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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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#1
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Vintage equipment voltage measurement
Gentlemen,
One of the drawbacks of attempting to fix vintage stuff is the expected voltage readings given in the service manuals of the day. The manuals usually state that the readings given were measured with analogue VMs of a certain ohms-per-volt rating - most commonly IME 20k. Consequently if you measure with a modern DVM with stupendously high Zin you're screwed and will get unrealistically high values. That's never worried me as I keep a vintage AVO for just such circs. All the British service manuals seem to reference 20k OpV AVOs. However, I'm currently TS on a mid 70s Tek scope the manual for which states the readings given are valid for a meter with a Zin of between 100k and 200k (specifically a Triplett 630NS see link). Anyone come up with a solution to the problem of making voltage readings on high impedance parts of a circuit with a meter of a different Zin to that used by the people who wrote the service manual? Never heard of an analogue meter with such a high Zin, but here it is: https://tinyurl.com/ycjz9l4o -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition. |
#2
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Vintage equipment voltage measurement
Put the appropriate resistance across the test leads.
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#3
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Vintage equipment voltage measurement
Cursitor Doom wrote
Anyone come up with a solution to the problem of making voltage readings on high impedance parts of a circuit with a meter of a different Zin to that used by the people who wrote the service manual? If it is available look a the circuit under test, and see if the high impedance does make a real difference. Else use the scope probe... Do not some of them modern Di Gital makes also display volts? If meter impdance is too high and no other way add a resistor in parallel to your meter? |
#4
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Vintage equipment voltage measurement
On Sunday, 19 August 2018 16:17:51 UTC+1, Cursitor Doom wrote:
Gentlemen, One of the drawbacks of attempting to fix vintage stuff is the expected voltage readings given in the service manuals of the day. The manuals usually state that the readings given were measured with analogue VMs of a certain ohms-per-volt rating - most commonly IME 20k. Consequently if you measure with a modern DVM with stupendously high Zin you're screwed and will get unrealistically high values. That's never worried me as I keep a vintage AVO for just such circs. All the British service manuals seem to reference 20k OpV AVOs. However, I'm currently TS on a mid 70s Tek scope the manual for which states the readings given are valid for a meter with a Zin of between 100k and 200k (specifically a Triplett 630NS see link). Anyone come up with a solution to the problem of making voltage readings on high impedance parts of a circuit with a meter of a different Zin to that used by the people who wrote the service manual? Never heard of an analogue meter with such a high Zin, but here it is: https://tinyurl.com/ycjz9l4o 100-200k is 5-10v scale on a 20k/V meter. Or use a digital & add your R. High R meters give a more realistic reading than old analogues on high R circuitry. NT |
#5
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Vintage equipment voltage measurement
On Sun, 19 Aug 2018 15:17:49 -0000 (UTC), Cursitor Doom
wrote: Gentlemen, One of the drawbacks of attempting to fix vintage stuff is the expected voltage readings given in the service manuals of the day. Why not ignore the voltage notes and just fix it? -- John Larkin Highland Technology, Inc lunatic fringe electronics |
#6
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Vintage equipment voltage measurement
On Sun, 19 Aug 2018 09:24:57 -0700, John Larkin wrote:
Why not ignore the voltage notes and just fix it? You're obviously not a service engineer. ;-) -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition. |
#7
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Vintage equipment voltage measurement
On Sun, 19 Aug 2018 16:13:00 +0000, 698839253X6D445TD wrote:
If meter impdance is too high and no other way add a resistor in parallel to your meter? Oh, I see. I didn't quite understand what Clive was getting at. Would that do the trick, d'ya rechnung? -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition. |
#8
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Vintage equipment voltage measurement
On Sun, 19 Aug 2018 16:41:26 -0000 (UTC), Cursitor Doom
