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 July 17th 17, 10:50 AM posted to sci.electronics.repair
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Default Resistance measurements

On Monday, 17 July 2017 09:31:17 UTC+1, Cursitor Doom wrote:
On Mon, 17 Jul 2017 09:08:01 +0100, Mike Coon wrote:

It also weighs 5lb (2+kg). I guess in those days servicemen were MEN!


Yes, and built like a tank! I have a Model 7, too, IIRC it was made in
1943 and is still going strong. I'll wager when it was first produced,
techs of the day marvelled at how light and portable it was.


My 1920s v/i meter weighs a small fraction of that. Avos were high impedance accurate bench meters.


NT

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Old July 17th 17, 11:17 AM posted to sci.electronics.repair
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Default Resistance measurements

On Mon, 17 Jul 2017 02:50:34 -0700, tabbypurr wrote:

My 1920s v/i meter weighs a small fraction of that. Avos were high
impedance accurate bench meters.


"High impedance" back then, yeah.


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Old July 17th 17, 11:24 AM posted to sci.electronics.repair
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Default Resistance measurements

On Mon, 17 Jul 2017 05:00:55 -0400, oldschool wrote:

I do have to ask, why these meters used BOTH the D cells and other
batteries as well. (In other words, more than one kind of battery). Why
didn't they just use one battery or one set of batteries for the whole
device?



Dunno. I'm sure someone here will, though.
Fortunately, although 15V batteries are largely unobtainium these days,
10x1.5V AAA cells will get you there and the battery compartment is
capacious enough (AVOs are anyway) to house them all comfortably.

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Old July 17th 17, 01:39 PM posted to sci.electronics.repair
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Default Resistance measurements

On Monday, 17 July 2017 11:21:54 UTC+1, Cursitor Doom wrote:
On Mon, 17 Jul 2017 02:50:34 -0700, tabbypurr wrote:

My 1920s v/i meter weighs a small fraction of that. Avos were high
impedance accurate bench meters.


"High impedance" back then, yeah.


They were, you could always get lower resistance meters for a lot less. Why it took so long for analogue meters to get FETs I don't know. My 1920s meter is moving iron, so the resistance is dreadful & it's nonlinear. But its worst shortcoming is that the case is the -ve electrode, you hold it in your hand and it's bare metal. AND it's low resistance, so measuring radio/TV HT was always a fun experience. Maybe they figured if they killed their customers there wouldn't be any requests for refund.


NT
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Old July 17th 17, 01:40 PM posted to sci.electronics.repair
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Default Resistance measurements

On Monday, 17 July 2017 11:05:20 UTC+1, wrote:

I do have to ask, why these meters used BOTH the D cells and other
batteries as well. (In other words, more than one kind of battery). Why
didn't they just use one battery or one set of batteries for the whole
device?


A 1.5v cell is high capacity, high current & cheap. 15v batteries are low capacity, low current & never cheap.


NT


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Old July 17th 17, 03:59 PM posted to sci.electronics.repair
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Default Resistance measurements

On Mon, 17 Jul 2017 10:17:54 -0000 (UTC), Cursitor Doom
wrote:

On Mon, 17 Jul 2017 02:50:34 -0700, tabbypurr wrote:

My 1920s v/i meter weighs a small fraction of that. Avos were high
impedance accurate bench meters.


"High impedance" back then, yeah.


Not high enough. If you want to measure really high resistances, such
as insulation leakage, you need a Megger (which is actually the name
of the company that makes them but has become somewhat of a generic
term for high voltage resistance testers):
https://www.google.com/search?q=megger+meter&tbm=isch
If you want to see if you really have water in the coax cables, you
need one of these insulation testers.

I have an old and ugly meter, which has a hand crank generator. It
produces enough voltage to have given me a rather nasty shock. It's
fairly difficult to electrocute oneself while operating the crank, but
I managed. Some modern Megger models still have such hand cranks
generators:
http://www.tequipment.net/Megger212160.html
http://us.megger.com/extended-range-insulation-resistance-testers-210170-and-210600-
These small testers will deliver 1000V in order to measure up to 2000
Mohms. Now, does anyone still want to complain about 15v batteries?

--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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Old July 17th 17, 05:47 PM posted to sci.electronics.repair
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Default Resistance measurements

On Sunday, July 16, 2017 at 8:36:16 PM UTC-4, Phil Allison wrote:
Chris wrote:

--------------


I'm finding I get different results (vastly different in some cases) when
measuring the total resistance of a circuit with a) a DMM and b) an old
analog meter with a physical needle. And this doesn't only happen at high
impedance points, either. What could account for this?


** The fact you are totally clueless ?

Semiconductors are not resistors and there is no right value to measure.

DMMs are designed NOT to cause didoes or BJT junctions to conduct when using the ohms ranges.

Also, DMMs ohm ranges are very sensitive to any residual DC or AC voltage on a component while analogue meters are much less so.

Interesting fact: you can measure the resistance of a loudspeaker voice coil with either type, but not if the room is full of loud bass noise.

Think about it.


...... Phil


Come on Phil, lighten up. The guy didn't know and asked the question. We aren't all born full of knowledge; it's acquired by experience and asking questions.

Remember when you asked your mother why you have no friends, and she told you that you're obnoxious, pig headed and your feet smell like a fetid swamp? Same thing..

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Old July 17th 17, 07:32 PM posted to sci.electronics.repair
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Default Resistance measurements

On Mon, 17 Jul 2017 07:59:41 -0700, Jeff Liebermann wrote:

Not high enough. If you want to measure really high resistances, such
as insulation leakage, you need a Megger (which is actually the name of
the company that makes them but has become somewhat of a generic term
for high voltage resistance testers):
https://www.google.com/search?q=megger+meter&tbm=isch
If you want to see if you really have water in the coax cables, you need
one of these insulation testers.


Yeah, I have one. They can still be used perfectly servicably if they're
within spec. The people at Megger tell me that every so often, an old
hand-crank version from the 50s or 60s will come in for re-calibration!
The one I have is the 250V model which is relatively unusual here in the
UK as almost all of them here are 500V. We would typically use the 500V
version for testing our 240V domestic wiring. I guess the 250V model was
intended for export to countries which use 110/120V.

The current range of Meggers are quite expensive, IRO $1200 but at least
you don't have to crank them any more.
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Old July 17th 17, 07:39 PM posted to sci.electronics.repair
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Default Resistance measurements

On Mon, 17 Jul 2017 09:47:17 -0700, John-Del wrote:

Come on Phil, lighten up. The guy didn't know and asked the question.
We aren't all born full of knowledge; it's acquired by experience and
asking questions.


It's no problem. I plonked Phil some time ago on the advice of other
posters here so I rarely get to see any of his unfortunate, socially-
embarrassing outbursts. ;-)

Remember when you asked your mother why you have no friends, and she
told you that you're obnoxious, pig headed and your feet smell like a
fetid swamp? Same thing..


LOL!!! Most amusing. :*D



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