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21
Klaus Heyne's Mic Lab / Re: Neumann km54 faulty
« Last post by Kai on May 11, 2018, 04:17:02 pm »
Check PSU voltages on the mic side (this checks the cable too).
Remove the capsule and screen with alu foil or a dime, and check if noise is still present.
Identify the version, check all the voltages according to the schematics below.
Check (-) side of C6, DC voltage should be 0mV, else C6 is broken.
I calculated and noted the anode voltage according to specs, but usually it's closer to 40V, not 24V.
If anode voltage is off and everything else is correct R4 or the tube might have failed.
To test R4 bridge it with any high Ohms resitor (>=4.7MOhms) that is lying around.

If that all sounds strange to you, send microphone back to seller or to Klaus for repair 8)
22
Klaus Heyne's Mic Lab / Re: Which T14/1 for a DIY 251 ?
« Last post by vinylwall on May 11, 2018, 01:40:32 pm »
I believe you are speaking of the larger Hiller-made T14, right Klaus?

Sorry, I meant Hiller T14. I corrected my previous post. KH
23
Klaus Heyne's Mic Lab / Re: Which T14/1 for a DIY 251 ?
« Last post by vinylwall on May 11, 2018, 01:22:34 pm »
Great looking build ! Do you imply that current Haufe transformers could all be bass-heavy, and not just the ones made for Telefunken USA ?

No, and I don't have any first hand knowledge on Haufe T14/1's in anything other than the one microphone I have shown with it installed.  And keep in mind, it is a combination of the vintage CK12, GE 6072 and Haufe T14/1 giving these results.  I can't pinpoint it to just the Haufe transformer and I'm not willing to swap components to test.

I also have an UPTON 251 and Dallas uses his own T14 in those builds, but I can't say that my C12 type build is heavier on the low end than the UPTON 251.
24
Klaus Heyne's Mic Lab / Re: Which T14/1 for a DIY 251 ?
« Last post by Avgatzeblouz on May 11, 2018, 11:37:38 am »
I have a new genuine Haufe T14/1 in a point-to-point C12 style DIY build using a genuine AKG CK-12, GE 5 Star 6072 tube in a FLEA body (built by Mark at OPR).  The Haufe was purchased early in 2017. 

I find the bass response in this microphone to be very accurate and pleasing.  I don't find the low end to be over-hyped and the high end response is exactly as would be expected with a C12 style build.   

Compared to the genuine FLEA 12's that I have, the low end is more pronounced in this build.  Hope that helps.
Jimi Ray

Great looking build ! Do you imply that current Haufe transformers could all be bass-heavy, and not just the ones made for Telefunken USA ?
25
Klaus Heyne's Mic Lab / Re: Which T14/1 for a DIY 251 ?
« Last post by Avgatzeblouz on May 11, 2018, 11:35:06 am »
Avgatzeblouz, I'll get the blues, too, if you don't play by the rules and identify yourself with your real name!

It's a simple rule that makes for an honest, respectful community.

Oups, yes sorry ! Done. At least you did get the fun of the username, people usually miss it !
26
Klaus Heyne's Mic Lab / Neumann km54 faulty
« Last post by fffaustino on May 11, 2018, 05:34:13 am »
Hi Klaus,

I have recently adquired an original Neumann km54 with nickel capsule and selected ac701k.
I correctly tested it and it was working good with no issues but after a few days of use the mic suddently lost it sound and began to generate a loud “fire, crackling” noise. The noise seems to go down a few dbs after waiting for tube heating but it does not disappear and the mic does not work at all..

Any advice really appreciated..thanks!

Alfredo
27
Klaus Heyne's Mic Lab / Re: Which T14/1 for a DIY 251 ?
« Last post by klaus on May 11, 2018, 01:56:17 am »
Far is it from me to comment on other peoples' transformer choices, especially if they work out well.

Just a clarification, if I may: Oliver and I had plenty of (fruitless) discussions about the mythical "original Hiller T14" he so ably imitated and modified in  thousand varieties...

There are a couple of early C12 drawings mentioning T14, but in the hear and now, no one, including Oliver, has ever seen that transformer, let alone caught one inside an AKG mic.

If any of you have any images of a T14 I would love it! (Trying Google images did not lead to anything.)

28
Klaus Heyne's Mic Lab / Re: Which T14/1 for a DIY 251 ?
« Last post by AusTex64 on May 10, 2018, 09:10:42 pm »
I’ve not used the Haufe, but have built several mics with the AMI/Tab Funkenwerk T14 and been quite pleased with the results.
29
Klaus Heyne's Mic Lab / Re: Which T14/1 for a DIY 251 ?
« Last post by vinylwall on May 10, 2018, 05:48:44 pm »
I have a new genuine Haufe T14/1 in a point-to-point C12 style DIY build using a genuine AKG CK-12, GE 5 Star 6072 tube in a FLEA body (built by Mark at OPR).  The Haufe was purchased early in 2017. 

I find the bass response in this microphone to be very accurate and pleasing.  I don't find the low end to be over-hyped and the high end response is exactly as would be expected with a C12 style build.   

Compared to the genuine FLEA 12's that I have, the low end is a little more pronounced in this build.  Hope that helps.
Jimi Ray
30
Klaus Heyne's Mic Lab / Re: Neumann M49b Making High Frequency Noise
« Last post by klaus on May 10, 2018, 04:57:55 pm »
I should have mentioned why one should measure the heater voltage of any tube mic at the tube itself, rather than at the power supply:

Depending on the length of the cable, there is a voltage drop due to wire resistance that cannot be generalized. Measuring heater voltage at the tube itself eliminates guessing the voltage drop.
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