Guitar Tube Amp
Nov 12, · Many have asked for a step by step process for making a bare chassis amplifier, so here it is. This project is based on a Fender Princeton 6G2 circuit, retro. Dec 13, · Josh Phelps guides you through the journey of building your BUD Tube Amp Kit. - PCB Construction - Chassis Prep - PCB Installation - Time.
Well, yes and no. While tubes are no longer the technology of choice in the computer industry, they are very much alive and well when it comes to modern high-end guitar amplification. It is because of the electric guitar amp that vacuum tubes are still being manufactured today. Guitar amps with tubes are currently front and center in the high-end market because many guitar players find their sound characteristics to be superior to solid-state amps i.
Boutique amp builders are individuals or small companies who build a relatively small number of amps each year with an emphasis on quality and attention to detail. Boutique amps are usually priced in the thousands of dollars, because they require a lot more time and skill to produce. The builders will often customize circuit designs to satisfy the different tastes and styles of individual guitarists. Most boutique amp builders at one time started out as electronics hobbyists who thought it would be fun to modify or build their own tube amp.
The internet continues to make it easier to find books and parts to help you build your own boutique quality guitar amp. The quickest way to get acquainted with how do you sanitize granite countertops parts and standard layout techniques used in tube amp building is to build an amp kit. Most kits come with a pre-punched chassis, parts and instructions to assist you in building it.
Find a Fender schematic and its related layout drawing what size is a bath sheet start making a parts list. Most of the boutique amps being made today are cloned vintage Fender and Marshall amps or at least heavily influenced by their circuits. There are also many books on the subject of tube amp circuit theory, design and building that you can read to help make your first build of boutique quality.
Kurt began playing guitar at the age of nine in Kalamazoo, MI. Why Tubes? Circuit Schematic Resource Links. Share your projects, experiences, and experimental fun with us!
Before you start
Here's the standard disclaimer: This is dangerous, high voltage stuff. OK, it's not "High Voltage," technically, but it's high enough to kill you. The power supply in this projects kicks out V, which is plenty, with startup spikes near V or more Don't believe it when they say "it's not the voltage, it's the amperage that kills you"--because it's both.
Amps AND volts together dictate the danger level. If it were amps alone, then even a AA battery can supply many times what's needed to stop a human heart. The volts do the "pushing," and overcome the natural resistance of your skin. And there's plenty of current available to harm you in any tube audio amp Remember: --Always drain the power supply filter caps before touching the circuitry. First, I like the sound of the 50L6 power tube in my vintage Kay amp.
Although weaker than many common types 6V6, 6L6, etc. And I have several spare 50L6's on hand There's a long history of small practice amps with these tubes, yet they are generally ignored today. Secondly, this build has always intrigued me: Super SE 6V6 , a parallel single-ended two output tubes together in parallel 6V6 amp. A parallel SE design would be a true Class A amp, too, with all the of the richness and aural mystique of the class and more punch than my Kay.
Lucky Find Thirdly, when gutting an old TV set I found a decent and massive power transformer appropriate for this build. A bit of explanation: The 50L6 and it's variants 25L6, 12L6 are power pentodes with a maximum operating voltage of V. Consequently, the majority of power transformers supply V or greater.
A medium-voltage power tranny is actually tougher to find than the higher-voltage variety. AC voltage is RMS--essentially the average voltage for the wave form. Once it's rectified and filtered, it's higher. Depending on the rectifier, the DC output voltage will approach the "peak voltage" of the waveform.
Immediately, I rejected the use of a tube rectifier--what I had on hand wouldn't be as efficient as a solid state rectifier.
A V RMS transformer is nearly ideal. With luck, I could get very close to the V max using a SS bridge rectifier! So finding the transformer first was the real motivating force behind the build Next, I chose the preamp tube, a 12AX7. That was easy--they're the most common preamp tubes, and the majority of guitar amps include one or more. Enter the 6DG6GT as output tubes While I was aware of the other variants, I hadn't heard of this one.
Bravo, Ohm! Now I could plan on three tubes that would run with 6V heaters, and the TV transformer included a 6. Well, I just HAD to build this! It couldn't be the first, but it looks pretty rare for guitar amps, anyway Choice of components are alway contentious for tube amp builders.
