Hi,
I'm trying to build a Tube PSU for my amp. When I look up some of the electronic articles I find they do not target a novice and more to an expert which I'm not. I want to put a limiting resistor so that I can increase the size of the second cap over 20uF for a 274B tube. The circuit I'm using is from Emission labs circuit #5 (link http://www.emissionlabs.com/datasheets/EML274.htm).
With the first cap at 2.2uf and second at 15uf I get a bit of a hum. nothing changes when the first cap is increased to the max 4uF but when the second is increased to 30uf there is a significant drop and is audible only from a meter away from the speaker. I tried a 47uf first and 100uf second and no hum at all.
The specs say "For a total (C1 + C2) capacitance above 24uF, a limiting series resistor must be used, so the peak in-rush current through the choke is limited to the saturation current of the choke, or max 600mA, whatever comes first. Otherwise tube damage can result. MUST MEASURE. Can not be calculated in a reliable way. For lowest hum, this resistor is in series with the choke. So you get a C-LR-C filter. In this way 200uF is possible."
The saturation current of the choke is 290ma, specs of the tube are on the link above. I'm not sure what is to be measured and how to calculate the resistor value.
Any help is appreciated.
I'm trying to build a Tube PSU for my amp. When I look up some of the electronic articles I find they do not target a novice and more to an expert which I'm not. I want to put a limiting resistor so that I can increase the size of the second cap over 20uF for a 274B tube. The circuit I'm using is from Emission labs circuit #5 (link http://www.emissionlabs.com/datasheets/EML274.htm).
With the first cap at 2.2uf and second at 15uf I get a bit of a hum. nothing changes when the first cap is increased to the max 4uF but when the second is increased to 30uf there is a significant drop and is audible only from a meter away from the speaker. I tried a 47uf first and 100uf second and no hum at all.
The specs say "For a total (C1 + C2) capacitance above 24uF, a limiting series resistor must be used, so the peak in-rush current through the choke is limited to the saturation current of the choke, or max 600mA, whatever comes first. Otherwise tube damage can result. MUST MEASURE. Can not be calculated in a reliable way. For lowest hum, this resistor is in series with the choke. So you get a C-LR-C filter. In this way 200uF is possible."
The saturation current of the choke is 290ma, specs of the tube are on the link above. I'm not sure what is to be measured and how to calculate the resistor value.
Any help is appreciated.