Tube boost + overdrive running off a 9 volt battery

[Papa_lazerous]

Dano thats a real clean layout you drew, what software you using and how long did you ahve to put into that?

[kurtlives]

Regarding the 386 amp, that's the route I'm taking with my wired tube socket thing. Trying to fit it in a small plastic case.

For the questions about using a tube other than the 12AU7, as said earlier, they are higher gain and won't work nicely unless you modify the circuit, I don't know how to do that part.

tubesandmore.com has the tube and sockets, it is the standard 9-pin tube socket you would use for guitar amp preamp sections.

Here is a rough *unverified* wiring diagram for anyone who wants to try it.

Thanks for the layout. It does however make it look like R2 is connected to pin 5 which is not the case.

Also why is lug 3 on the volume pot jumpered to lug 3 of the tone?

[Fuzz]

Thanks for the layout. It does however make it look like R2 is connected to pin 5 which is not the case.

Also why is lug 3 on the volume pot jumpered to lug 3 of the tone?

R2 IS connected to pin 5, since both (R2 and pin 5) are connected to V+. Lug 3 of tone pot in jumpered to lug3 of volume pot just because the author inverted the order of tone pot & cap, with no remarkable differences.

[dano12]

Dano thats a real clean layout you drew, what software you using and how long did you ahve to put into that?

Thanks dude. I use Microsoft Visio. That one took about 20 minutes.

[dano12]

Thanks for the layout. It does however make it look like R2 is connected to pin 5 which is not the case.

Also why is lug 3 on the volume pot jumpered to lug 3 of the tone?

Some of the wires follow a rather tortuous route, but I'm pretty sure it is all correct at this point.

I've tried to share lugs as much as possible to reduce the number of wires needed.

[kurtlives]

Cool

I also just realized there is no bypass switch. So basically I need to know which wire is the effect INPUT and OUTPUT. Thanks...

[Papa_lazerous]

I am not familiar with Visio at all 

[mojo_hand]

I think if you tried to modify the circuit for 12AX7 use, you might end up in a no-win situation....they're really supposed to run on 100+volts, and at 9v, that's just asking a lot!

Yeah... I think what you're going to run into is that the 12AX7's gain is high enough (in this topology) that, with only 9v to work with, it's automatically going to clip the bejeezus out of any but the tiniest of input signals.  You could redo the topology to cut gain and use some negative feedback, but then you'd get a squeaky clean sound, which probably isn't anything anyone would want.

I wouldn't doubt that the low gain was exactly why the 12AU7 was chosen.

[kurtlives]

How does they look for a full layout?

[kurtlives]

No one?

[gluedtogether]

I think if you tried to modify the circuit for 12AX7 use, you might end up in a no-win situation....they're really supposed to run on 100+volts, and at 9v, that's just asking a lot!

Yeah... I think what you're going to run into is that the 12AX7's gain is high enough (in this topology) that, with only 9v to work with, it's automatically going to clip the bejeezus out of any but the tiniest of input signals.  You could redo the topology to cut gain and use some negative feedback, but then you'd get a squeaky clean sound, which probably isn't anything anyone would want.

I wouldn't doubt that the low gain was exactly why the 12AU7 was chosen.

Apologize for the newbish question. I am looking to try a tube project down the road and don't want to have to have a separate power supply on my board from my current. I get either 9 or 18 volts. Can this be converted to run of 18 instead of the 12 suggested for a 12AX7? Thanks

[bancika]

It's not good to run tube heaters that high, you can go lower than recommended 6.3V per heater (like this one does, with 4.5V per heater) but anything higher than 7V will reduce tube life noticeably. What you can do is put a resistor in series with heaters and run it of 18V, you'll get higher plate voltage which is good and you'll be able to tune heater voltage to 12.6V.
Let's see, if you start with 18V, minus 12.6V = 5.4V. From ohm's law you'll need resistance of approx. 5.6V/0.15mA = 37ohm. Approx power dissipation is 0.8W. I'd take 2W resistor of closest value to 37ohm. Any clearer?

[Fender56]

From ohm's law you'll need resistance of approx. 5.6V/0.15mA = 37ohm

Small typo!!! It is not 0.15mA, but either 0.15A or 150mA (which is the 12AX7/12AU7 heater current). All the others values are right!

[gluedtogether]

It's not good to run tube heaters that high, you can go lower than recommended 6.3V per heater (like this one does, with 4.5V per heater) but anything higher than 7V will reduce tube life noticeably. What you can do is put a resistor in series with heaters and run it of 18V, you'll get higher plate voltage which is good and you'll be able to tune heater voltage to 12.6V.
Let's see, if you start with 18V, minus 12.6V = 5.4V. From ohm's law you'll need resistance of approx. 5.6V/0.15mA = 37ohm. Approx power dissipation is 0.8W. I'd take 2W resistor of closest value to 37ohm. Any clearer?

So if I am reading this correctly, I can use the layout above, but add the proper resistor to lower the voltage down to approx 12.6volts and that should work? I have a couple 12Ax7's lying around which is why I am very interested in giving this a shot.

[bancika]

good point, it's A, not mA

As you can read above, 12AX7 are not good candidates for this. Your voltage thingy is ok, however.

[gluedtogether]

I thought the problem with the 12AX7 was 9 volts was too low. If it was 12, that was okay. Did I mis-read. Again, new to building anything with a tube in it. If not, I will have to shop for a tube as well.

does the change from mA to A change the resistor value?

[bancika]

yeah, changes 1000 times
with 0.15mA you'd need 37K resistor instead of 36 ohms.
If you want to utilize 12ax7 try something like shaka tube or tube driver.

[kurtlives]

How does they look for a full layout?

Anyone?

[LMJS]

I think some of you guys will like this link http://www.takamine.co.uk/preamps/cooltube.html

[mojo_hand]

I thought the problem with the 12AX7 was 9 volts was too low. If it was 12, that was okay. Did I mis-read. Again, new to building anything with a tube in it. If not, I will have to shop for a tube as well.

It wasn't really a tube-specific problem, it's that the gain of a 12AX7 is about 5 times as high as that of a 12AU7.  In the circuit shown, that would mean around 25 times more gain total.  So you might get a good clean out of it if you breathed gently on the strings, but anything more than that would clip.  I guess you could stick a pot in front of it, although that would raise the noise level.  Or always keep your guitar's volume control between 0.00 and 0.01.  But I suspect that you'd be happier in the long run if you spent the $8 and got a 12AU7.  That's not a very steep a price by tube equipment standards. ;-)