wrote: On Sun, 19 Aug 2018 09:24:57 -0700, John Larkin wrote: Why not ignore the voltage notes and just fix it? You're obviously not a service engineer. ;-) I'm an engineer, not a service technician. This is an electronic design group. I think there is an electronic repair group. The engineering approach to fixing things is to probe around, understand how it's supposed to work, and figure out why it doesn't. -- John Larkin Highland Technology, Inc lunatic fringe electronics |
#9
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Vintage equipment voltage measurement
On 19/08/18 17:56, John Larkin wrote:
On Sun, 19 Aug 2018 16:41:26 -0000 (UTC), Cursitor Doom wrote: On Sun, 19 Aug 2018 09:24:57 -0700, John Larkin wrote: Why not ignore the voltage notes and just fix it? You're obviously not a service engineer. ;-) I'm an engineer, not a service technician. Spot on! |
#10
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Vintage equipment voltage measurement
On Sun, 19 Aug 2018 09:56:08 -0700, John Larkin wrote:
I'm an engineer, not a service technician. Good Lord!! I've only been reading your comments on this group for the last 20+ years and never really noticed that before! ;-) -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition. |
#11
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Vintage equipment voltage measurement
John Larkin wrote:
This is an electronic design group. I think there is an electronic repair group. This thread is cross-posted to both ... |
#12
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Vintage equipment voltage measurement
On 8/19/2018 8:17 AM, Cursitor Doom wrote:
Gentlemen, One of the drawbacks of attempting to fix vintage stuff is the expected voltage readings given in the service manuals of the day. The manuals usually state that the readings given were measured with analogue VMs of a certain ohms-per-volt rating - most commonly IME 20k. Consequently if you measure with a modern DVM with stupendously high Zin you're screwed and will get unrealistically high values. That's never worried me as I keep a vintage AVO for just such circs. All the British service manuals seem to reference 20k OpV AVOs. However, I'm currently TS on a mid 70s Tek scope the manual for which states the readings given are valid for a meter with a Zin of between 100k and 200k (specifically a Triplett 630NS see link). Anyone come up with a solution to the problem of making voltage readings on high impedance parts of a circuit with a meter of a different Zin to that used by the people who wrote the service manual? Never heard of an analogue meter with such a high Zin, but here it is: https://tinyurl.com/ycjz9l4o What's so hard about putting a resistor in parallel with your meter? |
#13
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Vintage equipment voltage measurement
On 08/19/2018 12:56 PM, John Larkin wrote:
On Sun, 19 Aug 2018 16:41:26 -0000 (UTC), Cursitor Doom wrote: On Sun, 19 Aug 2018 09:24:57 -0700, John Larkin wrote: Why not ignore the voltage notes and just fix it? You're obviously not a service engineer. ;-) I'm an engineer, not a service technician. This is an electronic design group. I think there is an electronic repair group. The engineering approach to fixing things is to probe around, understand how it's supposed to work, and figure out why it doesn't. The engineering approach to climbing Mt. Everest is to find out where it is. Learn to climb stuff. Get a bunch of money. Buy the stuff and hire the people you need to climb it. Go to where it is. And then climb it using the stuff. |
#14
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Vintage equipment voltage measurement
On Sun, 19 Aug 2018 11:28:10 -0700, mike wrote:
What's so hard about putting a resistor in parallel with your meter? Never even occurred to me. -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition. |
#15
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Vintage equipment voltage measurement
Cursitor Doom wrote:
On Sun, 19 Aug 2018 11:28:10 -0700, mike wrote: What's so hard about putting a resistor in parallel with your meter? Never even occurred to me. That's what you get when people lack basic understanding of the matter. |
#16
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Vintage equipment voltage measurement
On 2018/08/19 11:53 AM, Cursitor Doom wrote:
On Sun, 19 Aug 2018 11:28:10 -0700, mike wrote: What's so hard about putting a resistor in parallel with your meter? Never even occurred to me. Resistance used depends on the range: https://canadianvintageradio.com/how_to/example-how-to/ better explanation: https://www.allaboutcircuits.com/tex...sured-circuit/ John |
#17
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Vintage equipment voltage measurement
On Sun, 19 Aug 2018 19:09:10 +0000, Rob wrote:
Cursitor Doom wrote: On Sun, 19 Aug 2018 11:28:10 -0700, mike wrote: What's so hard about putting a resistor in parallel with your meter? Never even occurred to me. That's what you get when people lack basic understanding of the matter. I've only recently discovered that I invariably overlook simpler solutions. Fortunately I'm only a hobbyist and don't do this for a living! -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition. |
