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 Post subject: Choke question
PostPosted: Jan Fri 12, 2018 10:25 pm 
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Location: Warner Robins, GA
I've got a collins R-390 where I went solid state with the regulator.

There is a choke after the standby switch.

Anyways after two operations of the standby switch the regulator was toast.

Now can I stop that by putting a reverse biased diode across the choke and if so what diode should I use?


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 Post subject: Re: Choke question
PostPosted: Jan Sat 13, 2018 1:19 am 
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Well not quite understanding, a 1N1004 would work... That is what I generally put across a relay coil that has DC, reverse, absorbs the coil kickback.

But your scenario suggests that in standby position B+ is soaring and the regulator is dumping the excess current...

Possibly the regulator should be after the standby switch.

Post a sketch of the problem area for all. I may still not get it right but others may...

Chas


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 Post subject: Re: Choke question
PostPosted: Jan Sat 13, 2018 2:45 am 
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Doubt thats it as the regulator was designed with that in mind.

Plus I think that I tested it no load just to be sure.

Think what happened is the inductive kickback arced across the switch and was of a higher voltage than any of the parts could withstand as I know inductive kickback is usually a higher voltage than the voltage that normally goes through it.

I can post some stuff tomorrow maybe.

Down with the flu right now.


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 Post subject: Re: Choke question
PostPosted: Jan Sat 13, 2018 3:27 am 
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Why are you using a choke with a regulator ? ? ?

- Leigh

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 Post subject: Re: Choke question
PostPosted: Jan Sat 13, 2018 4:53 am 
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Because that's how the R-390 was designed from the factory and I didn't see the point in trying to second guess the engineers and remove the choke.


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 Post subject: Re: Choke question
PostPosted: Jan Sat 13, 2018 7:51 pm 
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Are we talking about an R-390 or an R-390A ?

- Leigh

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 Post subject: Re: Choke question
PostPosted: Jan Sun 14, 2018 1:18 am 
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Yes we are talking about the R-390.

The schematic in the back of TM 11-5820-357-35 shows a 4H choke labeled L601 on the audio chassis which is shown connected after the standby switch which provides filtering just for the audio chassis.

At one point I tried several 20 volt 5 watt zeners in series to drop the voltage low enough to where when loaded it would be high enough to properly regulate while keeping the heat down in the heatsink.

Even though calculations said 5 watt zeners were a little higher than needed they still got hot enough to melt the solder holding them together.


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 Post subject: Re: Choke question
PostPosted: Jan Sat 20, 2018 4:01 pm 
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What I might do is set up a power supply somehow and use a variac to control the voltage then connect my oscope to the choke and operate the standby switch to see if there's a voltage spike. If so I will put the scope on the power supply side of the switch to see if there's a voltage spike there as well. If so then I know putting a reverse biased diode across the choke will solve the problem.

Suppose I could also put a reverse biased diode between the regulator output to ground.

Looking at the schematic it seems like the 1N4007 and 1N4148 would provide protection.

Attachment:
R-390 regulator 2.jpg
R-390 regulator 2.jpg [ 97 KiB | Viewed 396 times ]


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