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| ultraman_cosmo |
 Posted: Tue Aug 12, 2008 8:14 pm Post subject: |
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Mod Squad
Joined: 29 Oct 2004
Posts: 1665
Location: Mines resort city
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Cut n paste.
Proper Care of your Tube Amp
Tube Amps are generally going to be just as reliable as their solid-state counterparts if you just observe the following things about them. Besides that tube amps kick butt... Read ON....
1. Take a little extra care in transporting them. While you can generally bang around and lightly toss solid-state amps into trunks, back seats of cars, truck beds, etc., with tube amps you have to be a little more careful. What i generally do when transporting tube amps is set aside a special place in the car so that the amp isn't going to be jostled around with hard shocks when i make abrupt movements with the car or hit bumps. Generally this means the back seat or the trunk with some towels or clothing around the amp. When you get to the gig, just make sure that you take special care not to bump the amp into other things, or to just drop the amp on the floor, if you're in the habit of doing that.
2. Make sure that there is proper ventilation for the tubes. Tube amps run hot--especially if they are wired in class A--and they need proper ventilation. Generally this just means that you shouldn't put your polish cloth or set lists over the ventilation holes, and you shouldn't set the amp right against a wall so that there is no air to get to the vents. Some players even keep a fan on the amp, though i don't think this is necessary.
3. Change the power tubes regularly. "Regularly" means a lot of things to a lot of different people. GENERALLY SPEAKING, six months to a year is fine for most power tubes if you're gigging regularly (say, once a week or once every other week) and rehearsing regularly--and this means at typical club volumes. If all you do is play the amp at home at bedroom levels, the tubes can last two years or more. If your amp is bias-adjustable, then you need to make sure that the bias is set when you change power tubes. If your amp is fixed-bias, it's generally a good idea to stick with the same power tubes that came with your amp.
4. Make sure that a speaker is ALWAYS plugged into the amp. Tube amps need to see speakers plugged in at all times, so you cannot run a tube head or tube combo without the speaker plugged in! This is a big mistake and can cost you $200-300 if your amp blows a transformer. Even after you replace the tranny, the amp often sounds different--some describe the amp as being "neutered" after replacing a blown transformer.
5. Make sure that the speakers are plugged in at the proper impedance--or at the very least, a mismatch in the "safe" direction. The best scenario is to match the impedance of the speaker or cabinet with the amp--if your speaker cabinet is 8 ohms, your amp should be set for 8 ohms for best results. If you plug this same 8-ohm cabinet into the 4-ohm setting on your amp, that will also be safe, but you will generally lose about half of your power as a result of the mismatch. If you take this same 8-ohm cabinet and opt for the 16-ohm setting on your amp, you're going to likely blow the head up as it tries to produce twice as much power. again, this can result in a blown transformer and the same neutered tone if you have to replace it.
6. Use the standby switch when powering up and powering down. The standby switch allows the amp to sort of "warm up" and allows the tubes to settle into a sort of equilibrium state before it gets slammed with high voltage. If you generally let the amp warm up or down in standby for about 30 to 60 seconds when powering up or down, you'll find that the tubes last longer.
That's about it, really...taking care of a tube amp is really not as difficult as one might make it out to be. With a little care and some maintenance, the amp is going to sound fantastic for a lifetime!
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Maiden, loudness, ACDC, black sabath, deep purple, jimmi and vinnie moore
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| ultraman_cosmo |
| Posted: Tue Aug 12, 2008 8:16 pm Post subject: |
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Mod Squad
Joined: 29 Oct 2004
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Great article.
paste it here, so ia tak hilang dan senang baca kat satu tempat jer
Tube Amplifier Care and Hygiene
by César Diaz and Daniel Jacoubovitch
Like teeth, amplifiers are a lot less exciting to routinely clean and care for than they are to repair in an emergency.
Not that amps need daily flossing and brushing, but they do get gummed up with use. If the crud they pick up over time isn't cleaned off occasionally, they'll develop serious problems requiring professional care.
Many of the irritating, sound-robbing problems that plague older tube amplifiers can be traced to dirt and oxidation that have accumulated on contact surfaces over the years. Dirt and oxidation deposits in tube sockets and amplifier controls cause unwanted distortion, loss of volume and a wide range of crackling and popping noises.
The vintage Fender, Magnatone, Ampeg and other tube amplifiers that have come to be prized by rock and roll players have all seen enough use and age to suffer from these symptoms.
Just because an amp says Fender on the front and is covered in tweed doesn't mean it will put out the sweet, singing tones that you expect from it. During the years that fifties and sixties tube amplifiers have been picking up value and a cult following, most of them have also been picking up sound- and power- robbing dirt and oxidation.
Airborne dust that settles in amplifiers is conductive and electrostatically charged. Dust deposits interfere with signal transfer between components, causing stray noises, distortion, and generally dissatisfying amplifier performance. The dust's electrostatic charge attracts more airborne dust, causing more interference with the amp's circuitry, further hastening amp failure.
Oxidation deposits on amplifier-control and tube-socket contact surfaces also impede signal transfer, causing unsatisfactory amp performance. Sewing machine and 3-in-1 oil foolishly squirted into amp controls fouls the components and attracts more sound-robbing dirt. The more conductive contaminants settle on amplifier surfaces, the higher the risk of arcing – current taking a component-destroying jump between normally unconnected electrodes.
In the worst case, dirt and oxidation can combine with moisture to cause the big "C" – catastrophic failure: the destruction of multiple components due to arcing and consequent short-circuiting across a large surface of amp circuitry. In the usual -less drastic-case, dirt and oxidation rob an amplifier of power and clarity.