#18
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Vintage equipment voltage measurement
On 19/08/18 20:41, Cursitor Doom wrote:
On Sun, 19 Aug 2018 19:09:10 +0000, Rob wrote: Cursitor Doom wrote: On Sun, 19 Aug 2018 11:28:10 -0700, mike wrote: What's so hard about putting a resistor in parallel with your meter? Never even occurred to me. That's what you get when people lack basic understanding of the matter. I've only recently discovered that I invariably overlook simpler solutions. Fortunately I'm only a hobbyist and don't do this for a living! And that is clearly true for more than just electronics! |
#19
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Vintage equipment voltage measurement
On 8/19/2018 12:14 PM, John Robertson wrote:
On 2018/08/19 11:53 AM, Cursitor Doom wrote: On Sun, 19 Aug 2018 11:28:10 -0700, mike wrote: What's so hard about putting a resistor in parallel with your meter? Never even occurred to me. Resistance used depends on the range: https://canadianvintageradio.com/how_to/example-how-to/ better explanation: https://www.allaboutcircuits.com/tex...sured-circuit/ John Or you could just read the question: I'm currently TS on a mid 70s Tek scope the manual for which states the readings given are valid for a meter with a Zin of between 100k and 200k (specifically a Triplett 630NS see link). |
#20
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Vintage equipment voltage measurement
On Sunday, August 19, 2018 at 11:30:00 AM UTC-7, mike wrote:
What's so hard about putting a resistor in parallel with your meter? Even better would be to understand why they specified VOMs with 20k/V sensitivity, and the implications with modern instruments. Back in those days, the commonly-available multimeters were 1k/V and 20k/V VOMs and 11 Meg VTVMs. The cheaper 1k/V would load down the circuit and give an erroneously low voltage reading. With the 20k/V VOM and the VTVM, this error was usually smaller than the inaccuracy in the analog meter movement. |
#21
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Vintage equipment voltage measurement
On Sun, 19 Aug 2018 19:41:48 -0000 (UTC), Cursitor Doom
wrote: I've only recently discovered that I invariably overlook simpler solutions. Nothing is simple or stays simple. Everything becomes more complexicated. Fortunately I'm only a hobbyist and don't do this for a living! I know the feeling. Three times in my life I've turned my hobby into a business. Now, I'm getting ready to begin to start planning to retire and I'm turning my business into a hobby with at least one of my hobbies into a potential business. Perhaps it would be better for the skools to teach hobbies instead of professions? -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#22
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Vintage equipment voltage measurement
On Sun, 19 Aug 2018 09:56:08 -0700, John Larkin
wrote: The engineering approach to fixing things is to probe around, understand how it's supposed to work, and figure out why it doesn't. Nope. The difference between engineering and repair is that the engineer assumes that the problem is due to a design error and fixes the problem by redesigning the circuit. The repair tech assumes that it was designed and built correctly, therefore something has blown. The engineers needs to make production lots of an instrument work. The repair technician usually needs to make one work. The engineer tries to determine how the circuit should work. The repair tech tries to determine what the engineer was thinking when he designed the circuit. The engineer understands how the circuit should work. The technician understands what the circuit actually does. The engineer has experience making the instrument work under laboratory conditions. The technician has experience making it work in the rather nasty "real world" environment. The engineer selects components based on availability, performance, price, and lifetime. The repair tech substitutes whatever can be found in his junk box. The engineer writes the documentation partly to demonstrate to the world the cleverness and greatness of his design. The repair tech doesn't read the documentation unless he's desperate. The engineer makes measurements in order to find problems. The repair tech looks for smoke, burned parts, bulging capacitors, broken connections, manufacturing errors, and mechanical damage. Well, maybe he does take a few measurements like the power supply voltages. All this works very nicely as long as engineers don't try to act like technicians and technicians don't try to act like engineers. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#23
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Vintage equipment voltage measurement
On Sun, 19 Aug 2018 16:22:39 -0700, Jeff Liebermann wrote:
