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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Old May 17th 19, 06:26 PM posted to sci.electronics.repair
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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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Old May 18th 19, 04:22 PM posted to sci.electronics.repair
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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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Old May 18th 19, 04:28 PM posted to sci.electronics.repair
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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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Old May 18th 19, 05:25 PM posted to sci.electronics.repair
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Default Value drift over time

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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Old May 18th 19, 07:13 PM posted to sci.electronics.repair
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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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Old May 19th 19, 02:20 AM posted to sci.electronics.repair
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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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Old May 19th 19, 12:09 PM posted to sci.electronics.repair
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Default Value drift over time

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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