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Old 30th October 2006, 03:57 PM   #1
sgerus is offline sgerus  United States
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Default What is a reasonable amount ripple voltage for a 300B?

Iím working on a 6sl7 - 300B stereo amp and need some advice on the best way to configure the power supply.

I plan on running the 300Bís at 365 B+ (300V -61V 60mA) and the 6sl7 in SRPP at about 365V.
For the psu I have two 7H chokes and four 30uF oil capacitors to work with.

Whatís the best option for the psu

1. LCLC config (7H,60uf,7H,60uf) with one B+ for all

2. LCLC plus left and right RC config (7H,30uf,7H,30uf) for B+ and then (R,30uf) for Right B++ and (R,30uf) for the left B++

I understand that with config 2 I will have more flexibility and way less ripple for the 6sl7ís, but the cost is 2 times more ripple at the B+

How much ripple is allowable on the 300Bís running at 360V?
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Old 30th October 2006, 06:26 PM   #2
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With those components, I'd use L then 30 uF, L then 60 uF, and RC for the first stage. Crosstalk will be much less if they are isolated from the output stage. Assuming that the output transformer is 30:1, you'll need to be below 30 mV (RMS - about 100 mV p-p) of ripple to be below 1 mV at the speaker.
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Old 30th October 2006, 06:46 PM   #3
sgerus is offline sgerus  United States
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Tom,

Just so I understand: I use 3*30uf for the LCLC stage for my B+

and add a RC stage (with the 4th cap) for the B++ (both Left and Right) ?

I can fit in 2 more 30uf if needed...
That way I would have a total of 120uf in the LCLC stage and still have
left and right B++

-Scott
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Old 30th October 2006, 09:44 PM   #4
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Yes - the first stage needs better filtering, because hum here will be amplified by the output stage. So it needs to be about 10X better.

7H:30 uF:7H:60 uF shows about 30 mV p-p ripple in PSU designer - should be good enough for the power stage.
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