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Why do you need DC heating ?

Hi ,
If your pre hums then it could be a number of things apart from the heaters .

1. Pre providing too much gain
2. Heaters not floated
3. Poor heater to cathode insulation on the 6SN7
4. Hum loops within wiring
5. Hum loop between pre and power amp
6. Valve microphony caused by mechanical transformer buzz
7. Insufficient value of grid stopper resistor

I have never had problems killing hum with AC heaters . Check the above first before messing around with batteries or implement a DC supply , it's much easier . If you do go with batteries , you will probably need a battery per valve , also remember that a valve that draws 0.6amp will soon drain a battery down , really you need a 8A/h+ battery to keep your 6SN7 heaters running within spec for any period of time . Something like a motorcycle battery per valve should work ok

cheers


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