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Best position for bleeder resistor?
Best position for bleeder resistor?
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Old 15th February 2011, 08:48 PM   #1
phrarod is offline phrarod  United States
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Default Best position for bleeder resistor?

I'm finishing up the power supply and I need to put in a bleeder resistor. Someone told me to go with 200K and I wondered if I just put it at the last cap to ground? Also from what I've read in other posts that seems very high value. If someone could confirm to correct it I would appreciate it.

Since this is an unregulated supply would that bleeder resistor factor in in any way as to the final resistance which sets the voltage? The resistor in the end of the power supply duplicates the tube/OT resistance.
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Last edited by phrarod; 15th February 2011 at 08:53 PM.
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Old 15th February 2011, 09:00 PM   #2
stenak is offline stenak  Norway
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Default Bleeder

Put the bleeder resistance on the first cap. 200k is probably ok, 2-3W?.

U
- = the current running through the bleeder resistance.
R
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Old 15th February 2011, 09:05 PM   #3
bob91343 is offline bob91343  United States
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A bleeder has a few purposes. One is safety, so you may want to use a value that causes the voltage to drop to a safe value within about 10 seconds. Another is reduction of unloaded voltage to protect the filter capacitors etc. I would put it across the largest filter capacitor and yes, it is part of the circuit all the time and needs to be figured in with whatever else is in there.

Another use is to improve regulation, namely the difference between full and minimum load voltages. I don't think this use applies in your situation, since your load is probably relatively constant.
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Old 15th February 2011, 09:14 PM   #4
aardvarkash10 is online now aardvarkash10  New Zealand
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I normally put an LED in the bleed resistor circuit too - a visual indication of the voltage in place assists when I'm in my more forgetful moments... Physical location and circuit location is pretty irrelevant really if its only purpose is to bleed down hte power caps.
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Old 15th February 2011, 09:40 PM   #5
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by bob91343 View Post
A bleeder has a few purposes. One is safety, so you may want to use a value that causes the voltage to drop to a safe value within about 10 seconds..
I waited 10 seconds for my amp to discharge, grabbed a component and got a huge shock. I forgot to turn it off !
I dont work on valve amps very often, my nerves wont take it lol
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Old 15th February 2011, 09:56 PM   #6
phrarod is offline phrarod  United States
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If C2 is the place and this will become what is essentially R1 @200K (2W) that really screws up my calculations since I based it all on the present value of R1. Ugh.

I have all the bits in place after 5 months of pulling it all together. I will have to really play with C1 to get the voltage up to 200V like the schematic.
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Old 15th February 2011, 10:17 PM   #7
aardvarkash10 is online now aardvarkash10  New Zealand
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here you go...
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Old 15th February 2011, 11:22 PM   #8
phrarod is offline phrarod  United States
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Thanks! Will that allow me to figure out C1? I think I have to go back to that other program and insert the new resistance.
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Old 15th February 2011, 11:30 PM   #9
aardvarkash10 is online now aardvarkash10  New Zealand
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Quote:
Originally Posted by phrarod View Post
Thanks! Will that allow me to figure out C1?
No, but it will let you find a realistic value for the bleed resistor
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Old 15th February 2011, 11:35 PM   #10
phrarod is offline phrarod  United States
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Cool, thanks!
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