A simple amp tune-up requiring only a few tools and supplies can clean up the sound of any older tube amp considerably. The tune-up is part of the maintenance routine that a good service shop will do as part of most repair jobs. Many amps brought in for repair only need this basic tune-up, and perhaps a tube or so, to get back into service.
Doing the job at home will avoid needless service expenses by eliminating the common causes of poor amplifier performance. When the amp does need to go to the shop, having it clean will save you from paying for the bench time it would otherwise take to get that part of the job done. Also, from the repairman's point of view it's no fun to have to go wading through someone's audio toilet bowl – dust, grease, rust and beer that leaked in and crystallized on the chassis and circuitry – looking for a failed component.
After the amp is cleaned up, some attention to how it's stored and used will protect it from dirt and oxidation build-up, and keep it working and sounding right.
It's a good idea to let your amp sit unused for a couple of days before the tune-up. This will give the filter capacitors some time to lose their charge and you a chance to round up supplies for the job.
Letting the capacitors discharge slowly is preferable to having them do it all at once through your body while you're poking around inside the amp. Having the supplies you need on hand makes the job go faster; you'll want screwdrivers, some contact cleaner (César uses Gunk brand choke & carburetor cleaner and WD-40), a toothbrush and – unless you own an air compressor – an aerosol can of compressed air. If you know how to use them, soldering supplies and a volt/ohm meter can also come in handy – but aren't essential.
Start by unplugging the amp from the wall, the speakers from the amp, and removing the amp chassis from the case. For Fender amps, removing the chassis involves unscrewing the upper back case panel, then unscrewing the chassis from the top of the case. Put the screws, nuts, and lockwashers where they won't get lost.
With the chassis out of the case, you can locate the filter capacitors you'll want to avoid touching as you perform the tune-up. These will be cardboard cylinders (usually orange or tan or vintage Fenders) with "+" printed near one terminal. It's also a good idea to steer clear of wiring connected to the power transformer (that's the large, heavy one); it's a discharge path for the filter capacitors.
If you haven't given the capacitors a couple of days to discharge – or if you just want to be cautious – you can use a short length of insulated wire with alligator clips on the ends to discharge them. First, make certain that the amp is unplugged. Attach one alligator clip to a capacitor's positive (+) lead, then touch the other clip to the amp chassis several times. Repeat the procedure for each capacitor marked with a voltage (VDC) rating higher than 25. The time spent on this precaution can spare you from a numbing electric shock that you'll remember long after the amp is back together.
Now that the coast is clear, you can proceed with the tune-up. Start by cleaning dust and dirt off of chassis, component, and connection surfaces. Use compressed air to blow loose dirt away. For dust stuck to component and chassis surfaces, César works with a toothbrush in one hand and a can of compressed air. Don't waste time on crud that's leaked out of dead capacitors; it's there to stay.
As you clean off solder joints, examine each connection carefully to see if the wire is solidly joined to its terminal. Wires that wiggle loosely from their connections and solder joints showing visible breaks can degrade your sound. If you have a volt/ohm meter and soldering supplies, this part of the operation is a good time for checking circuit continuity and desoldering and resoldering worn connections.
Tighten down the power transformer screws. On tweed Fender amps, the only way that the transformers are grounded is through their mounting screws. A poorly grounded transformer can cause intermittence in the amp's output. You may need to substitute mounting screws one size larger than the old ones to restore a good connection between transformer and chassis.
With the underbrush cleared, you can start work on the tube sockets and tone and volume controls – areas particularly sensitive to interference from dirt and oxidation. You'll be using solvents and friction to clean contact surfaces. The cleaner you get and keep these surfaces, the louder and clearer your amp will sound.
Clean one tube socket at a time. Take out the tube, spray contact cleaner – or Gunk followed by WD-40 – into the socket, then re-insert it and shake it around in the socket to expose clean contact surface. Be careful with the spray, the idea is to use enough to clean the part you're working on, without saturating the surrounding area. If the socket was particularly dirty, repeat the procedure before moving on to the next one.
Clean the tone and volume controls – potentiometers, or "pots", for short – by spraying contract cleaner through the openings in their covers. Spray in a little cleaner, turn the shaft briskly back and forth a few times, then flush with another shot of cleaner. If you're using Gunk, flush with WD-40 right after you spray the carburetor cleaner; leaving Gunk on too long can freeze the control shaft.
Re-mount the amplifier in the case and reconnect the speaker. Now that your tube sockets and pots are clean, you can troubleshoot your tubesa – another potential source of stray noise, distortion, and weakened sound.
All tube amplifiers have at least one power tube (such as 6L6, 6V6, or 5881), and at least one preamplifier tube (such as 12AX7 or 7025). Most older amps will also have one rectifier tube (such as 5Y3GT, 5U4, or GZ34).
Drugstore tube testers can be used to tell if tubes are dead or alive, but they don't tell you anything about whether a live tube is causing sound problems. Tube problems that won't show up on a standard tube tester can be diagnosed in the amp.
With all the tubes in their sockets, the tube covers off, and nothing plugged into the amp inputs, turn the power on and crank all the controls up to maximum.
Troubleshooting rectifier tubes is easy; they're either dead or alive. If the rectifier tube lights up when you turn the amp on, it works.
A power tube that doesn't light up is dead for sure. A healthy power tube will light up and give off a medium-intensity orange glow. Don't worry about power tubes that give off a dull blue glow; they don't necessarily need replacement unless they have other problems.
