Subway Blues user manual-pc
Contents
1. Qo The send level strength is determined by the VOLUME Gain control From this recording jack adequate signal level will be available for most of your recording or live direct sound reinforcement needs lan Precautions Overview 1 REAR PANEL FX LOOP SEND amp RETURN These two 1 4 jacks are the patch point for external processing effects The FX LOOP is wired in parallel with the normal signal Connect the Send jack to your Effects Input jack Connect the Return jack to the Output jack of your GROUND 12A DFuseq Q 2 A4orr DB RECORDING SEND 117V 1A 60HZ RETURN effect The FX LOOP is a patch point between the pre amp and power section There fore the Return jack can double as a Power Amp Input jack MIX control level should be set to 100 for this application FX MIX This control determines the dry wet blend of the FX Loop signal in relation to the unaffected signal Set to 0 you will experience only the dry signal no effect and at a setting of 10096 the entire signal will be wet total effect GROUND 12A Gu D q 9402 A lt OFF bB RECORDING SEND RETURN For the best results Set the mix of your effect to 100 wet Then dial in the amount of effect that you wish to hear starting at 096 with the FX LOOP MIX control The drier closer to 0 signal you use the better your tone should be This is one of the advantages in having a parallel type FX Loop2. cause of a blown FUSE Follow the cold start procedure mentioned in the ON STANDBY switch section and watch the power tubes as you turn the STANDBY to the ON position If a power tube is going bad or is arcing you will see it Flip the cum STANDBY switch to STANDBY immediately and replace the faulty power tube and the FUSE if nec as essary If you see nothing abnormal as you lift the STANDBY it is possible that a power tube shorted nee 1ASB temporarily and blew the FUSE If this is the case it may work again normally To be extra safe you iod dus may want to replace all power tubes in the shotgun troubleshooting tradition and save the replaced set as spares NOTE Like tires on a car spare FUSES are always a measure of good insurance Your SUBWAY BLUES amplifier was carefully constructed with reliability in mind Given the proper care and maintenance it will deliver years of trouble free service However any pro guitarist who gigs a lot will tell you spare FUSES are a must for the fabled cord bag and may someday be worth their weight in gold Spare tubes are also a very easy way to ensure an uninterrupted performance RECORDING This jack provides direct to console interfacing for recording or sound reinforcement applications It is a circuit dedi cated to reproducing the roll off that occurs in the output section with a speaker connected With GROUND 12 accuracy it faithfully captures the SUBWAY S soulful character Od 0
3. flowing and that s basically how a tube works Say that again because it s super important A small change in voltage at the grid causes a large change in current flowing to the plate See that s the essence of amplification A small change causing a large change And here it s a small voltage change causing a large current change The bias conditions are what determines how much current flows through the big power tubes when you re not playing And what drives your speakers is flucuations in that current flow when are playing If the amount of current increases and decreases 440 times per per second then you ll hear an A note If the fluctions in current flow are large and still at 440 per second you ll hear an A that is loud But for purposes of biasing it s the amount of plate current flowing with no signal applied that s important Unfortunately current is hard to measure because the circuit must be interuppted as in cut the wire and the meter spliced in series with the broken circuit But measuring VOLTAGE is easy It is not necessary to interrupt the circuit because a voltage reading can be taken in parallel with the circuit intact Thus as a matter of convenience most bias settings are given in volts at the grid even though current through the plate is the important factor In fact plate current is so inconvenient and dangerous to measure that Fender doesn t even state what the correct value should be They only giv
