Apologies for starting a new thread, but I could only find bits and pieces of info buried deep in other threads and wanted to confirm a few things on a capacitor across the AC line for my tubelab SE (120V North America)
1) The Capacitor I got is an X1 .1uf rated for 530VAC. I believe this would be appropriate, right? I wasn't sure because people were talking about caps rated for 1-2Kv.
2) Any consensus on where to wire it in? Is across the AC switch okay?
3) I read some people have a resister involved as well -- what is the purpose of this? And if I wanted to do that since I'm in there anyway, what is an appropriate value and wattage rating?
Confirmation / help would be much appreciated - I'm nervous to put something that will be touching live AC 24/7 without completely understanding.
Thanks!
1) The Capacitor I got is an X1 .1uf rated for 530VAC. I believe this would be appropriate, right? I wasn't sure because people were talking about caps rated for 1-2Kv.
2) Any consensus on where to wire it in? Is across the AC switch okay?
3) I read some people have a resister involved as well -- what is the purpose of this? And if I wanted to do that since I'm in there anyway, what is an appropriate value and wattage rating?
Confirmation / help would be much appreciated - I'm nervous to put something that will be touching live AC 24/7 without completely understanding.
Thanks!
Thanks this is super helpful -- only thing is I am not sure how to do the calculation? What would the load resistance and load current be of the SE circuit?
You don't need to know the load resistance to calculate the values of C and Rc, but you would have to be able to estimate the load current (I) prior to the switch contacts being opened to use the first two formulae for calculating C and Rc.
Thankfully, the choice of capacitor and resistor value is quite flexible so you don't have to bother with the calculations.
A widely used combination is 0.1uF + 100ohm so use the capacitor you have. Go for 0.5W minimum rating on the resistor.
Wire the combination across the AC switch.
Thankfully, the choice of capacitor and resistor value is quite flexible so you don't have to bother with the calculations.
A widely used combination is 0.1uF + 100ohm so use the capacitor you have. Go for 0.5W minimum rating on the resistor.
Wire the combination across the AC switch.
To reassure you, an X class capacitor is best for connecting across a switch, since it is designed to fail open circuit.
I have recently replaced the switch suppression capacitor in my valve amp. The 50 year old 250V AC film capacitor failed short circuit. However, the low wattage series resistor acted as a fuse and broke the circuit. I replaced the cap with a modern 630V DC film cap which should see me out!
I have recently replaced the switch suppression capacitor in my valve amp. The 50 year old 250V AC film capacitor failed short circuit. However, the low wattage series resistor acted as a fuse and broke the circuit. I replaced the cap with a modern 630V DC film cap which should see me out!