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GZ34/ 5ar4 minimum 1st capacitor for datasheet output voltage.

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Posted on January 19, 2023 at 08:39:24
Iczerman
Audiophile

Posts: 147
Joined: July 23, 2000
 Datasheet say 40 uf for capacitor input for 2x 400 transformer to output 430 volts.
Anyone know minimum value for the same voltage output?
I would like to go down to 10uf.

 

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You should play with DuncanAmps PSUII, posted on January 19, 2023 at 09:06:36
Chip647
Audiophile

Posts: 2649
Location: The South
Joined: December 24, 2012
 It can show you the voltage drop at various cap input values. 10uf should not have much of a voltage reduction compared to 40uf

 

RE: GZ34/ 5ar4 minimum 1st capacitor for datasheet output voltage., posted on January 19, 2023 at 17:13:04
Alpha Al
Industry Professional

Posts: 2958
Location: N. Carolina
Joined: February 16, 2004
Contributor
  Since: December 3, 2015
 I dont think there s a minimum value. I have seen them used in Choke input circuits with no input cap.

But if you exceed the maximum value, you can expect shorts and arc-overs.

 

RE: GZ34/ 5ar4 minimum 1st capacitor for datasheet output voltage., posted on January 20, 2023 at 05:52:43
sony6060
Audiophile

Posts: 1465
Location: USA
Joined: August 8, 2014
 10uF for what reason? I design high voltage power supplies for PP amps with no more than 5% AC ripple and SET amps at 2% AC ripple at full power output.

 

RE: GZ34/ 5ar4 minimum 1st capacitor for datasheet output voltage., posted on January 20, 2023 at 08:45:04
Tre'
Industry Professional

Posts: 17294
Location: So. Cal.
Joined: February 9, 2002
 PSUD II will show the peak repetitive current. As long as the input cap is not so big as to cause the peak repetitive current to exceed the rectifier tube's ratings then what is the point of making the input cap small?

Here's the rating for a 5ar4,




Here's what happens when there is only 31 ohms per plate of series resistance and you're using a 40uf input cap and you draw 200ma through the rectifier tube. The peak repetitive current rating is exceeded.





Here's what happens if you use a 10uf input cap with only 31 ohms per plate series resistance drawing 200ma through the tube.





and if you just increase the per plate series resistance to 110ohms you can use 40uf while drawing 200ma without exceeding the peak repetitive current rating of the rectifier tube.




The moral of the story is, know the peak repetitive current rating of the rectifier tube you are using, know the per plate series resistance and current draw of your circuit and then calculate to make sure you're not burning down your amplifier needlessly!

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

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