4. sound that can t be dialed out because excessive BASS has been introduced to the pre amp in the early stages Try setting the BASS to while using the BRIGHT input jack and e when using the FAT input jack These settings will vary with the amount of VOLUME and TREBLE you have dialed up N VOLUME TREBLE MID BASS Precautions Overview 1 CONTROLS Continued REVERB The SUBWAY BLUES has an individual REVERB control This enables different amounts of the rich ALL TUBE REVERB to be mixed with the dry sig nal NOTE It s normal for Maximum or even very high settings of the REVERB to al ter the amplifier s voice slightly This is a result of listening to the REVERB return stage high in the mix and no cause for alarm VOLUME TREBLE MID BASS REVERB TOGGLE SWITCHES ON STANDBY Perfect for set breaks this toggle switch also serves an even more important purpose In the STANDBY position the tubes are at idle so that during power up they may warm up before being put to use Before the POWER is switched on make sure the STANDBY switch is in the STANDBY position Wait at least 30 seconds and then flip the STANDBY switch to the ON position This helps in pre venting tube problems and increases their toneful life substantially ON c STANDBY POWER This switch delivers the A C POWER to the SUBWAY BLUES Make sure the unit is grounded all three terminals of the A C POWER cord must be connected w
5. the whole personality of the channel becomes darker fatter and more overdriven In the SUBWAY we worked hard to make sure the entire range of Gain available is usable and more importantly musical Don t think for a moment that this simple one knob layout limits you as to the VOLUME amount and texture of Gain Long neurotic hours were spent to ensure the range of Gain was stylisti cally accurate This would be a good time to mention that most of the great sounds can be found by setting the SUBWAY S VOLUME control moderately Use of moderation here will reduce the likelihood of pesky tube microphonic problems Precautions Overview 1 CONTROLS Continued TREBLE As with most guitar amplifiers tne TREBLE control is the strongest of the three rotary tone controls Its setting on the SUBWAY determines the blend and strength of the MIDDLE and BASS controls Set high it is the dominant control minimizing the amount of MID and BASS that would be possible in the mix Set low the TREBLE becomes the recessive control and a warmer darker blend is produced Dial with care Subtle tweaking of this control tends to produce the best results VOLUME TREBLE MIDRANGE Through endless daily tone dreaming the if only design dictum led to the creation of this very useful tone control From to about W amp to the taper is adjusted to act as a very effective MID control As you increase the MID to NI and above you will hear the lower mids get
6. you there s lot s of easy money to be made by sprinkling holy water on amplifiers uh what meant to say is Your amp needed biasing See what mean What customer is going to argue with that It only takes a moment and a volt meter The Fender diagram shows how Adjust this trim pot for 52 volts That s it Nothing more Now don t be fooled into thinking that tubes draw more or less bias they don t The way a bias supply is connected to a tube is akin to a dead end road it just trails off to nowhere without really completing a circuit It s a static voltage and regardless of what tube is in the socket or even if the tubes aren t plugged in at all it doesn t change the bias voltage a bit So the end of the short answer is this Since a bias supply needs to put out the right voltage and never vary wanted to build amplifiers that were individually hard wired to the correct values and NEVER needed adjustment And for 25 years that s how Mesa Boogies have been built Time to change tubes Just plug our tubes into any one of our amps and you re DONE No tech needed NO bills and no BS about biasing And most important The bias is RIGHT because it can t change Now you want the long answer Here s more information on how our hard wired bias avoids trouble Please read on But first let s make an important distinction Our business is designing and building high performance amplifiers And for this we need tubes whose var
7. M ESA BOOGIE 5UBWAY BLUES T he Spirit of Art in Technology ENGINEERING 1317 Ross Street Petaluma CA 94954 USA Hello from the Tone Farm YOU the smart player and all around intuitive human have put your trust in us to be your amplifier company This is something we do not take lightly Our reward is that we ve made a classic amplifier and by choosing this amplifier you have become part of the Mesa family Welcome Our goal is to never let you down Your reward is that you are now the owner of an amp bred of fine all tube amp heritage benefiting from the many patented pioneering Mesa Boogie circuits that led to the refinement of your new instru ment Feel confident as we do this amp will inspire many hours of musical satisfaction and lasting enjoyment It was built with you in mind by players who know the value of a fine musical instrument and the commitment it takes to make great music The same commitment to quality value and support we make to you our new friend UBWAY ROCKET Precautions Overview FRONT PANEL Power Up Inputs CONTROLS Volume Gain Treble Midrange Bass Reverb TOGGLE SWITCHES On Standby Power REAR PANEL Ground Fuse Recording FX Loop Send amp Return FX Mix Silent Recording Speaker Personal Settings Page TUBE MAINTENANCE Tube Noise amp Microphonics Diagnosing Power Tube Failures Tube Noise Diagnosing Pre Amp Tube Problems Bias Adjustment Part
