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Author Topic: NU67 puzzle  (Read 767 times)

NigelT

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Re: NU67 puzzle
« Reply #30 on: May 10, 2022, 04:35:28 AM »

Thanks Kai.
An update. All ten supplies are now working and in spec, sort of...my biggest problem now seems to be fluctuating line voltage. Today I am at 121vac. I have found that some of my units have a 110v tap and others at 117v. My procedure is switching between the high (127) and low (110 or 117) tap and swapping mics between all ten PSU's and by doing that, I am getting all of them within spec. I have also found that these need at least 30 minutes to warm up and stabilize. Thanks for all your help, I have fallen in love with these mics! Although I am blessed with all of the great ones,  (251x2, U47x2, M49, C12x2, C24) and they all sound amazing, something keeps pulling me back to the U67. Out of ten, there are four that are just outstanding but only when compared side by side and by very minute differences. Any of them alone are amazing.
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Kai

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Re: NU67 puzzle
« Reply #31 on: May 10, 2022, 10:47:49 AM »

Your mains voltage seems to be on the high side, even a bit out of standard.

Maybe your supplier can do something about that, switch to another transformer tap for your individual household supply, if exists.

For the tubeís heater supply:
In general little undervoltage is more preferable than overvoltage, if you canít get it stable.

Anode voltage (the high one) is uncritical.
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NigelT

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Re: NU67 puzzle
« Reply #32 on: Yesterday at 05:04:44 AM »

Guys, thanks again for all your help. The mics are all working great. I ran into a problem I didnt expect but should have, and that is sourcing proper replacement parts. For example, the B30C500. I cant find it anywhere. Someone has hacked in a black one that has a different layout and way thicker pins. Are there still direct drop-in OEM replacements available?  If not, maybe a list of alternate parts would be good.
For example, I found Zeners, but not the exact same one.
I replaced part # Zx15 with
 Newark part #: 1N3314B Zener Single Diode, 15 V, 50 W, DO-5, 5 %, 2 Pins, 175 įC
https://www.newark.com/solid-state/1n3314b/zener-diode-50w-15v-do-5/dp/10P4821?gclid=Cj0KCQjwhLKUBhDiARIsAMaTLnHJXQ3u2KPr_XJzfzIDeKF_GDrq46xk1HiA_Kiy-xlJ1ZRhERVN2tMaAi38EALw_wcB&mckv=_dc
If anyone wants to add to this, please do.
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