[R-390] When to replace carbon composition resistors (CCR)
Barry
n4buq at knology.net
Fri Nov 15 18:57:16 EST 2024
I hadn't considered those. They do look more like a "real" resistor. I'll try to remember those when next I place an order.
Thanks,
Barry - N4BUQ
> You might consider ceramic composition resistors.
> The will look closer to the carbon composition resistors.
> They will handle surges better than metal or carbon foil resistors and
> are mostly non inductive.
>
> Glenn
> WB4UIV
>
> On 11/15/2024 12:23 PM, Barry wrote:
>> Hi Bob,
>>
>> Actually, they're both 150 ohm, 1/2W, metal film resistors. I ordered them from
>> Mouser. I'm pretty sure even the smaller ones would work but they just look so
>> odd in comparison to the vintage carbon comps. I don't expect them to look
>> exactly alike but they just look "so wrong". The slightly larger ones on the
>> left will be what I'm going to use but wondered if there are other types that
>> I'm just not seeing. In reality, unless there were to be significant
>> inductance (as in a wire-wound), most anything would work in the circuit. I
>> just want to use something that's dependable and will last.
>>
>> Thanks,
>> Barry - N4BUQ
>>
>>> Hi
>>>
>>> The resistors in the picture are carbon film rather than carbon comp. That is
>>> the main
>>> reason they look odd. It also is why the size to power rating is a bit different
>>> than what
>>> you are expecting to see.
>>>
>>> Cost and availability wise, they are “what you use”. Authenticity wise, no they
>>> don’t look
>>> like the original parts. Assuming they came from reasonable sources and the part
>>> number
>>> is correct, they should meet their stated power ratings.
>>>
>>> My guess is that the ones on the right in the photo are not the correct part.
>>> That could
>>> be confirmed by digging into the data sheets and looking at the dimensions on
>>> the various
>>> power ratings. A vernier caliper comes in handy for those sort of checks ….
>>>
>>> Bob
>>>
>>>
>>>> On Nov 15, 2024, at 11:35 AM, Barry Scott<72volkswagon at gmail.com> wrote:
>>>>
>>>> Regarding replacement resistors, what are folks using these days?
>>>> Lately, the resistors I've been getting from Mouser haven't been
>>>> exactly what I'd like to use. I'm attaching an example of some I
>>>> ordered this week. Both are 150-ohm, 1/2W, metal film; however, the
>>>> ones on the right side are SO TINY! It's hard to imagine those can
>>>> actually dissipate that much heat but I presume they can. My issue is
>>>> just the overall look of them. If those are placed in the circuit
>>>> where the old ones were, they would look so much out of place. I
>>>> ordered two different types and will be using the ones on the left as
>>>> they're at least somewhat larger. I hesitatingly used one much like
>>>> it in a Tek scope and it worked fine. It just looks weird. I
>>>> hesitatingly used one much like those smaller ones in a Tek scope and
>>>> it worked fine. It just looks weird but I wasn't finding much else
>>>> for the specs I needed so I used it.
>>>>
>>>> I know I can order from sources like eBay and get packages that are
>>>> more in line with the sizes of their older counterparts, but I don't
>>>> like to get those as it's questionable as to where they're sourced,
>>>> their reliability (which is probably better than I'm thinking they
>>>> are), etc. Just wondering what others might be using.
>>>>
>>>> Thanks,
>>>> Barry - N4BUQ
>>>>
>>>> On Mon, Nov 11, 2024 at 2:04 PM Jim Whartenby via R-390
>>>> <r-390 at mailman.qth.net> wrote:
>>>>> It is my understanding that after the CCR was manufactured, it went through a
>>>>> sorting for tolerance. All resistors that were within 5% of the mean value got
>>>>> the gold stripe. The silver stripe was given to all that were above +/- 5% but
>>>>> at or below +/- 10% of the mean value. The remaining were given no stripe if
>>>>> they were within 20% of the mean value. So there are no 10% resistors that are
>>>>> within 5% of the mean value unless they have drifted to this value over time
>>>>> and temperature.
>>>>>
>>>>> Jacques makes a reasonable suggestion that resistors that are 20% or more above
>>>>> or below the mean value are suspect. The accumulative effect of component
>>>>> tolerance, "the tyranny of numbers," as it was described in the mid 1950s, was
>>>>> the downfall of tube based electronics. The more complex the circuit, the more
>>>>> prone it was to a failure. This led to the military specifications for all
>>>>> types of circuit components from vacuum tubes to resistors.
>>>>>
>>>>> I believe that all of these military component specifications have been
>>>>> rescinded such is the quality of modern components. So if one is inclined to
>>>>> replace a CCR, the better resistor to use is the carbon film resistor. They
>>>>> are more stable in value and less affected by time and temperature.
>>>>>
>>>>> One last thing, the least reliable component is the vacuum tube followed by the
>>>>> capacitor. I will always check tubes first, follower by a visual inspection.
>>>>> Capacitors are eyeballed next followed by resistors. Then it is time to
>>>>> troubleshoot.
>>>>>
>>>>> Regards, Jim
>>>>> Logic: Method used to arrive at the wrong conclusion, with confidence. Murphy
>>>>>
>>>>> On Sunday, November 10, 2024 at 09:05:07 PM CST, Jacques Fortin
>>>>> <jacques.f at videotron.ca> wrote:
>>>>>
>>>>> Hello Barry,
>>>>>
>>>>> IMHO, if all the resistors in your RF deck are at ~20% higher than their
>>>>> marked value, it can be well the cumulative tolerance of all those making
>>>>> trouble more than only one individual value.
>>>>> Sorry to deliver the same message again, but every part which is not 5%
>>>>> close to the stocklist value should be changed.
>>>>> The Solid Carbon resistors may also develop a funny behavior in the sense
>>>>> that they measure a given value when they are cold which drifts to a higher
>>>>> one when the current passes thru.
>>>>> Nothing that was used in a R-390 at the build time was expected to be still
>>>>> OK 70 years later...
>>>>>
>>>>> 73, Jacques, VE2JFE in Montreal
>>>>>
>>>>> -----Message d'origine-----
>>>>> De :r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> De la
>>>>> part de Barry Scott
>>>>> Envoyé : 10 novembre 2024 20:56
>>>>> À : R-390 Mailing List<r-390 at mailman.qth.net>
>>>>> Objet : [R-390] Cathode Resistors in 1st and 2nd Oscillators in R-390/URR
>>>>>
>>>>> I mentioned that the screen/plate resistors in my R-390/URR are a bit high.
>>>>> Today, I removed the oscillator deck and measured those. The 68k is about
>>>>> 71k so not too bad. The 82k is at 87k so a bit worse but I'm still not sure
>>>>> how much that affects the performance.
>>>>>
>>>>> What I did find is the 150-ohm cathode resistors are both at 190 ohms.
>>>>> I presume that may be the primary cause of the low output for both of the
>>>>> oscillators. The 2nd mixer has a bit lower voltage at the test point than
>>>>> does the 1st mixer so that 82k may still need to be replaced although it is
>>>>> still in tolerance.
>>>>>
>>>>> Thanks,
>>>>> Barry - N4BUQ
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> --
> -----------------------------------------------------------------------
> Glenn Little ARRL Technical Specialist QCWA LM 28417
> Amateur Callsign: WB4UIVwb4uiv at arrl.net AMSAT LM 2178
> QTH: Goose Creek, SC USA (EM92xx) USSVI, FRA, NRA-LM ARRL TAPR
> "It is not the class of license that the Amateur holds but the class
> of the Amateur that holds the license"
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