I know the feeling. Three times in my life I've turned my hobby into a business. Now, I'm getting ready to begin to start planning to retire and I'm turning my business into a hobby with at least one of my hobbies into a potential business. Perhaps it would be better for the skools to teach hobbies instead of professions? Not sure about the US, but schools in the UK are teaching kids *what* to think rather than how to. Very little of a typical school day is now spent learning anything genuinely useful. The kids the schools turn out into the world of work nowadays are mostly only suited to flipping burgers or delivering pizzas. -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition. |
#24
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Vintage equipment voltage measurement
Cursitor Doom wrote:
On Sun, 19 Aug 2018 09:56:08 -0700, John Larkin wrote: I'm an engineer, not a service technician. Good Lord!! I've only been reading your comments on this group for the last 20+ years and never really noticed that before! ;-) Your nym isn't that old. What was it before? |
#25
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Vintage equipment voltage measurement
On 2018-08-19, Cursitor Doom wrote:
Gentlemen, One of the drawbacks of attempting to fix vintage stuff is the expected voltage readings given in the service manuals of the day. The manuals usually state that the readings given were measured with analogue VMs of a certain ohms-per-volt rating - most commonly IME 20k. Consequently if you measure with a modern DVM with stupendously high Zin you're screwed and will get unrealistically high values. That's never worried me as I keep a vintage AVO for just such circs. All the British service manuals seem to reference 20k OpV AVOs. However, I'm currently TS on a mid 70s Tek scope the manual for which states the readings given are valid for a meter with a Zin of between 100k and 200k (specifically a Triplett 630NS see link). Anyone come up with a solution to the problem of making voltage readings on high impedance parts of a circuit with a meter of a different Zin to that used by the people who wrote the service manual? if too high add parallell resistance. if too low select a higer voltage range. https://tinyurl.com/ycjz9l4o unreal 5uA full scale. -- ت |
#26
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Vintage equipment voltage measurement
On 20/08/18 01:14, Cursitor Doom wrote:
On Sun, 19 Aug 2018 16:22:39 -0700, Jeff Liebermann wrote: I know the feeling. Three times in my life I've turned my hobby into a business. Now, I'm getting ready to begin to start planning to retire and I'm turning my business into a hobby with at least one of my hobbies into a potential business. Perhaps it would be better for the skools to teach hobbies instead of professions? Not sure about the US, but schools in the UK are teaching kids *what* to think rather than how to. Very little of a typical school day is now spent learning anything genuinely useful. And if the ex Secretary of State for Education (and poisonous brexiteer) Michael Gove got his way, they won't be taught to think at all, only to regurgitate "useful" facts such as when King Henry II reigned. But then he also wanted more madrassahs, under the guise of wanting more religion in education. He even approved the creation of three Creationist schools. But of course the success and failure is far more nuanced than CD states. The kids the schools turn out into the world of work nowadays are mostly only suited to flipping burgers or delivering pizzas. Old farts have always said that, and always will. When doing A-level pure maths, homework often consisted of doing questions from past exams. The older ones were more difficult than the recent ones, with those from the early 50s being bloody hard. |
#27
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Vintage equipment voltage measurement
Jasen Betts wrote:
On 2018-08-19, Cursitor Doom wrote: Gentlemen, One of the drawbacks of attempting to fix vintage stuff is the expected voltage readings given in the service manuals of the day. The manuals usually state that the readings given were measured with analogue VMs of a certain ohms-per-volt rating - most commonly IME 20k. Consequently if you measure with a modern DVM with stupendously high Zin you're screwed and will get unrealistically high values. That's never worried me as I keep a vintage AVO for just such circs. All the British service manuals seem to reference 20k OpV AVOs. However, I'm currently TS on a mid 70s Tek scope the manual for which states the readings given are valid for a meter with a Zin of between 100k and 200k (specifically a Triplett 630NS see link). Anyone come up with a solution to the problem of making voltage readings on high impedance parts of a circuit with a meter of a different Zin to that used by the people who wrote the service manual? if too high add parallell resistance. if too low select a higer voltage range. In the old analog meters, there basically was only a current meter, often 50uA full scale, and when measuring