Recently a few newer amplifiers have came across my bench for repair they were the ones that had a single tube. They were billed and sold as a Tube amplifier. After opening them up I noticed that there was no power transformer after checking further I found that only the 6.3 volt heaters were connected and no power to the grid of this tube. So what does this mean ? the tube would require at least 200 volts across the grid to produce gain and be a true preamp. Basically the tube you see in the little window is just for looks (pilot light) what a farce with only the heaters hooked up the tube will glow but do nothing. So I will warn you Watch Out for that China crap. What will these marketing guys thank of next.
Recently I have been asked for 100watt amplifiers, I have to ask why? Yes I played through a 100 watt (Fender Twin Reverb) great amp buy I could never turn it up past 3-4 . The thought was have a big powered amplifier gave you better sound. Unless you are playing a stadium type gig and even at that the amps are now miked through the house system. The real deal is getting an amp that is powered where you need it by that I mean getting the amp to interact between the guitar ans speaker. What I am saying is powering the amplifier where the tube are working getting tube saturation and sustain by driving them with some power. This how you get the real break-up if you like your sound to be a little dirty you can get this by using a amp that is geared with the power that you need for the venue. You can throw out the distortion pedals and let you amp do the work and you will get a better sound and real tone. I prefer a 30 – 50 watt amp it will rock the house and still get the desired effect.
I would like to mention a little about speakers. I used to think a speaker is a speaker there is much more to it. By matching the speaker to the power of the amplifier it will interact better with the amplifier. Lets say you have a 30 watt amp the speaker should only be about 20% rated more than the amp by that I mean 30 watts amp the speaker should be rated at no more than 50 watts. This way the speaker is doing its job and moving air at the way it was designed. Over the past years I have bought and tried allot of speakers many good and many more junk especially the generic China stuff. I bought a few and they just sucked the sound from the amp and lowered the output. I have found the real Vintage speakers work the best. While we are on speakers I want to mention the quality of the cabs, many low priced cabs regardless of brand use particle board, this is Junk. Why because it does not add and reflect the sound it absorbs it dampens it and takes away the tone and power. The cab should be made out of lets say Pine and the baffle board should by plywood this will reflect and project the sound and add the speaker output by vibrating along with the speaker.
2/2013 I have been asked many times to hold a class that would help people understand the tube amplifier, I tell them to go online and pick up some old class room books on electronics like ebay has them all the time. I have to admit they are very dry and hard to read yet even harder to understand. So I am going to start a thread on the basic amplifier design and I will add to it as I find time. This is based on early Tube Design, and I would like to state this is not to only amplify but to add to the guitar experience by making the amplifier a instrument in its self. This is described by tube saturation and rectifier sag and the bell like chime a tube produces these can not be found in a Solid State design. To be debated I am sure. Do not take this a Gospel Truth but just an overview.
First we will start at the plug the back end of the amplifier, our electrical outlets in the house is generally rated at 117 volts and now commonly refereed to as 120 volts AC (Alternating Current) this consists of a Ground, Neutral and a Hot, when we plug in the amplifier the 120 goes to the Transformer this is a electromagnetic device that increases the line voltage to the desired voltage normally in the 400+ range this is AC and there are taps on the transformer that are lower voltage one is 6.3 volts which is used to heat the tube filaments and one 5 volt used for the rectifier tube filament. Now we have the high voltage required for the tubes but this now has to be converted to DC direct current like in a battery this is done through the rectifier tube or diodes now we have what is called B+ this is where we find the filtering capacitors these are usually the big firecracker looking devices what they do is filter the stray AC out of the circuit , before I get out of this area of rectification I want to discuss the Tube Rectifier using a tube instead of a diode allows the voltage to flux and surge this is referred as Tube Sag this is a desired effect in many cases. Now we are going to move to the front of the amplifier this is where we input the guitar, at the input jack one of the first thing the signal sees is the pre-amp tube like a 12AX7 this is the first stage of gain (amplification) this takes the minimal signal from the guitar and steps up the amplification, also built around this stage is the Volume which is an adjustable resistor (pot) this increases or decreases the amount of voltage that passes thus volume, also there is the EQ like Bass and Treble these are also pots which can control and filter certain frequencies. There may be one or several pre-amp stages depending on the amplifier. The next tube you will normally see is the Phase Inverter Tube as used in a Push Pull operation this is used to correct the phase at the peak of the first tube and the bottom of the second tube 180 degrees of phase. The next tube is the Power Tube in a single ended design or a Pair of Tubes Push Pull like the 6L6 – El84 – EL34 amd many more, these tube take the amplification introduced by the pre-amp tube and amplifiers it even further this is where the main jump in power occurs. Throughout these operations the current is usually DC (direct Current) from here we want to get this amplification to the speaker but in order for the speaker to function it needs to be converted back to AC (alternating Current) this is where the Output Transformer comes in this is a electromagnetic device (like the power transformer) most output transformers have several taps to match the ohms of the speakers for the efficient resistance to the speaker. Remember that a Tube Amplifier must have a speaker connected so the transformer does not get hot and fail (this is one of the most common failures) . This is only a simple description and does not apply to all amplifiers.
I would like to Rant On at this time. This post is about the trend in the Modern Guitar Amplifier (excluding Boutique amps) most amps built today are now made offshore where labor is cheep and forces the builders to live in poverty in most cases they could never afford the product they build much less a Player. That is only one aspect the manufacturing process is built on boards using micro components and chips. These boards are Not made to be serviced or repaired let alone modded. Think about it would you buy a car that you could not replace the starter. These amplifiers are not cheep and can run over $1000 and when it goes, it winds up in a landfill. It is truly a shame that Artist are forced to join this viscous cycle due to price. As you already know I have been working on amps for over thirty years and now I have to tell the person the amp is trash, well I am doing my best to stop this nonsense, first I designed a amplifier that uses full size components and can be easily removed replaced and modded and at a price just above the mass market junk. So keep in mind next time you go to GC and look, there are Choices spend 20% more and get a amp that will last generations unless you plan on using it for a short time. Larry, to be continued