Help with hum small hum problem...

Guiness · 3rd May 2003, 07:30 PM

So I helped my son build his first tube amp. It is the 807se I was have talked about. The layout is not as clean as it could be but it is not that bad either. I checked all the solder joints and wiring. The amp sounds really really good and the hum is not even audible unless I put my ear right by the speaker cone. But I don't like it. The tubes are AC heated by twisted wire, center tap is grounded. Nothing special. The only other thing to consider is I let him use a 5H choke in the power supply, should we have used a higher H value?

Thanks

Bas Horneman · 3rd May 2003, 11:01 PM

Hi Guiness,

Do you have a schematic of the PSU?

How much current is drawn from the PSU?

Cheers,
Bas

Guiness · 4th May 2003, 12:48 AM

Well the amp consists of (2) 807 and (2) 6SJ7WGT. The 807's are running at 350V's and the 6SJ7's are around 300V. Current i around 120mA for both channels. The 807's each draw 50mA. I will draw up a power supply schematic right now. I will post it when done. One further note. I made him rewire the filaments will shielded wire and the hum is still there. It does not effect the sound, but I just do like it there,

Guiness · 4th May 2003, 01:00 AM

power supply we am currently using...

Guiness · 4th May 2003, 07:48 PM

What do you guyz use? Also how important is it to ground the power transformer to the chassis? I have done this and not in the past and never noticed a difference.
thanks again

fragman56 · 4th May 2003, 08:47 PM

Maybe it's picking up hum from other sources? Have you tried moving the power cords and amp around? I have eliminated hum just by changing power outlets.

$0.02 worth,
Rick

Bas Horneman · 4th May 2003, 08:52 PM

Hi Guiness,

I ran your psu past Duncan amps psu designer and got this result.

Quite a lot of ripple...i.e. hummmm

I would suggest toying around with this program..until you get around 10mV or so?

Bas Horneman · 4th May 2003, 08:54 PM

This is what I fed psu designer

fragman56 · 4th May 2003, 09:08 PM

I did not run it but it looks right. I agree, too much ripple--go for 10mv or less. Maybe tack on another rc filter.

EC8010 · 4th May 2003, 11:54 PM

Yes, for a single-ended triode amplifier, 1V HT ripple is too much. (I'm assuming the 807 is triode-strapped?). As Fragman 56 suggests, 10mV is a reasonable target (without spikes).

3rd May 2003, 07:30 PM	#1
Guiness diyAudio Member Join Date: Dec 2002 Location: USA	Help with hum small hum problem... So I helped my son build his first tube amp. It is the 807se I was have talked about. The layout is not as clean as it could be but it is not that bad either. I checked all the solder joints and wiring. The amp sounds really really good and the hum is not even audible unless I put my ear right by the speaker cone. But I don't like it. The tubes are AC heated by twisted wire, center tap is grounded. Nothing special. The only other thing to consider is I let him use a 5H choke in the power supply, should we have used a higher H value? Thanks __________________ Guiness

4th May 2003, 12:48 AM	#3
Guiness diyAudio Member Join Date: Dec 2002 Location: USA	let me see... Well the amp consists of (2) 807 and (2) 6SJ7WGT. The 807's are running at 350V's and the 6SJ7's are around 300V. Current i around 120mA for both channels. The 807's each draw 50mA. I will draw up a power supply schematic right now. I will post it when done. One further note. I made him rewire the filaments will shielded wire and the hum is still there. It does not effect the sound, but I just do like it there, __________________ Guiness

4th May 2003, 07:48 PM	#5
Guiness diyAudio Member Join Date: Dec 2002 Location: USA	it has got to be his grounding... What do you guyz use? Also how important is it to ground the power transformer to the chassis? I have done this and not in the past and never noticed a difference. thanks again __________________ Guiness

4th May 2003, 08:47 PM	#6
fragman56 diyAudio Member Join Date: Jun 2002 Location: Denver, CO	How small? Maybe it's picking up hum from other sources? Have you tried moving the power cords and amp around? I have eliminated hum just by changing power outlets. $0.02 worth, Rick

4th May 2003, 09:08 PM	#9
fragman56 diyAudio Member Join Date: Jun 2002 Location: Denver, CO	Nice going, Bas! I did not run it but it looks right. I agree, too much ripple--go for 10mv or less. Maybe tack on another rc filter.

3rd May 2003, 11:01 PM	#2
Bas Horneman diyAudio Moderator Emeritus Join Date: Apr 2002 Location: The Netherlands Blog Entries: 18	Hi Guiness, Do you have a schematic of the PSU? How much current is drawn from the PSU? Cheers, Bas

4th May 2003, 11:54 PM	#10
EC8010 diyAudio Moderator Join Date: Jan 2003 Location: Near London. UK	Yes, for a single-ended triode amplifier, 1V HT ripple is too much. (I'm assuming the 807 is triode-strapped?). As Fragman 56 suggests, 10mV is a reasonable target (without spikes). __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

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