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DHT SE amp with ultrapath

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I did build 2E22 SE amp with AC filament (because I like AC for filament:) ). Sound is so sweet and warm. Hum is > 13mVac, so I can hear them at my chair.

I intend to take an ultrapath with a Capacitor between power tube's cathode to B+ in oder to get lower hum AC and lower gain. There are some ultrapath schemas on the internet, but the tube is auto bias. Mine is fixed bias :D .

So :

- How can I calculate the value of this capacitor ?
- 2 these capacitors will be connected to the same point, B+. Is it OK ?

Thanks and regards,

QA.
 

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AC for tubes is normal to indirectly heating cathodes.Direct heated cathodes needs DC to get rid of all the hum.On a PP the hum is commonmode and is cancelled in the OPT,but I suspect that even then you have to adjust the balance regularly.
Conclusion,use DC,
Mona
 
Hi,
Have you tried winding a filament transformer with bifilar wound
3.15V windings, connect them in series and use them to power the
filament? Sensing resistor is soldered to the junction of the two windings.
I once did this with my 3C24 and there was no audible hum a foot
from my 12" fullranger.
As always, YMMV.
Reza
 
Hi,
Have you tried winding a filament transformer with bifilar wound
3.15V windings, connect them in series and use them to power the
filament? Sensing resistor is soldered to the junction of the two windings.
I once did this with my 3C24 and there was no audible hum a foot
from my 12" fullranger.
As always, YMMV.
Reza

I use separate toroided transformer for 2E22 filament, so hum get a bit low. I will try CT transformer.

There are some ways of hum cancelation for DHT. I never try this way : http://www.dmitrynizh.com/dht-filament-hum-cancel.htm
 
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