Frequently Asked Questions

Can I mix and match speakers in my cabinet?

Using different speakers in a single cabinet is totally fine as long as the impedance of both speakers match and they are wired to the correct impedance for your amp. Many people use different combinations of speakers in order to mix the qualities of each speaker.

How many watts should my speaker be and how will this affect my sound?

In a nut shell, a speaker with a higher power rating will be "cleaner" than one with a lower rating. This is to say that there will be less "speaker distortion" in the higher powered speaker. When we're talking about distortion in amps, obviously there are a number of factors which come into play; e.g. power tube distortion, preamp tube distortion, and speaker distortion. With a higher wattage speaker displaying less speaker distortion, one will hear more of the power and preamp tube breakup. With that said, there are also many other factors that make up the overall "tone quality" of a speaker, eg. voice coil size, paper type, efficiency, etc. All of these things can have as much or more effect on tone than just the power rating alone.

There is also the concept of how a particular speaker interacts with your amp and your specific playing style. Given that there are so many deciding factors, it is always best to try out as many speakers as you possibly can. This way you will be able to determine which kinds of breakup you prefer and which speakers pair best with your amp, guitar, and playing style.

I have some old Mojotone speakers that you no longer sell, what are they?

Mojotone introduced a line of speakers back in the 1990's that showcased the perfect marriage of versatility and affordable performance; below is a list of those speakers. If you want the same quality and value today, try one of our current production Mojotone speakers.

• Mojotone Black Beauty BB10G
  10", 20oz. Ceramic magnet, 70 cnt watts/140 pk watts, 8 or 16 ohm, 97db eff., 1 1/2" Kapton voice coil
• Mojotone Black Beauty BB12G
  12", 46oz. Ceramic magnet, 100 cnt watts/200 pk watts, 8 or 16 ohm, 101db eff., 2" Kapton voice coil
• Mojotone 8" M815
  1" voice coil, 15 watt, 15 oz. magnet, 4 ohm
• Mojotone 10" Alnico MP10R
  1" paper voice coil, 30 watt, 6 oz magnet, 8 & 16 ohm
• Mojotone 10" MP10RHD
  1" kapton voice coil, 40 watt, 6 oz magnet, 8 ohm
• Mojotone 10" M10VT32
  2 " voice coil, 100 watt, 30 oz magnet, 32 ohm
• Mojotone 10" M10RR
  1.5" voice coil, 50 watt, 20 oz magnet, 8 & 16 ohm
• Mojotone 12" Alnico MP12R
  1" paper voice coil, 20 watt, 8 ohm
• Mojotone 12" Alnico MP12RHD
  1" kapton voice coil, 30 watt, 8 ohm
• Mojotone 12" M121660
  2" voice coil, 60 watt, 20 oz magnet, 8 ohm
• Mojotone 12" M12B
  1.375" voice coil, 80 watt, 38 oz magnet, 8 & 16 ohm
• Mojotone 12" M12V30
  1.5" voice coil, 50 watt, 30 oz magnet, 8 & 16 ohm
• Mojotone 15" MJ15B Bass
  2" voice coil, 100 watt, 38 oz magnet, 8 ohm
• Mojotone 15" MJ15G Guitar
  2.5" voice coil, 150 watt, 56 oz magnet, 8 ohm

What is Impedance?

In electrical engineering, impedance measures how easily a circuit conducts current when a voltage runs through it. Measured in Ohms, impedance is a way of telling you how much of the voltage introduced at one end will really make it to the other end. Impedance depends on other qualities of electricity, such as resistance, reactance, inductance, and capacitance.

The simplest kind of impedance happens with direct current, or DC, electricity. In this case, it's the same thing as resistance. All that gets in the way of electrons making it through the circuit is the circuit's resistance to the flow of current. Resistance usually takes the form of leaked energy that gets diverted from its intended pathway and creates extra heat.

