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Old 3rd May 2003, 06:30 PM   #1
Guiness is offline Guiness  United States
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Angry 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?

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Old 3rd May 2003, 10:01 PM   #2
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Hi Guiness,

Do you have a schematic of the PSU?

How much current is drawn from the PSU?

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Old 3rd May 2003, 11:48 PM   #3
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Default 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,
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Old 4th May 2003, 12:00 AM   #4
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Default done...

power supply we am currently using...
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File Type: jpg power-supply.jpg (28.9 KB, 244 views)
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Old 4th May 2003, 06:48 PM   #5
Guiness is offline Guiness  United States
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Default 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
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Old 4th May 2003, 07:47 PM   #6
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Default 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
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Old 4th May 2003, 07:52 PM   #7
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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?
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Old 4th May 2003, 07:54 PM   #8
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This is what I fed psu designer
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Old 4th May 2003, 08:08 PM   #9
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Default 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.
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Old 4th May 2003, 10:54 PM   #10
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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).
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