Old ribbon mics - do magnets go bad?

[zebra50]

The patient's vital signs will be closely monitored throughout the procedure 

Zebra 50 is that a Sowter Tx you put in ?

Yup - well spotted. It's the 1:40 version (8074) to squeeze out as much level as possible. As Marik points out above, the RCA transformer is not great.  FWIW the stock tranny measured at 1:20  / 1:30 (tapped tranny).

Has anyone got opinions on the cheapo gauss meters on ebay? Any use or just junk? Many of them seem to be sold as 'paranormal' detectors. Maybe my microphones will turn out to be haunted...

 

[ArR]

Yup - well spotted. It's the 1:40 version (8074)

He he, only spotted it because I put one in a Chinese ribbon mic just yesterday.
Early to tell, but initial impression was very good.
Did you have to wait ? mine took 5 weeks 

As for ghosts, maybe that's the secret to the vintage mics
The good ones come with Jazz era ghost inside 
Damn useless gaussmeter we have doesn't have ghost range setting 

 

[Marik]

Has anyone got opinions on the cheapo gauss meters on ebay? Any use or just junk? Many of them seem to be sold as 'paranormal' detectors. Maybe my microphones will turn out to be haunted...

Nah, that cheapo stuff won't really work. You need something with range of at least 1T (10,000Gauss). On top of that, look for a probe which would fit small gaps.

There is a local company here in Salt Lake City, which makes Gaussmeters:

http://www.trifield.com/

I stopped by (quite a few years ago) and was able to buy an old, out of production model for some $150--still works perfect.
If you want, they are some 10 minutes drive from my house, and I pass them at least twice a week, so I can ask if they have something.

Best, M

 

[zebra50]

Hi Mark,

Thanks for the kind offer and link. I just saw an alphalab on ebay for $125, an older model, but it comes with a probe & looks like it might do the job. Even with shipping and tax it's better value than I can find locally.

http://www.trifield.com/content/DCMHS-ACDC/

I might give it a shot if it's still there. I'm also working on a re-magnetising power supply & coil in my free moments. With a meter I can actually measure my results, and move from guesswork to some kind of scientific approach.

Also, meters are cool!  

 

[Marik]

Hi Mark,

Thanks for the kind offer and link. I just saw an alphalab on ebay for $125, an older model, but it comes with a probe & looks like it might do the job. Even with shipping and tax it's better value than I can find locally.

http://www.trifield.com/content/DCMHS-ACDC/

I might give it a shot if it's still there.

Careful, my friend! Don't make mistake--that is a 200Gauss version. With that one you won't be able to measure even way out of wack magnets. Again, you need a 20,000Gauss (the increment that company makes) version. Mine has two ranges--1,999, and 19,999--that's what you want.

Best, M

 

[ArR]

I think there will be a problem with getting enough turns around the magnet for the low current I have available.
I can get my hands on about 10F at 200V for the pulse option.

So looks like the add more magnets solution may be the most practical.

Anyhow, we are here to learn .....

Background reading the easy version
http://www.oersted.com/about_magnets.PDF

The long version
http://www.oersted.com/magnetizing.PDF


May get a chance to take some initial measurements today / tomorrow

 

[zebra50]

Careful, my friend! Don't make mistake--that is a 200Gauss version. With that one you won't be able to measure even way out of wack magnets. Again, you need a 20,000Gauss (the increment that company makes) version. Mine has two ranges--1,999, and 19,999--that's what you want.

Best, M

Thanks Mark - I actually posted up the wrong model number. The one I found was the multi range version - AC & DC, three ranges, from 0.01 to 999, then up to 1999.9, then 19,999 gauss.

ArR - thanks for the reading. Not had chance to look but will keep me busy tonight.

 

[emrr]

Tangent question.

I have an NOS/NIB RCA 900898, part # 19698, potted transformer that measures as if it must be a ribbon mic transformer, but so far I haven't been able to identify it.  Anyone know that #?  It has a 2 wire pri and 4 wire sec.

 

[zebra50]

I had imagined building a supply along the lines of figure 15, but the voltages and currents shown (fig 17) are scaring me at the moment.


emrr - have you tried the technical manuals at coutant.org? They have a few for RCA ribbon mics. Might be worth a look.

 

[Marik]

Tangent question.

I have an NOS/NIB RCA 900898, part # 19698, potted transformer that measures as if it must be a ribbon mic transformer, but so far I haven't been able to identify it.   Anyone know that #?  It has a 2 wire pri and 4 wire sec.

Doug,

You might want to contact Stephen Sank:

http://www.thuntek.net/~bk11/home.htm

or Wes Dooley:

http://www.wesdooley.com

They might know.

Background reading the easy version
http://www.oersted.com/about_magnets.PDF

The long version
http://www.oersted.com/magnetizing.PDF

Good stuff! Thanks!

 

[emrr]

Any recent refinements with increasing magnet strength in old ribbons?  I've a 77-D that was just rebuilt, and it's still pretty low output with a touch of obvious hiss. 

 

[Bill Wilson]

Hi Zebra: You could also contact Enack Microphone repair. He used to build & install the ribbons in the 44BX & 77DX; at the RCA factory in Camden, New Jersey. When RCA folded their microphone mfg., he bought all of the fixtures & supplies. His rates are reasonable; $150- to reribbon an RCA mike.

His address: Clarence Kane, Enak Microphone Repair,  420 Carew Ave., Pittman, New Jersey 08071
Phone: 1-856-589-6186