Hello Again!
I'm back with a new Instructable! Wheeyy!
In this 'able, I'll show you how to make a Low-Voltage (Around 60 Volts) Tube Pre Amplifier for your Guitar!
Youll need, lets say Basic Electronics Knowledge for this.
UPDATE 20.12.2010':
Ive uploaded some examples with different Pickups and Gain settings.
Youll' need a mediaplayer that is able to encode AAC Music Files. Apple Quick Time Player should do the Job.
AllSamples.zip2 MB
BridgePU_LoGain.AAC295 KBBridgePU_MidGain.AAC341 KBBridgePU_MidHiGain.AAC353 KBBridgePU_HiGain.AAC366 KBNeckPU_LoGain.AAC308 KBNeckPU_MidGain.AAC314 KBNeckPU_MidHiGain.AAC335 KBNeckPU_HiGain.AAC325 KB
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Signing UpStep 1: Parts Youll need
I've listed all parts youll need here.
One thing I have to say before I write further.
I cant' tell you the exact sizes of the holes etc you need to drill because it depends on which parts you use and what kind of housing you choose.
So, Youll need :
A Case.
1 12AX7 or ECC83 Tube
1 9 Pin Tube Socket + Screws
1 200V 470uF Electrolytic Capacitor
1 1M Ohm Logaritmic Pot
1 100k Ohm Logaritmic Pot
2 Switches, 1 DPDT and 1 SPDT
2 35 V 2.2uF Electrolytic Capacitors
2 6.3mm Jacks
1 400V 0.68uF Polyester Capacitor
1 100V 1uF Poly Capacitor
Lots of wire.
Resistors :
2 4.7k Ohm 1/4 Watt or Higher
1 68k Ohm 1/8 Watt or Higher
2 100k Ohm 1/2 Watt or Higher
3 10k Ohm 1/4 Watt or Higher
1 1.5k Ohm 1/4 Watt or Higher
1 100k Ohm 1/4 Watt or Higher
Tools :
Soldering Iron
Solder
Wirecutters + Strippers
Needle Nose Pliers could be helpfull
Drill to drill holes in your Case
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At first, youll have to rectify your AC Voltage, coming from your transformer. Thats normally done with 4 rectifier Diodes ( eg. UF4007 or 1N4007) and then filtered with capacitors. With the rectified AC voltage, you are able to supply your circuit at the points, where that voltage is needed (if you take a look at the last step of this 'Table, youll find a supply-point named 'V+').
The low AC voltage for the filaments is wired directly to the filaments of your tubes (hint: the Datasheet of a tube could be a really great helper!).
If the Capacitors and Resistors in your circuit are able to withstand the higher Voltages, there shouldnt be a reason to reduce your perfectly good 200V to 60V.
Stay safe and have fun!
hazza
The emmitter-follower stage has to be DC-Coupled, meaning there should be no coupling-capacitors between the anode-connection of your last tube section and the base of your NPN-transistor. The collector is tied directly to V+ and the emmitter should be tied to ground with a 4.7k-22k resistor, depending on the type of your transistor.
otherwise, you could send me a schematic of your actual set up and I could try to fix it for you.
If it isnt driving your power stage enough, you might try to put another amplifing transistor stage after the tubes, as they normaly put out only a relatively small potential at the output. That amplifing stage should have a gain no higher than 2 or 3.
here is the original: http://hackaweek.com/hacks/wp-content/uploads/2011/08/class-ab-amp-schematic.jpg
My modifications include: output npn to bc337, output pnp to bc327, driver npn to bc547, as well as a couple of small resistor changes. This was to accomodate for me not having exact resistor values and transistor types. The output stage itself is sensitive enough to amplify a guitar signal. Is this sensitive enough to amplify the high impedance signal from my 12ax7 preamp's output?
