Tube pedal.....Mctube? Hotbox? Alembic?

[Michael Allen]

I want to put together a tube pedal but I can't decide which to build.  

The McTube seems like a really simple build but after searching the archives and other forums I gather that it's not capable of high gain and it can sound pretty buzzy?

The Hotbox seems like a higher gain pedal, and then there's the Alembic with a switchable channel. How does the Alembic sound? I like the idea of switching a channel in series to boost the output.

Any other ideas? I think i'm leaning to the Alembic right now. Does anyone know what kind of transformer to use? That's one thing i like about the mctube, using easily available transformers....

Thanks all,
Michael

[MartyB]

I'd say the McTube is great for rock, blues.  If you're looking for metal it ain't gonna do it.   Listen to the sound samples of the McTube.  You're right.  It's an easy cheap build.  With a treble boost and a vibrochamp, you got all sorts of classic rock tone.

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

[Michael Allen]

Hmm, how about winding my own transformer for the Hotbox? It needs 190-0-190 secondaries......

Anyone have experience doing these? How would i go about determining the wire size and # of turns?

Thanks

Michael

[cd]

When high voltage is required I'd stay away from winding your own transformers.  Just use a couple of 240V primary/12V secondary transformers and run them back to back.  That is:

wall > A(240 primary > 12V secondary) > B(12V secondary > 240 primary)

You can run the heaters off the secondary of transformer "A" and the plates off the 240 primary of transformer "B".

[Michael Allen]

Am I incorrect in assuming that you would need 240v from the wall outlet in order to have a 240v primary? Would someone explain please?

As far as I know, it would be a  115v to 12v and then 12v to 115v and that would only put out 115v right? because that's all I started with....

Thanks

Michael

[cd]

Am I incorrect in assuming that you would need 240v from the wall outlet in order to have a 240v primary? Would someone explain please?

As far as I know, it would be a  115v to 12v and then 12v to 115v and that would only put out 115v right? because that's all I started with....

Thanks

Michael

Oops, I should have mentioned you should use a transformer with dual primaries (120/240V) - you only need one of them.  The other one can be a 240/12.  Either way they're ridiculously cheap and work fine in a low complexity circuit like a Hotbox.

[Michael Allen]

I'm sorry, I don't understand the talk about the Primaries.....In order to beef the voltage back up to 240, wouldn't I have to start with 240v?

Could you perhaps recommend a Mouser part so i could chekc out the spec on the transformer?

Thanks

[bobbletrox]

psst...Ruby Tuby Preamp

[Michael Allen]

How about his one?
http://www.diystompboxes.com/pedals/schems/nady/nadymodschem.gif

has anyone ever seen it before? Any info? it says to use the same transformer set up as with the McTube....

[Lonestarjohnny]

How bout a Matrix ?
JD

[cd]

I'm sorry, I don't understand the talk about the Primaries.....In order to beef the voltage back up to 240, wouldn't I have to start with 240v?

Could you perhaps recommend a Mouser part so i could chekc out the spec on the transformer?

Thanks

A transformer has two "sides", or a primary and a secondary.  With a transformer that has a 120V primary and a 12V secondary, you apply 120V onto the primary, and on the other side, you get 12V (10:1 ratio).  If you applied 100V on one side, you'd get 10 on the other, and so forth.

Some transformers have DUAL primaries, that is you can wire them in such a way that you can have either 120V OR 240V on the primary side, and say 12V on the secondary side.  The transformer has multiple windings, so you can wire them either in series or parallel to get 120/240.

So what you need are two transformers:

(1) 120V primary and 12V secondary (I presume you're in North America where 120V is used)

(2) 240V primary and 12V secondary

So the 120V from the wall goes to the 120V primary, where it gets dropped down to 12V.  You use this 12V on the heaters of the 12AX7 tubes.  You also wire the 12V from the first transformer to the secondary (12V side) of transformer #2.  The 12V then gets bumped UP to 240V.

Once you rectify the 240VAC you'll end up with something like 340VDC, so experiment with appropriately sized resistors to drop the voltage down.

[Michael Allen]

Aw, sweet. I understand transformers and such, but I wasn't getting the combined effect. I see, so i only need one with a 240v primary.  

Am i thinking Center tapped? or no?

Thanks