With alternating current, or AC, impedance is much more complicated. The best way to understand how this characteristic works is to use an extended metaphor of freeway traffic. The whole point of a good freeway system is to transport people in vehicles, the way that a circuit carries electrons. The system might become less efficient if there are fewer people on the freeway, too many people, or too few lanes. There could even be bumps or obstacles in the road that cause cars to slow down, or lanes that accidentally route traffic away from its destination. Electrons face similar impediments.

Impedance is determined by resistance and another value, reactance. Reactance takes into account opposing forces and frequency; in other words, cars headed in the other direction and how many cars move past the same point at one time. Of course, more people will get to their destination if there are more net cars moving in one direction past a certain point, analogous to the effect frequency has on electron's energy. Two elements of reactance, inductance and capacitance, correspond to frequency. Inductance is in proportion to frequency while capacitance is inversely proportional to frequency.

Here at Mojo, in regards to amps, we use the Impedance rating on different items we sell, such as a pickup’s impedance (which is AC voltage), power and output amp transformer, and of course speakers. Here is a simple explanation of the transformer impedance:

Generally, there are 2 “sides” to the transformers we sell, known as the primary side, which handles the “input” or the line voltage to be transformed in the transformer. The other is the secondary, which has the voltage that is transformed to be fed, via different coils, to different parts of the amp.

Please note that with the transformers we sell, the “transformation”, in a power transformer, is taking the 120V from the wall basically a low voltage- high current supply and making a high voltage low-current supply to feed various voltages throughout the amp. With output transformers, it does the exact opposite. It takes a high voltage low-current DC voltage via rectification (usually known as B+), and makes a low voltage -high current feed for the speaker to translate what the amp has amplified.

Now, that being said, the impedances that relate to the output transformer primaries and secondary’s has to do with what is feeding the transformer (tubes) and what the transformer feeds (speaker). If you notice, different amps use different tubes, and those tubes have different power and signal input requirements, e.g. plate resistance, for the type of amp you have such as cathode biased Tweeds and Vox, fixed biased Blackface and Marshalls, Ultra-linear Silverfaces, etc. and the multitude of different tubes you can use for the amp.

One last word…. About speaker impedance….. people generally relate the impedance and resistance of the speaker voice coil as to what the meter tells them. Everyone has noticed that an 8 ohm speaker is actually 6.6~6.8 ohms, which is the actual resistance, not impedance of the voice coil. Most speaker companies rate speakers by Nominal impedance, not resistance. Which is, again, is the total of the resistance, plus reactance, capacitance, and inductance.

See sample of a Celestion G12M below, noting the resistance vs. impedance.

• Chassis type-Pressed steel
• DC resistance, Re- Available 6.7Ω or 13.1Ω
• Frequency range- 75-5000Hz
• Magnet type- Ceramic
• Magnet weight- 35oz, 0.99kg
• Nominal diameter- 12", 305mm
• Nominal impedance- Available 8Ω or 16Ω
• Power rating 25Wrms
• Resonance frequency, Fs- 75Hz
• Sensitivity- 98dB
• Voice coil diameter- 1.75", 44.5mm
• Voice coil material- Round copper

What's the difference between Mojotone BV speakers and Goldtone Celestions?

The idea for the BV series came when Celestion moved much of their operations to the far east and began sourcing what we considered critical parts there as well. To our surprise, the Asian-produced Celestion's have turned out to be excellent speakers but we often hear complaints of customers having cone cry issues. We sourced the original soft parts (cone, spider, dust cover) from the correct British manufacturer and then had our own baskets and magnet assemblies tooled in the US. The result is an American-made speaker with a British sound that is unmistakable.

We did a lot of testing with some very demanding players and amp builders - mostly the kind who like their British stacks and Gibson Les Paul's. We weren't done until they were certain the tone was as good, if not better than their vintage equipment and the incidence of cone cry was substantially reduced. Since Mojotone introduced the BV series, every other speaker manufacture has attempted to do the same thing - including the most obvious one! Those who have had a chance to try them, all agree the BV series stands out.

