In article ,
says...


How stable do they need to be in an old radio where components values
can vary, sometimes by quite a bit, and the radio will still perform
just fine?


Well lets see how this plays.... I have to take this old solder joint
apart anyway to removed to leads from the capacitor.... or rubber insulated
wire... and in this same hole is this old resistor thats 19% off value..
Now this new resistor is going to cost me a whole 3 cents.... or even
if the thing was a dime ... now this new part doesn't look quite
like the old one.... it doesn't look like a dogbone... and it doesn't
even look like a AB Striped Resistor.... but its UNDER THE CHASSIS ..
and for 99% of the old radios that we restore... whats UNDER THE
CHASSIS is acceptable as long as it is good electrical practice
and makes the radio play like it is supposed to play....

Now if I am doing up a $10,000 Zenith Strat .... or a $75,000 Sparton
Nocturne.... then I'll make those new parts UNDER THE CHASSIS ....
look exactly like the old ones.... most any radio other than those high
end ones.... or if a customer want to pay me enough money I'll do it
on an AA5 plastic 1950's kitchen clock radio.... So where is the beef
about using a new part that is a whole lot closer to tolerance.. and
will stay there.... and the cost of the part is so cheap that it just
doesn't make sense to me to leave that 19% off resistor ...

I bet that you don't replace those little dog turd looking capacitors
that RCA used in the front ends of their radios either.... little black
sort of pointed on each end... like the 811K and 19K and a bunch of
these things...... now for a whole 15 to 25 cents each I can have
these nice looking new.. 1% tolerance silver mica caps .. and when I do
the alignment on that radio.. it will play like it is supposed to..
and stay that way for a lot of years...

John k9uwa

"Bill Turner" wrote in message
...
On Wed, 8 Dec 2004 16:42:48 -0500, " Uncle Peter"
wrote:


What you say is true, but still doesn't answer his question.

The reason that "The manufacturers saw no need to use high tolerance
components" had more to do with cost than careful engineering decisions.

I would especially be wary of "NOS" carbon comp. They do NOT get better
with age. If you want to use them to maintain the authentic look of an
old radio, fine, just be aware that metal film is far superior.

When I graduated from high school in 1959 I spent the next few years
making a living by repairing those old tube radios and TVs, and a fair
amount of the time was spent replacing carbon comps. They were state of
the art at the time, but time has marched on.

Caveat fixor.

--
Bill W6WRT

Well, I test every component before I install it, and so far most of
the NOS carbon resistors have been well within tolerance.
Carbon resistors made much before 1950 do have some issues
with aging, and I find 50 to 75% well out of spec and they do get
changed. I'd bet most of the resistors
you were changing in 1959 are probably the same vintage that are
found bad today. I won't argue metal films aren't better, but I
haven't had problems with good quality carbons either.

Pete

On Wed, 8 Dec 2004 20:30:07 -0500, " Uncle Peter"
wrote:

Well, I test every component before I install it, and so far most of
the NOS carbon resistors have been well within tolerance.
Carbon resistors made much before 1950 do have some issues
with aging, and I find 50 to 75% well out of spec and they do get
changed. I'd bet most of the resistors
you were changing in 1959 are probably the same vintage that are
found bad today. I won't argue metal films aren't better, but I
haven't had problems with good quality carbons either.

Over the years, I have found that carbon comp resistors with a matte
finish are much more likely to increase in ohmic value that those with
a glossy finish. I surmise that the former are much more hygroscopic
than the latter.


Brian McAllister

Sarasota, Florida

email bkm at oldtech dot net

"Bill Turner" wrote in message
...
On Tue, 7 Dec 2004 18:12:35 -0500, " Uncle Peter"
wrote:

I wish I could find carbon comps (decent values) for two cents
each! Those days are long gone around these parts.

__________________________________________________ _______

The days of carbon composition resistors are gone for good reason.

Unless you are an antique collector and like to restore equipment using
original parts, use metal film resistors instead. Their stability and
reliability are far superior.

