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Old 17th July 2007, 04:00 AM   #1
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Join Date: Mar 2004
Location: Albury NSW Australia
Default dc or not dc

Hi
About to start building my 300b power amp with seperate power supplys. I know the low voltage transformers i have had wound will give me more than 5 volts and 6.3v respectively( for 6sn7 in srpp feeding 6ca7 which then drives the 300b). In albury v out of power point is 253v AC whereas they have beeen wound for 240V. I plan on using resisors to trim the voltage to the desired voltage for the heaters.. then i read the thread re incorporating a 15mH choke (for speaker building as an example) into a dc supply.. problem is i am short on space in psu.
My question is.
Are dc heaters absolutely essential for my amp ( i have hum pots at the ready for the 300b side of things- but what of the 6sn7/6ca7 side of things?)
If dc for the heaters is not essential for low hum/ripple then what is the next best thing?
I could just do rc fliters i know but if the lc versions are markedly better then i will have to bite the bullet and go with the inductors.
Thanks for any advice/help
Nick
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Old 17th July 2007, 06:45 PM   #2
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You can use AC but their will be a small amount of hum. You can try to get rid of it with a hum bucking coil, etc.

Or you can run the filaments on hf ac.
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Old 17th July 2007, 07:20 PM   #3
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when I made a 300B amp a few years ago, I used AC on the filaments with a hum pot on the 300B filament. I still got a small amount of residual hum with my 96dB speakers even with an offboard regulated B+ supply and DC for the input tube filaments.

If I was going to build it again, I would try DC using a common mode choke or try DC current regulation.
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Old 17th July 2007, 10:21 PM   #4
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Location: Albury NSW Australia
Default Could you provide specifices?

Thanks to AK47 and KStagger
Given my level of experience, i was wondering wether you could supply a diagram if possible. Where can i get the choke you speak of stagger?
I live in australia and we do have rs components here or i will order from mouser if needed.
Thanks again
Nick
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