Power tubes that glow bright red, however, are a sign of trouble. Try another power tube of the correct value in the socket. If the new tube still glows bright red, there is probably a failed component in the circuitry to that tube, and you should take your amp to a professional to get the problem tracked down and fixed.
Tap each power tube with our fingernail, tubes that send a loud, low-frequency noise through the speaker when they're tapped should be replaced.
Inspect the shaft on the base of each rectifier and power tube to make certain that its guide pin – the ridge that slides into a groove in the socket's center hole, aligning the tube pins with their proper socket connections – is intact. Incorrectly inserted tubes due to broken guide pins are probably the single most common cause of amplifier failure.
Use your fingernail to tap each preamp tube. If the tapping is amplified and comes out of the speaker as a loud, high-frequency noise, the tube is causing problems. If there's another socket that takes the same value tube, try the questionable tube in that socket. Because of differences in circuitry leading to sockets that use identical tubes, a tube that makes noise in one socket can work just fine in another. If the tube causes problems in all the sockets you try, you'll need to replace it with a new one.
You can now check out the amp's speaker(s) as the last operation in your tune-up. Plug in your guitar and set the amplifier to a low volume; you won't be able to tell the difference between amplifier and speaker distortion at high volume. Slowly play a few full chords. If the speaker sounds distorted or gravelly it may need repair. Try the amp through another speaker (one you know is working right). If the problem goes away, go ahead and get the first speaker reconed.
Now that you've rid your amp of dirt and oxidation and substituted or replaced problem tubes, it should sound clearer, louder, and generally healthier than it did before the tune-up. a clean amp is a happy amp.
There are precautions you can take to keep it clean and happy. Protect it from dust by keeping it covered when it isn't in use. You can slow down oxidation build-up by keeping the amp away from damp places and protecting it from rapid temperature changes. These changes cause condensation inside the amp, depositing moisture on components and connections. The moisture is particularly harmful to components that are made with paper or cardboard – capacitors and transformers – weakening them and hastening component failure. The moisture also cause oxidation, fouling the tube sockets and controls you've just finished cleaning.
Never power up a cold amplifier; let it come up to room temperature before you turn it on. Sudden heating can crack cold power tubes. Cold air inside the chassis condenses as the amp warms up, depositing moisture on component surfaces that can cause arcing and component failures.
Don't keep the amp anywhere you wouldn't be comfortable sleeping. Unless you're a lot weirder than most vintage amp owners, this means you'll never leave your amp in a car trunk overnight or store it in a damp basement.
Semi-annual tune-ups and regular attention to how you use and store your amplifier will keep it sounding sweet and strong – and save you the pain and expense of avoidable breakdowns.
_________________
Maiden, loudness, ACDC, black sabath, deep purple, jimmi and vinnie moore
And Now all jazz. |
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| browndog2woof |
| Posted: Tue Aug 12, 2008 8:38 pm Post subject: |
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Mod Squad
Joined: 10 Nov 2006
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yo cosmojojo.
hensem man...
woof! |
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| ultraman_cosmo |
| Posted: Tue Aug 12, 2008 9:20 pm Post subject: |
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Mod Squad
Joined: 29 Oct 2004
Posts: 1665
Location: Mines resort city
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So next time kalo orang tanya pasal tube amp care, aku juat point to this tread. Sebab gua selalu bz semacam mengalahkan menteri, so senang semua boleh baca.
Amp Care & Abuse
Roccaforte Amplifiers are built to the highest industry standards. Even though you can tour with a Roccaforte product and play night after night shows with no problems, there is still a level of care required to maintain this level of reliability. The following is a list of rules that, if kept unbroken, will insure the warranty stays valid.
Power Attenuators
Using a "dummy load" or "power attenuator" will damage your Roccaforte product, and void its warranty. These type of products wear out tubes at an accelerated rate, and in some cases cause RF to be generated in the output, which can destroy an output transformer.
Pulling Power Tubes to Lower Output
Your Roccaforte amplifier produces more output than its' advertised specs. Removing output tubes on the 80+100 watt models to lower their power ratings will not reduce overall volume. Because these amplifiers have higher current power supplies, damage may occur if two tubes are removed, and this will void your amplifier warranty.
Variacs
Do not use a variac to lower voltages below the amplifier's rated input. Running vacuum tube "heaters" at a lower than rated voltages causes premature tube wear. There is only person in the world who has ever been able to get great tone using a variac, and he has to change his tubes every night. Tubes that show any "cathode stripping" will not be covered by warranty. Depending on where you live and how close you are to a powergrid, you might be over powering your amplifier. I know people here in the US that have as high as 130V coming from their wall outlets. Its good to know where you stand here, so check it or have it checked. It could also be low too. This is one area where the variac is acceptable to use, you can adjust it to the proper amplifier input voltage. Make sure your variac is grounded.
Power & Standby Switches
The purpose of the "standby" switch is to allow the output tubes to heat up fully before they see any high voltage. The tube's "cathodes" can be worn out prematurely if not fully heated and the tube is conducting. The power switch should be turned on first with the amplifier in the standby mode. I recommend the amp be turned on in standby mode for at least 3 minutes before switching from standby to full power. When powering down, the amplifier should be first put on standby, then the power switch turned off. This practice will give your set of tubes a much longer life.
Speaker & Instrument Cables
Here's what I use: ProCo or any MI gear cable manufacturer that uses American made Beldon wire, or an equal equivalent. I like to see Switchcraft cables ends, which have been an industry standard for many quality musical equipment products. Be warned that many other high end cable manufacturers use low cost low quality overseas made parts that fail very early, sometimes even right out of the box!