Yeah, Sure you are able to get this running on 12V, at first, you may want to consider using a 12AU7 as the Tube as of its lower internal resistance. Further, the resistor values stay pretty much the same, but its best to use 2 Preamp Tubes for 3 Gainstages and 1 Cathode follower. On the other hand, you could use a single Tube and a NPN-Emitter follower for a low output impedance. Otherwise you may loose some of your tippy-top highs. I would use a 220k (a) and a 4.7k bypassed with 0.47µ (c) on the first stage an maybe a 100k (a) and a 3.3k on the second.
Yeah, you could easily do that, just leave out the Gain pot, from that point the Volume Pot would be the Gain pot.
With two additional Gain stages you are able to get some Rock tunes and maybe some High-Gain distortion, depending on how exactly you combine the two stages.
The 262B12 is a pretty neat Transformer for this application, Just make sure you use Capacitors with a voltage rating thats high enough to take the 170 or more Volts DC. But that shouldnt be a problem.
Have Fun Building it!
It should have something around these Values:
Primary: 110 or 230V Input (Depending on where you live)
1. Secondary: 6.3Volts @ 1 Ampere
2. Secondary: 100 - 200 Volts @ 50 mA (Note: the DC-Voltage will be multiplyed by the Factor 1.41, If you have a Output of 100 Volts AC, youll have a DC Output of
141 Volts)
You should use Fuses with a Value twice the Amperage,which you drain through it. Otherwise, it will blow, even if theres no Failure.
Youll need a CLC or CRC filtering supply. I Prefer CRC, they are easier.
For a simple preamp, you should use a Bridge rectifier, after that a charging Capacitor (the first C), that one should be around 47µF and rated 1 and 1/2 Volts more than your Filtered DC Voltage.
Example:
You got a 100 Volt AC Secondary.
After the Rectifier you got very Unsmooth 141 Volts, the next Voltage-rating on Caps should be 200 Volts, so use one 47µF @ 200 Volt Type.
After your Charge-Cap, youll need a resistor and another Capacitor, to complete the CRC - supply.
The Resistor should be a 2 Watt type and should have a value around 10 - 22 Kilo Ohms.
After that, use another cap to finally smooth out any spikes, that are in the Supply voltage.
For that, you can use another 47µF @ 200 Volt type.
http://www.bottlehead.com/store.php?crn=221&rn=439&action=show_detail
http://www.tubedepot.com/tr-pw-13.html
http://www.hammondmfg.com/261.htm
If you could look through these and let me know your thoughts on them, it would be much appreciated!
The first one looks pretty Solid, the second one looks a bit Underpowered for me (It could get very warm in use).
And with Hammond-transformers, you can do nothing wrong.
You could use the Hammond 262B12, but then youll have to connect the Filaments of the 12AX7 in series instead of parallel, thats just one Wire less, so easy to do.
With what values have you actually ended up using for the inductors?
Would one of those here work?
Sorry, I have no Exact values of the Inductor. I winded it myself, I think 50 Turns of 25AWG Copper Wire... I would use a 330 µH Type, just to be Safe.
Which kind of Project is it? Normally, they should work.
But If you only have got an Transistor Amp (Like me, until I finished my Tube Amp) this is a good option to bring some soft drive in your Songs.
Well, I dont have big Transformators at home, so now Im' thinking of Building the 5 Watt amp with a Switchmode, too. But in that case, I would build myself a step up transformer or I have to look for an ooooold TV. Otherwise, the big advantage of SMPS is, they have a much higher Frequency, which means you have no 50 - Hertz humming in your Powerline. SMPS handle frequencies, which are muuuuuch higher than the Human ear could Recieve.
includien the step up converter?
if not
send me a better drawn one and i will draw it for you (high qualety)
Well, the Schematic ive drawn have a very high resolution ( I think 7k x 3k Pix)
And I gonna put some Eagle Schematics online.
i just found the enlarge button (sorry)
i sm so gonna build this
i have 5 of thos those here
i can get them for 10$ new
Well, it has to be the 12AX7 or the 12AU7. The AX has a Higher gain so it will overdrive faster.
so if all parts are +300 V it should work
The Anode Caps something like 400 Volts and 2.2µF Elkos.
In my new Full-Tube Amp, I got the 12AX7 powered with 270 Volts, it sounds great!