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Old 7th Oct 2018, 4:59 pm   #1
vaslejean
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Default Analog avometer to measure AC on 60Hz

Hello everyone,

I am just curious to know if someone know if the Avometer sold on the american continent were ever corrected for the 60 Hz. A/C supply (as opposed to the 50Hz in U.K & Europe) or if the intrinsic accuracy or resolution of the instrument never called for it ?
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Old 7th Oct 2018, 5:18 pm   #2
merlinmaxwell
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Default Re: Analog avometer to measure A/C on 60Hz

The AVO 8 is rated from 25 to 2000 Hz for AC measurement so will be fine on 60Hz. As an aside I have one of my AVOs (the last model, found in a skip) at work, no one nicks it!
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Old 7th Oct 2018, 5:41 pm   #3
turretslug
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Default Re: Analog avometer to measure A/C on 60Hz

The AVO 8 was an expensive instrument even in its heyday- a substantial proportion went to the UK military who would have expected the accuracy of its AC ranges to extend to AC generators at 400Hz, 1600Hz etc. as well as the 50Hz mains supply and would certainly have specified an expectation of this performance.
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Old 7th Oct 2018, 5:48 pm   #4
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Default Re: Analog avometer to measure A/C on 60Hz

Quote:
The AVO 8 was an expensive instrument
I remember the last on RS (Radio Spares as was) a few years ago (looked it up, 2008, how time fly's by) was about £700, no that isn't a typo, £700.
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Old 7th Oct 2018, 5:54 pm   #5
barrymagrec
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Default Re: Analog avometer to measure A/C on 60Hz

When my Dad bought his AVO 8 MkII new circa 1956 it was a very substantial investment to him at the time - but it still works and he occasionally still uses it.
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Old 7th Oct 2018, 6:28 pm   #6
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Default Re: Analog avometer to measure A/C on 60Hz

I've found Avo 8's to read fine on AC at any frequency.
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Old 7th Oct 2018, 6:35 pm   #7
The Philpott
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Default Re: Analog avometer to measure A/C on 60Hz

They would not have made any adjustment for the 60hz market simply because they didn't need to. Avo 8/III rear panel advises variation plus or minus 2% from 15 cycles to 15 kilocycles, from 10v to 250v. (plus or minus 4% on 2.5v range) In practice won't be measurable. Even the WW2 era meters claim accuracy from 25 to 100 cycles.

If however a pure sine wave is not encountered a (slightly) false reading would be given.

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Old 8th Oct 2018, 11:25 pm   #8
Phil G4SPZ
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Default Re: Analog avometer to measure A/C on 60Hz

The OP didn't specifically mention the Model 8. The Model 7 has a "capacitance" range which needs an external mains-derived AC voltage source, and of course this does need to be 50Hz for the capacitance readings to be accurate. I don't know whether the Model 7 was ever marketed in Canada or the USA, and if it was whether any internal component changes were made to ensure the accuracy of the capacitance range.

I have a 1940s US-made Weston tube checker designed for 110 volts 60Hz mains. This has a capacitance range too, using a similar principle, which works but it is decidedly inaccurate when the instrument is run on 110 volts 50Hz!
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Old 10th Oct 2018, 2:36 am   #9
vaslejean
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Default Re: Analog avometer to measure AC on 60Hz

...Thank you all for your comments and input.

Vaslejean.
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Old 10th Oct 2018, 11:44 am   #10
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Default Re: Analog avometer to measure A/C on 60Hz

Quote:
Originally Posted by merlinmaxwell View Post
Quote:
The AVO 8 was an expensive instrument
I remember the last on RS (Radio Spares as was) a few years ago (looked it up, 2008, how time fly's by) was about £700, no that isn't a typo, £700.
I remember when I was an apprentice back in nineteen hundred and frozen to death (actually the early 1960s) I was given an AVO 8 MK2 with a damaged movement. I sent it away to be repaired and the cost was about £12 which was more than twice my weekly wage at the time. I was recently advised in the AVO survey thread here that £12 in the 1960s was about half the cost of a new AVO 8.

Although I tend to use modern digital instruments now it is still in good working order.

Anyway, back to topic.
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Old 11th Oct 2018, 3:37 pm   #11
Craig Sawyers
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Default Re: Analog avometer to measure AC on 60Hz

I've just taken one of my AVO's off the shelf - an 8mkII - and connected it to my HP745A AC calibrator. On the 10V AC volts range, it is within the thickness of a meter needle from 10Hz to 100kHz. That suggests that it goes a whole lot higher than 100kHz without losing accuracy.

First time I've tried that, and the result is astonishing, candidly.

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Old 11th Oct 2018, 4:24 pm   #12
barrymagrec
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Default Re: Analog avometer to measure AC on 60Hz

The little meter rectifier stack on the Avo 8 MkII looks very similar to ones I have seen on old EMI Tape Machines used for the bias and erase metering, so I imagine they have a pretty reasonable frequency response, by the standards of the time.
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Old 11th Oct 2018, 5:27 pm   #13
merlinmaxwell
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Default Re: Analog avometer to measure AC on 60Hz

Quote:
it is within the thickness of a meter needle from 10Hz to 100kHz
Surprised and pleased, darn good meters. One of the few that are under specified.
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Old 13th Oct 2018, 10:57 am   #14
The Philpott
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Default Re: Analog avometer to measure AC on 60Hz

...All achieved with a copper oxide rectifier, which they saw fit to replace with germanium diodes when the MkIII was introduced. I have only ever had to replace one of the former, and it's under-performance was backed up by the appearance of corrosion on the ends.

You notice how the early Mod 8/9 pamphlets are open about BSS89/1954 Sec.6 not (necessarily) being met on DC volts ranges; old fashioned full disclosure! It's probable that most of the meters, when newish, DID meet the spec. anyway.

(i stand corrected on the 50-60hz capacitance issue, learned something today, thanks Phil!)

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