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Vacuum Tube Amp Circuit

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fernando_g

New Member
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

New Member
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

Well-Known Member
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.
 

Mdkanz

New Member
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

New Member
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

Super Moderator
Most Helpful Member
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?.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
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.
 
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