Speaker cable does not need to be the size of your finger around. Going from a guitar amplifier to a cabinet (3-4ft), 18ga will never go bad. Don't be fooled by "audiophile" type speaker cable reviews, you will only hear a difference if you think you will, not because you actually can.
Transporting Amplifiers
OK, this where some major common sense comes into play. Your amplifier has vacuum tubes in it, and they are made of glass. Never set your amplifier down hard, bang it against anything, drop it or roll it across rough terrain.
Biasing
Running any Roccaforte product at a higher than rated bias spec for the tube type and plate dissipation ratings will void your warranty.
Cleaning
Amplifier and speaker cabinets can be cleaned with a damp cloth using a mild soap and warm water. Never use any plastic or tire shine products that coat with an "armor" type liquid. These type of products over time will cause discoloration of the vinyl and cause your amplifier to become a dust magnet.
Tube Replacements
OK, the Internet is a great place to ask about tube types, right? Wrong! Many people giving advice have less experience than the person asking for it. I recommend you ask the manufacturer what to use and what to stay away from. Never assume a vacuum tube is good and install it into your amplifier.
Fuses
A fuse is a protection device that's designed and rated to blow if any related circuitry gets shorted. This keeps you from having major damage or a fire. Never replace a fuse with anything but the proper replacement. It's not too common that fuses just get old and fail. If a fuse fails, replace it and, if it blows again, stop. The amplifier has a problem and needs to be seen by a qualified tech.
Your Amplifier is Not a Coaster
Never set any drinks on top of your amplifier. Find a table and use a coaster!
Doug Roccaforte
_________________
Maiden, loudness, ACDC, black sabath, deep purple, jimmi and vinnie moore
And Now all jazz. |
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| ultraman_cosmo |
| Posted: Tue Aug 12, 2008 9:27 pm Post subject: |
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Mod Squad
Joined: 29 Oct 2004
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Location: Mines resort city
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biasa biasakan lah berpinar pinar bijik mata yaaa... hehhehehe
Tone Tips: Tube Amp Maintenance
Like just about anything worth owning, even the best tube amplifiers available need occasional maintenance to continue performing at their peak. In this age of low or no-maintenance consumer goods, where you’re more likely to toss your DVD player in the nearest Dumpster and swing by the local big box retailer to pick up another one for $49.95 than to actually get a small fault repaired (which, no doubt, would cost you considerably more than the new unit), the notion of routine maintenance for electronic goods has largely fallen by the wayside. Genuine all-tube guitar amps, however, even brand new ones, are not like other consumer electronics products; they are the archaic technology of a bygone era, and thanks to that they can sound sweeter than any fancy box of bits that has been conceived to replace them. As such, though, they need a regular check and tune up. Treat them right, and they’ll reward you not only with stunning tone, but flawless performance.
I have known plenty of guitarists who were very much into tube tone, but went from amp to amp with a turnaround rate that found them changing amps every couple of years or so—coincidently, about the amount of time it took for the new tubes the amp came with to grow a little tired sounding, and for a few other minor maintenance items to raise their heads. Re-tubing an amp is something you can almost always do yourself (although some fixed-bias amps will require rebiasing when output tubes are changed, and that’s a job for a professional). If you are gigging or even rehearsing regularly, output tubes are almost certain to need replacement every two years at best, and possibly even every six months or so if you are really playing a lot. Even tubes that are sonically “good” can become noisy or microphonic, and thus require replacement. Preamp tubes generally last a lot longer, but it’s worth swapping in a fresh, high-quality preamp tube in the preamp and phase inverter positions every so often—ideally after you have put in new output tubes—to see if it perks up your amp considerably. If so, you’ve got a tired preamp tube or two on your hands as well. Find the culprit by process of elimination. Be sure to follow your amp manufacturer’s owners manual’s instructions for tube replacement, and use good, properly tested tubes as your replacements.
Every few months, the tube amp user ought to also perform certain items of routine physical maintenance to keep the structure of the amp firm and rattle free. These are no-cost jobs that you can perform yourself with the average home tool kit. Check that all speaker-mount nuts or bolts are tight, and if not, adjust. Don’t wrench them down with all your might, but turn each nut or bolt until it is finger-tight (meaning you can’t turn it any more with your fingers), then give it another 3/4 to 1 1/2 turn or so with the appropriate tool. Tightening the speaker mounts “as much as you possibly can” is not the goal, and can do more harm than good, possibly warping the speaker frame (basket) and/or damaging the wooden baffle that it’s mounted to. Anything else that is bolted or screwed to this vibrating mass of wood and iron called a guitar amp will occasionally need to be tightened too: check the mounting screws or bolts holding your power transformer and output transformer to the chassis, the speaker baffle, the back panels on the cabinet, the handle, the feet/glides, and even the mounts of the chassis itself. Anything that is loose can and will rattle when you get that amp cranked up. I can’t count the times I was convinced that I had a speaker that was on its way out, only to find it was a loose handle or back panel vibrating sympathetically to the music.
