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Old 31st March 2003, 05:11 AM   #1
JDeV is offline JDeV  South Africa
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Default How much ripple??

How much ripple is exceptable on a GOOD powersupply?
I am bussy to repair 2 x Mullard 5-20's, which was totally modified (for the worse). On the existing powersupply a 2H inductor and 2 x 30uF caps are used. (PI filter) I replaced the caps with 220Uf ones and now get a relative smooth DC output with a 50mVpp ripple - under load.

1) Is it possible to improve this more while still using the 2H choke?
2) Just for a matter of interest, how much ripple to you have on your PSU?
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Old 31st March 2003, 05:50 AM   #2
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Depends on topology. Triodes will be very sensitive to hum due to their low Rp, whereas pentodes will be rather insensitive for their high Rp (though screen still has to be well filtered).
PP operation cancels common-mode effects such as hum, so far more ripple can be tolerated, triode or pentode.

You could even analyze this based on a desired amount of hum on the output. Say 10mW hum on the output, if the primary is 2.5kohms that's 5V across the OPT primary. If the tube is a 6L6 in pentode, about 25kohm Rp, 10 times the Rl. So approxametly 50V ripple could be tolerated, theoretically. Of course, since this is a whopping 20% of the supply voltage, IMD should be pretty bad. And much more filtering is easy anyway.

If it were a triode, only maybe 6V of ripple would be tolerable given the 10mW spec above. Of course, a perfectly balanced PP amp would tolerate 100% (i.e. no filtering) hum, but we're not in a perfect world.. especially not when there's a signal applied.

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Old 31st March 2003, 06:52 AM   #3
SHiFTY is offline SHiFTY  New Zealand
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220uF

Thats a big load for a tube rectifier...
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Old 31st March 2003, 07:38 AM   #4
EC8010 is offline EC8010  United Kingdom
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Default <1V

For a push-pull amplifier like yours, anything less than 1V peak to peak ripple at the output transformer centre tap is fine since it will be rejected by push-pull action. Single-ended amplifiers need far less ripple because they have virtually no rejection.

The maximum allowable capacitance for a GZ34 is 60uF. All other valve rectifiers are even more fragile.
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Old 31st March 2003, 08:47 AM   #5
JDeV is offline JDeV  South Africa
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Default Re: &lt;1V

Quote:
Originally posted by EC8010
The maximum allowable capacitance for a GZ34 is 60uF. All other valve rectifiers are even more fragile.
Should have said, my amps get DC from silicone rectifiers, not org. GZ34 - part of some of the weird previous modifications, but at least gives me more volts now.
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Old 31st March 2003, 09:23 AM   #6
EC8010 is offline EC8010  United Kingdom
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Quote:
Originally posted by JDeV
silicone rectifiers,
Silicone: soft, squidgy polymer used for breast implants.
Silicon: hard, brittle, metallic element used for semiconductors.
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Old 31st March 2003, 09:27 AM   #7
dhaen is offline dhaen  Europe
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Quote:
Originally posted by EC8010


Silicone: soft, squidgy polymer used for breast implants.
Silicon: hard, brittle, metallic element used for semiconductors.
But the former describes the supply rail regulation best ..soft..squidgy..
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Old 31st March 2003, 09:30 AM   #8
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Hi,

Quote:
Silicon: hard, brittle, metallic element used for semiconductors.
But the latter describes the sound of diodes perfectly well ...hard, brittle...
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Old 31st March 2003, 09:47 AM   #9
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Quote:
Originally posted by dhaen


But the former describes the supply rail regulation best ..soft..squidgy..
Not in class A PP.

Silicon rectifier = hashy, grey sound.
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Old 31st March 2003, 10:05 AM   #10
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Default Re: &lt;1V

Quote:
Originally posted by EC8010
For a push-pull amplifier like yours, anything less than 1V peak to peak ripple at the output transformer centre tap is fine since it will be rejected by push-pull action.
Perhaps my CLCLC - LCRCRC power supply is a bit of overkill for a class A PP? (the last section suited what I had on hand to get the right voltage for the driver)
<5mVp-p ripple at the OPT c/t, and not visible on my scope at the driver.
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