Howdy all!
1st post here so here is to hoping someone can make some sense of this mess as I swear I am getting it right but keep blowing fuses!
I totally recapped this amp a few years back and it was working fine with the 2 prong original set up but I decided to rewire with a 3 prong and ground it properly.
It had the respective 100v and 117v wires from the mains going to their respective fuse lugs but of course the 100v was the only one currently wired into the ground switch death cap set up.
In the image below you will see what is what and I wired up the 117v to the respective switch lug and each time I turn it on I blow the 2A fuse within 2 or so seconds after getting a hum from the tranny.
I have included the schematic for this amp along with a shots of my recapping etc incase anyone can see anything wrong however each cap and wire was replaced one by one and wired exactly as it was originally.
Do you think I should pull one of the tranny wires off and see if it blows a fuse then to rule out a cap issue etc?
Much appreciated for any input!
https://postimg.org/image/il61jwav3/
https://postimg.org/image/ar5fyi327/
https://postimg.org/image/fflftos8v/
https://postimg.org/image/zbhf989a7/
Original Wiring
https://postimg.org/image/4ju1yc7b3/
1st post here so here is to hoping someone can make some sense of this mess as I swear I am getting it right but keep blowing fuses!
I totally recapped this amp a few years back and it was working fine with the 2 prong original set up but I decided to rewire with a 3 prong and ground it properly.
It had the respective 100v and 117v wires from the mains going to their respective fuse lugs but of course the 100v was the only one currently wired into the ground switch death cap set up.
In the image below you will see what is what and I wired up the 117v to the respective switch lug and each time I turn it on I blow the 2A fuse within 2 or so seconds after getting a hum from the tranny.
An externally hosted image should be here but it was not working when we last tested it.
I have included the schematic for this amp along with a shots of my recapping etc incase anyone can see anything wrong however each cap and wire was replaced one by one and wired exactly as it was originally.
Do you think I should pull one of the tranny wires off and see if it blows a fuse then to rule out a cap issue etc?
Much appreciated for any input!
An externally hosted image should be here but it was not working when we last tested it.
https://postimg.org/image/il61jwav3/
https://postimg.org/image/ar5fyi327/
https://postimg.org/image/fflftos8v/
https://postimg.org/image/zbhf989a7/
Original Wiring
https://postimg.org/image/4ju1yc7b3/
Can you explain in more detail what you mean by the 100v and 117v connections?
The schematic doesn't seem to help me figure that out - sorry to be 'slow'.
The schematic doesn't seem to help me figure that out - sorry to be 'slow'.
Hello fellow Victorian.
Well the amp has a 100v and a 117v feed to it and has a respective fuse to go with it.
Most Japanese amps came with transformers that could do 100 and 117 volts but only the 100v was wired up.
Well the amp has a 100v and a 117v feed to it and has a respective fuse to go with it.
Most Japanese amps came with transformers that could do 100 and 117 volts but only the 100v was wired up.
I would replace the two power diodes. A common diode sometimes morphs into a Zener diode, starting to conduct current above a certain block voltage.
Disconnect the secundaries of the transformer.
Isolate them so you do not get hurt.
Switch the amp on.
If all is well, switch the amp off.
Remove the isolation of the wires of the secondaries.
Check the voltage of each secundary while it's not connected to anything then the power transformer.
Switch off the amp.
With all tubes removed, measure the voltages of the secundaries.
Reconnect the heater wires from the transformer.
Switch the amp on and measure the voltage.
Repeat the previous step for each transformer winding.
Measure V1..V3 if all went well.
Insert the preamp tubes and measure V1..V3.
Insert the power tubes and measure V1..V3.
If all is well your amp should work for 95%.
But probably it will fail during one of these tests.
The figure out what can be the cause.
Repair and continue with the rest of the tests.
There can allways be more then one problem.
Isolate them so you do not get hurt.
Switch the amp on.
If all is well, switch the amp off.
Remove the isolation of the wires of the secondaries.
Check the voltage of each secundary while it's not connected to anything then the power transformer.
Switch off the amp.
With all tubes removed, measure the voltages of the secundaries.
Reconnect the heater wires from the transformer.
Switch the amp on and measure the voltage.
Repeat the previous step for each transformer winding.
Measure V1..V3 if all went well.
Insert the preamp tubes and measure V1..V3.
Insert the power tubes and measure V1..V3.
If all is well your amp should work for 95%.
But probably it will fail during one of these tests.
The figure out what can be the cause.
Repair and continue with the rest of the tests.
There can allways be more then one problem.
Awesome, much appreciated!
When you are saying "With all tubes removed, measure the voltages of the secundaries." are you saying after they are resoldered back in place to check the voltages?
Also you are suggesting I remove all wires from the transformer at once, I assume, since you said to reconnect the 5v heaters or is after the tubes are removed?
The two diodes making anode voltage. I would not do as Tarzan suggested, unless thou want to learn a long lession, because it will be a mess to open connections of wires which have been threaded thru holes, twisted and soldered.
Well that isn't to hard.
Once removed I can cut them and use fresh ends to resolder.
I tested the red and brown wires (disconnected only those) and the red reads 55v and the brown 45v.
Once removed I can cut them and use fresh ends to resolder.
I tested the red and brown wires (disconnected only those) and the red reads 55v and the brown 45v.
Did not** blow a fuse. Man I hate how I cannot edit posts and have to wait for them to be moderated.
I guess due to me being a noob lol.
Also, it appears the red/brown wires are like a voltage doubler so neither the red or brown wire is referenced to an AC ground (like a center tap) in the schematic, correct?
I guess due to me being a noob lol.
Also, it appears the red/brown wires are like a voltage doubler so neither the red or brown wire is referenced to an AC ground (like a center tap) in the schematic, correct?
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