hazard is the main one. As noted earlier, the bleeder can be set up to assist with regulation as well
Of any part exposed to permanent DC. Capacitors of course are made of aluminium foil which is not magnetic,but what about other parts?
I'd like your opinion.Is there any scientific base on this?
I'd like your opinion.Is there any scientific base on this?
There are no significant effects I can think of, no.
The only other function of a bleeder resistor I can think of is in regulated power supplies that need a minimum load in order to maintain regulation. But in that case, I wouldn't speak of a bleeder anymore. That leaves just safety, nothing more.
The only other function of a bleeder resistor I can think of is in regulated power supplies that need a minimum load in order to maintain regulation. But in that case, I wouldn't speak of a bleeder anymore. That leaves just safety, nothing more.
The current through a bleeder resistor will normally be small when compared to other currents in a typical amplifier. If it were a problem then it would be a much smaller problem than magnetisation caused by other currents. I don't believe it is a problem.
That's not what I ment. I was thinking that when the amplifier is off and the PSU contains plastic caps, the HT is apparent even months after cutting the power.
And an other issue is that of shortening the lifetime of the caps.
I have seen a document by Philips where the lifetime is declared to be 100.000 hrs at 50% of the nominal voltage (but this refers to 105 C electrolytics). I'm sure that plastic caps can last longer but what about the case with HT of 750 V 24h a day?
And an other issue is that of shortening the lifetime of the caps.
I have seen a document by Philips where the lifetime is declared to be 100.000 hrs at 50% of the nominal voltage (but this refers to 105 C electrolytics). I'm sure that plastic caps can last longer but what about the case with HT of 750 V 24h a day?
But the whole point of a bleeder is to ensure that the caps are discharged. Note that magnetisation comes from current, not voltage. I'm not sure which of us is confused?
No. If the voltage is static and there is no current, there is no magnetic effect...
Kind of a straw man really - just put a bleeder circuit of some sort in.
Ok, thanks for answering. Actually I'd really like to avoid adding bleaders since the amplifiers are too heavy to lift and sending them back to the bench is not easy.
As a generic design point, if you've got a long CRC chain then capacitor voltage ratings can be lowered further down the chain, but only if you put a suitable bleed at the far end of the chain, or if you put a zener at the end (but still need a bleed somewhere for discharge).
I've used zeners at the end of CRC chain to cope with starting the amp without valves - the zener doesn't come in to play otherwise.
One safety standard I have seen has discharge required to achieve <60VDC after 1 minute I think.
Ciao, Tim
I've used zeners at the end of CRC chain to cope with starting the amp without valves - the zener doesn't come in to play otherwise.
One safety standard I have seen has discharge required to achieve <60VDC after 1 minute I think.
Ciao, Tim
Just calculate the current drawn by your bleed resistor, and enter it as a current tap. It will be close enough to evaluate the circuit. A 200k resistor at 200V will draw 1mA. Unless your circuit draws less than 10mA, it won't have much effect, wherever you put it.
BTW I model the supply with current taps for the amp too. It's generally easier, because the current draw for the circuit is easier to calculate than the resistance. Also, you can model stepped loads to look at ringing or overshoot.
Sheldon
BTW I model the supply with current taps for the amp too. It's generally easier, because the current draw for the circuit is easier to calculate than the resistance. Also, you can model stepped loads to look at ringing or overshoot.
Sheldon
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