Frequently asked


Below are some answers to commonly asked questions. If however, you have a question that remains unanswered, please don’t hesitate to get in touch.

Class A vs. Class A/B Guitar Amplifiers
Class A and Class A/B are terms that describe how the power tubes work within the power section of a guitar amplifier. To properly explain the technical differences between these classes of operation would require a lengthy discussion. However, in short, the differences can be summarized as follows:

Class A/B amps tend to have greater dynamics, sound punchier, tighter, cleaner, and have cooler running tubes. The Class A amp sounds more vintage and squishy, because it’s compressing and distorting more. Tubes in a Class A amp tend to run hotter, as well. For the same given tube compliment, Class A/B will produce two-to-three times as much power as Class A. An example would be an amplifier with two 6L6s in the power section. Operating in Class A, the maximum power we could expect would be around 20 watts, while operating in Class A/B would easily yield 50 watts.

Just for tube life alone, I believe Class A/B is the way to design any amp. The amp will run more efficiently with more power and you’ll enjoy not having to replace power tubes as often. If the tonal characteristics of a Class A are desired, an A/B amp can be carefully designed to do that (the Soldano Astroverb is a good example of such a design).

Guitar Amplifier Tube Maintenance
How do I know if I need to change my tubes?

You probably need to change your tubes if your amplifier makes strange noises (hisses or squeals) or if it experiences a lack of power or a lack of bottom end.

My amp is making strange noises (fizzy crackling sounds or popping noises)? How do I get it fixed?

Most of the problems that we hear about with amps are due to the tubes—and are pretty straightforward to fix. Close to 90% of the problems that people call us about are due to tubes—or tube sockets. Sometimes they get dirty and mucked up. (Tubes get very hot and can burn you, of course; don’t touch them when they are hot.)

With the amp on, wiggle the tubes a little to alter the contact points. If this recreates or stops the noise, you have isolated the problem tube (or socket). If it doesn’t, turn the amp off and let the tubes cool. Then pull and reinsert each tube several times to try to establish better contact. Test the amp after you adjust each tube to see if you have found the problem.

Hopefully, this will fix the problem or determine the tube that needs to be replaced. If you have pinpointed a problem tube, but not fixed it, you probably need to replace the faulty tube.

How do I determine if my preamp tubes or my output tubes need to be changed?

If you’re experiencing a lack of bottom end and power, it’s probably your output tubes. If you’re hearing strange sounds coming from your amplifier, turn your gain section up in volume, and slowly turn the master volume down. If the noises persist after the master volume has been turned down, it’s an output tube. If the noises go away after turning the master volume down, it’s an input tube.

How often should I change my tubes?

Tubes are like light bulbs—they could go out at any time. Generally, if you’re playing hard, tube life can be anywhere from six months to a year, although we’ve seen tubes last much longer than that. Preamp tubes can last indefinitely.

Good quality tubes are the key to keeping your amplifier working great. Should you start to experience strange noises, microphonic squealing, hiss, or other strange and unwanted phenomena, check your preamp tubes. One of them may need replacement.

If strange noises do appear, unplug your guitar cord from the input to help isolate the problem and switch to the Overdrive Channel. Then, turn the Overdrive Channel’s Volume Control to ‘0.’ If the noises go away, it is likely that a preamp tube is at fault. If the noises persist, you probably have an Output tube that needs to be replaced.

What kind of tubes are in my Soldano amp?

We use 12AX7preamp tubes and 5881 power tubes.

What should I do to be prepared for tube problems?

You should keep a couple of good spare 12AX7 preamp tubes around at all times for any tube amplifier. This will save you a lot of trouble when you do need them. If you suspect that one of the tubes in your amp may be faulty, replace it with a known good tube and see if that alleviates the problem. If not, replace the original tube and try swapping out the next 12AX7 in the signal chain.

As with the preamp tubes, it is important to always keep a spare 5881 output tubes on hand. This will save you much time and frustration when replacement is needed.

Beware! In certain instances, you may actually run into two microphonic tubes and have to replace them both so do not overlook this possibility. Also, just because you purchased a brand new 12AX7 does not mean that it is not microphonic. Make sure you test the tube to make sure that it is in fact good. The best way to do this—presuming you don’t have access to a tube tester—is to swap out your tubes with spares when your amp is working fine. That way, if one of the spares is faulty, you will know it immediately.

