31-03-2013, 11:39 AM
Al,
That's what Advance says it does - see attached for the 'C'.
Alan
That's what Advance says it does - see attached for the 'C'.
Alan
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Advance VM77 Valve Millivoltmeters
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31-03-2013, 01:13 PM
The attachment shows OK here Joe. It's a jpg of a page of the Manual.
I've got a djvu version of the 'B' Manual which is clearer. I'll send it to you. Alan (31-03-2013, 11:39 AM)AlanBeckett Wrote: Al, Hmm, so I see. That 'specification' is not exactly 'informative' is it?  Quote: "Freq. range: 15 Hz to 4.5 MHz". O.K., what's their definition of 'frequency range'? Are those the bandwidth limits for - 3dB? - 1dB ? Without a relative signal level, those 'bandwidth' freqs. are meaningless. Then we have the 'accuracy' figures beneath: which I can't 'square' with those bandwidth figures. Quote: "Amplifier freq. response 12 Hz - 200 kHz (100 kΩ / 40 pF load). Response rises to 3 MHz and falls away above that freq." That clearly contradicts the "15 Hz to 4.5 MHz" figure. So I reckon that we can safely assume that for the purposes of measurement, the bandwidth is actually 12 Hz - 200 kHz. Since the 'amplifier' drives the front panel meter, that would make sense. And when they say "rises to 3 MHz and then falls away", that is so vague as to be a worthless comment! If this was mine, I'd run my own series of measurements on this, using suitable test equipment: calibrated sig. gen. + calibrated 'scope. As I have said countless times before, equipment whose calibration or spec. you cannot trust is worse than not having that kit in the first place. Without kit, you can sometimes make an informed guess; with kit of dubious spec. / calibration, all you get are measurements that you think you can trust - and then later on you wonder why things are failing to make sense. Now please don't misunderstand me: I'm not knocking this piece of T & M kit. I am sure that the VM77 series of VTVMs are perfectly adequate for, and are quite capable of, doing their designed job - but one has to know, reliably and with a reasonable degree of accuracy, their limitations - as with any piece of T & M kit, produced by anyone. Al. / March 31 //
31-03-2013, 01:30 PM
Al,
Yes, it does seem slightly odd. I've attached the 'B' Manual which has a better descrition of the Amplifier etc and how to Callibrate it. Alan 
MANadvvm77b.djvu (Size: 155.03 KB / Downloads: 91)
31-03-2013, 01:38 PM
Rats! I've just been two hours sorting a version of that out for The Archive.
Yours is better though. - Joe
31-03-2013, 01:51 PM
Insert Emoticon for sticking tongue out and waggling fingers behind ears
 I was meaning to send what I've got to you but didn't get round to it, sorry. Alan
31-03-2013, 02:54 PM
(31-03-2013, 01:30 PM)AlanBeckett Wrote: Al, So I see: thanks. Having read it through, most of same vagueness and apparent inconsistencies remain. Plus I found these: Quote 1: When the amplifier jack is inserted, [this being the output of the amplifier], the meter function is inaccurate: the jack plug must be removed for use as a voltmeter. Unquote. Quote 2: The amplifier output, in r.m.s. volts, with 100 kΩ, 40 pF load, is within 2 dB of meter on top scale, at half scale This holds on all range settings. Unquote. So on that basis, the "within 2 dB of the meter top scale . . ." {quote 2} is an inaccurate indication. {quote 1}. Elsewhere in the spec. write-up, implications are given that 2 dB indications are 'accurate'. Huh? Plus when they say "within 2 dB of meter on top scale, at half scale", do they really mean "within 2 dB of meter on top range {of meter}, at half scale" ? If I was working for Advance as a technician, I would want to re-write that entire spec. so that it was a good deal 'tighter' and more consistent. Now some might claim that I am now becoming a bit of a pedant and possibly hair-splitting - but, (of course), I would disagree with that. And that is simply because I have spent many hours writing test procedures for electronic equipment, using those procedures - and using those written by others. And it was my name that appeared on the 'Tested (to spec.)' sheet that was issued with the item to the customer - who, more often than not, were highly-trained, qualified and experienced engineers and technicians. And should that item fail its Goods Inwards test at their establishment, guess who would get a rocket? Correct! I know all this sounds a bit negative, and I do indeed try to avoid undue criticism - when it is clearly unwarranted, but for reasons I have previously explained, I place great store in having T & M kit that you can trust and rely on. Would you be happy with a 12" ruler that now and again reported that a certain length was "somewhere between 11.5 and 12.5 inches"? Al.
31-03-2013, 03:06 PM
""Plus when they say "within 2 dB of meter on top scale, at half scale", do they really mean "within 2 dB of meter on top range {of meter}, at half scale" ?""
Hi Al, I'm reading that as half FSD on the top printed scale. Lawrence. |
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