AKG BX 20 problems

[pidah]

I'd be happy to join in as well!
cheers,Pieter

 

[haima]

I guess if Jeremy isn't able to do this, perhaps I could donate one of my dud coils to be analysed...

Does anyone know someone who can wind VERY fine wire coils like these? and is smart enough to reverse engineer the original?

Perhaps Oliver Archut? Although I'm sure he's very busy.

Maybe Dan Kennedy had someone in mind when he suggested getting them re-made...?

 

[telefunk]

I'm still in!

Max of IOAudio perhaps?

 

[edchocolate]

Hi!
I have a BX20 in need of coils too.....please add me to the list if you ever get them made...Cheers!!
8^)

 

[zebra50]

I had completely missed the developments in this thread. I might be able to help.

I do now have a nice coil winder and a stash of enamelled wires so I guess I could give it a try. The tricky bit will be reverse engineering it, but if we share our findings here, I'm sure we can crack it.

Does anyone know someone who can wind VERY fine wire coils like these?

Just how fine are they? My winder copes well down to guitar-coil size (42 AWG, 43 at a push). Beyond that the winder, or more likely the operator is struggling.

Does anyone in Europe have a duff coil to hand that they could send me? Or even just some better photos and some measurements. My BX20 isn't very accessible at the moment.

Stewart

 

[haima]

Hey Stewart,

I think they are Quadrifilar wound...?

The best photo I know of is this one:

The coil seems like it's almost two interlocked rings - the red/copper coloured bit that extends inside the end of the spring in the photo above.

You can see the winding wire come off, curl around a few times and head towards the gold, wire terminating "dead-bug" thing...

I'm sure I could get some better photos and even one of my dead coils -  if I ever got time to open mine up - I don't relish the task!

 

[zebra50]

I think they are Quadrifilar wound...?

Well, that may be beyond me! Or maybe not.

That photo is really pretty blurry. I can't work out what the core is, or if there even is one. Humbucking air coils?

I don't relish the task!

No, nor I. That's why I was hoping someone had one lying around.

 

[gyraf]

From what I remember, the pickup is just two simple aircore coils glued together. Shouldn't be that difficult to wind on some material that can be removed afterwards (wax).

Jakob E.

 

[haima]

Hmm interesting Jakob. I thought there might be some kind of ferrite/iron cores - you might be able to see a little bit of grey core material at the top of the second coil (closest to the gold dead bug termination device) - but this could just be a "former" or just an blurry optical illusion in that photo.

That photo IS pretty blurry unfortunately - I just found it on the web...

Anyway, the coils appear to be two small ovals, maybe 7mm long by 3mm wide?

Here's hoping someone has one in pieces already - otherwise it might be a while before I get time to open mine up... 

 

[zebra50]

Thanks Jakob,

If it is aircores then we stand a chance, especially if the wires are not too tiny.

Well, I should just bite the bullet and open mine up. I don't really want to risk screwing the one working channel, but no pain = no gain. 

 

[gyraf]

Wires are pretty tiny - exactly how tiny (and how many turns) could probably be measured from the coil's [physical dimensions + DC resistance + inductance]

Jakob E.

 

[zebra50]

exactly how tiny (and how many turns) could probably be measured from the coil's [physical dimensions + DC resistance + inductance]

Indeed - that and a bit of trial and error should get us there. From the photo and DCR values above of around 200 ohms, I would guess we are in the same ballpark as guitar coil wire, which is OK for winding.

So what is that gold can component?

 

[haima]

I believe the gold can is just to provide a termination point for the winding wires and also the spring?

 

[telefunk]

Found few pics we took from mine while ago.

I think it's just double aircore with glue. Quite thin wire but still solderable...

 

[telefunk]

other view. The golden can is just a termination solder pins for the wires.

As you can see in this picture the thin wires were not connected as we took the picture but right after taking this, we soldered them back again, VERY carefully.

 

[telefunk]

I hope these are useful...

 

[haima]

Thanks Telefunk! these are much better photos.

Have you done repairs on a BX20?

 

[telefunk]

Have you done repairs on a BX20?

We tried to fix the coil that you see in the pics but no luck. It was broken from inside, we hoped it would have been just one of the wires connecting to the golden termination cap... My friend who was assisting me actually managed to fix two coils from another BX20 but those had the wires broken at the termination point. Very delicate soldering.

So, we are still lacking one coil and it would be amazing if somebody here could do it!

 

[gyraf]

Any access to a precise inductance meter and a still-working (half-)coil? An inductance reading (preferably out of the magnetic field) would help quite a lot..

Jakob E.

 

[zebra50]

Thanks for those - much better!

So, two small air coils at 90 degrees? Not some bizarre twisted figure of 8 coil I hope. 

The wires don't look impossible small. I think it is do-able. 

I wonder what the glue/lacquer is? Normally I wax pot things, but something more permanent will be needed here.

Thankfully, we are very busy at the moment. but I will try to find some time to open mine up and see if I can take some measurements on the coil on my dead channel.

Stewart