Guitar Amplifier Tube Swapping
I want to swap out my tubes with EL34s to fine tune my amp. How do I do that?

Even though the EL34s will plug right in and work, we do not recommend them for two reasons. First, they draw more heater current and will cause the power transformer to run a bit hotter. The extra heat probably won’t damage the transformer because we design our transformers with some extra margin (overkill). But why risk it? The second reason is more important: The output transformer impedance match is not correct for EL34/6CA7/6550/KT88 type tubes. It was designed for the 6L6/5881/7027/KT66 family of tubes. You won’t hurt the transformer at all with the EL34s, but the efficiency and performance will be less than ideal. The screen resistors will also have to be changed or your tube life will suffer.

If you are looking for a different sound, try different speakers. Unless you run the amp wide open on the master volume all the time, the changes that you will notice by changing tubes will be minimal because, until they reach clipping, 5881s and EL34s sound and perform exactly the same. Even if you are running at full power all the time, changing speakers is a better way to fine tune your sound than changing tubes.

If I change my tubes, do I need to re-bias my amplifier?

Most often, the answer to this is “No.” If you’re buying stock tubes, such as 5881’s or 6L6’s, there won’t be any problem. For other applications, such as a using KT66 or 7581A tubes, call Soldano for re-biasing recommendations.

How Do I Boost my Volume When I Play Solos Live?

There are two approaches to solving this problem: Active or Passive. We like the passive approach.

Active electronics, by design, alter your signal path. All too often, this alters your tone, as well. There are other potential issues, as well, such as the signal-to-noise ratio. If your goal is only to raise your volume for a lead solo, a passive solution is likely to be superior. A passive approach takes a backwards approach. Instead of boosting volume for solos, you reduce your volume when you aren’t soloing. No active electronics are involved and your signal is not at all altered—it is simply reduced.

How can you achieve this? Here are three ideas:

  • Volume control on your guitar. This works great for a clean signal solo. Keep your volume a little lower when you aren’t soloing, turn it up when you are. Because of the preamp electronics, turning down the volume on your guitar while playing high gain actually has little impact on your volume—it has more impact on the cleanliness of your sound.
  • Volume Pedal. This works well if it is in the effects loop (and thus between the preamp and the power amp). This allows you to alter your volume for both a high gain and a clean sound. It takes a little work to master the subtleties of the effect, but you can get nice swells and additional effects.
Point-to-Point vs. Printed Circuit Boards
In the early days before circuit boards were designed, technicians relied on various “anchor points” to connect wires together. Primitive layouts consisted of terminal strips screwed to the chassis or even pieces of cardboard fitted with brass eyelets. Components and wiring were then soldered, point-to-point, to these terminals or eyelets to create the circuit. As time went on, clever technicians figured they could etch the wiring patterns into copper foil laminated to a strong and rigid phenolic board. The components could then be soldered directly to these copper “traces.” This was the beginning of modern printed circuit (PC) boards. In modern boards, epoxy reinforced glass fiber replaces phenolic and more than one layer of copper is now possible. When using PC boards, precise part placement and consistent wiring is guaranteed.

I feel that point-to-point wiring is still very useful when designing an amplifier prototype or building a custom one-of-a-kind amp. It’s quicker, easier, and cheaper to do than a one-off printed circuit board and it’s generally easier to make circuit modifications when using this method. Well done point-to-point wiring is also very nice to look at—if you’ve ever seen the inside an early Hiwatt, you’ll know what I mean.

In my opinion, however, it is far more cost effective and less labor intensive to use PC technology in a production environment. To the consumer, this means a better amp for less money. I believe that a guitar amp with well designed circuit boards is easier to work with, is far more consistent and reliable, and is more rugged mechanically than a point-to-point wired guitar amp. Another advantage is that, since the circuitry is clearly mapped out on the board, PC boards are also quicker and easier to service.

One should also bear in mind that there is absolutely no sonic difference between point-to-point and printed circuit board wiring. Detractors of PC boards have argued that they are less reliable due to cracked solder joints or failure prone to burned traces—neither of these complaints are ever an issue with a properly designed board.

Tube vs. Solid State Rectifiers
The job of the rectifier is to convert alternating current (AC), which is received from the wall socket into the power transformer, into direct current. Direct current (DC) is needed to operate all of the circuitry in a guitar amplifier. This process takes place through a device called a diode. Diodes act like a one-way valve, allowing current to flow in one direction only.

