Hammond 156C dissected

[Landins]

Having browsed Groups interesting dissections and rewinds I decided to sacrifice a Hammond 156c (150H, 3,5 dcr, 8ma) to see what this is all about. I do not have the theoretical knowledge as others on the forum but my conclusion is: One chamber bobbin, no layers in winding, air gap yes (film placed on core) and what looks like a ferrite core. Have at you!

 

[Landins]

Cream cheese lids gave three chambers. New and totaly unscientifical wind with wire I had lyin' around. Lets see what happens with layers and more chambers.

 

[MatthisD]

Can you post the core dimensions? did you put those DIY flanges on in two halves and then glued?
Thanks

 

[Landins]

Here are stats for ei-48. As you see core is not interleaved. Yes I just cut out plastic intersections and fixated them with a ridge of woven tape closest to the core. Three layers per chamber. I did the wind while waiting for the laundry so its quite quickly done. Unfortunately I believe my wire is to thick; 0,1 mm/42awg as dcr only reads 1,3 k when all chambers are packed. Scope is in studio so i cannot calculate L-value. But I doubt it will work as plate choke.

 

[MatthisD]

It looks like EI625. If thats 0.1mm wire you wound on then I'd guess there is at least 7000 turns total. If it has too low inductance you could get an EI625 edcor and swap the laminations over. With a very small gap I reckon you would have around 100H or possibly 150H. How much signal and DC current it would handle is the conundrum!

 

[Landins]

Indeed that is a tough question. I will deep down further in forum articles. I recently found CJ:s deconstruction of the V-series chokes and will dig into understanding and hopefully try and wind one. The labour part is just a fraction of what it takes to build. Thanks for the tip concerning Edcor and the approximations. Ive had my eyes on Edcor but see no distributors in Europe. Im Swedish.

 

[Kingston]

But I doubt it will work as plate choke.

It has been used as a plate choke in RCA OP6 clone: http://groupdiy.com/index.php?topic=50018.0

I've been meaning to test it myself as well. But I don't expect it to perform mastering grade.

 

[MatthisD]

But I doubt it will work as plate choke.

It has been used as a plate choke in RCA OP6 clone: http://groupdiy.com/index.php?topic=50018.0

I've been meaning to test it myself as well. But I don't expect it to perform mastering grade.

But maybe not now that it has a lot less turns with the thicker wire.

 

[Landins]

Readings were terrible on the H:s. Too loosly wound and done in too much haste. Have unwound the spool and will try again with homemade paper bobbin an lego-tech winding machine.

 

[Landins]

Ok. Couldnt resist tryin with the 0,1 mm wire I had and more serious winding machine. Built dividing walls of cardboard soaked with loctite brush-on glue. Really sturdy. Managede to get 8500 turns in there. As I have problems with finding a good forulma/calculator for high inductances maybe someone could file judgement on performance.

DCR: 1600ohms, wired in series with 1500 ohms resistor, 1 V pp from funky gen. Measured at junction with scope. At 10hz signal is cut to 50% and signal decreases rapidly up the hz and at 10Khz I have like 4mV.

 

[Landins]

Took it apart and rewound with 0,05 mm wire like crazy, approx 25000 turns. Took out the lams and re-varnished them. Due to this airgap should be enough to handle the 3ma current from a ef804. Readings are:

100hz - 395 H
120 hz - 392 H
1 Khz - 506 H
10 Khz - 8 H

DCR 17kohms

Lets see what gives in application

Peace!

 

[emrr]

Seems like the best place to drop this:

Bought a pair of 156C to play with, still cold from the UPS truck which will somewhat affect readings.  Here's what the handheld meters tell with 0mA current.  This is as much a testament to what handheld meters can't tell you as anything, operation at expected levels and current will be different. 

DC 3243R / 3212R (spec 3K7)
120Hz 63.4H / 66.8H, 337K / 357K AC Z
1kHz 69.3H / 74.3H, 156K / 179K AC Z
27-27nfd

The other thing that's been pointed out is that you can stack these in series to benefit:

With the low cost of these chokes you can use 2 in series. This has 3 things going for it.

1st, the inductance is double so you get 1 more octave on the bottom end of the frequency range.

2nd, because the capacitance of the chokes acts as 2 caps in series you will get better high frequency response. In a preamp I built the 3dB down point went from somewhere near 30K to out past 70K. The single choke had a 4dB dip around 40K. With the pair of chokes the dip was only 2dB.

3rd, you can mount the chokes on standoffs, bottom to bottom and wire the chokes with one winding backwards. This makes the pair of chokes humbuckers. In my test setup the pair of chokes picked up 20dB less hum than a single choke.