked on an old Ampeg amp one time that had the tubes rusted into their sockets and the amp was still working.
Today, you're lucky to get a year out of a modern tube. NOS tubes will likely last a lot longer but they aren't immune to defects either and you have no idea how they were handled VaughnCJul 12, HipKitty and wetordry like this. Jul 12, 3. Messages: In many amps the phase inverter has its own power node with voltage higher than all the preamp tubes, so yes, the PI position can be tougher on the tube than the other small bottle positions. Jul 12, 4. Thanks, will pick up a few spares and maintain low expectations!
Avatar TechLes Paul Louie and chillybilly like this. Jul 12, 5. Messages: 3, Might want to invest in a decent old stock tube for the phase inverter. Tone MeisterJul 12, Jul 12, 6. It depends on the amp. In some amps, the cathode follower is the one being subjected to the most abuse. In others, it might be the reverb driver.