[R-390] When to replace carbon composition resistors (CCR)

Renee K6FSB k6fsb.1 at gmail.com
Sat Nov 16 14:02:59 EST 2024 

Dave et all,
  the ceramics did not hold up well in surges (my application - some 
areas of  Implant machines) ...blew to smytherines first hit  as did MF 
and CF ( far worse) where Carbon Comps would survive a dozen or so hits 
. it all depends on application......in this application any of these 
will be fine......just pick a size that "looks" right....HOWEVER, one 
more thing to consider -the bad news is that using a higher wattage may 
cause failure of downstream component instead of acting as a ( CHEAP) 
sacrificial componen/fuse protecting a potential unobtainable/expensive 
item.
so one may have to balance looks vs true functionality.
Renée

On 11/16/24 10:18 AM, David Wise wrote:
> Today I learned that there are Ceramic Composition resistors.  Literally never heard of them and I've been doing EE for 40 years.
>
> Ceramic comp is far more expensive than metal oxide film.  The latter is not as surge-tough but way better than MF or CF and fine for all but the most punishing industrial stuff.  When I rebuilt a HP 740B 1000V 25W voltage standard with silicon switching transistors (was germanium) and a homemade ferrite-core transformer (was lossy soft iron tape), I used MOX for the new snubbers required to tame the spikes.
>
> Dave Wise
>
> ________________________________
> From: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> on behalf of Barry <n4buq at knology.net>
> Sent: Friday, November 15, 2024 3:57 PM
> To: Glenn Little WB4UIV <glennmaillist at bellsouth.net>
> Cc: R-390 Mailing List <r-390 at mailman.qth.net>
> Subject: Re: [R-390] When to replace carbon composition resistors (CCR)
>
> 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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