8. Sheet 0 O Ci 9 10 11 amp 12 13 Your MESA Boogie Amplifier is a professional instrument Please treat it with respect and operate it properly USE COMMON SENSE AND ALWAYS OBSERVE THESE PRECAUTIONS Do not expose amplifier to moisture rain or water direct sunlight or extremely high temperatures Always insure that amplifier is properly grounded Always unplug AC power cord before changing fuse or any tubes When replacing fuse use only same type and rating Avoid direct contact with heated tubes Insure adequate air circulation behind amplifier Keep amplifier away from children Be sure to connect to an AC power supply that meets the P PP y power supply specifications listed on the rear of the unit If there is any danger of lightning occurring nearby remove the power plug from the wall socket in advance To avoid damaging your speakers and other playback equipment turn off the power of all related equipment before making the connections Do not use excessive force in handling control buttons switches and controls Remove the power plug from the AC mains socket if the unit is to be stored for an extended period of time Do not use solvents such as benzene or paint thinner to clean the unit Wipe off the exterior with soft cloth YOUR AMPLIFIER IS LOUD EXPOSURE TO HIGH SOUND VOLUMES MAY CAUSE PERMANET HEARING DAMAGE No user serviceable parts inside Refer service to qualified person
9. ace because compensating for the mis match causes the push pull circuit itself to become unbalanced Two wrongs don t really make a right Precautions 0 Overview 1 Some of the other recommended biasing methods such as tubes running red hot increase the bias sounds harsh and runs too cool turn it down are guesswork at best Luckily one of the great things about tube amps is that they can usually stand some abuse without causing any real harm at least not immediately But don t these alterations imply that you are second guessing the amp designer and that there s a better set of operating conditions that the designer missed but the tube sellers have discovered Now some players may like the sound of their amp altered by tubes with extreme characteristics and with the bias set to help compensate But often it is the mere novelty of change that they re really responding to and when the amp goes back to the proper original way we ve seen them be far happier still Because every part in every one of our designs has been meticulously evaluated compared and stressed over no matter how seemingly insignificant it might be And with every design we look for a sweet spot where all the parameters including the bias come together to give the best sonic performance consistently and reliably Every part and voltage is important yet no one complains that these other parameters aren t available for tinkering C
10. designed pe into your SUBWAY amplifier This circuit allows the amplifier to retain its FX MIX purity with the least possible degradation due to effects impedance mismatch ing SILENT RECORDING This rocker switch which is located down under the chassis and selects between the live SPKR ON setting and the silent SPEAKER MUTE setting This is a perfect solution for all nighters This switch mutes all of the signal at the power GROUND AC OFF DB 1ASB RECORDING SEND 117V 1A 60HZ RETURN section driver stage removing the need for a speaker load IN THIS POSITION ONLY I NOTE When this switch is set to the ON position a om LB speaker load must be maintained by either a load resistor I 8 ohms or 4 ohms and rated at least 30 watts power ca FX MIX pacity or a speaker itself Failure to comply with this in struction could result in major damage to the amplifier Leave your speaker connected MUTE lt SPKR gt ON SILENT RECORDING SPEAKER Sensitivity to SPEAKER mismatching in regards to ohmage differences is low as long as a load is used at all times Hence no damage to the amplifier will occur However very low ohmage loads will cause the power tubes to wear faster The SPEAKERS WY 8 OHM 4 OHM 4 OHM Precautions 0 Overview 1 SUBWAY BLUES is equipped with a single 10 inch 8 ohm SPEAKER but as you can see other SPEAKER configuratio