voltage a suitable series resistor is switched in to make it draw 50uA at the full scale reading. So a 10V range would have a total resistance of 10V/50uA = 200k (which would be the resistance of the meter itself plus the series R). At 10V measured voltage there is 50uA through the 200k resistance. When looking at this, any range will have a resistance of 1V/50uA per volt of range, hence "20K per volt". The 100V range will be 2M. This is no longer true for a modern DVM. They usually have a 10M series resistor on the input with selectable resistors to ground to make a voltage divider that outputs the desired voltage for the ADC. So, depending on the range you select, the input resistance will be 10M plus a small value that will get smaller when you select a higher range. Therefore there is no fixed "K per volt" input resistance anymore, and selecting a higher range will not result in a higher resistance. However, as already can be seen, the "20K per volt" is not really telling the input resistance to be used in the measurement. It depends on the selected range, and available ranges vary between meters. One may have ranges of 10-30-100 and another maybe 10-50-200. When you need to measure a 24V testpoint, on one meter it may be on the 30V range (and thus 600k resistance) and on another meter it would be the 50V range (and thus 1M resistance). It is expected that the person doing the measurement understands how this could affect the result, if it does at all. (when measuring a supply voltage, there should not be a noticable difference. when measuring in a high-impedance signal circuit, there could be) |
#28
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Vintage equipment voltage measurement
On 20/08/18 00:44, Jeff Liebermann wrote:
On Sun, 19 Aug 2018 09:56:08 -0700, John Larkin wrote: The engineering approach to fixing things is to probe around, understand how it's supposed to work, and figure out why it doesn't. Nope. The difference between engineering and repair is that the engineer assumes that the problem is due to a design error and fixes the problem by redesigning the circuit. The repair tech assumes that it was designed and built correctly, therefore something has blown. The engineers needs to make production lots of an instrument work. The repair technician usually needs to make one work. The engineer tries to determine how the circuit should work. The repair tech tries to determine what the engineer was thinking when he designed the circuit. The engineer understands how the circuit should work. The technician understands what the circuit actually does. The engineer has experience making the instrument work under laboratory conditions. The technician has experience making it work in the rather nasty "real world" environment. The engineer selects components based on availability, performance, price, and lifetime. The repair tech substitutes whatever can be found in his junk box. The engineer writes the documentation partly to demonstrate to the world the cleverness and greatness of his design. The repair tech doesn't read the documentation unless he's desperate. The engineer makes measurements in order to find problems. The repair tech looks for smoke, burned parts, bulging capacitors, broken connections, manufacturing errors, and mechanical damage. Well, maybe he does take a few measurements like the power supply voltages. All this works very nicely as long as engineers don't try to act like technicians and technicians don't try to act like engineers. There is, of course, one domain where that engineer/technician distinction is almost completely meaningless: software, particularly "enterprise" software. Worse, they are proud of it, and actively seek to merge all development phases. The end result is that many sticky fingers poke at the various parts of the system, and eventually nobody knows a system's specification or what it actually does. Provided it doesn't fail the tests, it is defined as working. |
#29
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Vintage equipment voltage measurement
OK - Let me start off with the statement, paraphrased from A.A. Milne:
When you are a Bear of Very Little Brain, and you Think of Things, you find sometimes that a Thing which seemed very Thingish inside you is quite different when it gets out into the open and has other people looking at it. I have been repairing and restoring vintage equipment, as a hobby, for over 40 years now. For over 25 years of that time, I have used a Fluke auto-ranging DMM, and never a VTVM or similar vintage equivalent, although I have used same for comparative purposes. Discovering the following: a) Yes, I have gotten different voltage readings 'from the book'. b) Many (but not all) of which are explained by higher wall-plate voltages. c) The differences not explained by wall-plate voltages are usually consistent. d) Meaning that I can account for, and adjust to these differences without having to introduce outboard solutions. Peter Wieck Melrose Park, PA |
