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Manley Labs - Trouble Shooting Manley or Langevin Gear

Bet you don't see many audio manufacturers with a trouble shooting guide for owners on their website! Don't get the wrong idea. Our stuff is road-worthy, dependable and usually really easy to work with.

The object of this document is an alternative way to help you out at 2 AM or answer a question before you ask and it might just show you that our gear is pretty easy to maintain. RTFM. **ALL** Manley and Langevin OWNER'S MANUALS are available online here.


Funny thing about tube gear - it's usually pretty damn easy to fix. A lot of guys think "if it's tubes - it must be fragile and unreliable" - au contraire! Even a "guitar player" can keep his stack on the road reliably with a handful of tubes ;-) There is probably a lot more old tube gear up and running (and worth a lot of money) than early solid state gear. Fixing tube gear can be the next simplest thing to changing a light bulb. If you have a problem solid state you would generally call the factory for an RA number, then FED-EX and send it back for repair and with a computer problem you could be "on hold" for hours. Tubes are easy.


Being a tube unit, you can probably find the problem and fix it yourself in a few minutes. Not too many years ago, even your parents could "fix" their own TV by taking a bag of tubes down to the corner and begin checking the tubes on a tube tester - but these testers are hard to find today.

A visual inspection can usually spot a bad tube. Be careful - there are some high voltages inside the chassis and tubes can get pretty warm, but if you can replace a light bulb you should be able to cruise through this.

Before you remove a tube, just take a look at them powered up. They should glow a bit and they should be warm. If one is not glowing and warm to the touch, you have already found the problem. The tube's filament (heater) is burnt out or broken like a dead light bulb.

The other big visual symptom is a tube that has turned milky white - that indicates air has gotten into the tube or we've joked "the vacuum all leaked out". Either way, replace this tube. He's bad.

If you have a stereo unit, use the redundancy to your advantage. You can swap similar tubes (one at a time) to verify which tube is the culprit. If the problem follows the tube you found the problem - a bad tube. It's easy and that way you know for sure if a new tube would solve the problem. No soldering, no meters, one screwdriver. You don't have to be a super-logical technical wizard either.

Before you pull a tube, pull the power out, let the unit sit and cool and discharge for a minute or three, then swap the new tube in, then power, then check. Gentle with those tubes, don't bend the pins by trying to insert the tube not quite right. A little rocking of them as you pull them out or put them in helps.

If you need to order a replacement tube, look at the markings on it and read your Owner's Manual to be sure of what tube type you are trying to order and also have your unit's serial number handy.

Then yc

What else could my trouble be? There are a number of possible symptoms of something not quite right, some may be interfacing, others we will touch on as well. If you suspect a problem the following paragraphs should help.


Probably something to do with AC power. Is it plugged in? Check the fuse on the back panel. A blown fuse often looks blackened inside or the little wire inside looks broken or it's resistance measures higher than 2 Ohms. A very blackened fuse is a big hint that a short occurred. Try replacing the fuse with a good "SLO-BLO" fuse of the same value and size. If it also blows, then prepare to send the unit back to the dealer or factory for repair. The fuse is a protection device and it should blow if there is a problem. If the unit works with a new fuse, fine, it works. Sometimes fuses just blow for unknown reasons. If you need some spare fuses, you can goto TUBESRULE.com and order some with your credit card. Easy.


Manley pro gear has used 4 different input and output techniques over the years. You should check your original owners manual if in doubt. Early Manley gear (pre 96) was "California Standard" with PIN 3 = signal HOT. When the AES XLR standard was introduced, we changed to PIN 2 = signal HOT. Up to '96 our single ended designs provided unbalanced +4 dBv outputs only. Yes, it interfaced quite well with both balanced and unbalanced inputs but it was a source of confusion to many. The confusion is for people who presume unbalanced always means -10 dBv. In '96 we added balanced transformer floating outputs to the XLR outputs (witout boosting the price). The only other variation of output is on some of the Langevin gear. The XLRs marked "Balanced" are designed to only mate with balanced inputs and the 1/4" unbalanced are for unbalanced +4 inputs. You will short out one line driver if you try to connect either pin 2 or pin 3 to ground or pin 1 (only on Langevin). If you use the 1/4" with a "stereo" plug be sure the opposite is true. The "ring" must be connected to the "sleeve" or you lose 6 dB. We have never had -10 standard (semi-pro) unbalanced inputs or outputs on any pro gear but sometimes you can do it with an accepted loss of level and higher noise levels. -10 dBv is the Hi-Fi standard and we only use it on our Hi-Fi products. The following paragraph applies to the newer Manley gear with transformer XLR inputs and outputs and 1/4" unbalanced +4 dBv inputs and outputs.

