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375 Joules PS for my monoblock tube amps
375 Joules PS for my monoblock tube amps
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Old 30th August 2019, 08:25 PM   #1
hifiamps is offline hifiamps  United States
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Default 375 Joules PS for my monoblock tube amps

My working monoblock tube amps for the last 10 years have a 500V 3000mF power supply. No RC filter in the supply. LM317 voltage regulated driver stage and screens on the 4 output tubes/channel. The voltage and PS ripple is well within the specs of the filter caps, yet I am concerned about failure with 375 joules. Should I be? Any experience?

Last edited by hifiamps; 30th August 2019 at 08:53 PM.
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Old 30th August 2019, 08:51 PM   #2
amplidude is online now amplidude  Denmark
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Old 30th August 2019, 08:56 PM   #3
rayma is offline rayma  United States
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Check the capacitor's ripple voltage periodically. If it increases significantly,
think about replacement.
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Old 30th August 2019, 09:13 PM   #4
hifiamps is offline hifiamps  United States
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Quote:
Originally Posted by rayma View Post
Check the capacitor's ripple voltage periodically.
Excellent advice.
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Old 30th August 2019, 11:16 PM   #5
GoatGuy is online now GoatGuy  United States
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And… be very very very careful when checking the ripple. Shorting the 3000 F at 450-to–500 volts delivers
E = CV
E = 0.5 300010⁻⁶ F • (450 to 500)
E = 300 to 375 J
That'll definitely wake you up and make you go crazy. Instantly. I know, I've accidentally done it.

Blew apart the tip of a multimeter tester. I wasn't even using 450 to 500 volts. Only about 170 V on a 2,200 F big tin can capacitor. I “slipped”, shorting the contacts. Entirely vaporized the errant meter probe. Nothing left. Same for most of the screw-terminal. Poor capacitor. Couldn't hear a thing for at least a minute.

The one 'nice' thing about the higher-voltage electrolytic capacitors is that during their useful life, before they start drying out, the dielectric actually becomes 'stronger'. The high voltage induces further electrolytic deposition of oxide goodness at a very slow rate. Once they dry out though… just the opposite. The film goes to pop, fast.

Just saying,
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Old 30th August 2019, 11:23 PM   #6
rayma is offline rayma  United States
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It's best to power down the amp, allow the supply to discharge,
connect the test leads (rated for 1kV or more), and then power back up
for measurement. Then power down and discharge to remove the test leads.

Last edited by rayma; 30th August 2019 at 11:39 PM.
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Old 30th August 2019, 11:30 PM   #7
hifiamps is offline hifiamps  United States
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Same thing happened to my friend. He said it was like a pistol shot. Vaporized the contacted part of the probe.

Again, outstanding advice. Thank you.
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Old 30th August 2019, 11:45 PM   #8
6A3sUMMER is offline 6A3sUMMER  United States
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1. Safety First!
Do calculate and wire in a proper Bleeder Resistor(s).
Be sure to calculate how many minutes it takes to discharge to a safe voltage.

Suppose the filaments or filament supply dies at turn on. But the B+ is alive.
When you turn the amp off, there is nothing other than [You] to discharge all those Joules.

Most of us on this forum know all this. I am only preaching to those who are not using a Bleeder, or do not know to use a Bleeder.

2. Just to bring us all up-to-speed, the commonly used terms for capacitance changed decades ago.
I think you meant 3000uF.
3000mF is sometimes interpreted as 3000 milli Farad. That would be 3 Farad.

3 Farad is getting to within a few decades of a linear accelerator's supply.

Last edited by 6A3sUMMER; 30th August 2019 at 11:51 PM.
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Old 30th August 2019, 11:59 PM   #9
hifiamps is offline hifiamps  United States
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Yes, 3000 micro farads. I'm using caps in series with parallel resistor voltage dividers and the Maida type LM317 HV regulator, and both bleed off the charge.
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Old 31st August 2019, 12:16 AM   #10
TonyTecson is offline TonyTecson  Philippines
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375 Joules PS for my monoblock tube amps
hey, i have a bunch of these 3000ufd/450 volt dc caps and will put them to use in the near future....
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