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 Post subject: Re: Capacitor blowup
PostPosted: Jun Thu 06, 2019 9:38 pm 
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Location: Dayton Ohio
It is a special resistor which is so constructed to start off as a high resistance and drop down to near zero ohms as it heats up due to current flowing.

Called a Negative Temperature Coefficient (NTC) Thermistor.

They used to sell small button types which fit onto light bulbs. When the light switch would be flipped on, the lightbulb would warm up gradually within a few seconds.
This limits the inrush current which eventually kills incandescent bulbs. In turn making them last much longer.

-Steve

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 Post subject: Re: Capacitor blowup
PostPosted: Jun Fri 07, 2019 12:30 am 
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Location: Cincinnati, Ohio
Got it playing. But I have to touch the 24 tube. Does this mean a bad antenna coil?


https://youtu.be/JQ_RWTvdGyI

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 Post subject: Re: Capacitor blowup
PostPosted: Jun Fri 07, 2019 4:51 am 
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Joined: Sep Thu 23, 2010 6:37 am
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Location: Powell River BC Canada
Please show the schematic of the radio on the you tube.

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 Post subject: Re: Capacitor blowup
PostPosted: Jun Fri 07, 2019 11:41 am 
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http://www.nostalgiaair.org/pagesbymode ... 009673.pdf

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 Post subject: Re: Capacitor blowup
PostPosted: Jun Fri 07, 2019 3:42 pm 
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Location: Somers, CT
Make two resistance measurements.

First, 24 tube grid to ground. You see a low value, maybe 20 ohms or less if the secondary coil winding is good.
Next, measure from the antenna terminal to ground, but with the volume control set for full volume! You should see a few ohms resistance. If the resistance is the same as the volume control pot, then the primary winding was likely damaged by a static discharge.

In some cases they materials used for the coil forms can cause corrosive damage to the fine wires used in the coils, especially at the solder terminals. Something else to watch for if the resistances are off.

The primary winding turns count is not critical, but the secondary is tuned and the winding is critical.

Pete

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 Post subject: Re: Capacitor blowup
PostPosted: Jun Fri 07, 2019 6:05 pm 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 11620
Location: Powell River BC Canada
The radio uses a number of high value resistors and a 'power detector'. Make sure all the resistors are in the correct ballpark, and capacitors free of leakage. Also no gunk around sockets.

That will be a nice radio when you get it working, and may pull in some dx at
night with a good aerial.

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 Post subject: Re: Capacitor blowup
PostPosted: Jun Sat 08, 2019 8:30 pm 
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Location: Perrysburg, OH, U.S.A.
ktewell wrote:
I got new capacitors is their a negative side to these caps?

The "MKP" in the type number indicates a metallized polypropylene film type so there's no polarity. There are variations of this type that includes AC rated parts, too.
John

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 Post subject: Re: Capacitor blowup
PostPosted: Jun Wed 19, 2019 2:49 pm 
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Location: Wayside, NJ Monmouth
I had to rebuild this cap bank for a Three phase 90 KW supply. The caps are 6000 Mfd @ 450 VDC, wired up in series / parallel. All thirty caps vented. Talk about a mess


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 Post subject: Re: Capacitor blowup
PostPosted: Jun Wed 19, 2019 4:30 pm 
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Location: Fernandina Beach, FL
N2LXM wrote:
I had to...
All thirty caps vented. Talk about a mess


Lightning strike?

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 Post subject: Re: Capacitor blowup
PostPosted: Jun Wed 19, 2019 6:01 pm 
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Location: Wayside, NJ Monmouth
[DON Wrote "Lightning strike? ]

No. The customer tied to pulsed the output. So the heavy current flow through the caps, overheated them and they vent. Cap Crap everywhere. BTW. It was over $12,000 to get this beast fixed. Guess they won't doing that again.


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 Post subject: Re: Capacitor blowup
PostPosted: Jun Wed 19, 2019 7:34 pm 
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N2LXM wrote:
[DON Wrote "Lightning strike? ]

No. The customer tied to pulsed the output. So the heavy current flow through the caps, overheated them and they vent. Cap Crap everywhere. BTW. It was over $12,000 to get this beast fixed. Guess they won't doing that again.

Thanks! W-O-W!!!

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 Post subject: Re: Capacitor blowup
PostPosted: Jun Thu 27, 2019 7:46 pm 
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Location: Brooklyn, NY 11217
I had an 82uf MIEC at 600v vent in my New London 901A. Thankfully I had put it inside the old can, so when it did pop, the vent was contained in the old cap can. It's in the negative supply, which is regulated. I bought a Nichicon replacement at 500v. It has not let go yet, but I always think I should get a 600v cap and replace it. The schematic and original cap was only for 500v. That said, it is a second cap in an RCLC supply after the 6X5. There is a 200 ohm 3W resistor (I replaced that one with a 5 watter because the ceramic had broken down and the wire was all that was holding the cap together), then a cap at 40uf 500v, then a 10.5Hy choke, and finally an 80uf 500v cap. I don't think I will trust one unless it is rated way over voltage at this stage...


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