#30
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Vintage equipment voltage measurement
On Monday, August 20, 2018 at 9:14:49 AM UTC-4, wrote:
OK - Let me start off with the statement, paraphrased from A.A. Milne: When you are a Bear of Very Little Brain, and you Think of Things, you find sometimes that a Thing which seemed very Thingish inside you is quite different when it gets out into the open and has other people looking at it. I have been repairing and restoring vintage equipment, as a hobby, for over 40 years now. For over 25 years of that time, I have used a Fluke auto-ranging DMM, and never a VTVM or similar vintage equivalent, although I have used same for comparative purposes. Discovering the following: a) Yes, I have gotten different voltage readings 'from the book'. b) Many (but not all) of which are explained by higher wall-plate voltages. c) The differences not explained by wall-plate voltages are usually consistent. d) Meaning that I can account for, and adjust to these differences without having to introduce outboard solutions. Peter Wieck Melrose Park, PA Just to add (and not referring directly to any measurements you may have made) that many discrepancies in measurements are the result of not following the service manual specifics regarding test conditions. A properly prepared SM will include the conditions of measurement - such as line voltage, warm up time, impedance of the meter, whether or not a signal is applied, setting of customer controls and service adjustments and placement of switches or functions selected. There are others I'm sure. |
#31
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Vintage equipment voltage measurement
On Monday, August 20, 2018 at 10:21:20 AM UTC-4, John-Del wrote:
Just to add (and not referring directly to any measurements you may have made) that many discrepancies in measurements are the result of not following the service manual specifics regarding test conditions. A properly prepared SM will include the conditions of measurement - such as line voltage, warm up time, impedance of the meter, whether or not a signal is applied, setting of customer controls and service adjustments and placement of switches or functions selected. There are others I'm sure. Yep. Try aligning any of several multi-band radios without following the manual - and see how far you get. Peter Wieck Melrose Park, PA |
#32
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Vintage equipment voltage measurement
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#33
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Vintage equipment voltage measurement
When calibrating tube testers it really matters. Otherwise a parallel resistace should work. Many DMM's have a 10 M input Z.
A "Typical" scope might have a 1 M shunted by 22 pf or so. When you add a x10 probe the input Z should be 10 ohms resistive. Many DVM' had say a 50 uA movement with some sort of resistance (meter movement+series), Ohms/V is the reciprocal of current. So, your actually measuring a current through a fixed resistance with a scale in volts.` |
#34
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Vintage equipment voltage measurement
Most DVMs I've worked with are 11 Meg regardless of voltage settings. This is not 'stupendous'. A 50 KΩ/Volt meter on a 1000 setting will be 50 Meg but is only 250K on a 5 Volt setting. I've been using DVMs for service for nearly 40 years and have not run into any faulty readings because of an 11 meg load with one exception. In a Sony BVP30 broadcast camera they use a 200 Volt power supply for the electrostatic deflection. The 11 meg load was way too LOW to get valid readings We had to get a high voltage probe which is over a giga ohm to get useful readings.
G² |
#35
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Vintage equipment voltage measurement
I figured I have to back my statement up:
from: PDF page #1: https://www.desmith.net/NMdS/Electro...ion%20V4.1.pdf Use this procedure to test and calibrate the Hickok Model 539C mutual conductance (AKA transconductance) tube tester. Except as noted, all of the readings are taken with a 1000 ohms per vol t meter. If an accurate 1000 ohms per volt meter is n ot available a modern high impedance analog or digital voltmeter can be used with appropriate shun t resistors in parallel with the input to simulate proper loading. The following resistor values shoul d be used: 10 volt scale use 10K, 50 volt scale use 51K, 250 volt scale use 250K. All resistors are 1/2 watt 5% carbon composition. Calibration will be easier if you supply AC power through a constant voltage regu lation type transformer to do the tests, but this i s not essential. Recalibrate the tester any time eith er rectifier tube is replaced. The correct type #81 (#63 for 230VAC mains) fuse lamp must be installed in th e tester or false readings can result. |
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