Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Default Value drift over time

Before I junked that RF sig gen I snipped a selection of resistors out of
it just to see how far away from their nominal values they have strayed
over the past ~65 years. I shall report back in due course....



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Default Value drift over time

On Fri, 17 May 2019 21:19:07 +0100, Mike Coon wrote:

I can hardly wait!


Then I shall keep you in suspense no longer.

Here's what I found from a random selection of old components I snipped
out. Firstly, pretty much *all* the capacitors were fine. The 350VDC
Hunts capacitors could easily have been new. An Erie plate ceramic of
0.01uF likewise. A Dubilier type SM22 50pf cap, however, had gone up to
62pF. That one was one of the ones used for tuning. The biggest changes
were as expected in the carbon resistors, all of which aged to higher
values like so:

27k became 38.6k

another 27k ---- 29k

100k ---- 107k

10 ---- 10.7

3.3k ---- 4.2k

4.1k ---- 5.2k

15k ---- 20.7k

220k ---- 246k

8.2k ---- 9.9k

400k ---- 509k


These were all marked with a silver tolerance band, so clearly Taylor
back then at least not *that* bothered about accuracy.





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Default Value drift over time

On Sat, 18 May 2019 15:22:29 +0000, Cursitor Doom wrote:

The 350VDC Hunts capacitors could easily have been new.


Same type as this: https://tinyurl.com/y6a9ywtz





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On Saturday, 18 May 2019 16:22:32 UTC+1, Cursitor Doom wrote:
On Fri, 17 May 2019 21:19:07 +0100, Mike Coon wrote:

I can hardly wait!


Then I shall keep you in suspense no longer.

Here's what I found from a random selection of old components I snipped
out. Firstly, pretty much *all* the capacitors were fine. The 350VDC
Hunts capacitors could easily have been new. An Erie plate ceramic of
0.01uF likewise. A Dubilier type SM22 50pf cap, however, had gone up to
62pF. That one was one of the ones used for tuning. The biggest changes
were as expected in the carbon resistors, all of which aged to higher
values like so:

27k became 38.6k

another 27k ---- 29k

100k ---- 107k

10 ---- 10.7

3.3k ---- 4.2k

4.1k ---- 5.2k

15k ---- 20.7k

220k ---- 246k

8.2k ---- 9.9k

400k ---- 509k


These were all marked with a silver tolerance band, so clearly Taylor
back then at least not *that* bothered about accuracy.


Most Rs in valve kit are far from critical. 5% would have cost them more than 10%. 20% were more common.


NT
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Default Value drift over time

On Sat, 18 May 2019 09:25:35 -0700, tabbypurr wrote:

Most Rs in valve kit are far from critical. 5% would have cost them more
than 10%. 20% were more common.


I just put it down to post-war lack of availability but your guess is as
good as mine.
My experience with valves is not that great. I'm really more of the
germanium semiconductor era. ;-)



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Default Value drift over time

I was in the elctronic surplus bisness from the 60's to the end of the
century. Most people thought that
Allen-Bradleys were the gold standard. One cusomer complained and we
started checking samples.
They were all out of tolerance. A-B's speck sheet specified how to
measure. For a given resistance
range you applied a specified voltage and measured the current.

As an aside: In the 50's I ran across some carbon comp. resistors that
had been modified.
Apparently the person was short of cash or in a hurry. The person took
a CC and a triangular file
and raised the CC to the value neede.

CP

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On Sat, 18 May 2019 18:20:37 -0700, MOP CAP wrote:

Apparently the person was short of cash or in a hurry. The person took a
CC and a triangular file and raised the CC to the value neede.


We used to do the same sort of thing with xtals in the days when they
were expensive and hard to come by.



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Default Value drift over time

On Sunday, 19 May 2019 12:09:10 UTC+1, Cursitor Doom wrote:
On Sat, 18 May 2019 18:20:37 -0700, MOP CAP wrote:

Apparently the person was short of cash or in a hurry. The person took a
CC and a triangular file and raised the CC to the value neede.


We used to do the same sort of thing with xtals in the days when they
were expensive and hard to come by.


Couldn't do that with my oldest crystal, it's in a valve glass envelope. 5kHz IIRC.


