Where to find 50 mH / 3A inductor/coil ?

[Steben]

To use in a reactive load.
1mH / 3A is ok.
50mH / 3A is tough to get.

[Sir H C]

Those values sound more like a choke, check hammond and the like who make transformers for tube amps.

[Steben]

Are two 25mH chokes @ 1.5A IN SERIES the same as one 50mH choke?

[earthtonesaudio]

Two 25mH in series is 50mH of inductance, but be aware that the power handling is equal to the smallest rating in the chain.  Think of them like speakers.  If you have a 25W speaker and a 75W speaker, they might be 16 ohms in series, but the 25 Watter sets the power handling limit.

[Dai H.]

is this for the Aiken thing? Does it actually need to handle 3A? There was this one (German?) site where you could simulate the basic network (L, R, L+C), and according to the simulation (signal 20something volts AC, freq. 400Hz? IIRC) there was not much current going through the L(which is part of the L+C which gives the bass boost). Most of the current went through the C, which seemed to make sense since the C is a dead short for AC and L opposes (maybe the high rating is for worst case scenario??). And also, if the network is supposed to be an 8 ohm version of the 16 ohm load shown on the Aiken site, shouldn't the 50mH and 1mH be halved?

[morcey2]

Are two 25mH chokes @ 1.5A IN SERIES the same as one 50mH choke?

It would equal a 50mH choke, but would only be able to handle 1.5A, not the 3A that you said you need. 

You could always do 50 x 1mH/3A chokes in series 

Or not.

[km-r]

IMHO i really dont know much about inductors... but 50mh seems to be quite small... you could wind up your own choke in that value or more.

maybe old pc power supply chokes?

[Steben]

is this for the Aiken thing? Does it actually need to handle 3A? There was this one (German?) site where you could simulate the basic network (L, R, L+C), and according to the simulation (signal 20something volts AC, freq. 400Hz? IIRC) there was not much current going through the L(which is part of the L+C which gives the bass boost). Most of the current went through the C, which seemed to make sense since the C is a dead short for AC and L opposes (maybe the high rating is for worst case scenario??).

Of course the max current through the L will be below 80Hz, since the C is short for highs and the L for lows.
So one could put 50-60Hz in the calculation (not unreal: drop down guitar) and watch the current in the L go nuts, I guess.

In fact it could all come down the relation between internal choke resistance and the voltage. Since the internal can be around 0.5 ohms and the resistance in the load line is around 16 ohms, the voltage across the L will be max V*0.5/16.5. A 50 W amp gives 1.77 V at 16 ohms. So you get around 0.06V across the L with 0.5 ohms. That gives just 0.1A. 

Interesting link then? Someone care to share the adress?

And also, if the network is supposed to be an 8 ohm version of the 16 ohm load shown on the Aiken site, shouldn't the 50mH and 1mH be halved?

I'm not an expert. 
yet the circuit I would use it in has 8 ohms, yes, yet there is a switch between resistors in series; this means that on full attenuation (only dummy), the full resistance equals 16 ohms. Th 8 ohms only comes in place at -6db attenuation.

[Dai H.]

Of course the max current through the L will be below 80Hz, since the C is short for highs and the L for lows.
So one could put 50-60Hz in the calculation (not unreal: drop down guitar) and watch the current in the L go nuts, I guess.

ahh, so I guess that was a part missing when I was looking at it.

In fact it could all come down the relation between internal choke resistance and the voltage. Since the internal can be around 0.5 ohms and the resistance in the load line is around 16 ohms, the voltage across the L will be max V*0.5/16.5. A 50 W amp gives 1.77 V at 16 ohms. So you get around 0.06V across the L with 0.5 ohms. That gives just 0.1A. 

FWIW the one there (for the low freq. resonance) in my Marshall Power Brake (12.5mH) is a cored inductor and (in circuit) was around 0.7ohms. So it looks to me it's cored so it can be small, and the wire doesn't look very thick so I guess it doesn't need to handle max. current (from the amp output)?

