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 Post subject: EICO 950B Voltage Pot
PostPosted: Aug Sat 06, 2022 12:46 am 
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Posts: 1334
Location: Mesa, AZ 85206
Hi Folks

This topic has been covered in detail in prior posts.

My friend wanted me to get his 950B up and running, which is no problem, but as many of you know, the rapid turning of the voltage control to 0 after charging a cap can be the death of the 4W WW 100k pot.

Folks on the forum have done a good job of explaining this and coming up with nice solutions, but I was wondering about a simpler solution since my friend has no problem with drilling another hole in the face plate.

Can anyone see a problem with a momentary switch bridging the cap terminals through a 25W 1K resistor? If I did it, I would tell my friend to test the capacitor (DUT) at voltage, turn off the AC, and then discharge the capacitor (DUT). Obviously, discharging the DUT with the voltage on would burn out the transformer unless the resistor used to short circuit the DUT was sufficiently large to limit the current to maybe a few mA.

Anything I am missing?

Steve


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 Post subject: Re: EICO 950B Voltage Pot
PostPosted: Aug Sat 06, 2022 1:25 am 
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Joined: May Wed 18, 2011 1:40 am
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Location: Littleton, MA
drworry wrote:
Obviously, discharging the DUT with the voltage on would burn out the transformer unless the resistor used to short circuit the DUT was sufficiently large to limit the current to maybe a few mA.

Use an SPDT push button switch and wire it so that it disconnects the capacitor from the rest of the bridge when it is pushed to discharge the capacitor. This avoids stressing the 950B when (not if) the push button gets bumped when the unit still has power.

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Steve Byan https://www.byan-roper.org/steve/steve-at-play/


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 Post subject: Re: EICO 950B Voltage Pot
PostPosted: Aug Sat 06, 2022 1:44 am 
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Joined: Mar Sun 20, 2016 10:04 pm
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Location: Mesa, AZ 85206
Thanks, Steve...I also thought of that while eating dinner...I am glad you commented!

A momentary spdt it is!

Though, I guess wired this way it doesn't have to be momentary...if left in the discharged position the capacitor just wouldn't charge...

Steve


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 Post subject: Re: EICO 950B Voltage Pot
PostPosted: Aug Sat 06, 2022 5:34 am 
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Joined: Jun Sat 09, 2007 7:14 am
Posts: 5680
Location: Melbourne, Florida
Just turn the pot down slowly and you don't have to change anything.

RRM


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