JollyRoger523
New member
Can anyone help me with a question I have regarding a potential problem with the output transformer?
I am currently building a Mojotone 5F1 Champ clone kit that I got for X-Mas. Upon testing it I ran into a problem. Following Mojotone's testing procedure, everything was fine until the step of installing the power tube. I installed the 6v6 power tube (yes, the speaker was plugged in) and as soon as I turned the power on I noticed some smoking. The 470ohm resistor burned up.
I'm experienced at soldering guitar electronics and building pedals. I've never worked with an amp before. I'm fairly confident I followed the wiring diagram and instructions correctly. I checked and rechecked several times. The multimeter I had was very cheap. I picked up a better one today that has continuity feature. Checking the continuity of the circuit, I found the 4ohm wire from the output transformer is connecting to ground.
The output transformer from Mojotone only has 3 wires, blue, red, yellow. Blue and red go to the power tube and board respectively. Yellow goes to the center lug of the RCA speaker jack along with a wire from the board. There is a ground wire soldered directly to the transformer chassis, which in turn is grounded to the amp chassis when bolted together. I've checked from the OT chassis to the yellow wire, as well as grounding lugs in the chassis to the yellow wire. Both show continuity. At this time I haven't pulled the OT as that necessitates unsoldering lots of things to remove the eyelet board to access the OT bolts/nuts. I have a clear view of the entire wire to verify the insulation is not frayed, punctured, pinched, etc.
Am I correct in thinking that the yellow wire (4ohm output to speaker jack) shouldn't be connecting to ground? Is this the likely cause of burning out the 470ohm resistor?
Thank you for your assistance,
JR
I am currently building a Mojotone 5F1 Champ clone kit that I got for X-Mas. Upon testing it I ran into a problem. Following Mojotone's testing procedure, everything was fine until the step of installing the power tube. I installed the 6v6 power tube (yes, the speaker was plugged in) and as soon as I turned the power on I noticed some smoking. The 470ohm resistor burned up.
I'm experienced at soldering guitar electronics and building pedals. I've never worked with an amp before. I'm fairly confident I followed the wiring diagram and instructions correctly. I checked and rechecked several times. The multimeter I had was very cheap. I picked up a better one today that has continuity feature. Checking the continuity of the circuit, I found the 4ohm wire from the output transformer is connecting to ground.
The output transformer from Mojotone only has 3 wires, blue, red, yellow. Blue and red go to the power tube and board respectively. Yellow goes to the center lug of the RCA speaker jack along with a wire from the board. There is a ground wire soldered directly to the transformer chassis, which in turn is grounded to the amp chassis when bolted together. I've checked from the OT chassis to the yellow wire, as well as grounding lugs in the chassis to the yellow wire. Both show continuity. At this time I haven't pulled the OT as that necessitates unsoldering lots of things to remove the eyelet board to access the OT bolts/nuts. I have a clear view of the entire wire to verify the insulation is not frayed, punctured, pinched, etc.
Am I correct in thinking that the yellow wire (4ohm output to speaker jack) shouldn't be connecting to ground? Is this the likely cause of burning out the 470ohm resistor?
Thank you for your assistance,
JR