11. e the grid voltage that will produce that current That s the minus 52 But that only happens if the tubes being used are in spec As long as the tubes are in spec the right bias voltage will always give the correct plate current but then there s no need for the bias voltage to be adjustable If the tubes are not in spec then the only proper way to re set the bias is to cut the circuit and measure the current while adjusting the bias but no manufacturer know even states the desired current value Be that as it may when the original bias voltage is altered far enough it will compensate for the tube s abnormal performance and the correct amount of idle current flow may then be restored Clearly this is something most repair techs should not attempt Some newer amps have LED indicators connected to the circuit which will turn on when the right threshold of current flow has been reached This is an improvement and almost worthy if you re willing to except resistors and lights added into your amplifier s audio path which we aren t The other advantage of this system is that it allows some amp manufacturers to avoid matching their power tubes The thinking is that adjusting the bias to each tube separately eradicates the inherent differences between the tubes by insuring that the same current flows through each one Again this has some merit but it s still not as good as using tubes that are matched in the first pl
12. en glowing bright red for several minutes Because there is no physical short inside the tube just electrons rioting out of control merely switching to STANDBY for a few moments then back to ON will usually cure the problem at least temporarily Watch the tubes carefully now Should the problem recur the intermittent tube will visibly start to over heat before the others and thus it can be identified It should be replaced with one from the same color batch shown on its label Call us and we will send one out to you The severe short is not nearly so benign In the worst cases a major arcing short occurs between the plate and the cathode with visible lightning inside the glass and a major noise through the speaker If this is seen to happen IMMEDIATELY turn the amp to STANDBY By this time the fuse probably will have blown Such a short is usually caused by a physical breakdown inside the tube including contaminate coming loose or physical contact or near contact between the elements Replace it and the fuse with the proper slo blo type and power up the amp using the power up procedure as we described earlier in this manual TUBE NOISE Often caused by contamination within in a tube the culprit can usually be identified and by lightly tapping on the glass you will probably hear the noise change Hearing some noise through the speakers while tapping on the 12AX7 s is normal however And the one nearer the input will always sound louder becau
13. ets and this is why you should NEVER pull them all out at once and ALWAYS swap them one at a time ALWAYS return a perfectly good tube to its original socket Also it s a good idea to put the amp on standby when swapping tubes to reduce the heat build up in the tubes themselves and to prevent explosive noises which can still occur even if you are pulling the tubes away from their sockets gently from coming through the speaker Remember take your time be patient and chances are real good that you can fix your amp yourself by finding and replacing the bad tube It kills us to see someone who has shipped their amp back to us and all it needed was a simple tube replacement If you must send back your amp unplug the power cord speaker and reverb cables then remove the chassis from the cabinet by unscrewing the four mounting bolts on top The chassis then slides back like a drawer and comes out Remove the big power tubes and mark them according to their location from left to right 1 2 etc They need to be wrapped separately with plenty of wadded up newspaper around them and put in a smaller box within the larger carton To wrap the chassis use plenty of tightly wadded up newspaper so there is at least six inches of crush space between the chassis and the cardboard box Bubble wrap also works well but please DON T use styrene peanuts they will shift during transit and get lodged inside your electronics as well as allowing your amp to end up at the bott
14. has saved Mesa Boogie players you couldn t estimate Our rigorously tested and hand selected tubes are available at your nearest Mesa Boogie Pro Center or from us directly Nobody offers better price quality or warranty than we do so why swerve Next time we ll talk about our part in developing the great Sylvania STR 415 type 6 6 and how we re on the verge of seeing something fairly close reappear on the market Remember we still have some of these super rugged mondo bottles available for older amps Boogies only please Until then Relax Breathe and Nourish your soul Cheers Mesa Boogie Ltd Randall Smith Designer amp President Precautions 0 Overview 1 FRONT VIEW SUBWAY ROCKET KNOB pt SWITCH pt _605373 SWTCHES pt VACK all four 409124 601073 610120 KNOB ptt all four 408115 M ee Item uw e eo REIR Ge 592148 592736 592150 25 CONTOUR STANDBY POWER TREBLE MIDDLE REVERB UBWAY ROCKET PILOT LIGHT RED pit 703110 REAR VIEW SUBWAY ROCKET FUSE HOLDER ptt 790342 _ POT ptt JACK ptit 408004 all three 618100 ZA DYNA WATTPOWER 7 SUBWAY ROCKET g PREAMP PATENT 5 4 701 957 0 400 1ASB FX MIX ce gt JACK ptit 618100 t pe 600115 JACK pur 618100 JACK pur 618100 MUTE4 SPKR ON SILENT RECORDING Precautions Overview MESA BOOGIE The Spirit of Ar