--
Bill W6WRT


I agree that carbon comp resistors have better alternatives if you are
looking for accuracy and stability and low noise. OTOH, carbon comp
resistors are an excellent choice for pulse generators and shaping networks.
A metal film resistor will exhibit inductance and will often arc across its
trim line, usually with catastrophic results. You can hit a 2-watt carbon
comp resistor with repetitive pulses of hundreds of watts (peak, keeping the
duty cycle low) many times without significant resistance shift and
certainly without catastrophic failure.

The carbon comps are not the choice for all circuits, but they still have
their merits.

Ed
wb6wsn

"Ed Price" wrote in message
news:mqdud.3291$Af.1453@fed1read07...

"Bill Turner" wrote in message
...
On Tue, 7 Dec 2004 18:12:35 -0500, " Uncle Peter"
wrote:

I wish I could find carbon comps (decent values) for two cents
each! Those days are long gone around these parts.

__________________________________________________ _______

The days of carbon composition resistors are gone for good reason.

Unless you are an antique collector and like to restore equipment using
original parts, use metal film resistors instead. Their stability and
reliability are far superior.

--
Bill W6WRT


I agree that carbon comp resistors have better alternatives if you are
looking for accuracy and stability and low noise. OTOH, carbon comp
resistors are an excellent choice for pulse generators and shaping
networks.
A metal film resistor will exhibit inductance and will often arc across
its
trim line, usually with catastrophic results. You can hit a 2-watt carbon
comp resistor with repetitive pulses of hundreds of watts (peak, keeping
the
duty cycle low) many times without significant resistance shift and
certainly without catastrophic failure.

The carbon comps are not the choice for all circuits, but they still have
their merits.


1. Something that has to be kept in mind is that most "carbon" resistors
being sold today are "carbon film", not "carbon composition" and
won't stand repetitive surge pulses.

2. IIRC, a mil-spec "10%" carbon comp can vary 42.4% over its
life and still meet spec. Expect commercial parts to be worse.

3. There are ceramic composition resistors available that have all
the good properties of carbon comp (except, I'm sure, cost) with
none of the bad properties.

"Ken Finney" wrote in message
...

"Ed Price" wrote in message
news:mqdud.3291$Af.1453@fed1read07...

"Bill Turner" wrote in message
...
On Tue, 7 Dec 2004 18:12:35 -0500, " Uncle Peter"
wrote:

I wish I could find carbon comps (decent values) for two cents
each! Those days are long gone around these parts.

__________________________________________________ _______

The days of carbon composition resistors are gone for good reason.

Unless you are an antique collector and like to restore equipment using
original parts, use metal film resistors instead. Their stability and
reliability are far superior.

--
Bill W6WRT


I agree that carbon comp resistors have better alternatives if you are
looking for accuracy and stability and low noise. OTOH, carbon comp
resistors are an excellent choice for pulse generators and shaping
networks.
A metal film resistor will exhibit inductance and will often arc across
its
trim line, usually with catastrophic results. You can hit a 2-watt carbon
comp resistor with repetitive pulses of hundreds of watts (peak, keeping
the
duty cycle low) many times without significant resistance shift and
certainly without catastrophic failure.

The carbon comps are not the choice for all circuits, but they still have
their merits.


1. Something that has to be kept in mind is that most "carbon" resistors
being sold today are "carbon film", not "carbon composition" and
won't stand repetitive surge pulses.

2. IIRC, a mil-spec "10%" carbon comp can vary 42.4% over its
life and still meet spec. Expect commercial parts to be worse.

3. There are ceramic composition resistors available that have all
the good properties of carbon comp (except, I'm sure, cost) with
none of the bad properties.



The ideal resistors for abusive, high-speed transient applications are the
silicon carbide (ceramic) resistors (think Carborundum / Cesewid or whatever
they call themselves now). But the carbon comp resistors are much cheaper,
more versatile (lots more resistance values) and easier to use.

I don't know what you mean by the "life" of a carbon comp resistor. My
experience is that they last forever, until you kill them somehow. Drift,
under low power, hasn't been a problem for me. I have never seen 40% drifts,
except for very abused parts, and if you are using the 2-watt carbon comps,
you can hear or smell when you are abusing them.

