Nice little filter choke?

[momo]

I'm not sure, this reads 3.7 ohms on the scale.
I thought I could use it to add filtering on the power before it reaches the circuit.?
I can't find any info , it was used in a Realistic Mpa-20 amp on a 12v circuit.

[GibsonGM]

For our purposes, outside of real, vintage amplifiers, an R-C circuit is far easier to set up!     In the amplifier case, we'd find the correct 'choke' for it.

Something like 100R/100u or higher cap to ground is all it takes, USUALLY.  The parts are much smaller to incorporate into a stompbox design.

[momo]

thanks, it's just so cute!....would be a shame to not use it as it is small enough for some cases.

[GibsonGM]

Yes, you see those in some switching supplies; computer supplies...there is no law to say you cannot try it!  LOL 

[Rob Strand]

Those types of chokes are common on products running from 12V car batteries.    The main idea is to remove the buzz when the motor is running on a car.  Not sure if the Realistic Mpa-20 has a 12V DC input.

[momo]

Yes it does.
There are two versions, the early ones have germanium transistors.
The other have silicon car amps style.
I use the early one as a guitar amp, breaks up nice.
I gutted the later one, scored this choke and nice input and output transformers, 12v.

[momo]

These little ones clock in at 9 ohms....
Chokes?
Beautifully wound for sure.

[PRR]

... Chokes? ...

A kind usually called "Radio Frequency Choke" because they do not do much in the audio (or wall-power) band.

Yes, nice winding, there were machines to do that work.

[Rob Strand]

At one time that type of coil was very common.  I had heaps of these from radios and TV sets as a kid.   
Often used for DC choke, but not always.  There were similar looking coils with adjustable ferrite slugs - definitely not for DC chokes.

The winding is called a "progressive winding".  It does have a purpose.  The winding pattern reduces the self capacitance of the inductor and lets it look like an inductor at higher frequencies.   You often see multiple coils side by side and spaced apart on the bobbin to further reduce capacitance.

And (of course  ) there's guys on the web with DIY winders.

Some coils used litz wire to reduce high frequency losses (ie. improve the Q of the coil).

Hard to judge the inductance as some use thinner wire and more turns.  Perhaps 1mH as a ball-park.

[momo]

I will say this, they are so beautiful!

I always try to incorporate anything vintage in my builds as I find it adds so much to the vibe.
I don't know how I can use these but they sure would look great on a point to point build.
Not enough of Henry present for a wah, won't filter any audio range frequencies?
Can it be like a 30pf cap filter for high end radio frequencies?

Please please find me a use for these beauties!!!!

[Rob Strand]

Please please find me a use for these beauties!!!!

As PRR pointed out, not much use in audio.

Use as a filter generally requires low impedances circuits.  For high impedance guitar stuff they aren't very effective.  In fact they could pickup RF in some cases.

Even back in the day they only served humble positions filtering power rails in RF circuits, not representative of their beauty.    The best I can think of is an LC oscillator.   Probably end up 100kHz, pushed maybe 10khz.   Not much good for audio.

An alternative is to use it to check the 10kHz and 100kHz ranges on an LCR meter.    That's probably where the low capacitance will be most helpful.   If you put it in a clear box plastic with some banana sockets it will be on full display.

[momo]

Thanks much Rob. I love to learn and it's interesting to me even if I won't use it.
I have an idea though, I also do photography and will try some macro on the windings.
Will take it high resolution so you can do a poster with it if you wish.
:-)