How can I troubleshoot tube issues?

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Tips & Tricks for Troubleshooting Tubes:

A large percentage of problems we deal with here at Boogie turn out to be tube related. Knowing the following tips, having spare tubes to work with and a few minutes of time will allow you to troubleshoot and resolve most any tube related issue you encounter with a tube amplifier. 

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 that 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 can get extremely hot! If they are hot and you don't want to wait for them to cool off, try grasping them with a thick glove or cloth. The glass around the bulbous silver tip is usually not as hot and may be easier to handle. Tubes can be easily removed by gently rocking them back and forth as you pull them away from their sockets.

 

Tube Noise:

Tube noise is often caused by contamination within in a tube. Occasionally, the noisy culprit can be identified by lightly tapping on the glass of the tube (you may hear the noise change). Hearing some noise through your speakers while tapping on preamp tubes is normal though and the one nearer the input will usually always sound louder, as it is most often the first tube in the signal path and everything positioned after is further amplifying its output. 

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 amplifier on STANDBY, remove it from its socket and turn it back on. It will cause no damage to run the amp 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 trying some tube troubleshooting. 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 for any non-functioning or bad tube found at no charge.

 

Diagnosing Pre-Amp Tube Problems: 

With an all tube amp design, it is quite possible that at some point you will 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.

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 three categories; Noise, Microphonics and Signal Loss. 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. Mechanical vibration and shock cause microphonic noise: think of banging a microphone around and you'll understand where the word came from. Signal loss is little or no signal passing through the preamp.

The best way to approach a pre-amp tube problem is to see if you can narrow it down to one specific mode or channel. If you can isolate the issue to one part of the preamp, then the Tube Task Chart found on the sidewall of your cabinetry or in your Owner’s Manual may indicate which tube or tubes are specific to that channel or function. All that remains is to swap the suspect tube(s) for a known good performer.

If you cannot narrow down the trouble to a specific mode or channel, it may be that the issue lies with a tube that is common to all channels or functions (initial gain stage, effects loop driver, reverb driver or phase inverter/driver tube). 

Sometimes it is faster and easier to merely replace preamp tubes ONE AT A TIME with a tube known to be good (especially when a tube task chart is not handy). Start with the tube closest to the input jack and replace it with the good tube. If the problem persists, put the original tube back in its socket and try the tube in the next socket. MAKE SURE you keep returning the tubes to their original socket until you hit the one that cures the problem. Continue down the chassis until you find the culprit - once again - return a perfectly good tube to its original socket. It is also a good idea to put the amp on Standby when swapping tubes to reduce the heat buildup 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.

 

Diagnosing Power & Rectifier Tube Failures:

Most of the calls we receive about an amplifier blowing fuses turn out to be tube related. In the case of amps that have Rectifier tubes, the culprit can be either a bad Rectifier tube or a bad Power tube. If the amp does not have a Rectifier tube, it will most likely be a Power tube that is causing your problem. Should an amp be played through without a speaker load on it, disaster is lurking around the corner. It is of utmost importance that tube amps are always plugged into a cabinet (or load) when they are played through. If they aren't, the best thing you can hope for is that you blow a fuse and not a tube, resistor or the output transformer. 

There are two main types of tube faults: shorts and noise. Diagnosis and remedy is usually fairly simple.

As previously mentioned, 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 amplifier on Standby, remove it from its socket and turn it back on. It will cause no damage to run the amplifier 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.

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 tubes are often fine unless they've been 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 OPERATE will usually cure the problem... at least temporarily. Watch the tubes carefully now. Should the problem recur, the intermittent tube will visibly start to overheat before the others and thus it can be identified.

A 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.

To quickly determine whether or not you have a faulty tube that is causing your fuse to blow, remove any Power & Rectifier tubes and lay them out in the order they were arranged in the amp. Inspect all the sockets for burn marks. A violent tube failure can leave carbon deposits that’ll need to be removed before replacing tubes (remove build up if necessary). Now, replace the fuse with the proper slo-blo type and turn the power on. If the amp powers up at this point, it is quite likely that one of your tubes was causing the fuse to blow. Figuring out the culprit is now just a process of elimination. It may cost you about five minutes and another fuse. All you need to do is put one of the tubes you took out back in its original socket, power the amp up, let the amp warm up for 30 seconds and then take it off standby. Continue this process with each tube individually until you see a tube arc, start glowing unusually bright orange or you blow a fuse. If this occurs, then you’ve found your Culprit. Replace it (and its push-pull circuit mate – if a power tube) with the same type MESA/Boogie Tube.

Visit the following link for step-by-step instructions for troubleshooting amps that are blowing fuses:
My amp blew a fuse. What should I do?

What color code rating do you need? We’ve got seven power tube color code ratings and these color ratings represent current flow. The reason for having these ratings is so that you can match up, as closely as possible, a pair of tubes for use in a push-pull circuit. It’s a spec issue and not a tonal one. Any tonal difference between our colors would be hard to notice and not significant. How accurately should tubes be matched? The Industry standard is plus-or-minus 10%. That means two tubes could be as far apart as 20% and still considered matched. Our matching process at MESA is twice as stringent at plus-or-minus 5% before a tube moves into our next color category and is matched with another nearly identical one. More important is that ALL our color categories are within the “sweet spot” of tube performance. We simply reject all the tubes that test either under scale or over scale.

Such strict selection and close tolerance permits us to permanently set the bias in each amplifier so it never needs re-adjustment. For the optimum in performance from your amp, it is important to use matched pairs of power tubes in the amp. Amps having more than one pair of tubes don’t have to use the same color rating throughout. For example, there are two pair of power tubes in a Dual Rec Solo Head. The two tubes in the inner tube sockets work together in this amp as do the two tubes in the outer tube sockets (from left to right, tubes 1 and 4 are working together and tubes 2 and 3 are working together). When you replace these tubes, you can load tubes of one color rating in the middle two sockets and another color rating in the outside sockets. Because of our tight tolerance, you can do this without having to worry about a change in performance or tone. Keep in mind that when replacing any of the color-coded power tubes; it is always best to swap tubes in pairs. This will ensure tubes working together are matched as closely as possible.

 

When troubleshooting tubes, please take your time and be patient. Chances are quite good that you can "fix" your amp yourself by finding and replacing a bad tube.  

 

Video

We’ve got a troubleshooting video that is worth a view.

 

Service Options

If you’re not comfortable replacing tubes yourself or should the steps above not resolve your issue, you could certainly take your amplifier to an authorized repair center. Click here to find the closest.

If taking an amplifier still under warranty to an authorized service center, please provide them a copy of your sales receipt, so that any warranty service provided can be claimed.

You're also welcome to make arrangements to send your amplifier to our shop for service. Please contact us for an Estimate, Return Authorization Number and Shipping Instructions. We will need to know what issue your amp is exhibiting or what service you wish to have done, what model you have, its serial number and your contact information. 

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