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Hello AllLooks like there are some questions about the board, specifically to do with full and half bridge rectification. I dont think the hum is caused by the rectification. It is most likely a bad capacitor or more likely a bad regulator. I have done various tests with full and half bridge rectification specifically on the LA2A project and it matters verry little which is applied so long as the output voltage is adequate for the system to operate. I'm sure some might point out that there is a longer period between spikes but there is adequate filtring to achieve a relatively ripple free signal (about 1mV or so).The original 2A build uses a half bridge on the high voltage and AC voltage on the heater, mixing them does not matter much as long as done properly.When I designed the board I was using some Hammond transformers with much higher secondary outputs. I now recommend the Don-Audio units as they are about half the price and more redily available. This switch needed a full wave bridge mod to be done on the heater in some instances that the heater was not able to achieve the required 6,3vdc. Basically switching the polarity and output of two diodes D2 and D3.Take a look at the files atached from another builder [USER=61093]@timtom[/USER] , thanks for the pics
Hello All
Looks like there are some questions about the board, specifically to do with full and half bridge rectification. I dont think the hum is caused by the rectification. It is most likely a bad capacitor or more likely a bad regulator. I have done various tests with full and half bridge rectification specifically on the LA2A project and it matters verry little which is applied so long as the output voltage is adequate for the system to operate. I'm sure some might point out that there is a longer period between spikes but there is adequate filtring to achieve a relatively ripple free signal (about 1mV or so).
The original 2A build uses a half bridge on the high voltage and AC voltage on the heater, mixing them does not matter much as long as done properly.
When I designed the board I was using some Hammond transformers with much higher secondary outputs. I now recommend the Don-Audio units as they are about half the price and more redily available. This switch needed a full wave bridge mod to be done on the heater in some instances that the heater was not able to achieve the required 6,3vdc. Basically switching the polarity and output of two diodes D2 and D3.
Take a look at the files atached from another builder [USER=61093]@timtom[/USER] , thanks for the pics
