[NJARC] resistors

[Harry Klancer]

Victor,

Depends on the type of resistor and where it's used.

Carbon comp. resistors generally came in 3 tolerance ranges.
20 percent (no tolerance marking),
10 percent(silver band)
and 5 percent (gold band).
  If the manufacturer designed acircuit and used a 20 percent
resistor in a certain spot, thatmeans he believed the circuit
would work with a 20 percentresistor. 10 percent resistors
are a little better, and lots of them were used too.

As an example, a 180K   20 percent resistor might have a
value anywhere between 144K (180K - 20 percent of 180)
and 216K (180K + 20 percent of 180). When the radio was
built, think of it as if somebody reached into a bucket of
20 percent resistorsand what he pulled out and put in
the radio might have been anywhere betweenapproximately
140K and 220K.
Reaching in a bucket of10 percenters, he would have
got a resistor between approximately 160Kand 200K.
Better, but still not a very tight tolerance.

So if YOU put in a 220K resistor (as measured on your
digital ohmmeter), just remember that the original
might have been almost as high as 220K and the radio
still worked.(or the original might have been as low
as 140K, so you couldeven put in a 150K)

That's also why resistors come in RETMA standard
values, say 150K, 180K, 220K, 270K, and so on.
The 180 covers the range between the 150 and 220,
the 220 covers the range between the 180 and the 270,
and so on. Early radios with dogbone resistors tended
to have values suchas 100K, 200K, and so on. Don't
worry, just replace these with a close RETMA value.

HOWEVER, if the manufacturer used
a 5 percent resistor (which cost him more) or even
a special (and very expensive) resistor marked 1 percent,
that meansthe actual value was more important. In the case
we looked at above, a 5 percenter would be
between 170K and 190K. He spent the extra money
because he thought it was important. You should too.

Somebody else can talk about wirewound resistors.

Harry K


On 05/21/2013 2:16 PM, VICTOR BELLINI wrote:
> Just remember
> Reply = Poster
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> _________________________________________________________
> question....when replacing resistors in tube radios how important is 
> to replace with the exact ohms....can you replace with slightly higher 
> value.....I know that the watts rating is important as it affects 
> voltage but won't hurt to replace 1/2 watt with 1 watt but I am not 
> sure regarding the ohms.....thanks
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