SSE hum localization, how to improve RC Filter? - diyAudio
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Old 9th February 2014, 04:56 PM   #1
oxothuk is offline oxothuk  United Arab Emirates
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Default SSE hum localization, how to improve RC Filter?

want to start separate tread for SSE hum troublshooting, some details already shared in my previous post

In brief
My setup SSE with SOVTEK 6L6, 5AR4, EH 12AT6, Hammond 374BX, Trascendar 119OT, wired for UL with CFB. AUX 150uf CAP, No choke.

After warming up i can hear hum (not much but can hear from 1-2m distance), which is does not depend on inputs level are same regardless of volume settings.

If power off - hum disappear and can hear clear sound (until capacitors discharged). I've tried to play with powered aplifier
a) Disconnect filament for a short time (green wire) from PCB while AMP is working - NO Difference, can hear HUM
b) Disconnect central tap (red/yellow wire) for the short time - HUM Disappear

from this point i think that HUM comes from Anode (B+) Supply.

Next

c) adding second 150 oHm resistor in series with existing , HUM Level significantly reduced (probably power also reduced but not much)
d) replace resistor with 12H 100ma choke i have (can not use due to current limits) - HUM DISAPPEAR COMPLETELY
e) Install 150OHM resistor back and reduce filament voltage by placing 2 diodes in series with filament - No change for HUM
Click the image to open in full size.

Looks like i need to improve RC Filter, C1 and C2 capacitors i have is 33uf only R1 is 150 ohm, but also 150uf AUX Cap connected in parallel with C2 (all from Ebay), any suggestions?

I know that choke is the best but takes time to order, also will be very appreciated with someone can suggest compact chokes can be used for SSE
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Old 9th February 2014, 05:17 PM   #2
PDL is offline PDL  United States
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Use a choke, it will get rid of your hum.
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Old 9th February 2014, 07:21 PM   #3
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100mA choke should be ok you're probably not using that much more than the rating and most chokes can handle more current than what they are rated for. What brand choke do you have? You could probably get by with your 100mA choke until you get a bigger one. Have you calculated your output tube dissipation?

Cheers,
Bob
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Old 9th February 2014, 07:42 PM   #4
oxothuk is offline oxothuk  United Arab Emirates
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it is Hammond 193B

Voltage drop on 150 oHm is 25.3V means actual current approx 175ma (and choke dc resistance is 155ohm).
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Old 9th February 2014, 08:17 PM   #5
PDL is offline PDL  United States
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193H worked for me.
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Old 10th February 2014, 08:19 PM   #6
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Try using the choke in parallel with the resistor, it may work, it may not. You might need a larger value resistor. If the choke you have works you can probably use it until you can get something better. It will dissipate about 5 watts so it will get warm.

I have been using the cheap Triad chokes. They are ugly so I put end bells from an old power transformer on them, or hide them under the deck. You have 50 Hz power which is quite a bit harder to filter than our 60 Hz, but these work for me.

Triad Magnetics - C-14X - Passive Components - Inductors - Allied Electronics
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Too much power is almost enough! Turn it up till it explodes - then back up just a little.
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Old 24th February 2014, 04:41 PM   #7
oxothuk is offline oxothuk  United Arab Emirates
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Quote:
Originally Posted by tubelab.com View Post
Try using the choke in parallel with the resistor, it may work, it may not.
Thanks George, tried but no sense, will order choke soon.
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