1
Q & A / Re: 100s hum troubleshooting
« Last post by loudthud on June 14, 2024, 10:36:55 pm »OK, I see where you said the scope pic was across the speaker, but is the 50mV per div accurate taking into account any probe (x10) attenuation ?
most hum in an amp is 100HzYep, we gotta know what we're chasing. From the picture we see on the oscilloscope with divisions on the x axis being 5ms, its pretty much 4 divisions per cycle. 20ms -> 1000/20 = 50hz.
diode check with power offWhen I did this the other day I was getting with the DMM multimeter about 0.595v voltage drop and OL the reverse direction, so functionally they seem correct
Voltages around the 6AN8 are somewhat off,This is something i'll need to take another look at this weekend when I'll have the chance to go over things again
"Black Cat" capacitors that connect...Yeah I was thinking it might be these but I replaced with a modern 0.1uf 600v rated cap and it made no difference. The resistance of the 47k and the voltage across 100k i'll have to go back and check.
install a new or fresh one if you have itI have a backup and noticed no difference in hum between the two of them.
Adjust the value of the 680 Ohm resistor (between 470 and 1K) connected to pin 9 to obtain the 80VThis is something I will get to if the above does not reveal any issues.