Today’s diodes are made out of silicon.

The tube diode was the first diode ever invented (in fact it was the first tube ever invented). For many years it worked quite dependably and it was the only choice for rectifying current for high voltage power supplies. When solid state technology was developed in the 1950’s, it was found that solid state diodes could do the job of tube diodes, only better.

A tube rectifier has internal resistance. The more current that travels through a tube rectifier, the more the voltage drops. When the voltage drops, the power of the amplifier also drops. The tube rectifier has the drawback of not being able to provide a consistent voltage when it’s under load. The other drawback is that the tubes themselves run hot, and can be relatively short-lived. Unfortunately, modern day sources for rectifier tubes are not very reliable and, even in their prime, these tubes were usually the weak link in most amplifiers.

An amp with a tube rectifier tends to sound much spongier in the bottom end. Low frequency notes take more current through the power tubes to reproduce. This increased current causes a voltage drop in the rectifier tube and the amp loses power. So, when more power is actually needed, the amp gives less. Because of this, a tube rectifier amp will sound spongy and more distorted at high volumes. This, probably more than anything, is what gives a vintage amp its sound and color.

A solid state rectifier has no internal resistance whatsoever. It has a very consistent fixed voltage drop that occurs both at zero or full current (approximately .7 volts). When an amplifier needs power at low frequencies, there will be no limit to the current that travels through the rectifier. This results in an amp with more headroom that is punchier, more articulate and able to deliver the goods in the bottom end.

In my opinion, all amps should have solid state rectifiers. I don’t believe there are any really good rectifier tubes on today’s market and, even if there were, why use them? The technology is obsolete; they are horribly inefficient, and far more expensive and troublesome to build into an amp. These tubes, no matter how good, will routinely need replacing, adding to your maintenance expenses. Besides that, tube rectifiers kill the headroom of an amplifier. If you want that spongy, vintage sound, there are other ways to do it. I have successfully designed and built amps that have replicated that soggy bottom, vintage tube rectifier sound using solid state rectifiers and various circuit modifications.

Of course, if you have a vintage amp that uses a tube rectifier, by all means keep it that way! That’s what makes it sound the way it does. But if you’re contemplating getting a new amp, I recommend avoiding future headaches by staying away from tube rectifiers.

What’s the difference between a Series and a Parallel effects loop?
Up until just recently, almost all guitar amplifier effects loops were series effects loops. A series loop interrupts the signal path between the preamp and the power amp and inserts the effect processor signal into that path. This means the entire signal from the preamp travels through the processor and re-enters the power stage. It’s basically a one-lane road going from one place to another.

Parallel effects loops have just recently begun to surface. A parallel loop offers two paths from the preamp to the power amp. One path is a direct connection from the preamp to the power amp as if the amp had no loop at all. The other path sends the preamp signal to the effect processor (via the loop) and then routes it back to the power amp, mixing it with the direct (dry) signal. Most amps that offer a parallel effects loop have a variable mix knob, so that you can control how much of the effect you want mixed in with the dry signal.

How do you choose one over the other? In a series loop, many modern, high quality effects processors can be used effectively without any problems because the sound quality will not be degraded when traveling through the processor. Additionally, there is a mix control that allows the user to adjust the dry and wet signal within the processor itself. A series loop works fine in this case. Even though the entire signal is being routed through the effects unit, the tone is still coming out of it uncompromised.

The parallel loop is useful when using vintage effects and other effects that don’t have any kind of mix function and that sometimes suffer from bad signal-to-noise-ratios, which can lead to tone degradation. Lately it seems that there has been a return to vintage effects and stomp boxes, which has probably caused more of an interest in the parallel loop.

I think that a parallel effect loop is a good thing and the ability to be able to adjust the mix is nice. However, they don’t work well if you are using effects that change the volume of the signal (such as tremolo, compression, or noise gates), or when mixing the wet and dry signals causes an out of phase situation. Technically, if you turn the mix to 100% in a parallel effect loop, it should operate exactly like a series loop, although this is not the case with all amplifiers on the market.

In my opinion, if you don’t need a parallel loop, don’t bother. It’s generally a lot more circuitry, and can end up costing more money. However, if you do use older effects or stomp boxes, I highly recommend a parallel loop for its flexibility.

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