One item of more invasive maintenance that will need to be performed occasionally is one that is commonly referred to as a “cap job.” The electrolytic capacitors, also called “filter caps,” that perform filtering duties in your amp’s power stage, to keep troublesome electrical ripple and other noise out of the system, are inherently short-lived components compared to just about everything else in there, other than tubes. Good filter caps should last at least 10 years, and sometimes will go as long as 20 without causing problems. You even stumble upon 40 or 50-year-old vintage amps now and then which appear to be going strong with the original filter caps. By and large, though, these parts will need replacing 15 or 20 years down the road, and if you have acquired an older amp that has never had a cap change, it’s a good piece of preventative maintenance to get one done sooner rather than later. Faulty filter capacitors will lead to an amp that is noisier and flabbier sounding in the low end in particular, and at the extreme will also introduce dissonant harmonics called “following tones” or “ghost notes,” that sound a little like a lower and out-of-tune tone that follows everything you play (kind of like a very sick octave-divider sound). The cap job is one for the professional amp tech, because these parts lurk at points in the circuit where the highest voltages are handled, and they can also store high-voltage charges and release them—into you!—even when the amp is switched off and unplugged. That said, the average cap job shouldn’t be all that expensive, and getting it done can really sweeten and firm up a tired amp.
Resistors will also drift and sometimes fail entirely in older amps, and you will occasionally need to turn to a pro to change a few of these, too. In particular, the 100k ohm carbon comp resistors in the preamp stages of vintage Fender amps (and others) are often the culprits when an amp produces crackling, hissing, and sizzling sounds, particularly while warming up. Replacing these with fresh carbon comp resistors can frequently be an easy cure for preamp noise issues. The larger resistors in the power stage also occasionally wear out from all the heat and high voltages they have to deal with. These aren’t even in the signal chain, so don’t hesitate to have them replaced when necessary. If your amp is in the shop for any of these more invasive procedures, it’s also worth having the repairman check that your tube sockets are all tight, and retension the pins if not, and take a few minutes to squirt some contact cleaner into all the pots and jack contacts too.
This might sound like a lot of work, but is the kind of thing you’ll want to be prepared to deal with if you want to live in the tone zone. This is fact-of-life stuff for even the best tube amps out there, and you want to pony up and get it done. Chances are, even that mid-’60s amp from the golden days of tube tone that you acquired for top money, and which appears to be in unusually fine condition, will need to go through most, if not every one, of the items listed above. That doesn’t mean you were “ripped off,” and it might still be a great find and even in the “top original condition” it was advertised as being in. But it’s an old tube amp, it needs love and attention. Give it the time and the $150 or $200 it will take you to achieve all of the above, and it will astound you with the gratitude of superlative tone. In the end, that’s usually less trouble—and even less expense—than selling it off in a few years, or months, when it starts to sputter and cough and you begin the hunt for yet another great sounding amp … which in turn, will eventually sputter and cough and sound tired and need to be sold. Fix ’em up before you fire ’em off; in the end, the little time and money spent will pay dividends.
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Maiden, loudness, ACDC, black sabath, deep purple, jimmi and vinnie moore
And Now all jazz. |
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| ultraman_cosmo |
| Posted: Tue Aug 12, 2008 9:29 pm Post subject: |
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Mod Squad
Joined: 29 Oct 2004
Posts: 1665
Location: Mines resort city
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Tube Amps are generally going to be just as reliable as their solid-state counterparts if you just observe the following things about them. Besides that tube amps kick butt... Read ON....
1. Take a little extra care in transporting them. While you can generally bang around and lightly toss solid-state amps into trunks, back seats of cars, truck beds, etc., with tube amps you have to be a little more careful. What i generally do when transporting tube amps is set aside a special place in the car so that the amp isn't going to be jostled around with hard shocks when i make abrupt movements with the car or hit bumps. Generally this means the back seat or the trunk with some towels or clothing around the amp. When you get to the gig, just make sure that you take special care not to bump the amp into other things, or to just drop the amp on the floor, if you're in the habit of doing that.
2. Make sure that there is proper ventilation for the tubes. Tube amps run hot--especially if they are wired in class A--and they need proper ventilation. Generally this just means that you shouldn't put your polish cloth or set lists over the ventilation holes, and you shouldn't set the amp right against a wall so that there is no air to get to the vents. Some players even keep a fan on the amp, though i don't think this is necessary.
3. Change the power tubes regularly. "Regularly" means a lot of things to a lot of different people. GENERALLY SPEAKING, six months to a year is fine for most power tubes if you're gigging regularly (say, once a week or once every other week) and rehearsing regularly--and this means at typical club volumes. If all you do is play the amp at home at bedroom levels, the tubes can last two years or more. If your amp is bias-adjustable, then you need to make sure that the bias is set when you change power tubes. If your amp is fixed-bias, it's generally a good idea to stick with the same power tubes that came with your amp.
4. Make sure that a speaker is ALWAYS plugged into the amp. Tube amps need to see speakers plugged in at all times, so you cannot run a tube head or tube combo without the speaker plugged in! This is a big mistake and can cost you $200-300 if your amp blows a transformer. Even after you replace the tranny, the amp often sounds different--some describe the amp as being "neutered" after replacing a blown transformer.
5. Make sure that the speakers are plugged in at the proper impedance--or at the very least, a mismatch in the "safe" direction. The best scenario is to match the impedance of the speaker or cabinet with the amp--if your speaker cabinet is 8 ohms, your amp should be set for 8 ohms for best results. If you plug this same 8-ohm cabinet into the 4-ohm setting on your amp, that will also be safe, but you will generally lose about half of your power as a result of the mismatch. If you take this same 8-ohm cabinet and opt for the 16-ohm setting on your amp, you're going to likely blow the head up as it tries to produce twice as much power. again, this can result in a blown transformer and the same neutered tone if you have to replace it.
6. Use the standby switch when powering up and powering down. The standby switch allows the amp to sort of "warm up" and allows the tubes to settle into a sort of equilibrium state before it gets slammed with high voltage. If you generally let the amp warm up or down in standby for about 30 to 60 seconds when powering up or down, you'll find that the tubes last longer.
