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Ryssen 19th January 2004 08:03 PM

Overvolting e-lyts
 
I have an e-lyt in my tube headphone amp that is rated for 400VDC the voltage on it is now 407-415Volt, is this safe or not?

analog_sa 19th January 2004 08:27 PM

It's not safe anywhere, least of all in a headphone amp. You should use elcos at least at 20% below rated voltage.

316a 19th January 2004 08:31 PM

Re: Overvolting e-lyts
 
Quote:

Originally posted by ryssen
I have an e-lyt in my tube headphone amp that is rated for 400VDC the voltage on it is now 407-415Volt, is this safe or not?
It may help if you can post a schematic . What is the correct HT voltage ? Does the cap have a bleeder resistor across it ? Is the 400V reading off load or with the headphone amp circuitry attached ? Really electrolytics should be conservatively rated to allow for fluctuations in mains voltage

316a

Ryssen 19th January 2004 08:39 PM

Quote:

What is the correct HT voltage ? Does the cap have a bleeder resistor across it ? Is the 400V reading off load
I am trying another trafo,thats why the HT voltage is too high,
It has no bleeder resistor,what´s it for?400V reading is on load.

316a 19th January 2004 09:12 PM

New Trafo
 
Quote:

Originally posted by ryssen

I am trying another trafo,thats why the HT voltage is too high,
It has no bleeder resistor,what´s it for?400V reading is on load.

Hello ,
Ok , I see , it is a new build . Why don't you try using psud2 to model your power supply before implementing it ?

psud2

316a

Morse 19th January 2004 09:17 PM

Hi Ryssen;

>>>...400VDC the voltage on it is now 407-415Volt, is this safe or not?...<<<

>>>... am trying another trafo,thats why the HT voltage is too high, It has no bleeder resistor,what´s it for?400V reading is on load...<<<<

:bawling: Aaaaargh!!! :bawling:

Ahem, sorry Ryssen, but it was VERY frustrating reading that.

Please take no offence, but there are some things you MUST fix if you want to be safe!!

1. Bleeder resistors are there to SAFELY discharge capacitors. A cap charged to over 400V will give a NASTY shock if it's discharged THROUGH YOU.

2. NEVER run caps over their rated voltage. Frankly, 20-30% margin of safety is required for reliable, SAFE operation. Remember, that when the amp is first turned on and the valves are not conducting, the B+ voltage will climb well over what it is during normal operation. I've built amps that when loaded run 100 or more volts below this "unloaded voltage". BTW, that 20-30% safety margin should be OVER THE PEAK VOLTAGE EVER ENCOUNTERED ON THE UNLOADED AMP. That way you can expect many years of SAFE and RELIABLE operation.

Please be safe. Either lower the voltage on those caps or put in higher rated caps. And PLEASE put in a bleeder resistor AFTER you have SAFELY discharged your PS caps.

Good luck and all the best,
Morse

Ryssen 19th January 2004 09:31 PM

Quote:

Bleeder resistors are there to SAFELY discharge capacitors. A cap charged to over 400V will give a NASTY shock if it's discharged THROUGH YOU.
Ok,TROUGH MEEE!! What Wattage Ohm´s should they be?

dhaen 19th January 2004 09:41 PM

I normally use 220K 2W bleeders. Beware of the maximum voltage rating of resistors. It is often better to use 2 in series.

fdegrove 19th January 2004 10:42 PM

Hi,

Quote:

I normally use 220K 2W bleeders.
Bleeder resistors also prevent overvoltage on the caps and should be calculated accordingly.

They also provide for a discharge path when the gear is turned off.

IOW, if you don't use them you risk overvoltage on the caps at switch on and you risk an electrical shock (possibly lethal) when working on your gear before the caps had the time to discharge through the bleeder.

Thirdly and not unimportant, they can force a constant current draw from the PS.

There's a formula to keep things safe but I'll let you all google for it...I won't.

Cheers, ;)


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