15. henever possible to avoid injury to the user as well as to the unit and that the proper voltage is present Follow the cold start procedure described in the ON STANDBY section above when powering up your amplifier ON CED 0 OG POWER 4A DYNA WATTPOWER e 117V SPEAKERS 1 1A F GROUND 1ASB 8 OHM 4 OHM 4 OHM ENGINEERING HANDBUILT IN PETALUMA CALIFORNIA w MUTE lt SPKR gt ON SILENT RECORDING Precautions 0 Overview 1 REAR PANEL A lt 4OFF gt B DYNA WATTPOWER 117V SPEAKERS 1A 0 GROUND RECORDING RETURN IIIIIOIOIIIII III IT IIIII 100 QN A MAN w t MUTE lt SPKR gt ON TM 4 OHM ES zd SILENT RECORDING ENGINEERING HANDBUILT IN PETALUMA CALIFORNIA gt GROUND This switch reverses the polarity of the A C GROUND It can be helpful in eliminating annoying hum or A C buzz as well as those painful microphone shocks It should be left in the center OFF position when neither of these problems are occuring GROUND 12A OTN 0 9402 B 1A SB RECORDING FUSE This is the A C s Alternating Current main FUSE and provides electrical current protection from outside A C fluctuations as well as power tube failure damage Should the FUSE blow replace it with the same rating in a slo blo type package The domestic U S version requires a 1 amp slo blo FUSE A power tube short or failure is often the
16. hile adding a percussive quality to the attack It is very helpful when using guitars with lower output pick ups i e old single coils STANDBY POWER SUBWAY BLUES VOLUME TREBLE POWER UP Connect your favorite guitar to one of the two instrument input jacks Flip the POWER switch ON while leaving the STANDBY switch set to STANDBY It s always a good idea to practice this start up procedure as at least 30 seconds of warm up time lessens the shock on cold power tubes thus prolonging their life substantially Next set the controls per the example above NOTE When disconnecting the instrument cable from the Inputs it is normal to hear a metallic sound This is not a microphonic tube as you may have heard when tapping the faceplate of an all tube amplifier This noise occurs because the Inputs are wired in parallel and for a brief second they are floating as you unplug your instrument Again this is normal and no cause for concern This noise goes away completely as soon as you connect your instrument VOLUME Gain This is by far the most powerful control in the amp It not only determines the amplifier s overall Gain amount shape and sensitivity but it is also a powerful tone control Generally speaking whatever is dialed here ultimately determines the amps personality Set low it allows cleaner brighter sounds with enhanced dynamic response espe cially in the higher frequencies Set high
17. iance is within a narrow range Our warehouse is full of rejects oh they work they just don t perform within our tolerance range We have a very sophisticated computer based tube testing system nicknamed Robotube that matches and measures tubes over seven important parameters It can even predict which tubes are likely to have a shortened lifetime even though they work perfectly during the test Because our business is building quality amps we can afford to reject a lot of wayward tubes The guys you hear complaining because Boogies don t have bias adjusters are primarily in the business of selling tubes not amps They don t want to throw away 30 percent of their inventory so they promote the idea that tubes outside our parameters can be used to customize amplifiers and they criticize us because our amps can t be adjusted to accommodate their out of Mesa tolerance tubes Now you might be thinking But thought you just said that tubes don t draw bias therefore they don t effect the bias supply and thus it doesn t need to be adjustable And that s right Tubes don t effect the bias setting but how it effects the tubes is difficult to measure When you set the bias whether it s by selecting the right resistors as we do or adjusting a trimmer which is quicker what you are Precautions Overview 1 BIAS ADJUSTMENT Continued doing is establishing the correct amount of idle CURRENT that flows through the power tube