That's about it, really...taking care of a tube amp is really not as difficult as one might make it out to be. With a little care and some maintenance, the amp is going to sound fantastic for a lifetime!
_________________
Maiden, loudness, ACDC, black sabath, deep purple, jimmi and vinnie moore
And Now all jazz. |
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| ultraman_cosmo |
| Posted: Wed Aug 13, 2008 12:30 pm Post subject: |
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Mod Squad
Joined: 29 Oct 2004
Posts: 1665
Location: Mines resort city
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Article baik dari guitarnut.
Amplifier Myths, Fantasies, and Facts
Last Updated 07/08/2000
The guitarist cannot begin to make intelligent gear decisions without a basic understanding of tone, power, and volume. Many experienced guitarists still nurse and cherish "facts" that are so incorrect as to be pure fantasy. Some of these guitarists have achieved great tone – but only after years of very expensive trial and error and without ever really understanding what they did to finally get the killer tone they were looking for.
Knowing the facts about amplification can help guitarists take the fast track to their ideal rig and save them thousands of dollars along the way.
Each of the following paragraphs debunks a popular myth and tells the real story. Since most readers are probably more interested in playing than becoming technicians and engineers, I've intentionally simplified some of these subjects a great deal.
You'll find a lot less bias against solid-state amps here than in most articles. So much so that you might think I'm a fan of solid-state amps. That is not the case at all – I strongly prefer tube amps and suspect I always will (I'm a sucker for glowing lights and shiny things). However, this article is about facts and it is a fact that solid-state amps have come a long way and are an appropriate choice for some players and some situations. In fact, even though I still strongly prefer tube amps, if I were doing the weekend warrior thing I would probably use one of the better solid-state amps for gigs!
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Power Myths
Several common myths about amplifier power are debunked below. The bottom line is that you should select an amplifier for its features and tone, and consider power level as the least important criteria in your selection.
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1) My 100-watt amp is twice as loud as your 50-watt amp. This is one of those really sad myths that just won't go away in spite of volumes of empirically and mathematically proven, unambiguous, clear, undisputed, scientific knowledge to the contrary – knowledge that every tech worthy of a soldering iron learned very early in their training. Music store sales weenies on commission love this myth because it's sold thousands of 100-watt stacks (not to mention the follow-on sales of expensive replacement tube sets). Here are the facts:
All other things being equal, a 100-watt amp will be just perceptibly louder than a 50-watt amp. It takes about a ten-fold increase in power to double perceived volume. That's right, you'd need a 500-watt amp to be "twice as loud" as your buddy's 50-watt amp. Even more thought-provoking is the fact that a 50-watt amp will only be perceived as a little bit louder than a 15-watt amp driving the same cabinet!
All other things are almost never equal. There are so many variables controlling sound pressure level (SPL) and perceived volume that it is quite common for a small amp to sound louder than a much more powerful amp.
Cab design, speaker size and efficiency, signal compression, and several other factors have far greater impact on perceived volume than does power level.
The initial purchase price of a 100-watt amp will be significantly higher than a 30-watt amp with similar features.
It will cost you signficantly more to re-tube a 100-watt amp.
If you are driving a 30- or 50-watt amp hard enough to require frequent re-tubing, chances are very good that you will also drive the 100-watt amp hard enough to require frequent retubing (at significantly higher cost).
Am I saying 100-watt stacks are evil? No. No one really needs one (see below) but if you want one be my guest. All I'm saying is that you should be aware that you are spending a lot of money to purchase a miniscule increase in volume.
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2) I need a 100-watt amp 'cause my band has started gigging in clubs. This is a myth that I believe originates with hormonally imbalanced teens who have more experience watching movies about teen bands than they have playing real gigs. Unfortunately, it's a self-perpetuating myth because the rhythm player is going to get a big amp 'cause he's being drowned out by the lead player, then the bass has to get a 400 watt amp to be heard at all, then they need a 1200 watt PA system so that the vocals have some chance of being heard over the cacophony from the guitars and bass, and finally they end up having to mic the drummer even in a small club because the drummer is breaking sticks and skins and still can't be heard over the racket. Within a few years their hearing has been permanently damaged and they all decide that they need bigger amps! Three-quarters deaf, they finally make the big time and the guitar magazines write about the gang of three 100-watt stacks that the guitar hero uses on stage and all the wannabees have just gotta have the same rig. . . As you can imagine, this is another myth that sales weenies on commission are in no hurry to debunk! Well, here are the facts.
There is absolutely no venue that requires a larger amp and cabinet than one suitable for use as a stage monitor – provided that the members of the band don't get into a juvenile competition to outdo each other. Need more feedback? Fine, move closer to the amp, for crying out loud! Typically, a really good 30-watt rig with a suitable cab is ample! Depending on the composition of your band and the variety of venues you play, an even smaller rig mic'ed to the PA and then pumped to stage monitors may be even better. Note that while a good 30-watt rig has ample volume you may end up having to buy a more powerful rig to get other desired features.
At a small venue, a 15 to 30 watt amp can be placed behind the band in a traditional position and used without a mic. In this position the rig serves as a monitor for the guitarist and as the primary amplification for the guitar.
At a medium venue, the small rig can be placed in front of and facing the guitarist as a monitor, and be mic'ed and run through the band's PA. The band's PA speakers are placed along the front of the stage and facing out. This arrangement allows the sound to be balanced at the mixer and allows the band to flood a medium to large venue without damaging their hearing.