NT
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On Sun, 19 May 2019 10:19:17 -0500, Fox's Mercantile wrote:

Except you didn't use a file. You used 600 grit silicon carbide paper
and a piece of glass for a flat surface.


Yup, the principle is the same, though. For the final fine 'adjustment'
we'd use Vim, which is a kitchen scouring powder in the UK and many times
less aggressive than 600 grit.




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Default Value drift over time

On Saturday, May 18, 2019 at 8:22:32 AM UTC-7, Cursitor Doom wrote:

Here's what I found from a random selection of old components I snipped
out.
27k became 38.6k

another 27k ---- 29k

100k ---- 107k



Good to know, but the aging of composition resistors doesn't tell us much
about carbon film resistors (the common low-spec type nowadays) or
metal film (the common high-spec type) and manufacturer coatings
and such are likely to be changing from year to year as well.

Probably, because conductive (metallic or semimetallic) items are positive
valence, oxidation will raise resistance with time, for almost
anything. How much time, is still a mystery (for almost anything
we build today, at any rate).

There's too much chemistry involved to make a really good long-life
high accuracy projection for most real components. Humidity, ozone,
fungus, air pollution... so MANY variables.
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On Sunday, 19 May 2019 21:12:54 UTC+1, whit3rd wrote:
On Saturday, May 18, 2019 at 8:22:32 AM UTC-7, Cursitor Doom wrote:

Here's what I found from a random selection of old components I snipped
out.
27k became 38.6k

another 27k ---- 29k

100k ---- 107k



Good to know, but the aging of composition resistors doesn't tell us much
about carbon film resistors (the common low-spec type nowadays) or
metal film (the common high-spec type) and manufacturer coatings
and such are likely to be changing from year to year as well.

Probably, because conductive (metallic or semimetallic) items are positive
valence, oxidation will raise resistance with time, for almost
anything. How much time, is still a mystery (for almost anything
we build today, at any rate).

There's too much chemistry involved to make a really good long-life
high accuracy projection for most real components. Humidity, ozone,
fungus, air pollution... so MANY variables.


You can eliminate all those with glass, vacuum & getter. Then you find one day that the getter is oxidised & the bulb contains hydrogen.


NT


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Default Value drift over time

On Sun, 19 May 2019 13:24:18 -0700, tabbypurr wrote:

You can eliminate all those with glass, vacuum & getter. Then you find
one day that the getter is oxidised & the bulb contains hydrogen.


I was under the impression that glass was impermeable even to omnipresent
hydrogen. Or is there a path via where the base pins protrude?



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Default Value drift over time

On 5/19/19 5:45 PM, Cursitor Doom wrote:
I was under the impression that glass was impermeable even to omnipresent
hydrogen. Or is there a path via where the base pins protrude?


Hydrogen atoms are really really small.
Trying to keep hydrogen in or out is always problematic.


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On 20/5/19 10:50 am, Fox's Mercantile wrote:
On 5/19/19 5:45 PM, Cursitor Doom wrote:
I was under the impression that glass was impermeable even to omnipresent
hydrogen. Or is there a path via where the base pins protrude?


Hydrogen atoms are really really small.
Trying to keep hydrogen in or out is always problematic.


Also, a kilogram of hydrogen at a given pressure takes more space than
any other gas.

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On Sunday, 19 May 2019 23:45:14 UTC+1, Cursitor Doom wrote:
On Sun, 19 May 2019 13:24:18 -0700, tabbypurr wrote:

You can eliminate all those with glass, vacuum & getter. Then you find
one day that the getter is oxidised & the bulb contains hydrogen.


I was under the impression that glass was impermeable even to omnipresent
hydrogen. Or is there a path via where the base pins protrude?


Glasslinger did a mass spec analysis to discover that gassy valves contain hydrogen. I don't know whether that permeates through the glass (unlikely since most valves stay hard), leaks in through pin sealing defects or is the result of remaining water vapour reacting with the getter. Either way a getter that could capture it would be a good thing probably.

https://www.youtube.com/watch?v=16vOoF_XUB8


NT
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On 2019/05/18 11:22 a.m., Cursitor Doom wrote:
On Fri, 17 May 2019 21:19:07 +0100, Mike Coon wrote:

I can hardly wait!


Then I shall keep you in suspense no longer.

