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In Reply to: RE: 5R4G and 5U4G condenser output value posted by DAK on January 21, 2017 at 11:55:04
It's not hard to swap in a 4mf capacitor. At that size you could use a nice film cap. Or do an LC filter with a 10 henrie choke.
Either way I wouldn't push it with what you have in there. You might also think about a thermister on the line side of the power transformer to slow warm up.
Follow Ups:
As other have noted, it's peak repetitive current that's the actual limit. Cathode can only support so much current, and can be damaged it it's exceeded. As with most tube specs, you can usually get away with exceeding one limit if the others are well under limits. At maximum rated voltage, maximum rated DC current, minimum transformer winding resistance, your input cap should not exceed 4 uF.
"You might also think about a thermister on the line side of the power transformer to slow warm up."
The stated limit for the input cap value has nothing to do with turn on surge.
It has everything to do with peak repetitive charging current.
This is a "surge" that happen at twice the line frequency for as long as the unit is powered up.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
as the value of their first cap. For example, Heathkit did not bother with that cap limit and used a pair of 40uf x 400v (if memory serves) in series.
That net 20 μF. is in line with what some 5R4 data sheets show. Your 12 μF. should be just fine at the voltages found in most tubed audio circuitry.
You can make quite certain of safety by installing a CL-130 inrush current limiting thermistor between the rectifier and the PSU filter.
Eli D.
"You can make quite certain of safety by installing a CL-130 inrush current limiting thermistor between the rectifier and the PSU filter."
The max input cap value stated in the datasheets has to do with peak repetitive charging current rating.
The turn on surge current rating is much larger.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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