old sand covered resistor

[Ralph Mowery]

I reparied an old VFO for a friend. In it was a 10 K 7 watt resistor.
It is about the size of a USB memory stick and looks likeit was dipped
in a mix of sand like the mortor used for bricks.

I saw an artical where someone else had the same problem with that
resistor.

Are they just wire wound or something special, like a fuse resistor ? I
have seen just a few of them, but never checked them out.

[Scott Dorsey]

Post by Ralph Mowery
I reparied an old VFO for a friend. In it was a 10 K 7 watt resistor.
It is about the size of a USB memory stick and looks likeit was dipped
in a mix of sand like the mortor used for bricks.
I saw an artical where someone else had the same problem with that
resistor.
Are they just wire wound or something special, like a fuse resistor ? I
have seen just a few of them, but never checked them out.

Your description sounds like an ordinary ceramic wirewound resistor. Be
sure to replace with a noninductive type. (Note that noninductive wirewounds
are still really very inductive.)

If you're worried about it, measure it. When these things fail, it's
usually by rising in value and not falling.

If it's bad, try mouser part number 71-CP10-K-10K.

If it's in a VFO, it might be used as a heating element to keep the
electronics in the can at constant temperature, in addition to its obvious
application in the schematic.
--scott

[Ralph Mowery]

Post by Scott Dorsey
Your description sounds like an ordinary ceramic wirewound resistor. Be
sure to replace with a noninductive type. (Note that noninductive wirewounds
are still really very inductive.)
If you're worried about it, measure it. When these things fail, it's
usually by rising in value and not falling.
If it's bad, try mouser part number 71-CP10-K-10K.
If it's in a VFO, it might be used as a heating element to keep the
electronics in the can at constant temperature, in addition to its obvious
application in the schematic.

This resistor was used in a Knight VFO from about 60 years ago. It is
just a dropping resistor from the B+ to a voltage regulator tube. I
replaced it with a 10 K 10 watt resistor I had on hand. One that is
about 1/4 inch square, 2 inches long and ceramic on 3 sides and filled
with something on the other after the resistance element is put in. In
this case it doesn't matter if it is highly inductive or not. It was
not used as a heating element.

The resistor was totally open. I did check for shots to ground to see
if something was causing it to pull more current than it should. After
applying power the resistor was just barley warm to the touch.

I did see in another place where someone referred to it as a 'sandohm',
which I am sure that is not really a name,but just something to call
them.