Tube newbie gathering knowledge before building ;) Just some questions

[finkfloyd]

Hi,
I would like to build a tube pedal either this : http://www.muzique.com/schem/tubedrvr.gif as its 9v

or the shaka tube.

1:) But how do I know what pins are which? they arent numbered.
2:) is a tube "heater" really the sockets what the tubes rest in?
3:) Is there a difference between which tube i use? Ie* brandname.
As you can tell I have nearly zero knowledge on tubes.
Cheers,

[Dave_B]

1:) But how do I know what pins are which? they arent numbered.

Here's a pinout

2:) is a tube "heater" really the sockets what the tubes rest in?

The heater is inside the tube.

3:) Is there a difference between which tube i use? Ie* brandname.

Different brands sound different from each other, yes.  You might try searching on Google for 12ax7 comparisons to get a rough idea. 

Hope that gets you started!

[AdamB]

Pins are numbered differently depending on what tube you use, just check out the datasheet or something for info on this.

The heater is a fillament inside the tube, you apply a voltage to 2 of the pins in order to heat the tube up, the tube needs to be warm to operate. The fillament is basically the same as a light-bulb, it generates heat so that the tube will work, and also a little light (you should see the tube glow a little when it's on). With 12AX7 tubes (this is all I know about, as i'm a tube newbie too, building a similar pedal to the tube driver) you apply about 12.6V to pins 4 and 5 (doesn't matter which is +ve and -ve, the fillament is basically like a light bulb, it'll work either way round as it's just a high-resistance piece of wire). If you choose to use a 9V battery, you can just apply 9V to the heater pins, but be aware that it may shorten the tube life, or affect the sound of the tube, tho this is subjective. It will function at 9V, so if you simply must run off a battery, use 9V and see what happens.

I have no idea about brands etc. I'm using sovtek 12AX7's at the moment, seems like a good choice.

I think the tube driver will work alot better at 12V than 9V (I think the power of the system is a sqaure rule based on the voltage applied to the plates, so the bigger the voltage you apply to the tubes plates the better, hence why amp tube-preamps run at around 250V, not 12V or 9V). I'm running mine off a 24V supply, with the heaters at 12.6V.

Also, note that the circuit draws a lot of current (to heat the tubes up), and will drain a 9V battery in no time at all, so you are best off running it from a mains power pack, in which case, you might as well use a 12V DC wall-wart. It'll cost a fortune (and be a pain in the arse) to keep replacing the battery.

EDIT: Out of interest - Power output of a tube goes down as square of supply voltage. (It's not quite that simple, strange stuff happens at below 50V, but it's close enougth). At 12V, a 12AX7 tube will generate about 560 times less power than the same tube at 284V. What's happening inside these low-voltage tube pedals is that the tube isn't really overdriving at all. The solid-state gain stage is providing all the grunt, then the tube is adding it's tube-like warmth (That's what those opamps are doing in the circuit, there not there for no reason).

-Adam

[Headbuttking2]

I simulated this along with another tube distortion pedal that ran at 12 V, and I get an output in the order of nano volts...

I think its something wrong with the way I simulate using MicroSim though, since I simulated R.G.'s Tube wah and get an output of at the highest .02 fV and it shows no signs of being a wah, but when he simulated it, it worked fine..

If anyone has an suggestions I would really appreciate it.

[tubes]

If you want to start messing with tube overdrive I would build a Matchless hotbox.  I built one a few years ago and it is by far the best sounding tube pedal I have ever heard:

http://www.freeinfosociety.com/electronics/schemview.php?id=904

this is the xformer I use:

http://dobermanamps.com/shop/index.php?main_page=product_info&products_id=10&zenid=5c9594ea54db595644ba99d6fe151bed

the best place to find tube amp help is here (but read all the stuff in the library of info first):

http://www.hoffmanamps.com/Forum/yabb2/YaBB.pl?board=TubeAmpBuilding

This is my dumbox wich is a tube clean/overdrive pre amp pedal bassed on a dumble preamp.  To give you some build ideas.  I raped my Hot Box to build this one and have no pictures of the hotbox.  I would add a true bypass switch to the hotbox so you can have a boost and an overdrive.




kris

kris

[finkfloyd]

Hi, thanks for the help, But on the schematic above why does it have 2 12ax7 sockets? or am I mistaken, and how can you tell from that schematic which pins go where?


And "tubes", that pedal looks awesome, That is a little complex for my likings just yet, and I dont trust myself with mains voltage at the moment

[Dave_B]

Doesn't a 12ax7 heater pull 300ma?  That's gonna be tough on a battery, dude. 

[finkfloyd]

Hi, yeah the originals used mains power only I believe, so it makes sense to use a dc jack, and a wall transformer, and at least you have the choice of 9v or 12v

[tubes]

well maybe try this site. for a single tube box. 

http://www.dogstar.dantimax.dk/tubestuf/mctube.htm

It has all the info you need to build a tube pedal even if you use a different schematic.  Pin numbers... it's all here.

kris

[AdamB]

The heaters draw more around 200ma I think, but it's still gonna drain a battery in no time, hence, mains power pack.

The problem with the hotbox and similar pedals is they require a high voltage, so you have to tangle with mains power supplys in order to build one. If your not sure what your doing (like me), low voltage is the way to go.

There are not 2 12AX7 sockets on that schematic, there is 1. It's shown with 2 because your using the two halves of one 12AX7 tube seperatly. The first half is pins 1,2,3 and the second half is pins 6,7,8 (I think). They show it as 2 on the schematic diagram to make it easier to draw, I think. It also helps to seperate out the gain stages on the diagram (as each half is 1 gain stage).

I'd suggest if you build to tube driver, run it off of a 12V DC mains power pack (wall-wart) and just use 12V on the heaters (close enougth to 12.6V). That way you get a tubeish sound, without the risk of death and without eating through batterys in no time.

-Adam

[puretube]

like the datasheets tell us since 50 years,
a 12AX7 draws quite exactly:
150mA with filaments in series @ 12.6V;
300mA filaments parallelled @ 6.3V.

[finkfloyd]

Hi, thanks for the information, this forum is great!


I have now purchased a cheapish electro harmonix 12ax7 from ebay
But cannot find any suitable sockets in the UK anywhere!

Oh I forgot also, look at the top left of the schematic, why does it say "tube fil heaters"  That confuses me!!

Anyone know where to get the sockets I need?

Thanks again

[puretube]

http://www.diystompboxes.com/smfforum/index.php?topic=41718.0

look for:  Hotrox
and: Whatfordvalves

[finkfloyd]

http://www.diystompboxes.com/smfforum/index.php?topic=41718.0

look for:  Hotrox
and: Whatfordvalves

Thanks a lot, hotrox seems very reasonable on prices!