What if I told you that the Silverface amp you saw for sale in the local vintage shop was every bit as good an amp as the Blackface amp sitting next to it that cost twice as much? In some cases this can be true. Initially these amps were built just like the Blackface. The mystery behind these amps is the gradual changes that were made to them over the years, some good and some not so good, that ended up transforming them into a very different creature than they started out. These changes were not made universally to all the tube amps in the Fender line. Changes in a 1976 Twin Reverb, for instance, might not necessarily be applied to a Deluxe Reverb of the same year. With all the changes that were implemented through the Silverface years, sometimes it's hard to tell what kind of amp you have until you open it up and take a look inside to see what specific changes were made. Of course, your ears will usually give you some strong hints.

     The following are some of the more important changes:

     Capacitors - If you were going to reduce a tube amplifier down to it's most basic components, these would be the transformers, tubes, wires, resistors, and capacitors. Fender has used a number of different capacitors (caps) through the years. Generally speaking, if you have the blue colored caps, you have the good ones, although how well they are performing now may be questionable. If you have the brown caps, you have the lousy ones and are paying for it with substandard tone - poor frequency response, less definition, somewhat "lifeless" sounding. If you have these brown caps, do yourself a favor and book an appointment with your amp tech to have him change them. You'll notice the difference.

     Driver/Phase Inverter - CBS, Inc. took the idea of building amplifiers a little too seriously at one point. They decided to implement some changes based on the idea that an amplifier should not distort or color the sound, just amplify whatever was plugged into it. This is fine for a hi-fi stereo amplifier, but not for a guitar amplifier. The result was a re-worked driver/phase inverter circuit that was padded down to reduce gain and distortion (two things that guitar players like) and in the process created a less dynamic amplifier. Fortunately, this is not something you have to live with. Once again, take it down to your local tech and have him put in the older Blackface circuit.

     Transformers - This goes hand in hand with the circuit change mentioned above. In adopting the philosophy that amplifiers should be clean, and that distortion should be greatly reduced, CBS introduced some newer power and output transformers in the later 1970's on certain models - the 135 watt Twin Reverb and Bassman 70 come to mind. The newer power transformer brought more voltage to the tubes creating more headroom, more top end, and reducing distortion. The larger , more efficient output transformer made the amp louder, cleaner, and helped prevent the transformer from reaching a point of saturation. It should be noted that these transformers were technically more advanced than the previous ones used on Fender amps. Once again though, this did not necessarily make a better sounding guitar amp. If you have one of these amps, and want it to sound like a Blackface, you will be somewhat prevented from doing so by these transformers. The circuit changes can be implemented and the amps can be made to sound much better, but these transformers will make for a cleaner amp. The transformers can be swapped out for something closer to the Blackface, but this is a somewhat costly change.

     Wiring - The Blackface used the very cool-looking cloth covered wire, whereas the Silverface used plastic insulated wire. There actually is an advantage to using the plastic insulation as it is not prone to absorb moisture as can happen with the cloth-covered. Additionally, some of the Silverface amps used shielded wire in place of some of the longer wires (the ones coming off the input jacks and volume controls) which helped in noise reduction. Now for the downside. Some Silverface had the wiring routed differently inside the amp chassis which could cause the amp to become unstable as it allowed a parasitic oscillation to occur. The quick fix was to add a small value cap from the grids on the power tubes to ground. This fixed the oscillation problem, but sucked up a healthy dose of the top end. Many times you can remove this cap or replace it with a smaller value cap. Get rid of it if you can.

     Master Volume and Pull Boost - In the early 1970's, Fender added a master volume to their more powerful amps, and eventually added this control to other models with lower power as well. The idea was that you would be able to turn the preamp volume up to induce distortion, but be able to use the master volume to keep the overall volume level down. Unfortunately, since the amp design had been changed to prevent distortion, the master volume didn't do a whole lot except steal a little more tone away from the amp. Later, a master volume was added that was built on a push/pull pot that would kick on a gain boost when pulled out. Once again, it wasn't a very usable feature as most people did not like the sound of this boost.

     Bias Adjustment to Bias Balance - Most Blackface amps had a bias adjustment pot to make the job of setting the bias a lot easier. The Silverface amps took a little different approach and rewired this control as a bias balance adjustment (and also padded down the circuit in the process). This would allow you to use unmatched tubes by allowing you to compensate for the differences of the tubes with the bias adjustment pot. However, this control doesn't allow you to set the bias correctly, it just allows you to adjust both tubes so that they each have the same bias voltage. The act of setting the bias correctly is a little more cumbersome since you will have to substitute resistors instead of adjusting it with a potentiometer. Since it is common to purchase tubes in matched duets and quartets there really is no need for this type of control and it is typically rewired to serve as a bias adjustment control.

     Hum Balance Control - The Blackface amps did not have an adjustment for this, although some models used a couple of 100 ohm resistors to do much the same thing. This gives you a potentiometer to keep the AC hum from the filaments at a minimum. It's actually a pretty good idea, except that they sometimes burn out and create more hum.

     Line Out - Here's an idea that had no drawback. This gave the option of plugging directly into the PA whenever desired. A feature more popular now than when it was first introduced. In fact some people with Blackface amps pay to have this feature added on.

     There are a few other minor changes that were implemented, although not as significant as those listed above. The important thing to remember is that the Silverface designation covers a broad range of amplifiers, some of which have no distinguishable difference to their Blackface counterparts, others with only slight variation, and some that are quite far removed from the original. Most of these amps can be reworked into a Blackface clone, and all of the amps can become much better sounding ones. Remember, when it comes to tone it's not what you see, it's what you hear.

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