Hello,
I recently purchased a Tubecube7 from Tubedepot. I also brought some upgraded tubes. Today I took off the bottom of the amp. To my surprise, I see that this particular unit (which still had its warranty sticker firmly in place) has been modified.
Comparing to other photos of the miniwatt n3, and a rogue schematic if found online, it appears that the cathode biasing circuit which I thought was a current source, has not been stuffed on my board, and some other jumbers installed etc. The power supply looks unmodified.
-Top right corner, no TO-92 device or TO-220 case device stuffed.
- Black jumper wires around the 12AX7 socket.
- Some traces drilled out to disconnect them from others.
- No time to look at the other side but I suspect that we just have a cathode resistor bias.
Questions:
1. Have any of you seen this is a recent Tubecube7?
2. I am suspicious that this was done for cost reduction, but there may be other reasons.
3- I am still building my full-range efficient speakers to go with this amp and my rebuilt p-p EL84 amps, so I haven't listened to it. Does it perform as well as the original? My guess is no.
4- Does anyone have an accurate schematic of a Miniwatt n3 of Tubecube 7? My searching has been fruitless.
I would appreciate any insight anyone may have.
I have attached a photo of my Tubecube7 and a photo of a Miniwatt n3
-david BTW
I recently purchased a Tubecube7 from Tubedepot. I also brought some upgraded tubes. Today I took off the bottom of the amp. To my surprise, I see that this particular unit (which still had its warranty sticker firmly in place) has been modified.
Comparing to other photos of the miniwatt n3, and a rogue schematic if found online, it appears that the cathode biasing circuit which I thought was a current source, has not been stuffed on my board, and some other jumbers installed etc. The power supply looks unmodified.
-Top right corner, no TO-92 device or TO-220 case device stuffed.
- Black jumper wires around the 12AX7 socket.
- Some traces drilled out to disconnect them from others.
- No time to look at the other side but I suspect that we just have a cathode resistor bias.
Questions:
1. Have any of you seen this is a recent Tubecube7?
2. I am suspicious that this was done for cost reduction, but there may be other reasons.
3- I am still building my full-range efficient speakers to go with this amp and my rebuilt p-p EL84 amps, so I haven't listened to it. Does it perform as well as the original? My guess is no.
4- Does anyone have an accurate schematic of a Miniwatt n3 of Tubecube 7? My searching has been fruitless.
I would appreciate any insight anyone may have.
I have attached a photo of my Tubecube7 and a photo of a Miniwatt n3
-david BTW
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