Hi,
Have had a spot of trouble with the filament power supply on my Ear 834 clone. When trying to get the voltage set with the trimpot, said trimpot failed. No voltage anymore. Replaced the trimpot, still no voltage. So I replaced the existing LT1085 with an LM317 because the board stated it could take either one.
I now have an output voltage of 14VDC or so but as soon as I put just one tube in, the voltage sags to 1,4VDC, even with the trimpot at the highest setting.
Input voltage does not sag, 14VAC at the transformer is stable, voltage at the rectifier is also stable.
Short of pulling all the components and replacing them, is there anything you would recommend ?
I've reverse engineered the schematic as far as I can tell.
Thanks
Have had a spot of trouble with the filament power supply on my Ear 834 clone. When trying to get the voltage set with the trimpot, said trimpot failed. No voltage anymore. Replaced the trimpot, still no voltage. So I replaced the existing LT1085 with an LM317 because the board stated it could take either one.
I now have an output voltage of 14VDC or so but as soon as I put just one tube in, the voltage sags to 1,4VDC, even with the trimpot at the highest setting.
Input voltage does not sag, 14VAC at the transformer is stable, voltage at the rectifier is also stable.
Short of pulling all the components and replacing them, is there anything you would recommend ?
I've reverse engineered the schematic as far as I can tell.
Thanks
Attachments
What's the input DC voltage to the regulator open circuit? What is it when you plug in a tube?
Are you sure the pot is set right? It will go to zero at one end, there should be a series resistor.
You may have the pot set at zero ohms, which would give 1.2V output.
Try setting it at the midpoint to start, then adjust to the correct voltage open circuit.
Otherwise, there must be a short on the output. Has this board ever worked properly before?
Are you sure the pot is set right? It will go to zero at one end, there should be a series resistor.
You may have the pot set at zero ohms, which would give 1.2V output.
Try setting it at the midpoint to start, then adjust to the correct voltage open circuit.
Otherwise, there must be a short on the output. Has this board ever worked properly before?
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Turns out I am an idiot !
Because I wanted the tubes visible, I flipped all the components to the other side of the board. Got one of the regulators right ... mounted the other one the wrong way around.
Now quite how it initially worked is beyond me, but it definitely explains the trouble I had.
Banged a new LM317 in, lights are on.
Now I have to address the hum. My planning was a bit iffy for this project, and the transformer is too close to the circuit. Moving it around helps a bit, but I dont have much room in the enclosure. I'm thinking I might pull it out and put it in a seperate housing
Because I wanted the tubes visible, I flipped all the components to the other side of the board. Got one of the regulators right ... mounted the other one the wrong way around.
Now quite how it initially worked is beyond me, but it definitely explains the trouble I had.
Banged a new LM317 in, lights are on.
Now I have to address the hum. My planning was a bit iffy for this project, and the transformer is too close to the circuit. Moving it around helps a bit, but I dont have much room in the enclosure. I'm thinking I might pull it out and put it in a seperate housing