At a large to giant venue, that same small rig can be arranged much as described above but now the band's mixer feeds the house PA. This is the only way to reach the back of the room without dangerous SPLs near the stage at a large venue and would be required no matter how powerful a rig the guitarist has.
Smaller equipment takes up less space on cramped stages.
The money you save by purchasing a smaller amp can fund a nice power conditioner to protect your equipment and clean up powerline noise – the conditioner will cost less too since now you don't need one that will handle a billion watts.
If the band members will agree not to compete, all of them can recognize significant savings by not having to purchase unnecessary equipment.
Your band is far more likely to be called back for a repeat engagement if you provide a well-balanced, easily managed performance than if you are just obnoxiously and uncontrollably loud.
Many guitarists already have the monster amp – it isn't necessary to get rid of it. You can use an attenuator (see the attenuator myth) and perhaps a smaller cab.
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3) I need a small combo because I live in an apartment. This is sort of the opposite of myth two, above, and is closely related to myth one, above. While a small combo will certainly take up less room, it may or may not be easier to get good cranked tone out of it at apartment levels. First, read myth one again. If it's true that we have to increase power ten times to double perceived volume, then it is also true that we have to reduce power ten times to cut the perceived volume in half. Thus, even a tiny 5-watt single ended tube amp is going to sound about half as loud as a fifty-watt stack (actually, it will be a bit quieter than that because it is probably driving an eight or ten inch speaker instead of a 4X12 cab). Even that five-watt amp will be way to loud to run cranked in an apartment unless your neighbors are very tolerant. Here are some facts you should consider:
Even a 5-watt tube amp with an eight inch speaker is very loud by the time you crank it into distortion.
You can use an attenuator with either a large amp or a small combo. Keep in mind, however, that attenuating below about 1 watt per speaker starts to adversely affect tone – it seems that a certain amount of speaker drive is required to round out distortion (see recent articles on 3-stage amplification architecture tests at amptone.com). Even one watt into an 8" or 10" guitar speaker is likely to get you evicted.
Many small combos do not offer a master volume, thus making it impossible to even get preamp saturation at acceptable volume levels.
To get true "cranked tube tone" in an apartment at lease-safe levels you are almost certainly going to have to use a combination of attenuation and a sound-proof speaker isolation box with a microphone running to a mixer or stereo. This is true whether you are running a 5-watt, single-ended, class A combo with an eight-inch speaker or a 100-watt stack with a 4X12 cab.
It's not a good idea to run an amp inside of a sound-proof box, so even with a small combo you will need an extension speaker.
It's not much fun to try to enclose a 4X12 cab, so you'll also need an extension speaker with that kind of rig.
The lesson here, once again, is to select amplifiers based on features, not on power level. A tiny five-watt class-A amp with an eight-inch speaker and no features may not be very satisfying after a while, will be wholly inadequate for gigging, and still isn't quiet enough to run cranked in your apartment! Add a few features such as footswitchable channels, master volume, and an effects loop and that 5-watt amp starts to become pretty attractive!
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4) My tube amp has a master volume control that lets me get power-amp distortion at low volume levels. Yet another myth that sales weenies love (seems like there are quite a few of these, huh). The facts are:
With the possible exception of some very rare and expensive "boutique" amps, a so-called master volume does not reduce power output after the power-amplification stage as the name would seem to imply.
The master volume controls found on popular amps cut the power between the final preamp stage and the power amp.
In all popular tube amps, when you turn down the master volume, then turn up the gain controls to achieve overdrive, you are overdriving the preamp stages, not the power stage.
I firmly believe that manufacturers deliberately misnamed the "master volume" control to deceive consumers – but that does not mean that the control is useless. Quite the contrary, I regard a "master volume" control as an essential part of a good amplifier. The "master volume" control permits running the preamp at full saturation or beyond at reasonable volume levels and allows one to balance preamp and power amp saturation for a wide variety of sounds. I love "master volume" controls, I just think they should be named less deceptively!
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5) Power attenuators damage amplifiers. There is some truth to this myth. But, attenuators can be safely and successfully used – and every guitarist should know how and when they can be safely used. Here are the facts:
A properly designed power attenuator does not apply any more stress to the amplifier than does a speaker cab – in fact a good attenuator will usually apply slightly less stress than a cab alone. However...
...when using an attenuator, guitarists typically drive their amplifier much harder than they ever would when driving a cabinet directly. Driving the amp this hard will significantly reduce tube life regardless of whether the amp is driving an attenuator or a cab. As a consequence, it seems like the "attenuator wore out the tubes." In reality, the guitarist was just enjoying much more overdrive than he ever would have without the attenuator and is paying the piper.
Some amplifiers are simply not built to be driven hard. When the guitarist uses an attenuator and then runs the amp harder than he would have into a cabinet, very bad things happen and then the guitarist says, "that attenuator ruined my amp." No, driving the amp at "10" ruined it – the attenuator is only incidental in that you never cranked the amp to 10 because it was just too danged loud! This problem is particularly common with low-power combos. I have a little 15-watt class A Ampeg Jet J-12T. It's a great sounding little amp that I never cranked higher than about about "4." One day I decided to see if it would do "metal." Using a guitar with hot humbuckers I cranked the little Ampeg to "10" and played for about 2 minutes before the volume just became too painful (I was not using an attenuator, this was directly into the built-in 12" speaker). When I turned the amp back down to reasonable levels I could hear a crackling sound. In two minutes or so I'd blown both of the screen resistors and ruined the tubes. The tech at my local guitar shop called Ampeg (the amp was still under warranty). They told him, "fix it but tell the guy not to turn the amp up to 10 anymore."
