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Old 9th March 2009, 09:33 PM   #1
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Default 5U4GB PS question

I have an Aikido(sounds wonderful) that uses a tube HV supply. The PS is one of the overbuilt variety. I'm am currently running the heater supply for the 5U4GB on 5vac. The rest of the signal tubes heaters are DC. Does it matter on the 5U4Gb if it is AC or DC? I have a little residual hum when i put my ear right against the speaker. High level souces it's not audible. When I play phono it"s more audible because the volume is turned up. Increasing noise with volume turned up is a clue I'm sure. So has anyone seen a difference with AC DC on PS supply? PS is RCRC and has overkill capacitance. Duncan PS modeling
shows absolutely no ripple at 40mA draw but don't know that heater AC or DC is taken into account. Existing levels of hum are very good but I'm looking for absolute quite! Is that possible with Aikido??

Russ
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Old 9th March 2009, 09:48 PM   #2
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Default Re: 5U4GB PS question

Quote:
Originally posted by Freecrowder
I have an Aikido(sounds wonderful) that uses a tube HV supply. The PS is one of the overbuilt variety. I'm am currently running the heater supply for the 5U4GB on 5vac. The rest of the signal tubes heaters are DC. Does it matter on the 5U4Gb if it is AC or DC?
No. The only problem you might have is if the 5.0Vac winding is on the same core as the HV winding and the 5.0Vac winding is not center tapped. If this is the case, there is always the possibility that current pulses are inductively coupling into the HV supply.

If you want to quiet that PS, your best bet would be to supply the 5U4GB heater from a separate xfmr. DC heating won't help since the 5U4GB produces current pulses as it switches into conduction to charge up the resevoir capacitor. That's much worse than whatever AC couples from the heater to the plates via stray capacitance.

Quote:
Existing levels of hum are very good but I'm looking for absolute quite! Is that possible with Aikido??
Yeah, buy a bunch of car batteries, wire them in series, and use that for your DC and heater supplies. If you want even more quiet, invest in a liquid helium bath.
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Old 9th March 2009, 09:58 PM   #3
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Quote:
When I play phono it"s more audible because the volume is turned up. Increasing noise with volume turned up is a clue I'm sure.
This is a CLUE, the hum is being amplified which indicates that it could be getting into the signal path closer to the inputs. Make sure the PS is shielded well and all the signal wires are shielded to ground also.

In addition be sure the DC for the filaments is well filtered and regulated. I have had DC w/ripple sound worse than AC filaments.
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Old 9th March 2009, 10:02 PM   #4
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It may also be coupling from proximity. Try twisting all wire pairs and re-routing signal away from PS away from AC and if you must cross them - try to make right angle crossings. You could also look at your AC vs signal grounding.
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