Deepdark
Well-known member
Hi there.
I just finished a fed. AM864 for a client. So far so good, it was pretty straight foward. First thing first, I redraw the psu to a RC filtering topology with diodes, instead of the LC filter with the tube rectifier, as I just linked. This was done to simplify things and keep cost down. Transformer is Edcor XPRWR012, 350V C.T. at 10ma, 6.3V C.T. at 2A. Fed. AM864 is rated 30ma, so we know this is a good transformer for the task. Heater was connected the classic way, and not as on the schematic.
First time I fired up, teh voltages was low (175V after the rectifiers). I diagnose and found I forgot to connect the psu ground (the ground taking all 47uf caps.). Stupid me. Trouble came after I connected that ground. Now the fuse blow each time I fired it up.
I began to search over the circuit, testing continuity to be sure their was no missing wire somewhere, etc. I found that 6sk7's pins 1 and 6sq7's pin 1 weren't connected to ground (in fact, I used the federal manual's schematic which contain, as I found later, some error like that), and their were a missing link between R1/C1 and input transformer C.T. / R5. Once connected, I fired up and, fuse blown again
So now that I ran the entire circuit and everything was allright, along the good schematic, I suspected the trouble to came from the psu. So I disconnected the links to R6 and to the circuit, to isolate the psu alone. Fired up and fuse blown.
So we know the trouble sit in there. To be honnest, I'm a little in the dark right now. What can cause the fuse to blow. Next step I'll disconnect the heaters to isolate the trouble. I just checked the heaters conections and they are all good.
Fuses are 1A, from the top of my memory.
Do you guys have any cues or anything else to check, any ideas?? Thanks folks.
I just finished a fed. AM864 for a client. So far so good, it was pretty straight foward. First thing first, I redraw the psu to a RC filtering topology with diodes, instead of the LC filter with the tube rectifier, as I just linked. This was done to simplify things and keep cost down. Transformer is Edcor XPRWR012, 350V C.T. at 10ma, 6.3V C.T. at 2A. Fed. AM864 is rated 30ma, so we know this is a good transformer for the task. Heater was connected the classic way, and not as on the schematic.
First time I fired up, teh voltages was low (175V after the rectifiers). I diagnose and found I forgot to connect the psu ground (the ground taking all 47uf caps.). Stupid me. Trouble came after I connected that ground. Now the fuse blow each time I fired it up.
I began to search over the circuit, testing continuity to be sure their was no missing wire somewhere, etc. I found that 6sk7's pins 1 and 6sq7's pin 1 weren't connected to ground (in fact, I used the federal manual's schematic which contain, as I found later, some error like that), and their were a missing link between R1/C1 and input transformer C.T. / R5. Once connected, I fired up and, fuse blown again
So now that I ran the entire circuit and everything was allright, along the good schematic, I suspected the trouble to came from the psu. So I disconnected the links to R6 and to the circuit, to isolate the psu alone. Fired up and fuse blown.
So we know the trouble sit in there. To be honnest, I'm a little in the dark right now. What can cause the fuse to blow. Next step I'll disconnect the heaters to isolate the trouble. I just checked the heaters conections and they are all good.
Fuses are 1A, from the top of my memory.
Do you guys have any cues or anything else to check, any ideas?? Thanks folks.
