dc or not dc

duderduderini · 17th July 2007, 04:00 AM

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

ak_47_boy · 17th July 2007, 06:45 PM

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.

kstagger · 17th July 2007, 07:20 PM

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.

duderduderini · 17th July 2007, 10:21 PM

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

17th July 2007, 04:00 AM	#1
duderduderini diyAudio Member Join Date: Mar 2004 Location: Albury NSW Australia	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 __________________ "Better to say nothing and keep them guessing than to speak and remove all doubt."

17th July 2007, 10:21 PM	#4
duderduderini diyAudio Member Join Date: Mar 2004 Location: Albury NSW Australia	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 __________________ "Better to say nothing and keep them guessing than to speak and remove all doubt."

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read

17th July 2007, 06:45 PM	#2
ak_47_boy diyAudio Member Join Date: Sep 2006	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.

17th July 2007, 07:20 PM	#3
kstagger diyAudio Member Join Date: Dec 2003 Location: Grand Rapids	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.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)