Interesting link then? Someone care to share the adress?

the simulator thing? Here you go:

http://www.walter-fendt.de/ph14e/combrlc.htm

I'm not an expert. 
yet the circuit I would use it in has 8 ohms, yes, yet there is a switch between resistors in series; this means that on full attenuation (only dummy), the full resistance equals 16 ohms. Th 8 ohms only comes in place at -6db attenuation.

right, well I'm no expert by any means either. I just tried to follow this (from the Aiken site) :

    These circuits are designed to present a 16 ohm nominal load to the amp; if you want a different impedance, you will have to scale the resistive and reactive elements accordingly. The impedance scaling factor will be Z = Znew / Zold, and the new element values will be as follows:

        R' = Z x R
        L' = Z x L
        C' = C / Z

and I hope I got it right (I'm horrible at math). 

[Steben]

FWIW the one there (for the low freq. resonance) in my Marshall Power Brake (12.5mH) is a cored inductor and (in circuit) was around 0.7ohms. So it looks to me it's cored so it can be small, and the wire doesn't look very thick so I guess it doesn't need to handle max. current (from the amp output)?

Yes, the Power Brake has a much higher resonance freq, I thought a lot higher than 100 Hz. 50mH gets it lower to around 75Hz.

the simulator thing? Here you go:
http://www.walter-fendt.de/ph14e/combrlc.htm

thx !!!

right, well I'm no expert by any means either. I just tried to follow this (from the Aiken site) :

Yes, yet there is no actual filtering as long as you keep the load as one block (not tapping off somewhere in it).
I guess the scaling is important in relation to the pure resistance (ohms). The specific resonance freq of the LC pair is only determined bij the L en C, since it's completely imaginary math with phase etc. Yet the peak amplitude etc is something different. I don't care for some ohms when talking about 16 ohm base and 60 ohms peak, if you know what I mean. 

[Steben]

OK HERE WE GO !
This the total situation if 50W @ 16ohm:


If we zoom in at the last choke:


1.75A !!! at 1Hz
(+/-1.35A at 40Hz)

So it isn't a bad idea to choose a value >> 2A rating

[Dai H.]

does a gtr. amp put out frequencies that low? (If it does, I guess the 3A rating makes sense.)

[Steben]

does a gtr. amp put out frequencies that low? (If it does, I guess the 3A rating makes sense.)

Normally not, but be aware of subsonics crashing in the pickups.
Even the circuit hum at 50Hz (always there) gives at full 1.3A... 
bass guitar = 40Hz ...

No, I think we should at least go for 2A.

[Dai H.]

okay I guess the audible hum frequency makes sense.

No, I think we should at least go for 2A.

so you think at least a 2A? How about a 25mH instead(for 8ohms)?

[Steben]

okay I guess the audible hum frequency makes sense.

No, I think we should at least go for 2A.

so you think at least a 2A? How about a 25mH instead(for 8ohms)?

Of course is 25mH a good choice if the total circuit is designed for 8 ohm.
But the current will stay high.

[Dai H.]

how about lowering the inductor value and raising the bypass cap. Seems to give the same resonant frequency. Smaller inductor values are easier to find and less expensive.

[ricothetroll]

Hi,

Sorry for digging out this old post...

I have bought components to build an attenuator similar to Aiken's, to simulate my Greenback. My circuit is : 6,8R + 100uH in series with the input (Re, Le), 12R + 20mH + 235uF to ground (Res, Lces, Cmes)

I bought this inductor for Lces :

http://be.farnell.com/wurth-elektronik/744825320/choke-common-mode-20mh-3a/dp/1636301

I use the dummy load in parallel of the speaker (8 ohms), using the 4 ohm output of my amp.

The problem is, there is some very noticeable distortion on low frequencies. You can clearly hear it when hitting a palm mute on the E string. That excepted, the tone is much better than with a simple 8 ohms resistor in parallel of the speaker, though there is still some noticeable treble loss, like turning the tone pot of my AC15 at 12 o'clock (that I tend to like actually). When I remove Lces, the distortion disapears, but the tone is (slightly) worse.

Is there some kind of rule of thumb for determining if a specific inductor is prone to saturate, given its size, core material and the power it is used at ? I have seen some inductors made for speaker crossovers but they are expensive and generally rated for like 300W, that is way too much for my tiny AC15... Do you know any source for lower power ones, and thus less expensive and heavy ? I have some bobins and corresponding laminated cores that I could easily wind (EI type, about 44*11*35mm), but would it be big enough to avoid core saturation ? It's actually difficult to find infos on the internet about core size/saturation current.

Best regards.

Eric