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 Post subject: Fuse resistor watts
PostPosted: Sep Wed 13, 2017 8:31 pm 
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https://photos.google.com/photo/AF1QipM ... D4YzJ8jQTo

About finished rebuilding the V-M 307 PS and amplifier and found out the 22 ohm fuse
resistor is open . Schematic doesn't state watts . I have a 10 Watt but think it's too
high .

Can anyone please help .


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 Post subject: Re: Fuse resistor watts
PostPosted: Sep Wed 13, 2017 8:43 pm 
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Fuse resistors of that type are normally 1/2 (0.5) watts.

The intent is for them to get hot and burn open if the current through them gets too high.
Using a power resistor in that location would totally defeat the function.

- Leigh

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 Post subject: Re: Fuse resistor watts
PostPosted: Sep Wed 13, 2017 8:51 pm 
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It's a round ceramic fuse .Wire wound and markings are gone


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 Post subject: Re: Fuse resistor watts
PostPosted: Sep Wed 13, 2017 8:55 pm 
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davek65 wrote:
It's a round ceramic fuse .Wire wound and markings are gone
What makes you think it's a resistor?

That description sounds like a normal fuse.

Look carefully at the metal ends. The value is usually stamped into the metal.

- Leigh

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 Post subject: Re: Fuse resistor watts
PostPosted: Sep Wed 13, 2017 9:04 pm 
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It's hard to see on schematic but marked as 22 ohm fuse resistor in series with line.
WW-wirewound

https://photos.google.com/photo/AF1QipMvOlT5tbXeKUSS3zR0p7es9ZKwBvD4YzJ8jQTo


Last edited by davek65 on Sep Wed 13, 2017 9:10 pm, edited 1 time in total.

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 Post subject: Re: Fuse resistor watts
PostPosted: Sep Wed 13, 2017 9:07 pm 
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If you could post a photo of it, that would help.

Use the "attachments" feature in the post editor.

The link in the OP is only available to subscribers to that service, which I'm not.

- Leigh

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 Post subject: Re: Fuse resistor watts
PostPosted: Sep Wed 13, 2017 10:35 pm 
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http://www.byan-roper.org/steve/_Media/ ... ematic.png

Here's the schematic showing inline 22ohm fuse resistor lower left in schematic


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 Post subject: Re: Fuse resistor watts
PostPosted: Sep Wed 13, 2017 10:55 pm 
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Fuse resistors are a special breed of component. They are NOT ordinary resistors. They are specifically designed to open at a certain current value. Ordinary resistors are not and frequently tout their ability to tolerate overloads. You might be able to get away with an ordinary resistor with an appropriate fuse in series. The best course is to cross reference the VM part number and see if a suitable replacement can be had somewhere.

Good luck,

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 Post subject: Re: Fuse resistor watts
PostPosted: Sep Thu 14, 2017 2:02 am 
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I just ordered a 5 watt 33 ohm fuse resistor from mouser and going to install mini twist
fuse holder in series with fuse .

http://www.mouser.com/Search/ProductDet ... 5W33R00JCS


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 Post subject: Re: Fuse resistor watts
PostPosted: Sep Thu 14, 2017 3:33 am 
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davek65 wrote:
I just ordered a 5 watt 33 ohm fuse resistor from mouser...
That resistor will do absolutely nothing.

The datasheet doesn't even spec an opening time for power levels below 100 watts:
Image

100 watts is 2.2 amps through 22 ohms.

- Leigh

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 Post subject: Re: Fuse resistor watts
PostPosted: Sep Thu 14, 2017 4:42 am 
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Fuse resistors are in a death spiral - used for years in TVs and car radios (all the applications I've seen them in...) - they are now called "Fail-safe resistors." I got an engineering sample kit from IRC for their BWF fusibles 15 or so years ago and have used only two of the eighty or so. There's a whole smattering of them on fleabay in one auction:

http://www.ebay.com/itm/ELECTRONIC-Huge ... Swb2xZd8xG

Workman, Corning, IRC and GC all made/supplied them, with the ubiquitous 4.7 ohm Fuzit/Belimiter in the old RCA black and whites, typically a 5-7 watt ceramic fuse resistor. Admiral, GE, Philco (theres one in the Predictas..) and others also used them.

Image

http://www.ebay.com/itm/VINTAGE-FUSED-R ... Sw2gxY2tFM

Bendix and Motorola also used them to protect that DS-501/2N174 doorknob output transistor in the early transistor car radios. Technically an Emitter resistor, they were failsafe nonetheless.

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Brian
"Capacitor Cosmetologist since 1979"
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 Post subject: Re: Fuse resistor watts
PostPosted: Sep Fri 15, 2017 6:55 pm 
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Location: Near Brandon, Iowa
The fuse resistor is probably doing double-duty: first to serve as a current surge limiter and second to serve as a "fuse" should something go terribly wrong downstream.

You can replace the fusible resistor with two separate parts: a Bussman type fuse that will open if a current threshold is exceeded, and a plain resistor (carbon or wirewound, doesn't matter) that will serve as a "shock absorber" for the cold-turn-on current surge. The fuse needs to be sized so that it appropriate to the normal current draw of the device, and the surge resistor must be power-rated to withstand the normal operation current to which it will be exposed. A one- or two-watt resistor would probably be adequate but
a link to the schematic of the device under discussion would be useful in making that determination.


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 Post subject: Re: Fuse resistor watts
PostPosted: Sep Wed 20, 2017 12:46 am 
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Thought i would post some pictures of the rebuild of Amp chassis and Power chassis
with added twist lock fuse holder . 1 amp fast blow fuse .
Attachment:
P1010103.JPG
P1010103.JPG [ 152 KiB | Viewed 46 times ]
Attachment:
P1010105.JPG
P1010105.JPG [ 152.5 KiB | Viewed 46 times ]


I restuffed the can with new caps . The white sand resistor is connected to end terminal
of fuse holder .


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