Some insist that one part or another is integral to the process. Although there maybe some truth, there's lots of bunk, too. Capacitors, Non-Electrolytic Many swear by expensive polyester or polypropylene non-electrolytic caps. I used mylar caps. Here's a secret: mylar caps are polyester, mylar is just a proprietary name. All non-electrolytic caps should be rated for V, since they are usually in the signal path.
Small cathode bypass caps can have a lower voltage rating, however. Capacitors, Electrolytic Most caps 1uF or greater are electrolytic capacitors. They are a must for the power supply filter caps, and are also often used for cathode bypass caps. These come in two general flavors: polarized and non-polarized. For this project, the only non-polarized electrolytic used were for the preamp cathode bypass caps. Cathode bypass caps should be rated for twice the bias voltage.
There's a "can" type multi cap photo, just for reference. New multi-caps can be found, but they are expensive, and can be hard to replace. These are an option, and are very common in older amps Resistors Again, some will argue the merits of carbon comp vs. If you're a believer, knock yourself out ;-.
Normal off-the-shelf resistors work just fine. PRE tags have been removed for non-pro members. The chassis was originally a flat sheet of steel, which I reclaimed from a defunct VCR.
Check out that snazzy "high voltage" symbol stamped into the metal The steel was trimmed to size with a Dremel fitted with a cutting wheel. The sheet was then held in between the clamping sides of a "Workbench," and bent downward to a 90 degree angle, with a heavy steel carpenters square. This lent a decently uniform bend to the sheet, and there were few imperfections.
Most of the bend was done by hand and body weight. The bend was finished and the angle sharpened by pounding the top of the forming carpenters square layed atop the sheet steel with a rubber mallet.
Afterwards the formed chassis was cut to width, also with the Dremel. Cutting the chassis holes The large rectangular cutout for the transformer was made with a nibbling tool.
They are very handy tools. The power tube socket holes 1in. The rest of the holes were made with a stepped bit. This is a fantastic drill bit!!!! A pilot hole is needed for the stepped bit, so don't throw out the normal bits. They do made a smaller stepped bit, which I plan to get soon--then only the smallest pilot hole would be necessary.
Many pro and serious amateur builders use a die punch. Use rubber grommets in the holes to prevent any fraying or shorting. Traditional tube amp power supplies are old school--relatively high voltage, with big "iron," and generally not regulated.
Typically, they supply a range of voltages for different purposes--a current source for the output transformer, voltages for the preamp tube plates, and sometimes in this case a separate voltage for the pentode screens. Unlike regulated supplies, the different supply voltages are created with current-limiting resistors.
These are often called "voltage-dropping resistors," but their operation depends on the current draw of each stage. Designing a power supply The first step is choosing the right power transformer see the "How did this project get started? To pick the right transformer, look at the data sheets for the power tubes. In practice it's lower--the transformer is under load, there are losses in the caps, etc. So something less than 1. Gotta dig that crazy square root of I'm not certain about the availability of PTs with secondaries in the V range.
Another alternative is to use a "choke input" power supply--that's connecting the choke FIRST, before any filtering cap. A choke input should drop the secondary voltage to 0.
The solid-state rectifying bridge was chosen over a tube rectifier to retain as much of that voltage as possible. That's OK--the much vaunted "sag" effect of tube amps doesn't apply to single-ended, Class A amps.
They draw the same amount of current whether there's an input signal or not Also, the PT doesn't have a centertap, so unless I used two tube rectifiers or went with a half-wave design , solid-state was the best solution. These voltages were needed by the circuitry: B. That could be related to the unknown current-suppling potential of the TV transformer--but I'm beginning to suspect that the 6DG6GT screens draw much less current than noted noted on the data sheets A Redesign Partway Through the Project The design evolved.
Initially the first filter stage was an RC Resistance-Capacitance filter, but that changed quickly. To get a clean signal, I'd need to insert something like a 50 ohm, 20 watt resistor. Also a significant change--there was no B. I had planned that the preamp would run from the lower screen voltage V. For the 12AX7, that's a pretty low operating voltage. So the preamp supply was added. It's an unknown value inductors are measured in Henries , but it was matched with the TV power trannie, so I was sure it would work--and it did.
And honestly, an LC filter does a much more efficient job of smoothing out the supply ripples in a single stage than an RC filter does.