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 1 
 on: January 16, 2019, 07:21:54 am 
Started by Oleh Malyy - Last post by Oleh Malyy
Yes. Of course. Will tell.
A lot of thanks!

 2 
 on: January 16, 2019, 02:02:30 am 
Started by Oleh Malyy - Last post by klaus
Pass these tips on to your friend. They are all useful and methodical.

 3 
 on: January 16, 2019, 12:39:31 am 
Started by Oleh Malyy - Last post by Oleh Malyy
A lot of thanks for all replies, tips.
But as I see, I must to send it to my friend that have more skills/knowledges/instruments,  as I am.

Best regards

 4 
 on: January 15, 2019, 07:59:57 pm 
Started by Oleh Malyy - Last post by klaus
Thanks, Kai, super helpful hints.

The owner needs to troubleshoot filter caps as next step, but I recommend that a trained technician is doing the testing, because of dangerous voltage conditions inside the power supply:

Turn off power supply. with alligator clip wires, parallel the last of the heater filter caps with one of the same value/voltage rating. Turn on the supply. Hum gone? Make the reverse test: now disconnect one of the alligator leads: hum back? It's a bad filter cap.

If there was no change in the hum in the heater circuit, repeat the test for the B+ filter caps.

NEVER CONNECT a capacitor while the supply is switched on! ONLY REMOVE one while it's on.
Not following this will severely shorten tube life.

 5 
 on: January 15, 2019, 03:58:24 pm 
Started by Oleh Malyy - Last post by Kai
DC adjusting does not change AC ripple on the DC power lines.
You need to measure AC, not DC on the power lines.
Maybe something is broken in the PSU, maybe there is a bad construction (I've seen those with other manufacturers).
AC should be way below 0.001V, or it can creep into the audio.

 6 
 on: January 15, 2019, 02:44:29 pm 
Started by Oleh Malyy - Last post by Oleh Malyy
I have instruction from Flea how and where in PSU to adjust hitter (5.92v)
and anode voltages (55.1v at R17 400kOhm resistor - I think 64.9v at anode).
And all is done with this instruction.

 7 
 on: January 15, 2019, 02:34:10 pm 
Started by Oleh Malyy - Last post by Kai
I bet the supply voltages are not ripple-free.
How much AC voltage do you see on the anode and heating voltage?
Is your AC voltmeter sensitive enough to detect that - what is the lowest your meter is capable to measure.
Should be well below 1mV AC.
Measurement needs to be done on the connector, either on the microphone or PSU side, with the microphone connected.
If there is a separate PSU ground line in the cable this needs to be reference for the measurement, not the shield.
Be careful, there are dangerous high voltages.

 8 
 on: January 15, 2019, 12:09:14 pm 
Started by Oleh Malyy - Last post by Oleh Malyy
Thanks for your reply!

>>> What about the room the mic is located- is it dead quiet?
Yes. As possibly.

>>>No flourescent lamp active? They can have accoustic hum.
Tried without any lamps. Hum is.

>>>All connection balanced or shortcut to ground on a signal wire - check with ohm-meter (not likely, but...).
All connections are balanced.

>>> Did you check the DC supply voltages? They need to be perfectly ripple-free too (Oscilloscope or sensitive AC Milli-Voltmeter).
With sensitive Milli-Voltmeter, voltages looks like stable.

>>> What if you switch off the PSU - what happens in the few seconds the mic is still active, what afterwards?
After turning of PSU - hum not present.

 9 
 on: January 15, 2019, 07:52:55 am 
Started by Oleh Malyy - Last post by Kai
100Hz usually means a problem with the power supply, stray field induced hum has components at 50Hz, 150Hz, 250Hz...
These are not present in your file.

Checklist:
What about the room the mic is located- is it dead quiet?
No flourescent lamp active? They can have accoustic hum.
All connection balanced or shortcut to ground on a signal wire - check with ohm-meter (not likely, but...).
Did you check the DC supply voltages? They need to be perfectly ripple-free too (Oscilloscope or sensitive AC Milli-Voltmeter).
What if you switch off the PSU - what happens in the few seconds the mic is still active, what afterwards?
Hum with PSU off still there -> next step unplug the mains connector on the PSU, ... hum?

 10 
 on: January 15, 2019, 01:36:05 am 
Started by Oleh Malyy - Last post by Oleh Malyy
Yes. Thanks.
Has found that at the microphone side in the cable shield and ground was not connected. Conneted these. But without effect - hum still is.
Has checked all cables from microphone to preamp(s). Shield and ground connected at both sides (also has tried without this connetion at one side of cable - without effect too)

>>>> ... from head basket all the way to mic pre-amp input: with headphones on, hold the head basket against the XLR that plugs into your mic pre amp, and  report back whether the ground hum has disappeared. ...

No, hum not disappeared.

I thinking to buy and change transformer to Haufe T14/1.
Now in microphone is this tranformer
https://flic.kr/p/S5UyNW

But I donít think that hum can be connected with transfrmer.

Please tell me more ideas/tips.

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