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91
Yes, it is. And this mic's response, as that of the U87Ai, therefore is largely affected by the individual response of the actual capsule installed.
92
Thank you for such invaluable info. Is the capsule in the new U67 reissue the K870/K67? (as far as I know, there is no new capsule available as spare on the Sennheiser site).
93
Klaus Heyne's Mic Lab / Re: KM84 Low output suddenly
« Last post by BluegrassDan on June 26, 2018, 07:49:43 pm »
Thanks, Klaus. The transformer is dead.  UGGGH!

Know where I can find one easily, or do I just need to scope eBay and forums?
94
Klaus Heyne's Mic Lab / Re: KM84 Low output suddenly
« Last post by klaus on June 26, 2018, 12:17:39 pm »
The white wire is the inner connection between the two primary bobbins, and as such not a reliable way for a layperson to judge the primary.

Instead, unsolder the red wire from the circuitboard, and check between it and ground (where teh primary's black wire terminates) with an ohm meter for continuity, or measure roughly 600Ω.

If that connection is open, you have indeed a break in the primary wire, which renders the transformer dead.
95
Klaus Heyne's Mic Lab / Re: KM84 Low output suddenly
« Last post by BluegrassDan on June 25, 2018, 10:19:53 pm »
Okay. I have replaced the jfet, caps, and zener. Still the same issue.

There appears to be no continuity between the red and white wires of the transformer primary.

Could lightning have caused this?

What is the solution? New transformer? How hard of a job is that?
96
Klaus Heyne's Mic Lab / Re: KM84 Low output suddenly
« Last post by BluegrassDan on June 25, 2018, 09:10:18 pm »
Klaus and company,

A few folks I've talked with suggest replacing the old tantalums with new tantalums - that electrolytics will make the mic mushy in the low frequencies, and have only about 10-15 years of good life.

What say you?
97
I like this site very much. I did not make that kind of thing. Now it's all learned.
98
Klaus Heyne's Mic Lab / Re: consequences of incorrect plate voltage
« Last post by klaus on June 24, 2018, 05:45:03 pm »
Plate and B+ voltages are not necessarily interrelated. Bad tubes will cause low plate voltages, even if B+ is correct.

On the other hand, extreme B+ variations-too much or too little- will cause capsule distortion or noise, because capsule polarization voltage is usually divided off the B+ supply voltage. Here, even just a few more volts deviating in either direction will cause audible artifacts.

None of this answers your question. I have not experienced frequency deviations, because the other effects of too litte or too much B+ and plate voltages are overwhelming.
99
Klaus Heyne's Mic Lab / consequences of incorrect plate voltage
« Last post by Brian Campbell on June 24, 2018, 05:39:26 pm »
What are the effects of incorrect B+/plate voltages with regards to frequency response?
Is there a general guideline of tolerances?
100
Sometimes you will want to remove stains or residue from adhesive badges or labels on mic bodies. The art: to remove the stain without irreversibly altering or removing the micís surface plating.

Here is the general rule when choosing chemicals or mechanical means to remove foreign objects or dried, staining film from mic bodies: start with the lowest impact chemical and work up from there. The ultimate cure, mechanical abrasion, will usually also cause ultimate and irreparable damage to the surfaces they are applied to.

Here is how I usually proceed, in the order from mild to aggressive:

1. VM&P Naphtha - the same stuff luthiers use when they need to remove pickguard adhesive from even the most expensive acoustic guitars: it will not harm the surface of your mic but in many cases will dissolve the adhesive.

2. 100% or 99% Isopropyl Alcohol. Again, in this case it will not affect the nickel-plated surface of your mic.

If that still does not remove the yellow stains, and if you are sure that the letters embossed into the surface are anodized black, rather than painted black, choose:

3. Acetone. It's the most aggressive of chemicals I would use on a mic body. It does not affect or bite into metal, but if the lettering is painted, it will affect or dissolve the paint. If the lettering was black-anodized, acetone will not affect the anodization.

Test the acetone on a section of the lettering that is hidden or not in the center of viewing: put a small amount of acetone on a Q-Tip, and lightly rub it across a lettered area. If the Q-Tip turns black, the acetone dissolved paint. Even with painted letters, you can still use acetone on this mic, if you are very careful: remove the yellow film around lettering, and don't rub the acetone into it.

I would stay away from abrasive cleaning pastes: at minimum they will later the sheen of the affected area and make it brighter, at worst, they will leave scratches that cannot be removed without causing ugly shiny spots, if you try to buffer them out.
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