18. nel Always unplug AC power before removing chassis EXPORT MODELS Always insure that unit is wired for proper voltage Make certain grounding conforms with local standards READ AND FOLLOW INSTRUCTIONS OF PROPER USAGE SSUBWAY BLUES O perating Instructions Precautions 0 Overview 1 FRONT PANEL Power Up 2 Inputs 2 CONTROLS Volume GAIN 2 Treble 3 Midrange 3 Bass 3 Reverb 4 TOGGLE SWITCHES On Standby 4 Power 4 FRONT VIEW SUBWAY BLUES REAR PANEL STANDBY POWER VOLUME TREBLE f SUBWAY BLUES Ground 5 Fuse 5 a IA a Recording 5 FX Loop Send amp Return 6 A lt 4OFF gt B DYNA WATTPOWER GROUND 0 9 RECORDING gt 100 FX MIX MUTE4SPKR ON 8 OHM 4 OHM 4 OHM SILENT RECORDING ENGINEERING HANDBUILT IN PETALUMA CALIFORNIA Predlitions 6 0 6 l Silent Recording 6 FRONT PANEL INPUTS First familiarize yourself with the layout of the front panel Your SUBWAY amplifier is fitted with two INPUTS which are voiced individually for very different personalities and feel BRIGHT would be the choice for all clean playing styles where sparkling highs are needed This jack also lets the true sound of the instrument come through and would be the choice for traditional style solo work FAT enhances the lower to medium midrange frequencies producing a bolder voice that sings with conviction This jack helps saturate single notes w
19. ns may be used When using two 8 ohm SPEAKER use the 4 ohm jacks this will insure proper impedance matching MESA Boogie 4X12 and 4X10 cabinets come stan dard wired to 8 ohms They have four 8 ohm SPEAKERS wired in series parallel Some cabinets other than MESA Boogie may be 4 8 or 16 ohms To confirm how your cabinet may be wired and the impedance rating of your SPEAKERS you may need to remove the back panel to verify this information in regards to proper SPEAKER matching Feel free to experiment with the SPEAKER jacks trying different loads Keep in mind the greatest clean headroom is always achieved with proper impedance loads i e an 8 ohm SPEAKER connected to an 8 ohm jack PUBWAY BLUES STANDBY POWER VOLUME TREBLE REVERB SUBWAY BLUES ESE ob STANDBY POWER VOLUME TREBLE REVERB SUBWAY BLUES CES ob 0 STANDBY POWER VOLUME TREBLE REVERB SGUBWAY BLUES 0 STANDBY POWER VOLUME TREBLE REVERB SUBWAY BLUES Precautions 0 Overview 1 TUBE NOISE amp MICROPHONICS You may occasionally experience some form of tube noise or microphonics Certainly no cause for alarm this quirky behavior comes with the territory and the Tone Much like changing a light bulb you don t need a technician to cure these types of minor user serviceable annoyances and in fact you ll be amazed at how easy it is to cure tube problems by simply swapping out a pre amp or power tube First may we suggest tha
20. om of the box unprotected and possibly damaged Preamp tubes don t normally wear out as a rule Therefore it is not a good idea to change them just for the sake of changing them If there isn t a problem don t fix it If there is no result from your substitutions it may be possible that you have more than one problematic tube Though rare this does happen and though it makes the troubleshooting process a little more intimidating it is still possible to cure the problem yourself NOTE It is normal to hear a slight metallic ringing sound when tapping on the preamp tubes As long as the tube does not break into oscillation or start crackling or any other form of bizzare noise it is considered normal and functional Precautions 0 Overview 1 BIAS ADJUSTMENT Part of a continuing series BEAM CONFINING ELECTRODE NOTE Anarticle written by Randall Smith that we thought you might find interesting CATHODE GRID Here s a question we often hear SCREEN GRID PLATE Why doesn t Mesa put bias adjustments in their amplifiers Structure of a 61 6 5881 Well there s a short answer and a long answer to this question Beam Power Pentode The short answer is that during my 12 years of repairing Fenders one of the most frequent problems saw was bias controls that were either set wrong or that had wandered out of adjustment due to vibration As any honest tech will tell
21. onsider our patented Simul Class circuitry where there are two different bias voltages used for separate pairs of power tubes and changing one voltage also changes the other Great care goes into getting this just right and we think we d be asking for trouble to have it adjustable for the world to play with unless you like paying to have your amp messed up Sorry meant to say Uh your amp needed biasing If that doesn t appeal to you then merely plug a matched set of Mesa tubes into one of our amps and you re ready for tone Guaranteed You d be amazed at the number of service calls we field every day that lead to a diagnosis of out of tolerance non spec tube problems To think these would be prevented by including a bias adjustment is something of an insult to you and us If you put the wrong size tires on your car do you think changing the pressure will make them right Please don t think this is a blanket indictment of the other guys selling tubes it isn t And their tubes aren t all bad either It just doesn t make sense to pay more of your hard earned cash for tubes that were probably made in the same Russian or Chinese factory and which have the possibility of being outside the performance window we select for your amp And it pains us to hear the hype and mystique built up around biasing when twenty five years of evidence affirms our decision to make bias circuits that never need adjustment How much money and trouble that
