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 31 
 on: May 04, 2022, 01:42:53 AM 
Started by NigelT - Last post by NigelT
...and electrolyte leakage from the vent holes in the top of electrolytic capacitors does likewise not indicate damage!
Lift the plus (in the case of NU67 heater rail minus) connections of the cap and use a capacitance tester to determine health.
Will do.

 32 
 on: May 04, 2022, 01:42:02 AM 
Started by NigelT - Last post by NigelT
...If you don‘t break one by plugging into a faulty PSU.
Use resistive dummy loads for testing, not a valuable mic:
33 Ohms / 2 W (this simulates additional 1.5 Ohms cable resistance) and 240 kOhms.
Which is exactly why I am here asking questions. The next unit I am testing has voltages way to high to even plug a mic in. It's been recapped but something else is wrong. See below. So I will test using the dummy load before I plug in a valuable mic. Thank you.
C1-C3 caps can be basically checked in place by looking at their AC ripple voltage UNDER LOAD and comparing the result to a known 100% working unit (preferably with fresh caps).
Sadly my scope died. Although I do have eight working NU67's, all are really old. The voltages are in spec but I only have an RMS Fluke to measure ripple. I'll check them all but I dont have one I can say for sure is good enough to compare to.
Close visual inspection can reveal residue from cap leakage, but missing residue doesn’t mean the cap is fine.
All of the NOS caps visually look ok but some of the circuit boards are in pretty poor shape, they look like they have had a lot of crappy soldering done.

Electronic’s symbols vary all over the place, remember the 60 years that passed along since.
American symbols are often quite different to european’s, even denoted for resistors in the schematic!
Understood. I learn every day. I haven't had to use many 60 year old German schematics, in fact this is the first time. I assumed it was a Zener but again, that's why I ask. You know what they say about assume...


 33 
 on: May 02, 2022, 09:44:41 PM 
Started by Chris Jacobie - Last post by klaus
Sent you a PM.

 34 
 on: May 02, 2022, 09:30:53 PM 
Started by afterlifestudios - Last post by Krackle
I wish i could help.
Just funny that today i was re-auditioning some mics I hadn't used in a while and stopped at a KEL HM-1 I've had for years.

I was recording a 2x10 Fender Vibrolux and looking for a mic to sit 3-4 feet out for an image of both speakers in the room.
This little mic sounds great. Always was amazed at how it sits so far above its price point. I wish Kelly Dueck had continued on with KEL, he had a knack and a good ear.

Sorry for the intrusion but it's sitting on a stand a couple of feet away and i had to chime in.

 35 
 on: May 02, 2022, 08:42:53 PM 
Started by afterlifestudios - Last post by afterlifestudios
Any one familiar with the KEL MM-7U?   Housing cylinder doesn't want to clear the pad/hi pass switches to get access to the internals...  Anyone been inside?

 36 
 on: May 02, 2022, 02:55:24 PM 
Started by Chris Jacobie - Last post by Chris Jacobie
The screw-on -10dB and -20dB pads for AKG 451s and 452s are fetching outrageous prices. The mic is worth about $400-600 and the pads are going for like $150+.

Is there a non-AKG pad that I can screw in there like an Oktava 012 pad or a pad from some other SDC?

Thanks!

Chris

 37 
 on: April 29, 2022, 11:56:31 AM 
Started by NigelT - Last post by klaus
(...) Close visual inspection can reveal residue from cap leakage, but missing residue doesn’t mean the cap is fine.

...and electrolyte leakage from the vent holes in the top of electrolytic capacitors does likewise not indicate damage!
Lift the plus (in the case of NU67 heater rail minus) connections of the cap and use a capacitance tester to determine health.

 38 
 on: April 29, 2022, 07:48:19 AM 
Started by NigelT - Last post by Kai
...two left to go and I will have 10 working beautiful U67's.
...If you don‘t break one by plugging into a faulty PSU.
Use resistive dummy loads for testing, not a valuable mic:
33 Ohms / 2 W (this simulates additional 1.5 Ohms cable resistance) and 240 kOhms.

C1-C3 caps can be basically checked in place by looking at their AC ripple voltage UNDER LOAD and comparing the result to a known 100% working unit (preferably with fresh caps).
Close visual inspection can reveal residue from cap leakage, but missing residue doesn’t mean the cap is fine.

Electronics symbols vary all over the place, remember the 60 years that passed along since.
American symbols are often quite different  from European’s, even denoted for resistors in the schematic!

 39 
 on: April 29, 2022, 06:52:26 AM 
Started by NigelT - Last post by NigelT
Oh, and I am working with a known good mic and tube so I knew the filament was OK. Out of the six dead units, I have repaired three of them with various problems so far and now the fourth one thanks to you. The simple things get me sometimes...two left to go and I will have 10 working beautiful U67's.

 40 
 on: April 29, 2022, 06:50:03 AM 
Started by NigelT - Last post by NigelT
Klaus,
I see you changed your post, I dont take what you say as disrespectful at all but the exact opposite. I will say I work with other electronics, for the most part digital in avionics but where there is also lethal 115vac 400hz. So I am extremely cautious.

I am not very familiar with older stuff though and maybe I wasn't clear. For example, I know what a Zener is, I just never saw the symbol drawn that way. I am still curious about that, is it an older obsolete symbol? I am sure it's obvious to you, but I am way behind in this area.

Regarding caps, I meant that you guys must have seen about everything that can wrong in these units by now and thought maybe you would know signs of bad caps without having to pull them. I am willing to replace them no problem if necessary. I guess I'm asking if it's something I should start with, given the age of these units, they look all original. In my limited experience with my Neve console, I was always told to leave the electrolytics alone until there's a problem. I found that not to be true though.
     
I am trying to learn but nothing beats experience and from your one line explanation about the supply rail I knew where to look and I was able to figure out what was wrong in minutes.

Again, thanks. 
Regards
David

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