First try plugging the in and out cables into each other or some other piece of gear to verify that your wiring is OK. The XLRs are transformer balanced "floating" outputs which means the transformer winding is only connected to PIN 2 and PIN 3 (no ground connection - no ground loops). This requires both PIN 2 and PIN 3 to be connected somewhere. Some off-the-shelf "adapters" may not be wired this way. When driving an unbalanced input (the inserts on some consoles) PIN 3 needs to be grounded or connected to PIN 1. Same with the unbalanced 1/4 inch jacks - if driving a balanced input you can't ignore the negative side. It needs to be connected to the sleeve of the phone plug. Another way to do basically the same thing is join PIN 1 and PIN 3 on the XLR male at the destination. This shouldn't be a problem but Mr. Murphy has laws about this. Easiest way - if you need balanced, use the XLRs - if you need unbalanced use the 1/4" jacks. If there are VU meters - use em. They will help.


Several possible scenarios. Manley uses the professional standard of +4 dBm = Zero VU = 1.23 volts AC RMS. A lot of semi-pro gear uses the hi-fi reference of -10 dBm = Zero VU. This is a 14 dB difference that will certainly look goofy and may tend to distort. Often there are switches on the semi-pro gear to choose the nominal reference level. We do not provide that kind of switch because of inevitable compromises in the signal path. If the loss looks close to 6 dB and it sounds thin then one half of the signal is lost. The cause is probably wiring again. One of the two signal carrying wires (the third is ground / shield on pin 1) is not happening. Check the cables carefully because occasionally a cable gets modified to work with a certain unit and it seems to work but its wrong in other situations. Remember both pin 2 and pin 3 have to hooked up at both ends. If only one side of the unit exhibits this problem, it may be a problem in the unit. See the next item.


Again - check your wiring - swap left and right, both inputs and outputs. Problem still on the same side - it's the wiring. You can use the same technique with the tubes. Two channels - you can swap tubes between channels one pair at a time. If the problem follows the tube, then you found the bad tube. In a pinch you might pull a tube from a guitar amp to keep a session rolling - but get the right tube as soon as possible. We have included a list (further down) of acceptable substitutions.


Once again, several possibilities, several cures. Most likely it is a ground loop. Ideally each piece of gear should have one ground connection and only one ground. However, the short list of grounds include the AC mains plug, the chassis bolted to a rack with other gear, each input and each output. The most common procedures are:

Method one: Try a 3 pin to 2 pin AC adapter usually called a "ground-lift" or "cheater" (about a dollar at the hardware store). While this is legal in many countries, it can be dangerous and is not the right or safe thing to do and may increase the risk of electrocution, fire and loss of insurance. We provide a better way.

Method two: On the back panel loosen the GROUND TERMINALS and slide the small metal ground strap to one side. This is way better than "method one" because it is safer and removes another possible source - the chassis grounding via the rack. By the way, if the ground strap was already removed, you probably need to connect the two posts and the hum will be cured. A short piece of wire will work. Some studios have interesting "ground schemes" and these posts can be used to attach a wire from "circuit ground" to "technical earth".

Method three: Cutting the shield on one end of each cable. This is done by some studios at every female (or male) XLR to "break" all ground loops. All the other gear in the rack is "dumping" noise onto the ground. The ideal audio ground should be as quiet as possible (referenced to other audio ground points). Some of these techniques also use a separate ground wire which can be easily attached to the "circuit ground" post.

