Hi Guys, I have this Guitar amp that a customer of my restaurant asked me to look at.
His nephew was messing with it and not sure what he did to it .
This is how I think it was wired, minus the Grd wire.(I'll explain later why Im not sure.)
I had this powered from my Isolation transformer and switching between DBT and Full Mains.
To start it had two power cords connected into the amp and the original 2 cord wire was cut and had but connectors holding it together which one was
not connected. I guess they used a there pronged cord to try to eliminate hum maybe. Not sure why they had this in there but only the Ground wire was connected to the amp, so maybe they used the two wall sockets at the same time? Who knows.
So I decided to remove the two cord original since it was cute outside the amp and wire in the three cord plug. I followed the way the wiring was done.
Hot to the Fuse> lamp>switch.(Found it weird that the hot went through a 110 volt 1/3 watt lamp. then the switch)
Neutral to other side of Switch and GND to transformer screw( chassis) .
The two transformer wires one white and one yellow went as follows
Yellow to the Hot side of the switch and the White went to the end of the fuse hold that the light also went to.
Here is how it was ( I think ) I put the wires back just to show location with no solder on some FYI.
Well this had a loud 120hz hum, now I think it was wired up Said above . I say I think because I never took pics of it originally and then I began thinking of how it might be wired wrong and began to re wire it how I thought it should be.
Well At one point I got no hum but also no sound from the amp and a low voltage after the light( at the hot side of the switch) which I figured should be 120vac, it was like 20vac.
So I tried wiring it a couple different ways.
One way was I had the hot go from fuse to the lamp to the switch hot side where the yellow transformer wire was also connected, but I removed the Yellow and put it on the other side of the switch. I then connected the white transformer wire with the neutral power cord wire . I figured this would take the transformer out of the circuit with the switch.
Still had hum.
then I tried something else, for got how it was , and the DBT went full bright and the indicator lamp burned out.
So this is where I am at. Here is the schematic , it had no death cap as the schematic shows, also there is no indicator lamp in this schematic .
And I read somewhere this is a floating GND design. Not sure so I'll let you guys chime in.
I'll add more pics of the amp and its guts now
Some close ups of the wiring not soldered in, of how I think it was. Close ups of the above overall pic of the wiring.
Yellow wire is a primary, Black is one wire from the lamp and white is the neutral from the wall
( I think this is how it was, it might have had the other transformer white wire, but that didn't make sense to me)
Fat black wire is Hot mains in, thin black wire goes to lamp>switch, and White is from transformer primary.
Some board pics.
Two red wires on right side are the secondaries going to the rectifier. There is a thin black wire which I believe is the center tap, it goes to one
of the pads ( the large one) where the outputs to the speaker are also soldered in( fat black wires top right).
I will add I recapped the board and hum was the same as before the recap.
Burnt out lamp.
Also, while I wait for new lamps I found on eBay for this, can I just wire it from the fuse to the switch and bypass the lamp
or is it needed in the circuit , i can't see why it is as its not even in the schematic.
Thanks
Athanasios
His nephew was messing with it and not sure what he did to it .
This is how I think it was wired, minus the Grd wire.(I'll explain later why Im not sure.)
I had this powered from my Isolation transformer and switching between DBT and Full Mains.
To start it had two power cords connected into the amp and the original 2 cord wire was cut and had but connectors holding it together which one was
not connected. I guess they used a there pronged cord to try to eliminate hum maybe. Not sure why they had this in there but only the Ground wire was connected to the amp, so maybe they used the two wall sockets at the same time? Who knows.
So I decided to remove the two cord original since it was cute outside the amp and wire in the three cord plug. I followed the way the wiring was done.
Hot to the Fuse> lamp>switch.(Found it weird that the hot went through a 110 volt 1/3 watt lamp. then the switch)
Neutral to other side of Switch and GND to transformer screw( chassis) .
The two transformer wires one white and one yellow went as follows
Yellow to the Hot side of the switch and the White went to the end of the fuse hold that the light also went to.
Here is how it was ( I think ) I put the wires back just to show location with no solder on some FYI.
Well this had a loud 120hz hum, now I think it was wired up Said above . I say I think because I never took pics of it originally and then I began thinking of how it might be wired wrong and began to re wire it how I thought it should be.
Well At one point I got no hum but also no sound from the amp and a low voltage after the light( at the hot side of the switch) which I figured should be 120vac, it was like 20vac.
So I tried wiring it a couple different ways.
One way was I had the hot go from fuse to the lamp to the switch hot side where the yellow transformer wire was also connected, but I removed the Yellow and put it on the other side of the switch. I then connected the white transformer wire with the neutral power cord wire . I figured this would take the transformer out of the circuit with the switch.
Still had hum.
then I tried something else, for got how it was , and the DBT went full bright and the indicator lamp burned out.
So this is where I am at. Here is the schematic , it had no death cap as the schematic shows, also there is no indicator lamp in this schematic .
And I read somewhere this is a floating GND design. Not sure so I'll let you guys chime in.
I'll add more pics of the amp and its guts now
Some close ups of the wiring not soldered in, of how I think it was. Close ups of the above overall pic of the wiring.
Yellow wire is a primary, Black is one wire from the lamp and white is the neutral from the wall
( I think this is how it was, it might have had the other transformer white wire, but that didn't make sense to me)
Fat black wire is Hot mains in, thin black wire goes to lamp>switch, and White is from transformer primary.
Some board pics.
Two red wires on right side are the secondaries going to the rectifier. There is a thin black wire which I believe is the center tap, it goes to one
of the pads ( the large one) where the outputs to the speaker are also soldered in( fat black wires top right).
I will add I recapped the board and hum was the same as before the recap.
Burnt out lamp.
Also, while I wait for new lamps I found on eBay for this, can I just wire it from the fuse to the switch and bypass the lamp
or is it needed in the circuit , i can't see why it is as its not even in the schematic.
Thanks
Athanasios
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. I have 4 3300uf caps as smoothing caps. .
