Miracles do happen. Not always in an obvious way, like seeing a cripple throw down his crutches and breaking into an Olympic sprint, but nevertheless they do happen. A story comes to mind relayed to me by a customer of mine who knew a man that happened upon a garage sale, a known breeding ground for miracles which is why people flock to them in a Saturday Sabbath ritual, where he spied a dusty, beat up, cobweb-covered amp in the corner of the garage away from all the "bargains" proudly displayed. To make a short story shorter, he offered $40.00 for the amp and the garage seller accepted. He had to bite his lip to keep from laughing out loud as he loaded the amp into his car, as he had just scored a legendary 4 x 10 Tweed Bassman. For those of you who are unaware, these are considered to be perhaps the greatest sounding amps ever and are the electronic equivalent of finding the Holy Grail, of course assuming the Holy Grail was in production around 1958.

     Although I would be surprised if many people have been able to purchase an amp of this caliber at such a ridiculous price, I do talk to people who are still able to find good tube amps, like many of the silverface Fenders, at fairly reasonable prices. While these wouldn't be considered the Holy Grail, they're still a pretty good Grail capable of some extremely pleasing tones. The question that usually comes up after a purchase such as this is, "How do I clean up this amp tonally and make it perform like new?"

     Let's use a Fender Deluxe Reverb amp as an example, although the same principals will apply to other tube amps. It should be understood that working on tube amps can be dangerous and should be left to those who are familiar with working on this type of equipment and understand the proper safety precautions. Amplifiers contain lethal voltages and are to be considered dangerous even when unplugged.

     The place to start on a tube amp is with the tubes themselves. You'd be surprised at how a good set of tubes with the bias set correctly will wake up a tired amp. It's kind of like changing the spark plugs on your car. You'll notice that you have more power and performance available and that the amp has a nice, full-bodied sound, not thin and weak or fuzzy sounding.

     If you remove the back panel of the Deluxe Reverb amp you can see all the tubes going across the bottom of the chassis in a straight line. Tubes in an amplifier are labeled from right to left while facing the rear of the amp with the first one on the far right labeled as V1, the one next to it V2, etc. The "V" stands for valve which is basically a British term used for tubes. Tubes V1 through V6 in a Deluxe Reverb are the preamp tubes and have a removable, protective, metal shield around them. V1 affects the Normal channel and can use either a 7025, 12AX7 or ECC83 tube in this location, which are essentially different names for the same type of tube. If you are getting strange noises or microphonics from this channel, or if it is completely dead, you will want to replace this tube.

     V2 affects the Vibrato channel and, once again, can use either a 7025, 12AX7 or ECC83. If there is excessive noise, microphonics or if the channel is simply dead, this is usually the culprit, however, it should be understood that this channel also has an extra gain stage (which we'll get to in a minute) which could be the problem. Always use a quality tube for V1 and V2 as these will have a direct affect on your tone.

     V3 uses a 12AT7 tube, sort of a low gain version of a 12AX7, which is used to drive the reverb tank. If your reverb has failed, but you can hear the reverb pan make a "crashing" noise when you shake the amp, you will probably need to change this tube.

     V4 uses a 7025, 12AX7 or ECC83 and actually performs two functions. The first half of the tube handles the signal coming from the reverb pan. If the reverb does not work and if shaking the amp does not produce a "crashing" noise, you will probably need to replace this tube. The second half of V4 is the additional gain stage for the Vibrato channel, as mentioned earlier. This is to help boost the signal of this channel since it loses some power due to the reverb circuit. Most of the time there is a problem with the Vibrato channel it is related to V2, however if replacing this tube doesn't help you should try replacing V4.

     V5 operates the vibrato effect and uses a 12AX7, 7025 or ECC83. If the vibrato does not work, try replacing this tube. It should be understood that, unlike the reverb, you will need the footswitch plugged in to make the vibrato work. The footswitch provides a ground which closes the circuit and makes it operational.

     V6 is the driver/phase inverter tube and uses a 12AT7. This is the stage that drives the power tubes and is shared by both the Normal and Vibrato channels.

     V7 and V8 are the power section and use a pair of 6V6 tubes. Most Fender amps use 6L6 or 5881 tubes in their power sections. These are the tubes that amplify your signal and drive your speakers and are the ones most prone to wear out. Always keep a fresh set of tubes in this location and when you replace them do so as a matched set. Do not replace them one at a time. Cheating in this section of the amp translates to one thing - bad tone. This is a section of the amplifier that really performs it's best by having everything balanced and operating as evenly as possible. One additional consideration - you should always have the bias adjusted when you install new power tubes. It will affect your overall tone and the life of your tubes. Don't assume that installing the same brand of tubes every time will eliminate the need to adjust the bias because it won't.

     V9 is the rectifier tube and usually uses a 5AR4/GZ34, although some Fenders use a 5U4GB or 5Y3. The purpose of this tube is to convert AC into DC which is what your amp actually operates on. Although it is not the purpose of the tube rectifier to do so, it is commonly noted that they have a slower response, a "sag" if you will, which tends to give it a warm, bluesy characteristic. I have noticed that these tubes don't really add strange noises to the amps when they are failing, they just stop working.

     Once you've got all the tubes replaced with strong, fresh ones you can feel more comfortable about addressing some of the other areas of the amp that may have weakened over the years and will be able to use your ears more effectively to direct you in the next stage of electronic polishing.