Introduction: How to Turn a Guitar Tube Amp Into a Preamp/distortion Unit (with Load Box)
Hi everyone !!!
This is my first Instructables, i will explain you how to turn a little Tube guitar amp into a preamp unit/pedal, with load box; Im french and my English is limited, so if i made some mistakes please forgive me !! :)
I DO NOT RECOMMEND THIS INSTRUCTABLES IF YOU WANT TO MAKE IT WITH MORE THAN A 30 WATTS AMP , AS YOU CAN GET DEADLY ELECTRIC SHOCKS BY WORKING WITH TUBE AMPS, EVEN IF THE AMP IS OFF. BE REALLY CAREFULL !!!!!!!!!!!!!!!
The amp used here will be a Storm VT-10, 10 watts cheap tube amp you can get for 50$ used and 100$ new; I used to play with a Storm vt-10 when i was playing guitar; Lots of people thought Storm vt-10 were bad quality cheap tube amp, but its not right; The big problem in this amp are the genuine "ruby" tubes installed, which are REALLY horrible weak tubes, the worse i have ever heard ; If you want you can keep the original Ruby tube for this project, but i assure you your amp will sound better with other tubes .
One tube is a 6l6gc, the other one a 12ax7 ; After throwing the ruby tubes in the trash i decided to buy a 6l6gc jj tesla and a nos General Electric 12ax7 from the 60's; These Tube gave a real interest to the amp :)
Because i didnt got enough passion to still play guitar, i just left my amp in my attic, waiting for a project...Now im playing with analog synthesizer and some drum machines, and because i love the vintage grain of a tube amp, i would like to turn my amp into a tube "pedal" (its not really a pedal , it dont got a footswitch) , cause i will not need the speaker anymore....
BUT : as lots of people knows, you CAN'T use a tube amp without a speaker ; Without a speaker , who act as a 4/6/8/16 ohms resistance (depends of what kind of speaker is used) , the output transformer will be damaged, cause the resistance is infinite; So you have to add a resistance if you dont use a Speaker . Its called a LOAD BOX, and its simply a 4/6/8/16 ohms resistance ; Because the amp is a 10 watts amp, i choose a 20/25 watts resistor; If you use a load box, theres no problem to transform you speaker out to a line out, and turn your big cabinet tube amp into a small but effective tube preamp;
So , in this instructables, i will show you how to rehouse your tube amp and add a Load Box to it :)
WHAT YOU WILL NEED :
- a small guitar tube amp like a Storm VT-10, or a Goldenton for example
-Soldering iron + solder wire
-22mm core drill for the 12ax7 tube and a 25mm for the 6l6gc tube
-a 1/4 ts jack (for the line out)
- a 20/25w, 8 ohms resistor , look at the picture (it cost 5$ on eb*y)
-heat shrinkable tubes (you will need it when you will give extension to the wires, it will protect the solder point)
-aceton or white spirit
-pine wood (or any kind of wood)
Step 1: Open the Cabinet, Extract the Amp :)
-Unscrew the back plate, and the chassis ; Unplug the speaker .
now you got the amp :) the way to extact the amp will vary from what kind of amp you used , but you know, extract the amp is pretty easy, just take your time !!!!
Step 2: Upside Down
As you can see the Storm vt-10 amp is really strange : everything is upside down, the transformers are under the chassis , and the tubes are backside; the Potentiometers are solder directly on the PCB;
If you want to use the same chassis, you will have to twist it, so the transformers will be on the top of the chassis : but the potentiometers will be upside down this time :/ and the wires from the transformers and tubes are not long enough if you want to twist the pcb;
The Tubes HAVE to be place on the top of the chassis, you can let them in place , but it will be really unusefull and inesthetic :)
You will have to drill the top of the chassis with the core drills ;
BUT FIRST : lets unsolder the tubes and transformers wires from the PCB
Take a look to the wires : lots are red so you will have to take notes ; Personnally i choose to paint a bit the wires with posca, so im sure to not make mistake when i will sorder them again ;) Unsolder all the wires from the board, it will be easier for you to work with after.
Be very carefull when you will disolder and unscrew the Tubes base : its ceramic and its really fragile !!
Unscrew the ground connectors too, and the transformers ; Now you got a blank chassis so go step 3 !