Method four: Try removing the unit from the rack so that it is not touching any metal. You just may have cured a non-loop hum. Some gear radiates a magnetic field and some gear (especially if it has audio transformers) might receive that hum. A little distance was all it took.

Our Hi-Fi customers occasionally have a hum problem caused by a ground loop. We build a number of mono-block power amps supplied with normal IEC 3-prong AC power cables. Sometimes, if both amps are grounded with the AC third pin as well as grounded via the interconnects to the common preamp ground, it will hum. You should disconnect the shield in the interconnects at the end that plugs into the preamp but it seems most people just break the AC 3rd pin ground or use a 3 pin to 2 pin adapter. Again this will work but increases the risk of shock and fire.


An easy one. Some tubes become microphonic over time. That means they start acting like a bad microphone. Vibration has caused the supports for the little parts in the tube to loosen and now the tube is sensitive to vibration. Easy - Replace the tube. Which one? The one that makes the most noise when you tap it. Usually this will be one of the smaller (gain stage) tubes closest to the front. The unit will have to be on, connected and speakers up but not too loud (for the sake of your speakers).


Also easy. This is again a common tube symptom. If you have some gain, you'll have some hiss. Higher gain circuits will usually have more hiss than lower gain circuits. You should expect some hiss, but how much is too much? Maybe the background noise level has finally gotten intolerable. You could swap tubes to find the culprit but an educated guess is OK too. Generally the first tube in the path is the one with the most gain and dealing with the softest signals. The usual suspect is one of the shorter tubes. If it has a 6072, 12AX7, 12AU7/5814 or 5670 - start there. You may find that you need to choose the quietest tube out of several of that type - like we do at the factory. You can goto TUBESRULE.com and order a new tube for your unit. We'll test it for best operation in your unit.


This might be a tube. Swapping is a good way to find out. It may be a wiring thing or mismatch as well. Wiring problems usually accompany the distortion with a major loss of signal. Mismatches are a bit tougher. The Variable Mu and Pultecs may be a difficult load for cheap gear. The input impedance is between 2000 and 3000 Ohms. Anything that can drive 600 Ohms will have no problem with our gear. The trouble is that a lot of stuff uses op-amps as line drivers (bad choice) and most op-amps run out of steam with anything below 10,000 Ohms. The solution - use real pro gear to drive real pro gear. With Manley products, it never is "low headroom". All of our gear delivers at least +26 dBm which is the most solid state usually can achieve. Almost all Manley gear can deliver +30 or +31 dBv cleanly and that can seriously overload most solid state inputs when a peak hits. Also most "Input Level" controls on our gear is before any tube stages that can clip, so a very wide range of levels can be handled. Most modern gear (even some tube gear but not ours) has an input op-amp first (that clips) followed by the gain control. The problem is the other gear but the solution may be to reduce the level on the Manley unit.


The 1/4" unbalanced outputs have a frequency response that goes way down to below 1 Hz. A little very low frequency noise may be seen as speaker movement or breathing under quiescent conditions. The XLRs do not exhibit this because the transformers filter below 5 Hz. Also the unbalanced outputs do not like long cheap high capacitance cable. Occasionally a very high frequency oscillation (200 kHz to 400 kHz) may occur in these conditions. Once again use the XLR outputs or use better, shorter, lower capacitance cable. Problem solved.


If the problem only seems to be when the unit is just turned on, don't worry this is normal. It should warm up and stabilize. Everything should stabilize in about 15 minutes as the temperature reaches "normal". Your unit will have been factory calibrated and tested at least 4 times before you received it. Sometimes parts drift a bit in value over the years, or you have replaced tubes and want the unit calibrated at the same time, or you just want it as perfect as it can be. These are good reasons to go through the calibration procedure or have it sent it to a technician or the factory for a tweak. If you send the unit to a tech, you should include the manual because they will need the calibration procedure in it. If you do it yourself, you will need an audio oscillator and good voltmeter and a few screwdrivers and it would be nice to have a 'scope but not necessary. A little advice: if it ain't broke - don't fix it. We get a number of units back because someone thought they should tweak and couldn't. By the way, the "BALANCE" trims on a Variable Mu® limiter compressor have nothing to do with left-right balance. They are used to trim the symmetry of the positive and negative halves of the circuit to reduce distortion and thumps.