The silicon carbide resistors can be pushed so hot that you can use them as
room heaters, industrial furnace elements or infrared sources. Oxidation of
the plated silver terminals is a small problem. Also, they do have a
temperature dependent coefficient of resistance (not as bad as incandescent
light bulbs).

I agree about the carbon film resistors; they blow up about the same as the
metal film resistors.

Ed
wb6wsn

Ed Price wrote:


I don't know what you mean by the "life" of a carbon comp resistor. My
experience is that they last forever, until you kill them somehow.
Drift, under low power, hasn't been a problem for me. I have never seen
40% drifts, except for very abused parts, and if you are using the
2-watt carbon comps, you can hear or smell when you are abusing them.

You apparently don't play with many old 30s-40s sets. Finding half the
high-value resistors only 200% out of whack would be a good day.

-BM

Bill Turner wrote:
On Tue, 7 Dec 2004 18:12:35 -0500, " Uncle Peter"
wrote:

I wish I could find carbon comps (decent values) for two cents
each! Those days are long gone around these parts.

__________________________________________________ _______

The days of carbon composition resistors are gone for good reason.

Unless you are an antique collector and like to restore equipment
using
original parts, use metal film resistors instead. Their stability
and
reliability are far superior.

--
Bill W6WRT

I see a lot of circuit boards each week thru work and many of them
still use carbon comp resistors. I dont think they are near extinction
but the demand for them has slowed down quite a bit.

I always heard carbon comps were better in radio and audio circuits
because of their lack of or very low inductance as opposed to carbon
composition which use a spiral of conductive material around a ceramic
core which acts as a small inductor.........

"Bill Turner" wrote in message
...
On Fri, 10 Dec 2004 23:19:17 -0800, "Ed Price" wrote:

I don't know what you mean by the "life" of a carbon comp resistor. My
experience is that they last forever, until you kill them somehow. Drift,
under low power, hasn't been a problem for me. I have never seen 40%
drifts,
except for very abused parts, and if you are using the 2-watt carbon
comps,
you can hear or smell when you are abusing them.

__________________________________________________ _______

Then you just haven't been around long enough. I worked in the TV
repair industry for just under 20 years and I have replaced hundreds of
carbon comp resistors which were NOT abused in any way, but failed none
the less. It's an ancient design which time has passed by.

Yup. I just rebuilt an old Heathkit resistor substitution box, 1966 vintage,
and the resistors were absolutely wild. Some were better than double the
rated value. I don't think I saw any decrease in value. None had any obvious
sign of overheating.

Having said that, different manufacturers' resistors held up better than
others, but today, they are all doubtful. The ABs were good when they were
new, the Ohmites were OK, and the IRCs were questionable from the minute
they left the factory.

"Bill Turner" wrote in message
...
On Fri, 10 Dec 2004 23:19:17 -0800, "Ed Price" wrote:

I don't know what you mean by the "life" of a carbon comp resistor. My
experience is that they last forever, until you kill them somehow. Drift,
under low power, hasn't been a problem for me. I have never seen 40%
drifts,
except for very abused parts, and if you are using the 2-watt carbon
comps,
you can hear or smell when you are abusing them.

__________________________________________________ _______

Then you just haven't been around long enough. I worked in the TV
repair industry for just under 20 years and I have replaced hundreds of
carbon comp resistors which were NOT abused in any way, but failed none
the less. It's an ancient design which time has passed by.

--
Bill W6WRT


I didn't know anybody repairs TV's anymore! g

If you had read my entire post, you would have noticed that I wasn't
endorsing carbon comps for every resistor design. Consumer electronics is
better served by metal film discretes or SMT bricks.

I was addressing the sweeping condemnation of carbon comps (I suppose from
consumer techs with limited exposure). I suppose you might have noticed when
I was talking about my using 2-watt carbon comps in pulse generators and
dummy loads; you don't see much of that inside a TV.

Just as IC's haven't replaced tubes in EVERY application, carbon comp
resistors still are the best solution in a few instances, and I hope the
technology isn't completely abandoned.

Ed
wb6wsn