Attenuators can be used safely if you follow these rules:
Make sure that the attenuator contains some inductance. This will help maintain natural tone and causes the impedance to increase with frequency.
The attenuator should either have approximately the same inductance as a speaker or should be of slightly higher resistance than a speaker. It is better to reflect a slightly higher than normal impedance through the output transformer than too low of an impedance.
Have a reputable tech "cool off" your amp. Explain to the tech that you are going to be driving the amp very hard into an attenuator and you want it biased a bit cold to save the tubes. This will cost a bit in tone (chances are you won't notice this because you probably never drove the amp so hard anyway) but will make the tubes last a lot longer and reduce the chances of damage to other components such as the expensive output transformer. A knowledgeable tech can also tell you if the model of amp you are using is known for blowing transformers and what have you (many guitar amps have output transformers that are not rated anywhere near the amp's max output).
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6) Power attenuators kill tone. Actually, it seems that well-designed power attenuators with inductive elements have little effect on tone until you attenuate to below about one watt per speaker. I suspect that the real issue is not so much the power level as the excursion of the speaker coil. At very low power levels the coil has very slow linear movement for a given frequency and thus has very little momentum accumulated when it reverses direction. At higher power levels the linear movement rate is much higher and the speaker tends to overshoot much more, rounding out sharp corners in the input signal. That's just a hypothesis on my part but, whatever the cause, the effect has been tested and measured by cybermonk at amptone.com.
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Distortion Myths and Solid-State vs. Tube
There are so many myths, many of them conflicting, that it is hard to know where to begin. Probably the most important thing to realize is that distortion can be broadly characterized as "hard" and "soft." "Soft" distortion is the holy grail for most but it's important to realize that both types of distortion are useful.
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1) Preamp distortion is bad. Preamp (even tube preamp) distortion is much harder than tube power-amp distortion but the fact is that most rock-distortion uses both preamp and power amp distortion.
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2) You can get great tube tone using tubes only in the preamp. The fact is that the "creamy" soft distortion most of us desire occurs only in a saturated power tube section. Tubes in the preamp do warm up the signal by introducing small impurities not typically present in a solid-state circuit, however.
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3) Tube and solid-state preamps sound the same. The facts are:
Tubes "warm up" the signal by introducing impurities not present in most solid-state circuits.
Tubes, even preamp tubes, go into clipping more gently than most solid-state circuits resulting in a slightly smoother transition to distortion. Running preamp tubes just at full saturation gives a very full tone that simply isn't found in solid-state preamp circuits.
Amp and effects manufacturers have been fairly successful in modeling tube preamp sounds using digital (DSP) and analog solid-state techniques.
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4) Solid state amps suck. This is only half true. The facts are:
Many solid-state amps do suck, especially older models and entry-level models.
Some newer solid state amps actually sound pretty good, especially for clean tones. None have truly "nailed" power tube distortion but modeling amps are getting close.
Many guitarists and most non-musicians can't tell the difference between the best of the solid-state amps and a tube amp except in a side-by-side A/B test – and some can't tell even then.
A good tube circuit anywhere in the amplification chain can "warm up" a sterile clean signal.
Solid-state amps are much lighter, more rugged, and more reliable than tube amps.
Solid-state amps typically deliver a much more consistent sound over a wider range of output volumes.
Many, many, guitarists who absolutely swear by tube amps and won't even test drive a solid-state amp never push their tube amps into power-stage distortion – and power stage distortion is about the only thing that a good solid-state amp can't do well!
Solid-state amps have come a long way but are still not quite "there," in my opinion. Some of them do a pretty good job of modeling preamp distortion but they aren't quite over the top modeling the power amp with it's complex interaction between power tube, output transformer, and speaker. Even so, nine out of ten people in the audience at a typical live gig aren't going to know or care whether you are using a good solid-state amp or a tube amp. If you do the weekend warrior thing and either play mostly clean or mostly with very heavy "metal" distortion then your best choice of gear might well be a multi-effects unit with a tube preamp driving a good solid-state amp!
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5) The entire signal path must be tube, there mustn't be any solid state circuitry in the signal path. This is so silly it would be funny if not for the thousands who make inappropriate and expensive gear choices based solely on the presence or absence of an "all tube" decal on the front panel. The facts are:
We like what tubes do to tone because of coloring they add to the tone. This is true both of clean and overdriven signals.
Clean (non-overdriven) solid-state circuitry of even mediocre quality reproduces a signal extremely faithfully. It will not "sterilize" a signal that has been "warmed up" in a tube stage.
At least one tube stage should be present in the preamp chain to warm up clean tones. This can be a tube preamp in a tube or hybrid amp or it can be a tube pedal or tube preamp in a multi-effects unit such as the GSP-2101 or RP20.
Until modeling is perfected, tube power amp sections provide the most "liquid" distortion. But remember, this is only important if you are looking for liquid distortion! If you're playing mostly traditional country then you want an almost painfully clean signal anyway. Similarly, if you are playing in a shock-rock band you probably want mostly "hard" distortion anyway.
For clean tones there is little practical difference between a solid-state power amp and a tube power amp provided that the signal has been suitably "warmed up" in a tube preamp.
I've seen people pass up a good deal on a great-sounding tube amp because it had a solid-state reverb driver or tremelo circuit and then stick a half-dozen cheap solid-state pedals in the effects loop of the less-capable amp that they purchased because it was "all tube." P.T. Barnum was right!
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