AKG BX 20 problems

[capnspoony]

bumping this thread.  I have my broken beast taken apart and it looks like I'm dead in the water without a coil replacement.  I have no interest in keeping this unit as a mono unit so would be game for sacrificing the good parts in order to possibly replace both at once with some DIY natured help.  I'm in brooklyn if anyone wants to go at this.

 

[mjrippe]

The one I was servicing is in Brooklyn also - maybe you two should get together and make a stereo pair 

 

[zebra50]

I'm still keen to have a go at winding one of these - it does look like a challenge and it keeps on slipping to the back of the queue.

I haven't even got round to removing my dead one for analysis yet. Been a busy year!

 

[haima]

I'm still keen for you to have a go at winding one of these Stu!  ;D

Seriously, it would be super cool if we could figure this out one day. There seems to be so many BX20s out there that aren't working 100% - it's a shame... such a beautiful sound.

 

[Manitou]

Thought I might bump this & say I'm also keen to get my bx20e back to it's former glory!

Stu if you can find time to do these, you'll be up for sainthood 

 

[gyraf]

We'll need some more info to get going:

- Good in-scale close-up pics of the coils for mechanics.
- Measurements on a known-good coil: Free-air inductance and DC resistance for the two windings.
- Measurements from any coil: Individual coil length, width, outer and inner diameter. If possible, an estimate of wire size.

Jakob E.

 

[Manitou]

Ok, I'll have a go at getting some of this info posted by the end of the year.

 

[zebra50]

Well, I do have a good coil and a bad one, and some coil winders, and lots of wire. What I don't seem to have is much time to do the R&D. I can see it being a few days work to crack it.

I normally close the workshop for two or three weeks at Christmas to do some of my own projects. Last year it was hexaphonic pickups. This might be a good thing to do this year!

Stewart

 

[synthfrank]

OK guys, if you are still interested,

I have a number of original!!! New Old Stock upper and lower coils for BX20 available.

These are for BX20E or E1 or L or E/A or E1/A or L/A.
Not for the /B versions, but these are really rare.


The original parts numbers are:
1970M2002 lower coil (20pcs)
1970M2001 top coil Eur (6 pcs)

The actual coils are the same for top and lower part, but it is the attached spring part that is different.


This offer is closed now.

Best regards,
Frank

 

[telefunk]

So, synthfrank's coils are gone now apparently...

If somebody who bought one extra would like to sell me one, i'd be interested, otherwise: any progress on making these?

 

[haima]

I'm in the same boat..

Maybe some kind soul who got one of the NOS coils could measure it for us?

Inductance, resistance and some physical measurements... Some hires photos? (is that all we'd need?)

Hopefully then we can manufacture more for whoever needs them in the future!

 

[telefunk]

Yes, this should not be THAT difficult, eh?! Really, it's just couple of coils glued together, that's it.

Here's the info on AKG's spare part department: http://www.akg.com/Technical+Support-995.html

I think everybody who's missing a coil should write there, because there must be hundreds of broken BX20E's around that could be saved if they would just do a little run of them. They're still building mics, so it should be relatively small effort for them...

Meanwhile, let's DIY!!!

 

[zebra50]

Does anyone have a dead one or two available for R&D purposes? It would help greatly.

 

[haima]

maybe when people swap out their bad ones with the NOS ones then these bad ones can be used to study...?

this, along with the measurements of the NOS units will surely give us the info we need to re-make them...

 

[vineyardgray]

This topic has been silent for way too long.    Bump!  ;D

I've just recently purchased a BX20E, and I checked the resistance of the coils with a multimeter before payment, and I have no 'open' coils, but I don't get the resistances shown on the service manual.  On my unit, all the coils are around 200 ohms, which I assume means that I have one of the older BX20E units, although I'm having a little trouble understanding the german-to-english translation in this regard.  (The manual states that if I have an "unsigned" version, all the coils should be 200 ohms +/- 10%, but if I have a version signed A or B, the ohms should be as per the chart.  Anyone know where exactly AKG labeled these with A or B)?

So, although it appears that the coils are functional, for anyone who wanted to wind their own or have them wound, it appears there are two different models of coil.

I intend to disassemble and have a good look at the unit (for missing foam, etc.) and can take some detailed close-ups of the coils at that time to help the effort for winding coils.

Regards,

MR

 

[zamproject]

Anyone know where exactly AKG labeled these with A or B?

On mine it's a small sticker, white writeable paper , with "B" hand writed, located inside, close to the top hinge.

 

[vineyardgray]

For those who are curious, it appears – after closer scrutiny of the service manual - that any BX20 with the auxiliary amplifier board (the little daughter card that sits atop the amplifier boards) is an “A” or “B” variant.

Regarding coils - from section 8.2 of the manual: “The first and last spring ends…are exchangeable, upper and lower spring ends are different, if it becomes necessary, nevertheless to exchange different coils a loss of 2-3dB at higher frequencies can be expected”.

To me, the difference between ‘upper and lower’ and ‘first and last’ coils is not readily apparent, but I’d expect it to become so when I open the beast up.  Regardless, it appears there are _definitely_ two different types of coils for us to contend with. 

My question is for those with failed coils – which coil or coils went open (i.e. with reference to the user manual, between which connector pins show no continuity) ?    If we can determine that on average only the lower coils are going south (for instance) then we can focus on getting those made first.    Either that or we just say ‘bugger it’ and live with the potential HF loss.

Regards,

MR

 

[mjrippe]

Two types are probably send and receive.  In the one I serviced the send coil was open.

 

[vineyardgray]

Anyone from Germany (who speaks and reads German) following this thread?  ???  AKG kindly sent me some documents but without some translation, I can't determine if the information is of any use.  Looks more like information on the springs, not the coils, although the coil is shown in one of the drawings.

 

[DerEber]

yes.