# Parallel pwr supply chokes for add'l current?

#### rongon

A power supply choke good to over 300mA is expensive.

But I have a few pairs of 150mA chokes around. Would it be useful to parallel two 7H 150mA 140 ohm chokes to make the equivalent of a single 3.5H 300mA 70 ohm choke?

More importantly, is there a problem with this? (Other than the space it would take, extra holes in the chassis, etc.) Capacitance? Current sharing?

-=|=-

#### Andrew Eckhardt

Double the capacitance. It takes less wire to get the same inductance on a bigger core, which allows lower resistance and less capacitance. Other than that, halve the inductance and halve the resistance.

#### bob91343

This would only work if the dc resistance of the chokes is the same. Since they seem to be, the answer is yes it would work. The down side is that, since there are two magnetic fields involved, you are wasting space. A single choke would be smaller. But, as you say, more expensive.

#### Andrew Eckhardt

The DC resistance deosn't absolutely have to be the same, so long as the critical inductance is met at the current the higher resistance coil will see due to the hogging from the lower one, and of course max current for the lower resistance one, and both, should not be exceeded.

#### rongon

Thanks for the replies.

of course max current for the lower resistance one, and both, should not be exceeded.

So if I have two identical 7H 150mA chokes, and they're both pretty close to 140 ohms DCR (maybe one's off by 3 to 5 ohms) then those two in parallel could be safely used for 3.5H at 300mA? (I would think so.)

Or do you mean the two chokes in parallel would still only be good for 150mA, the current rating of each individual choke? (I wouldn't think so.)

I'm trying to clear out my collection of transfo's and chokes. It's time to start making things with what I already have, and I have a pair of those chokes... but I'm going to need a 300mA choke and I don't have one.

-=|=-

#### Andrew Eckhardt

> 300mA choke and I don't have one.

Yes you do You got it right, paralleling two same resistances give you half the two original values. Several ohm difference will not affect design.

#### andyjevans

Just resurrecting this to ask a question about capacitance. This is doubled with 2 chokes in parallel. I have some Hammond 156C which are 150H, 8mA and 3700 ohms. Don't know the capacitance. I was going to use these as plate chokes but wondered about using a pair in the PSU instead. So 75H, 16mA and 1850 ohms.

However, there's a lot of resistance in these chokes, so would the added capacitance be an issue for treble response? I don't have measuring equipment for capacitance, so can anyone hazard a guess?

#### andyjevans

Thanks Bela. I'll try a pair out in the PSU of a 6SN7 stage at 6mA per side. They do drop 22v at 12mA so I'll have to put more volts in.