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Author Topic: Substitute for .05 mfd 1600v tubular capacitor?  (Read 1760 times)
NZ5N
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« on: April 08, 2012, 10:40:27 PM »

Hello,

I was able to get an old 6 meter Gonset Communicator working this weekend. However, a tubular capacitor connected between the plates of the 6X4 rectifiers and ground appears to be in bad shape, it gets hot and appears to be leaking wax. It is .05 mfd 1600v. These does not appear to be a common value in today's market, only ones I saw were $10 each.

Any suggestions for a cheap substitute?  And is this component even necessary?  I have seen several schematics of 6X4 power supplies without any such capacitor.

73, Bill NZ5N
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AC5UP
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« Reply #1 on: April 09, 2012, 01:27:17 AM »

Remember that's an AM rig intended for 120 VAC or 6 / 12 VDC operation. I took a quick look at the squidmatics on BAMA and the DC power supply relied on a vibrator to tickle a step-up transformer for B+. Good chance the cap was intended to reduce vibrator hash.

Do you need it? No, not if you'll be running the radio from AC house power. If you decide to sub it just in case my quick look at the squidmatic wasn't long enough, I'd question if the 1600 VDC rating was absolutely necessary. Betcha' a pair of .1 uF @ 600 VDC polypropylene tubular jobbies (ol' Yellers) in series would fill the bill OK Fine.
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NZ5N
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« Reply #2 on: April 09, 2012, 02:47:25 AM »

Thanks, I was hoping that was just for the vibrator. If yes, I do not need it, just using with 120vac.
73, Bill
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G3RZP
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« Reply #3 on: April 09, 2012, 03:04:49 AM »

That would be the 'buffer' capacitor for use with the vibrator. Without it, you get pretty bad arcing at the vibrator contacts, but on AC, it isn't necessary. But I would suggest looking around for one as a longer term part to get, just in case you ever want to use it on DC. I'd also suggest a note somewhere that 'Not to be used on DC without new buffer capacitor' in case you forget.  Vibrators (of that sort!) these days are less common than rocking horse manure.
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KE3WD
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« Reply #4 on: April 09, 2012, 06:15:25 AM »

... Betcha' a pair of .1 uF @ 600 VDC polypropylene tubular jobbies (ol' Yellers) in series would fill the bill OK Fine.


I'm not a betting man, but that's good advice there. 

73
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N4NYY
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« Reply #5 on: April 09, 2012, 06:28:11 AM »

I would go the route of AC5UP. I found one here on Mouser, but sometimes not with buying a $3 cap and paying $5 or so shipping. But ig you have other parts you need and want to buy this, then here is the link:

http://www.mouser.com/ProductDetail/Cornell-Dubilier/942C16S47K-F/?qs=oi6qnwyrdkz1UwpjaxFusxu0%2faQNcY42u%2fMEUCX%252bn3g%3d
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G3RZP
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« Reply #6 on: April 09, 2012, 06:33:28 AM »

You could really need that 1600 volts as a peak. But there is a fair amount of current in the cap when on the vibrator. Have a look at the older ARRL Handbooks (circa 1948/9/50) for info on vibrator supplies.
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NZ5N
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« Reply #7 on: April 09, 2012, 06:40:54 AM »

Thanks, folks.  This unit came without the vibrator so hopefully it will be OK to remove that cap.

73, Bill NZ5N
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AC5UP
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« Reply #8 on: April 09, 2012, 06:49:47 AM »

You could really need that 1600 volts as a peak.

This is true... Considering the vibrator output is essentially a square wave, there may be spikes and transients well above nominal.

BTW: The final on a Gonset Communicator is the venerable 2E26 and although voltages are not marked on the squidmatic I looked at, plate voltage for the tube itself is rated @ 600 VDC absolute maximum with 500 VDC being typical for all modes (Class C, AB1, etc) of operation. Assuming Gonset chose the 500 volt concept, 1600 is plenty of margin.............  Cheesy
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