Help Please!!!!!!

[mongiak]

Hello
I´ve built a guitar tube amplifier, it´s a 15 W class A amp, and it doesn´t work.
I think that the trouble is in the phase splitter (shown in the attached picture) tube were I have 42 V betwin the catode and the grid, this is because I have a small current throught the resistors R17 and R18, so I think that the tube is in the cut off zone, and i don´t know the reason, I thought it was because the capacitors were no good, but I changed them and it´s still the same. (perhaps the new ones are not good either, don´t know).
in the rest of the circuit the V are just what they have to be.

Please can anyone tell me what it´s wrong with it?

Thanks to all.


Urko

 

[SY]

Measurement error. You can't measure the grid voltage directly with a normal voltmeter. Try measuring from grid to cathode- I'll bet it's near zero.

 

[moamps]

.... so I think that the tube is in the cut off zone....

Hi,
The anode current of each triode is V(R19)/2/R19, which is around Ia=0,7mA; perhaps not the optimum but certainly not in the cutoff zone.
Vg=- 2*Ia*R14=-1.7V
Your voltmeter has an input impedance around 1Mohm, which causes the high impedance network measurement error that SY pointed out.

Regards,
Milan

 

[mongiak]

anyways it doesn´t sound, I have just an anoing noise and nothing happens wen the guitar is conected or wen I move the volume or tone.
it doesn´t feel any noise before the phase splitter.

 

[SY]

Well, whatever the problem is, this stage seems to be working normally.