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    Building, troubleshooting and testing of these amplifiers should only be
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Bleeder resistor not needed for "pi" filter?

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shan_rish

Member
Joined 2006
#1
Hi All,

I came across an article in audio express which states that bleeder resistor is not needed in a "pi" filter in the power supply section. Can anybody shed some light on this, since I am not able to understand what author meant. I always assumed that bleeder resistor is necessary to discharge high voltages in tube rectifier circuits.

The audio express link is: The 2A3 Tube Amplifier - A Tribute to Simplicity and Warm Sound | audioXpress

Thanks and Regards,
Shan
 
#3
> bleeder resistor is not needed in a "pi" filter

"single section “pi” filter or a “capacitor-input filter” with no need for a bleeder resistor."

No need because, as Allen says, the amplifier needs a heavy bleed to work.
 

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#4
shan_rish said:
Hi All,

I came across an article in audio express which states that bleeder resistor is not needed in a "pi" filter in the power supply section. Can anybody shed some light on this, since I am not able to understand what author meant. I always assumed that bleeder resistor is necessary to discharge high voltages in tube rectifier circuits.

The audio express link is: The 2A3 Tube Amplifier - A Tribute to Simplicity and Warm Sound | audioXpress

Thanks and Regards,
Shan
Click to expand...


This design violates the conditions for the GZ34, maximum size of first cap
is 60uF. See https://frank.pocnet.net/sheets/010/g/GZ34.pdf
 
#5
It doesn't need a bleeder resistor because it t is a class A amplifier which is always conducting, not because it has a pi filter, and the article doesn't actually say otherwise. It says this design uses a pi-filter with no need for a bleeder resistor, but it doesn't link the two in a causation chain.
 
#10
Surviving spouses benefit from the lack of a bleeder resistor.
They get an inheritance.

Use a bleeder resistor and stay alive.
Calculate the time for discharge to a safe voltage (or remove the bottom plate very slowly, and check the voltage with a voltmeter before digging in).

Just imagine your amplifier 'dies' and you open it up.
Ahh, it was a dead output tube(s), and so the B+ still has high voltage, because you forgot to use a bleeder resistor.
Ouch!

Safety First!
 
#13
I have attached my amp's schematic and have drawn a redline of a path through which the bleeding might happen, even if the output tubes fail. Does anybody still think this amp's power supply needs a bleeder resistor, still?
 

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#15
I calculated it, 1.3 Meg Ohms to discharge 400uF will take a lot longer than
1 minute per screw on a 6 screw bottom plate.
In fact, the RxC time constant is 520 seconds (8.66 minutes).
In 520 seconds, the Bleeder will discharge B+ from 300V down to 109V.

A dead 6P3P may cause harm to anybody getting inside before 15 minutes of discharge time.

Remember, Safety First.

Repeat after me,
Surviving Spouse Syndrome
 
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