Custom Tube Guitar Amp

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Introduction: Custom Tube Guitar Amp

Have you ever wanted to have the warm tube sound of a guitar, but could not afford a good tube amp? If so, then this instructable is for you. A while back, a friend wanted me to build and sell him a guitar amp, so I found a few tubes and a cool chassis(CD Drive) and started building. The video below is a demonstration of the tube amp, it is played by my friend, Daniel. This instructable will show you how to build this awesome tube amp. Lets get started!

Step 1: Tools

For this project, you will need a few different tools. You will need:

  • A soldering Iron
  • A Drill
  • A hot glue gun
  • Metal and wood drill bits of varying sizes
  • Large 1/2 inch metal drill bit.

Step 2: Materials:

For this project, you will need quite a few materials:

  • Power transformer that can put out 277-300 volts
  • 6 volt filament transformer
  • Switch
  • 6V6 Beam Power Tetrode tube
  • 12AX7 Tube
  • Wood
  • CD Drive
  • 2x 100k Potentiometers
  • 1/4 inch audio jack.
  • 3x .02uF Capacitor
  • .002uF Capacitor
  • 120uF Electrolytic Capacitor
  • 10uF Electrolytic Capacitor
  • Resistors: 10k, 100k, 32k, 1M
  • Bridge Rectifier
  • Inductive Choke
  • Output Transformer 900:4

Step 3: Preparing the Chassis

When I started this project, I needed to find a metal chassis to house the electronics. After looking around, i came across an old CD drive from a computer. It makes a great chassis, and puts a modern spin on the age old idea of a tube amp. To start, remove the bottom of the drive and empty out all of the plastic components and electronics. After that, press inside the hole in the top to remove the piece of metal held in by the sticker. This should make a large hole in the top of the case, perfect for a power tube. Next, use the 1/2 inch drill bit to make holes for the preamp tubes. Finally, drill holes in the front of the chassis to mount the power switch, potentiometers, and audio jacks. These can then be screwed into place.

Step 4: Manufacturing Tube Sockets

The tube sockets are what electrically and physically connect the tube to the amp. You can buy ready-made tube sockets online, but I decided to manufacture my own out of wood. To do this, I used a pencil to coat the tube pins with graphite, then pressed them on a piece of particle board to make drill marks. I then drill holes on the marks and hot glue wires in place so one bare end is in the hole. The tube sockets are then cut down to the smallest size possible to save space in the chassis. One tube, the 6au6, serves as a pilot light, so it does not need wires. There is a hole in the middle for the LED. The sockets are now done.

Step 5: The Power Supply

To build the power supply for this amp, please refer to the above schematic. The power supply for this amp uses a miniature auto-transformer, so it is a hot chassis, which makes it more dangerous than a conventional amp. To make it safer, either use an isolation transformer or use a traditional power transformer. Also, make sure to use an inductive choke and smoothing transformer to reduce hum. This power supply should deliver a steady 300-350 volt B+ voltage and a 6 volt filament voltage.

Step 6: The Wiring

To wire the amplifier, reference the above schematic. Make sure to use leads that are very short to minimize hum. The pinouts of the tubes are also above. For this step, just be creative and solder the leads and components together in the best way you see fit. Also, make sure that wires that should not touch do not touch.

Step 7: Testing

After your amp is done, its time to test! Hook up the amp to an isolated variac transformer and steadily raise the voltage, just to make sure nothing shorts or starts smoking. If it works, then plug in your guitar, iPod, or banjo, and start playing your music really loud. This instructable does not show how to make a cabinet, but I'll save that instructable for a later day. Make sure to vote for me in the Amp and Circuits contests. Good luck building!

Disclaimer: This project deals with potentially lethal high voltage, build at your own risk.

Edit: I have been getting many complaints in the comments section regarding the safety of this amp section. I fully agree, this amp does pose a safety hazard to people without an adequate knowledge of electronics. These complaints also focus on poor design of the power supply section. The power supply does not contain a power transformer because I did not have one readily on hand. Same with the tube sockets. I built this out of the supplies that I had available. In addition, this amp will eventually be placed in a cabinet. Please stop with all the negative comments, I am fully aware of all the issues this amp contains.

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24 Comments

WOW!!!... IT BRINGS ME MEMORIES OF THE SEVENTIES WHEN I EXPERIENCED WITH CATHODIC TUBES AND SEMICONDUCTORS TO CONFIGURE THE PINS.... WONDERFUL JOB MY FRIEND!!!! EXCELLENT!!!!

This instructable should be changed to reflect the less lethal version suggested by rbd56home (among other users here who all agree this is not a safe design for a tube amp!!). Otherwise it is a death trap and should be taken off instructables. Playing guitar puts the player in contact with strings and this amp can potentially put high voltage/current through the strings/player. There are known instances of amps just like this one harming and killing people.

This version of the time amp is unsafe, I agree. I have since built a safer version with a better person supply. the only modification to this time amp needs to be replacing the bridge rectifier with a single diode. With this modification, as long as you use a polarized cord where the neutral is grounded to the case, the tube amp should be safe.

Why post this when you know it is dangerous? Having a disclaimer is no excuse, I can just see some 13-yr old trying to build this thing to save money and killing himself in the process...

A little natural selection goes a long way.

georgecarlin.jpg

I have been building valve amplifiers for many years and studied the circuit diagram in detail. The critical part is the isolation between the mains input and the rest of the circuit. A fully isolated transformer is absolutely essential as any hazardous voltages can be contained within the circuitry without coming into contact with the input and chassis. The bridge rectifier design that has been used here is grounded to the chassis which means that the chassis is floating with a DC potential far greater than the mains supply. If the chassis is connected to the ground for the input, the input will be negative by at least 300v with respect to the mains input. DC voltages at this level are lethal. To make this design safer, the bridge rectifier can be removed and replaced with a single diode so that the neutral feed from the mains is at the same potential as the chassis. The mains plug must be polarised to ensure this is never connected the wrong way round. The simplest way around this is to replace the mains transformer as suggested in other comments to be absolutely safe. To build this design will be lethal to anyone using it especially if other metal devices come into contact with anything connected to it. Please be safe.

PLEASE don't use auto-transformer in a guitar amp!

They are OK in old radios where the whole chassis is isolated by the wooden housing and the pot buttons are not conductive but with guitar amps you are connected to the chassis-ground through the strings. If anything goes wrong you are dead. And put a fuse in it at least. Just for example: Several guitarists died because of failing vocal amps that shocked the guitarist through the microphone and the current was going through the man and the guitar amp to the ground. They could have survived if the guitar amp had proper short-circuit protection.

HA! Flashing back to my high school electronics class, fall, 1965... built a Fender Deluxe guitar amp (stolen schematic) from a "raw" chassis as my project, part of final exam was sketching an AM 5-tube superhet schematic with appropriate tubes and approx. component values. I passed, end of my "electronics" education since "semiconductors" came on stage and made me obsolete at age 14!!! LOL The class was never offered again, one heck of a high school class though. Transistors... ugly little suckers. :-(

vtoL drone! The amp that they forgot to build long ago.

Don't let this happen again... oK?

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