Vacuum Tube Amp Circuit

[fernando_g]

At -10 volts the valve is operating well into cutoff.

Google the 12AX7 datasheet, and look for the grid-to-cathode voltage vs plate voltage curves.

 

[Mdkanz]

Ok, I got it working but only when the + probe on the volt meter touches the + of the 12v ac going to the tube, when i move the probe off it starts buzzing really loud then when i touch the probe back on it works.

 

[Roff]

Ok, I got it working but only when the + probe on the volt meter touches the + of the 12v ac going to the tube, when i move the probe off it starts buzzing really loud then when i touch the probe back on it works.

Connect the center tap of the 12V filament transformer winding to circuit ground.

 

[Willbe]

only when the + probe on the volt meter touches the + of the 12v ac going to the tube

Put 10 pF to ground from this point?

 

[Mdkanz]

Sorry, its the + out of the tube that i have to touch for it to work so i need a way to hook it to ground (earth not the ground on the circuit).

 

[Mdkanz]

Ok, i got it working but the gain is REALLY low, so what would happen if i added a second tube to the circuit? (hook the output of the first tube to the input of the second tube and the output of the second to the speaker)

 

[Nigel Goodwin]

Ok, i got it working but the gain is REALLY low, so what would happen if i added a second tube to the circuit? (hook the output of the first tube to the input of the second tube and the output of the second to the speaker)

It's a preamplifier valve, it's only going to have a very tiny output, plus you don't even have a real output transformer which is going to reduce it even further.

I'll ask again, what are you trying to do?.

 

[Mdkanz]

would it add gain if i had another tube connected right after the first one

 

[Roff]

would it add gain if i had another tube connected right after the first one

Why don't you pay attention and answer Nigel's questions?

 

[Mdkanz]

I want to make the amp just as a cool tube circuit.

 

[Nigel Goodwin]

If you want to do that (though why you would want to is a puzzle?), then use an output valve, a preamp valve, and a proper transformer.

Valve amps are low enough quality as it is, without such a complete bodge as this one.

 

[Mdkanz]

I want to make the amp just as a cool tube circuit.

 

[Nigel Goodwin]

Then you've made it - what else do you want?.

 

[Mdkanz]

Thank you all for your help.