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Auto capacitor "drain" fixture
Auto capacitor "drain" fixture
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Old 11th December 2012, 05:07 AM   #11
cyclecamper is offline cyclecamper  United States
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Sorry if I'm not making much sense, not having a good day.
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Old 11th December 2012, 05:37 AM   #12
Enzo is offline Enzo  United States
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Or put another way, if you are a one-in-a-million guy, that just means there are 10 of you in New York.
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Old 11th December 2012, 10:25 AM   #13
Rundmaus is offline Rundmaus  Germany
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Originally Posted by cyclecamper View Post
Is there any reason I can't make all my amps so they are safe after 5 minutes? Or would that just forster bad habits that kill me working on someone else's amp?
It is good practice to ensure that any HV cap is sufficiently drained before working on a circuit - a bleeder, a series resistor or a choke might have gone open circuit, a cap downstream of some regulator circuit might still be charged, whatever. Especially if the amp hasn't been constructed by you.

If I am working on a circuit that has been powered on before, I usually leave the DMM connected to the HV rail I am working on, so the '0.xxx V' reading is always in sight.

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Old 12th December 2012, 08:43 PM   #14
Struth is offline Struth  Canada
Join Date: Aug 2012
Location: books at londonpower.com
Hi Guys

If you encounter an amp without bleeder resistors, add them in.

You do not need a "fixture" to drain caps. At most just a loose resistor and an alligator clip. Clip the lead onto one end of the R and the other to ground, then touch the free end of R to the cap.

DO NOT use less than 1k. Make it a 5W to have plenty of distance between your fingers and the leads.

The TUT-series always states to add bleeders, and the projects in TUT3 and TUT5 all have them.

I did not read this entire thread but the second post gave the only answer required.

If servicing old Marshall amps, some disconnected the caps from the circuit where bleeders were so the caps stay charged up if you mistakenly use the standby switch - a completely unnecessary device on a guitar amp.

Also, anything below 300V or so is considered 'safe".

Have fun
Kevin O'Connor
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