22. problem may be the small tube that drives the power tubes which is operational in all modes and channels Though rare a problem with the driver tube would show up in all aspects of perfor mance so if you can t narrow the problem down to being mode or channel specific you may want to try replacing the driver tube Driver problems generally show themselves in the form of crackling or hum in all modes of performance and or weak overall output from the amplifier Occasionally an anemic driver tube will cause the amplifier to sound flat and lifeless but this is somewhat uncom mon as worn power tubes are a more likely suspect for this type of problem Sometimes making the diagnosis is more trouble than it s worth and it s faster and easier to merely replace the small preamp tubes ONE AT A TIME with a replacement known to be good But MAKE SURE you keep returning the tubes to their original socket until you hit the one that cures the problem You ll notice that tubes located nearer to the Input jacks always sound noisier but this is because they are atthe start of the chain and their noise gets amplified over and over by the tubes that follow The tube that goes into this input socket usually labled V1 needs to be the least noisy of the bunch The tube that goes at the end of the preamp chain just ahead of the power tubes can be quite noisy without causing any problem at all The tubes in your amp have already been located in the most appropriate sock
23. s But you can t adjust the current directly you can only change it by adjusting the amount of bias VOLTAGE that goes onto the tubes control grids Voltage and current are NOT the same Current is the AMOUNT of electricity the quantity and is measured in amperes Voltage is the degree of electric charge like the pressure to use the old water analogy Let me illustrate how different voltage and current are When you scrape your feet across a carpetted floor in dry wintery conditions your body can become charged with 50 000 to 100 000 volts of static electricity And when you reach for the door knob a spark jumps and you feel it The voltage is super high but the current measured in micro amps is tiny otherwise you would die from electrocution Contrast this with your car battery which puts out a mere 12 volts You can lay your hands right across the terminals and not feel a thing Yet the amount of current available can run to several hundred amperes enough to turn over a cold engine and get it started So current and voltage are two totally separate electrical parameters though when you multiply them together you get POWER which is measured in watts When you set the bias of an amplifier you are adjusting the static VOLTAGE at the control grid of the tube in order to produce a desired amount of idle CURRENT flowing to the tube s plate A small change in grid voltage produces a large change in the amount of current
24. se its output is being further amplified by the second 12AX7 The power tubes should be all but quiet when they are tapped If crackling or hissing changes with the tapping you have probably found the problem To confirm a noisy power tube merely put the SUBWAY BLUES on STANDBY remove it from its socket and turn it back on It will cause no damage to run the SUBWAY BLUES briefly with one power tube missing You may notice a slight background hum however as the push pull becomes unbalanced Whenever you are trying to diagnose a suspect tube keep your other hand on the Power and Standby switches ready to shut them off instantly in the unlikely case you provoke a major short If you think you ve located a problem tube but aren t sure we recommend substituting the suspect with a new one just to be sure of your diagnoses You will be doing yourself and us a big favor by just following the simple guidelines previously mentioned regarding tube replacement You ll probably be successful with much less effort than is required to disconnect everything and haul the unit to a technician who will basically perform the same simple tests If the tubes are still within their six month warranty period we will happily send you a replacement Just note the color designation on the tube label so that we can send you the appropriate match Precautions Overview 1 DIAGNOSING PRE AMP TUBE PROBLEMS Because your amplifier is an all tube design it is quite possible that
