DESPERATION! No heater voltage on Stellar/Alctron tube mic power supply

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Here you can hear and see the differences between the two power supplies.
(ca. 40-50dB preamp gain + 40dB boost in DAW - don't mind my wall clock in the background)

TBONE PSU NOISE:
bildschirmfoto-2020-02-04-um-12-08-17.png


AUDIO (online player - link corrected)
https://voca.ro/jcyyuAPg8Id

ALCTRON PSU NOISE:
bildschirmfoto-2020-02-04-um-12-08-33.png


AUDIO (online player - link corrected)
https://voca.ro/jBvB2AHnlkb
 
I found two old original PCBs from power supply of stock Alctron HT-11A (https://groupdiy.com/index.php?topic=51377.0) during a cleaning some bins today.
R15 is 2 Ohms in original design, not 20 ohms which is obvious error in a schematics floating around. Just for reference.
 

Attachments

  • hst-11b.jpg
    hst-11b.jpg
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Pleeeeease, I still need your help!!!

I still have hum inspite of:

- removed the LM317 circuit, replaced  with a 7805+diode
- replaced most capacitors on the B+ side with real Nichicon ones (left only 2 original caps).
- tightly twisted the tranny secondaries
- made sure all DC components are as far as possible from the high voltage AC lines and the tranny
- reflowed the remaining solder joints, cleaned the pub

it all works but I still get hum!!!!

>> turning PS off: hum instantly disappears
>> switching just the 6.5v heater off: hum remains

It drives me nuts, I mean it's a power supply. How can these things give u so much of a headache????
Please please help me with this, I really want to find and fix the problem.

Thank you so much!!!
 
I don't suppose the power supply has a ground-lift switch for the XLR output, does it?

I'm thinking there's a possibility of a ground-loop occurring between the mic supply and your preamp / mixer / interface.
 
Thanks Thron! Actually I had the same idea yesterday as I went to bed. I'm soldering a "ground-lift" cable now, see if that helps. Will keep you posted!

THANKS SO MUCH SO FAR!!!!
 
Unfortunately it doesn't make any difference with the ground lift.  :( . Does it help knowing that the hum is not there when I power it off? (instantly cuts off)

Any hints where I could be looking for the culprit?
 
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