ruby tuby with 2 x 12ax7's

[PurpleTheory]

At www.sopht.ca there are a few sound clips of the ruby tuby amp (http://www.sopht.ca/index.php?s=28), the last clip says that it uses 2 X 12AX7's, i was interested to know how to do that.

thanks,
matt

[smashinator]

I'm going to go out on a limb and guess that it's an additional stage that's identical to the first one.  So, just duplicate what's already there and stick it in front of the other tube.   

[PurpleTheory]

i thought that might be the case. do you think it will sound bad if my tubes aren't matched, or won't it make much difference?

thanks,
matt

[The Tone God]

In one of the later Ruby Tubys there was enough amperage on the adapter to run a second preamp tube for extra gain. There was an attempt to create a harder sounding all tube version of the Ruby Tuby but the gain is limited with the tube at only 12v. The opamp front end was put in to get some more gain while still creating all the distortion in the tube portion. The schematic was not published.

It was decided in a preliminary Ruby Tuby to leave the input all tube so if someone wanted more gain they could use a clean boaster of their choice.

Andrew

[brett]

Hi.
Although a bit more complex, the Firefly is also worth a look.  It uses a 12AU7 for output (capable of a bit less than 1W). A simpler version of the Firefly could be built by leaving out the cascode booster.
In the tuby ruby, it isn't obvious to me why you'd go through the op-amp input rather than straight to the grid.  The gain from 2 triodes is usually sufficient.  Maybe it's something to do with it running at only 12V.  Which makes me wonder why it's not run at 24V or more.  Cheap wall warts are available for 24V and 48V DC.  I've got a 24VAC 1amp one that I'm using on a smallish amp project.
cheers

[The Tone God]

In the tuby ruby, it isn't obvious to me why you'd go through the op-amp input rather than straight to the grid.

As I posted above in one of the earlier versions of the Ruby Tuby it was decided to keep the tube in front to give the user the option of increaseing the gain with a simple boaster of their choice. The Ruby Tuby with the opamp in front has that boaster built in.

The gain from 2 triodes is usually sufficient.  Maybe it's something to do with it running at only 12V.  Which makes me wonder why it's not run at 24V or more.  Cheap wall warts are available for 24V and 48V DC.

For much of the same reasons why most plate starved pedals use 12v. Its easier to use a standard voltage regulator and feed both the audio and the filimants. As for why not run a higher voltage adapater and perhaps regulated it down well I guess I could give you the extremely long technical answer that few if any would understand or can just say that is all we had lying around.

Andrew

[smashinator]

i thought that might be the case. do you think it will sound bad if my tubes aren't matched, or won't it make much difference?

Pre-amp tubes don't need to be matched, as far as I know.