What is the difference between a "switching" jack and a "shorting" jack?

People use "switching" and "shorting" interchangeably to describe jacks such as the J12A and the J1.

Why is there solder on my brand new Switchcraft switch?

All Switchcraft brand toggle switches are pre-tinned with solder from the factory. Don't worry, we would never sell you a used part unless specified.

How do I use Mojotone Tolex Glue?

Mojotone Tolex Glue will need to be applied to both the wood surface and the backside of the tolex itself. Once applied, let the glue sit for 1 hour. In this time period, the glue should transition from feeling thin and watery to feeling tacky and moldable; once this change occurs, the glue will be ready to use.

If adjustments are needed within the first 24 hours after application, a heat gun can be used to loosen the glue. You may then reposition your tolex as needed without applying any additional glue.

How much adhesive do I need for tolex?

If using Mojotone brand tolex glue, you will need roughly 1 quart of glue for every two yards of tolex you are working with.

How much tolex do I need to recover my cabinet?

Most small combos can be covered with one yard (36" x 54") of tolex. A Twin Reverb sized combo will take two yards, and if you are recovering a 4x12 cabinet, you will need four yards.

How do I know when I should change my output tubes?

There is a lot of information floating around on the net, some good, some bad. At Mojotone, we are not in the business of telling you to change out your tubes for one reason or another. However, you should be aware of some common signs that it might be time to change tubes...

• Output is weak or severely unbalanced
  This one is tricky because, in older amps, it can also be due to the output transformer. But, if only due to complexity, the tube change makes sense as a first step.
• Tubes show signs of overheating/darkening of the glass
  This can also be a sign of OT damage or decay or overbiasing. With any output tube change the bias needs to be checked but with this one it is especially important.
• Arcing over
  Make sure and check the tube sockets and screen grid resistors if this happens. Usually accompanied by B+ or mains fuse failure.
• Bad tone
  This one is highly subjective and if your output is not lowered it is likely that your tone issues lie elsewhere - the preamp tubes may make more sense in this case.
• Looking for a different sound
  Again, pre-amp tubes are probably a better choice for this but if you have some experience and have heard a lot of tubes, the output section can be a place to tweak your amp.
• Cracked glass
  No choice here. Pony up and get the best replacements you can!

Things that do not directly indicate time for an output tube change:

• Blue light in the tubes that pulses with your playing
  When tubes are flashed, the residual impurities in the vacuum are more or less removed. The less perfect the vacuum, the more blue pulsing you will see. By itself, this indicates almost nothing.
• Dirty tubes
  Wait until they are cool and clean them. Your amp will run cooler and love you for it.
• Humming, noise, hiss, etc
  None of these directly indicate power tube failure. If you don't know for sure and your tubes are relatively new anyway (say 1 or 2 years of moderate playing) then taking the amp to a tech may be less expensive in the long run. Hum, for instance, could come from out of balance on the output section. But that could be coming from a problem with biasing or the OT or it might have nothing to do with the output section and might be a crossed heater wire in the preamp or an unbalanced hum rejection circuit for the heaters, failing filter caps or any other number of things.

What are some common bias specs for tube amps?

Fender Amps

• (Most Fender 6V6 Amps) Nominal Output 20-30 watts - 18-30ma
• (Fender 5E3 Tweed Deluxe or equivalent) Nominal Output 15-20 watts - 35-50ma
• (Fender Tweed 6l6 Amps) Nominal Output 40-80 watts - 45-80ma
• (Fender Black Face style 6l6 Amps) Nominal Output 50 Watts - 25-40ma

Marshall® Amps

• Marshall® 50 Watt Amp (EL34's) - 25-42ma
• Marshall® JTM45 (KT66's) - 30-40ma
• Marshall® 100 Watt (EL34's) - 25-40ma
• Marshall® EL84 amps - 20-30ma

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Last Edited on 2016-02-08