Step 3: Cleaning and Drilling the Chassis
Now you got a blank chassis .Theres a aluminium plate glued on the front with the "volume", "gain", etc.. paint on it; Its now obsolete as we have to turn the potentiometers upside down;
Cool thing is that we can unglued the plate and continue to use the pre-drilled holes for the pot, line in , on/off swith and led .
Ok so just grab the aluminium plate and try to unglue it gently : the more glue you can keep attached to the plate and not the chassis, the better it is ;)
If like me you still got a lot of glue on the chassis, you will have to clean it, and , because it one of the most rubish glue i ever seen (it looks like resin ^^), you will have to clean it with something like : aceton, white spirit, synthetic cleaner.. this kind of stuff :) Its the part which annoyed me the most , because even with some White Spirit its really hard to clean the chassis, it just act as a resin and its very sticky;
Once you did that , its time to drilll the chassis for the new tube holes; And its a tricky part; You have to drill the chassis, but slowly , so like that theres not too much steel "eaten" by the core drill; Try to use the same space the tube gets when they were originally placed ; I choose to place the 6l6gc on the right side for esthetic, but you can place it were you want :)
After that , you have to drill the tube base holes for the screws ; BE VERY CAREFULL cause you dont got a lot of space to drill the hole ; take you time , not like me : on the last picture you will notice that i totally *%# my drill for the 12ax7 : the drill broke some steel from the chassis....but its not a problem , the aluminium tube base for the 12ax7 hide this mistake .
Ok now drill a hole for your output jack; I choose to place it behind the chassis but you can place it wherever you want ;)
Step 4: Add Extension Wires to the Transformers and Potentiometers
Put the the transformers back in their places , do the same for the tube bases.
Unsolder the Pots from the PCB and the Input jack too ( be carefull to note the original places and values for the pots )
.......Ok here is the long and monotonic part : you will have to add extension wires !
For the transformers and tubes bases : take wires of the same size as the ones used in your amp; solder extension wires to the short genuine wires, and put some heat shrinkable tube on the soldering point, it will prevent from static noises; (see the picture)
For the Potentiometers : take normal size wires .Just add some extention wires from the pots the the pcb (see the picture)
For the input Jack : you can take the wires you want its not a problem; just add extensions wires to the positive and ground socket (no need to solder all the 3 ground sockets, its just made for the input juck to be maintained by the PCB, you dont need this anymore cause you will have screw the input jack directly to the chassis.
Step 5: Installing the "load Box" and Re-solder Everything
Ok , so now its time to solder the resistance to the speaker out, and so make a Load-box betwen the speaker out and the line out;
To make a load box , just wire the jacks and resistor all in parallel , tip connections of both jacks to one end of the resistor, sleeve connections of both jacks to the other resistor connection;
As we dont got a jack for the speaker out but a red and black wire, the red (positive) wire will be the tip , the black one the (ground) sleeve;
(you can add some heat shrinkable tube to the resistance connections just like me but its not really necessary )
As you can see on the picture, i attached the resistance to one of the screw hole of the PCB, preventing it for "moving" inside the chassis
Now its time to re-solder everything like it was , and screw back the potentiometers, led ,switch and input jack on the chassis;
Once you did that , go to step 6 :)
Step 6: The Style and How Does It Sound
I choose to make a minimalist style , a simple pinewood board treated with mineral oil (for the esthetic) with skid resistant bases...you can see on the picture that i put some handle to the sides, but i think i will add some wood sides to make the chassis closed ; it will prevent from accidental electric shock :)) Its really simple to add this wood base to the chassis, just use the pre-existing holes on the chassis and drill the wood base;
Now you can plug the unit to an effect, stompbox, mixer, or an amp, as you want :)
How does it sound ? well , very good i think, good old time tube sounds, really pure with crispy distortion ;) It will sound like yr old amp without the wood cabinet, theres no real change to the tone, dont forget that the original Ruby tubes are too much cheap if you want a real tube sound.....
Guitarist will be a bit annoyed by the miss of speaker simulation....well you can buy one if you like , it cost between 40 and 100$ , depending the brands;
Because i use synthesizers and drum machines, i really dont care of a speaker simulation, it works really as i wanted to, great !!!
Hope you enjoyed this Instructables !!!!!!!!!! If you got any question about it no problem, just ask !