This is as easy as we could make it. Remember there are high voltages and hot parts inside the unit, so you should be pretty careful. Unplug the AC mains power, let the unit cool and discharge. There are capacitors inside that hold a charge after power is turned off and the AC is disconnected for (typically) 10 minutes. We recommend rubber gloves, insulated tools and not touching exposed circuit board traces. We have to say that even though there is more risk inserting the AC cable of a vacuum cleaner into a wall socket or screwing in a light bulb. High currents are more dangerous than high voltages. Wall current is dangerous, the high voltage in one of our tube products may jolt and surprise but it is much less of a lethal danger. You would have to try real hard to get killed swapping a tube but be careful, nobody we know likes to get zapped.

TUBESRULE.com, The Manley Labs webstore can help!

You can buy replacement TUBES, FUSES, & LAMPS,
and also score some SWAG here at TUBESRULE.com

You should really have a spare set of tubes, an indicator bulb, and a fuse onhand at all times. This way, if (or when) a tube (etc.) dies, you can be up and running again very quickly. For most people with solid state the equivalent is a spare working unit or full set of cards. Wiggle the tube around slightly to remove or insert it. If you need a tube(s), your dealer or the Manley factory can help you either by pointing you to a source or selling you the tube(s) directly. You should check in your user manual for the type used in your unit. Most of the tubes we use have military 4 digit numbers. These are NOS (new old stock) and generally higher spec than more common varieties. If the closest equivalent is not very close, it is in brackets, meaning it will get you by in an emergency in our gear. Here is a list of most of tubes we use and the closest working equivalent.

You should really have a spare set of tubes, an indicator bulb, and a fuse onhand at all times. This way, if (or when) a tube (etc.) dies, you can be up and running again very quickly. For most people with solid state the equivalent is a spare working unit or full set of cards. Wiggle the tube around slightly to remove or insert it. If you need a tube(s), your dealer or the Manley factory can help you either by pointing you to a source or selling you the tube(s) directly. You should check in your user manual for the type used in your unit. Most of the tubes we use have military 4 digit numbers. These are NOS (new old stock) and generally higher spec than more common varieties. If the closest equivalent is not very close, it is in brackets, meaning it will get you by in an emergency in our gear. Here is a list of most of tubes we use and the closest working equivalent.

6072A ........ 6072, 12AY7, [sub in a pinch: 12AX7, 12AU7]

5814 ...........12AU7, ECC82

12AX7 ......... ECC83, 7025, [sub if you have to: 5751]

6201............ 12AT7, ECC81

6414 .............................................. [Some circuits can use: 12BH7A]

7044 ........... 5687, 7119, 6900

5670 ............................................... [If you could get them: 6386 or Paul's T-BAR MOD]

Of course if you need other replacement parts, we are very accommodating. We can get them to you fast and at a reasonable price. We are not one of those companies that charge 20 times the original cost for replacement parts. Planned obsolescence is a very bad word around us. Customer service and long life is simply expected in high end gear whether it is pro or hi-fi. We want our gear to be working at full spec for 30+ years like the original Pultecs, Neumans, MacIntosh amps, etc. We expect it will be just as useful and at least as valuable then, as it is now.

If you do need or want to send a unit back for repair or calibration please go fill out the SERVICE FORM.

Manley Labs warranties tubes for 90 days. We also don't charge heavy rates on repairs out of warranty. 99.9999% of all parts are in stock at all times. We think its bad enough if one of our units has a problem, and we don't think you should be gouged on the repair or have to wait a month or two.


Please go look at our Tech Support Section to get SERVICE or schematics, etc.

This page on the web is intended to help you be back in business fast and minimize any downtime. Some of what we mention here may be helpful with your other gear as well. We hope it helped you out of a jam.