I just finished rebuilding my Hafler DH-500. Over the years this stupid amp has quit about 4 times and I have found it to be resistors either open or way out of spec.
So, I ordered the PC-19c circuit boards from Ebay and then ordered all the parts from Digikey.
Total cost was under 200.00 Canadian dollars.
Also, I replaced the two tall can capacitors for a PCB board I made with 10 smaller capacitors of 5600uf each for a total of 28,000uf per rail. I also tacked on some smaller value capacitors for better high frequency response.
As well, you will notice the two fuse holders for the left and right channels. I mounted them about 3 inches off the bottom using standoffs.
This made wiring much simpler and shorter.
I wired it with 12 gauge wire and focused on short runs rather than cosmetics.
So, other than the Hitachi outputs everything is brand new and it sounds awesome.
BUT, I do have a concern. The bias current is about 400mA with the bias setting at minimum. Both channels are the same and I have compared the new board to the old board using a meter so I can't see that it is anything I did wrong.
I did notice one of the small signal transistors has a slightly higher forward voltage than on the original board so maybe it has more gain causing the higher currents.
Does anyone have any idea why it is so high? I suspect anyone else who has ordered the PC-19c boards should have the same problem as I do.
So, I ordered the PC-19c circuit boards from Ebay and then ordered all the parts from Digikey.
Total cost was under 200.00 Canadian dollars.
Also, I replaced the two tall can capacitors for a PCB board I made with 10 smaller capacitors of 5600uf each for a total of 28,000uf per rail. I also tacked on some smaller value capacitors for better high frequency response.
As well, you will notice the two fuse holders for the left and right channels. I mounted them about 3 inches off the bottom using standoffs.
This made wiring much simpler and shorter.
I wired it with 12 gauge wire and focused on short runs rather than cosmetics.
So, other than the Hitachi outputs everything is brand new and it sounds awesome.
BUT, I do have a concern. The bias current is about 400mA with the bias setting at minimum. Both channels are the same and I have compared the new board to the old board using a meter so I can't see that it is anything I did wrong.
I did notice one of the small signal transistors has a slightly higher forward voltage than on the original board so maybe it has more gain causing the higher currents.
Does anyone have any idea why it is so high? I suspect anyone else who has ordered the PC-19c boards should have the same problem as I do.
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"I have found it to be resistors either open or way out of spec."
The 5% carbon film resistors have steel leads that are copper plated and then tinned.
The copper fails to adhere to the steel after many years.
This happens in any brand of amplifier using 'copperweld' leaded parts.
Hafler liked to buy NOS surplus parts, so they started failing earlier than you would expect.
I had some problems with Carver equipment with small capacitors with copperweld leads, I was told they liked to buy NOS parts as well.
I've had so much grief with old Hafler product that I think you did the right thing, new board, new parts.
The 5% carbon film resistors have steel leads that are copper plated and then tinned.
The copper fails to adhere to the steel after many years.
This happens in any brand of amplifier using 'copperweld' leaded parts.
Hafler liked to buy NOS surplus parts, so they started failing earlier than you would expect.
I had some problems with Carver equipment with small capacitors with copperweld leads, I was told they liked to buy NOS parts as well.
I've had so much grief with old Hafler product that I think you did the right thing, new board, new parts.
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