Tube Star: Anyone else built it?

[psychedelicfish]

So I was looking for a low voltage, high gain tube distortion circuit, and I came across Renegadrian's Tube Star here: http://www.aronnelson.com/gallery/main.php/v/Renegadrian/tube+star+schem+0_4_gain.gif.html
I put it together on my breadboard, and got something that was certainly not high gain distortion, but more of a light overdrive. I jury rigged a heater supply from a couple of high wattage resistors and a separate 24v smps I had on hand and got a fairly stable 12.7v across my heaters. I used a 10VAC plugpack running through a 2 stage %^&*croft-Walton Generator which gave me a fairly solid 50VDC for my B+.

Has anyone else tried it? If so, what where your results like?

Thanks,
Edward

*Edit*
I really dislike auto swear filters...

[Kesh]

that 250k on the first triode's cathode is pretty strange. most of the length of that should turn the triode off

[psychedelicfish]

I did notice a sudden change in output when turning the gain pot... I tried it with a 12ax7 too and still got low gain. I'll change the supply voltage and see what happens

[Kesh]

More voltage will mean less distortion.

The resistor at the cathode sets the tube bias (it also controls gain through cathode degeneration, a kind of negative feedback). Most of that 250k pot will be way too high to bias it properly, just compare it with the much lower 470R value resistor on the other triode's cathode.

I would put the gain pot at the input (replace the 1M resistor with a 1M pot, with the middle lug going to the first triode's grid), and replace the cathode pot with a low value resistor, or maybe a preset of about 2K-5k to play with bias, though playing with the second triode's bias will have more effect on sound. Also put an electro cap of about 100u across both cathode resistors for much more gain.

Even doing this two 12AT7 stages will only give you gain in the low 1000s, which isn't enough to drive a typical guitar signal into full-on distortion when your B+ is 48V or more. Two 12AX7 stages will be a bit more gain, though may be trickier to get the bias right (may need to play with both cathode resistors). ECC88s work very well at this sort of voltage, though less gain than both the others, and you may need another grid stopper (resistors right next to grid input, like the second triode currently has).

To get a very distorted sound you could drive the thing with some kind of booster first, though you may lose "feel".

The output, when on full, is also capable of putting most of your B+ voltage (as AC) into whatever comes after. Obviously you don't want 48V peak to peak going into a guitar amplifier. To be honest, it's a pretty stupid circuit.