a friend bring me his plexi marshall clone (old tube guitar amp), i`m trying to eliminate a noise coming from one of the first stages.
here is the schematic of the amp.
http://www.freeinfosociety.com/electronics/schematics/audio/pictures/marshall1987.gif
it has the one wire mod that basicaly put the first stages in cascade. I put it back at the original design but the noise is stil there.
here is how the noise look like. it have a 50Hz component but those spikes are strange to me. could it be noise induced to the ground? I have checked the b+ of the stage and it have no ripple.
the power supply use a brigde rectifier but use just two diodes of it. like a regular two diode full wave rectifier. Should I try some faster diodes?
the noise is just at that stage, I have tried filtering the anode resistor and it reduce the noise also a resistor from grid to ground reduce the noise, I have changed the tube and no difference . what I haven`t tried yet is replace the anode resistor but this noise does not sound like a bad resistor.
I`m running low of ideas so any help is welcome. thanks in advance!
Rafael
here is the schematic of the amp.
http://www.freeinfosociety.com/electronics/schematics/audio/pictures/marshall1987.gif
it has the one wire mod that basicaly put the first stages in cascade. I put it back at the original design but the noise is stil there.
here is how the noise look like. it have a 50Hz component but those spikes are strange to me. could it be noise induced to the ground? I have checked the b+ of the stage and it have no ripple.
the power supply use a brigde rectifier but use just two diodes of it. like a regular two diode full wave rectifier. Should I try some faster diodes?
the noise is just at that stage, I have tried filtering the anode resistor and it reduce the noise also a resistor from grid to ground reduce the noise, I have changed the tube and no difference . what I haven`t tried yet is replace the anode resistor but this noise does not sound like a bad resistor.
I`m running low of ideas so any help is welcome. thanks in advance!
Rafael