25. t in Technology Thank you for trusting MESA Boogie to be your amplifier company We wish you many years of toneful enjoyment from this handbuilt all tube instrument T he Spirit of Art in T echnology 1317 Ross Street Petaluma CA 94954 USA
26. t you set the amplifier up on something so that you can get to the tubes comfortably without having to bend down It also helps to have adequate lighting as you will need to see the tube sockets clearly to swap tubes Use caution and common sense when touching the tubes after the amplifier has been on as they May Be Extremely Hot If they are hot and you don t want to wait for them to cool off try grasping them with a rag and also note that the glass down around the bulbous silvery tip is considerably less hot which makes it easier to handle Gently rock the tube back and forth as you pull it away from its socket DIAGNOSING POWER TUBE FAILURES There are two main types of tube faults shorts and noise Both large and small tubes may fall prey to either of these problems but diagnosis and remedy is usually simple If a fuse blows the problem is most likely a shorted power tube Shorts can either be mild or severe In a mildly shorted tube the electron flow has overcome the control grid and excess current flows to the plate You will usually hear the amp become distorted and begin to hum slightly If this occurs quickly look at the power tubes as you switch the amp to STANDBY and try to identify one as glowing red hot It is likely that two of a pair will be glowing since the shorted tube will pull down the bias for its adjacent mates but one tube may be glowing hotter and that one is the culprit The other two are often fine unless they ve be
27. ting more pronounced and fatter At about the MID leaves behind the old notion of being a tone control and becomes a truly usable Gain control The upper range of the MID control is a smokin addition to the SUBWAY S VOLUME control for all kinds of higher gain rhythm lead sounds Try the MID set high and the VOLUME control at about for a cool blues solo sound If this still isn t crazy enough for you Max the VOLUME and TREBLE controls as well This should be sufficiently grinding for all you crunch fiends As you will hear the versatility found in the MID control greatly enhances the overall sound of this amplifier The described set ting procedeure for this control would be the same for either of the two input jacks VOLUME TREBLE NOTE The lower region of the MID control determines midrange punch and boldness in lower gain sounds and a smooth vocal blend in high gain sounds It can be very effective acting as a cut through the band control in certain situations Dial to taste remembering that the setting of the TREBLE control greatly affects this control s strength BASS This control blends in the lower frequencies and its effectiveness again depends on the setting of the TREBLE contra It should be set with moderation as extreme settings in either low or high directions can produce an unbalanced tone Be especially careful when using the SUBWAY at high VOLUME level settings because too much BASS will cause a flabby unfocused
28. you will at some point experience minor pre amp tube noise Rest assured this is no cause for alarm and you can take care of the problem yourself in a matter of minutes by simply swapping tubes Let us begin by saying It is a very good idea to keep at least a couple of spare pre amp tubes on hand at all times to insure uninterrupted performance These minor pre amp tube problems can take many forms but can generally be described in two categories Noise and Microphonics Noise can be in the form of crackling sputtering white noise hiss and or hum Microphonic problems usually appear in the form of a ringing or high pitched squealing that gets worse as the gain or volume is increased thus are more noticeable in the higher gain Lead modes Microphonic problems are easily identified because the problem is still present even with the instruments volume off or unplugged altogether unlike pick up feedback which ceases as the instrument is turned down Microphonic noise is caused by mechanical vibration and shock think of banging a microphone around and you ll understand where the word came from The best way to approach a pre amp tube problem is to see if it occurs only in one specific mode or channel Then refer to the Tube Task Chart found on page 15 and it should lead you to the tube needing replacement Then all that remains is to swap the suspect tube for a known good performer If you cannot narrow down the trouble to a specific mode or channel the
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