Here's what I found from a random selection of old components I snipped
out. Firstly, pretty much *all* the capacitors were fine. The 350VDC
Hunts capacitors could easily have been new. An Erie plate ceramic of
0.01uF likewise. A Dubilier type SM22 50pf cap, however, had gone up to
62pF. That one was one of the ones used for tuning. The biggest changes
were as expected in the carbon resistors, all of which aged to higher
values like so:

27k became 38.6k (bad)

another 27k ---- 29k (within 10%)

100k ---- 107k (within 10%)

10 ---- 10.7 (ditto)

3.3k ---- 4.2k (bad)

4.1k ---- 5.2k (bad)

15k ---- 20.7k (bad)

220k ---- 246k (barely bad - just above 10%)

8.2k ---- 9.9k (bad)

400k ---- 509k (bad)


These were all marked with a silver tolerance band, so clearly Taylor
back then at least not *that* bothered about accuracy.


No, those resistors have drifted since their original construction.
People did have ohm-meters back then and would verify values on
resistors particularly if they were colour deficient or colour blind as
I did, testing Rs when building kits - red/green deficient vision. I
still check almost all resistors I come across with a meter as I don't
trust my green, dark red, and brown differentiation.

If they are in power circuits - plate or cathode or voltage dropping
then those do drift as they were only compressed carbon and heat/cooling
cycles would cause them to change value - usually upwards as you have
discovered. I consider your values typical of tube gear that is 40 or
more years old.

1920s resistors were a chunk of carbon rod with a wire wrapped around
each end then dipped in a sealant - how long do you think that value
would last within X%? Wire wound resistors external connections were
pressure bonded to the resistance wire, not uncommon for that joint to
fail over time...

Like I said earlier you HAVE to verify all the resistors as they wander
over time. Modern Rs are much more reliable when operated under their
rated wattage.

John :-#)#

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On Monday, 20 May 2019 13:40:53 UTC+1, John Robertson wrote:

1920s resistors were a chunk of carbon rod with a wire wrapped around
each end then dipped in a sealant - how long do you think that value
would last within X%? Wire wound resistors external connections were
pressure bonded to the resistance wire, not uncommon for that joint to
fail over time...


I presume you mean carbon composition rod. Pure carbon would give too few ohms to have much use in a valve radio.

Some Rs used metal caps instead of wires, and were mounted in a clip-in holder. I guess they needed to be replaced sometimes as different valves sometimes needed different grid leak values.


Like I said earlier you HAVE to verify all the resistors as they wander
over time. Modern Rs are much more reliable when operated under their
rated wattage.

John :-#)#


as long as it's well under. Rated life for power Rs operated at specced power can be terrible.


NT
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On 2019/05/20 1:19 p.m., wrote:
On Monday, 20 May 2019 13:40:53 UTC+1, John Robertson wrote:

1920s resistors were a chunk of carbon rod with a wire wrapped around
each end then dipped in a sealant - how long do you think that value
would last within X%? Wire wound resistors external connections were
pressure bonded to the resistance wire, not uncommon for that joint to
fail over time...


I presume you mean carbon composition rod. Pure carbon would give too few ohms to have much use in a valve radio.


Thanks, I did mean composite.


Some Rs used metal caps instead of wires, and were mounted in a clip-in holder. I guess they needed to be replaced sometimes as different valves sometimes needed different grid leak values.


Ads in the early radio magazines are handy for that sort of data. And
yes, you did keep a drawer of grid resistors handy if you wanted best
performance out of your rig.



Like I said earlier you HAVE to verify all the resistors as they wander
over time. Modern Rs are much more reliable when operated under their
rated wattage.

John :-#)#


as long as it's well under. Rated life for power Rs operated at specced power can be terrible.


NT


Power derated curve curves can be surprising for almost any component.

Heck Molex pin connectors are rated at 25 insertions if I recall
correctly, and they are heavily used in arcade games...

Spec sheets do need to be read after all.

John :-#)#
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On Tue, 21 May 2019 10:20:02 -0400, Ralph Mowery wrote:

Hydrogen is also explosive or will burn. That is another reason not to
just spray it out for leak detection.

I think that hydrogen may be the smallest atom, but they often join in
pairs to make up a larger molicule. Some other atoms that are normally
gas do the same thing.


Oh boy. Where do I start?



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