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Thread: AVO mk3 HELP !!!

  1. #21
    Join Date: Mar 2015

    Location: Leics UK

    Posts: 11
    I'm Nick.

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    It is a valid point about calibration. I have had a CT160 and now have a VCM163 and I have calibrated them myself. If Andy has just acquired the Mk4 it is a valid and important matter to find out when it was last calibrated.

    Andy, assuming you are happy that it is calibrated or at least recently checked over to make sure it is working OK, then a little time with the manual should be enough to get you conversant with how to check a valve on the Mk 4. From memory it is similar to the CT160 in that it uses a 'backing off' method but it is quite easy once you get the hang of it.

  2. #22
    Join Date: Jun 2015

    Location: London/Durham

    Posts: 3,046
    I'm Lawrence.

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    Quote Originally Posted by Fourlegsgood View Post
    It is a valid point about calibration. I have had a CT160 and now have a VCM163 and I have calibrated them myself. If Andy has just acquired the Mk4 it is a valid and important matter to find out when it was last calibrated.

    Andy, assuming you are happy that it is calibrated or at least recently checked over to make sure it is working OK, then a little time with the manual should be enough to get you conversant with how to check a valve on the Mk 4. From memory it is similar to the CT160 in that it uses a 'backing off' method but it is quite easy once you get the hang of it.
    Thanks for backing up my advice Nick I thought I was in a group of 1 thinking that valve meters need calibrating before serious use.

    Sent from my BLN-L21 using Tapatalk

  3. #23
    Join Date: Apr 2012

    Location: London

    Posts: 556
    I'm James.

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    Lawrence, the issue is not that equipment should work and be of sufficient accuracy for the task, there is no rational argument against that for any piece of lab equipment.

    The issue is the word 'calibration' which is being used. For a piece of equipment to be properly calibrated it needs to demonstrate this, a certificate is required that the equipment meets it's standard, this issued from a testing lab that can demonstrate its own compliance against an independent standard. Otherwise there is no verifiable standard against which the performance of the equipment has been measured.

    To the best of my knowledge there is no independent lab that will calibrate these AVOs any more. We are left with servicing and assays carried out against a user's own equipment. The standard of that equipment may be verified, it might be calibrated or otherwise adequate for their needs, but it is not independently verifiable, and rather unlikely to meet AVO original specification across all ranges. At the end of the day, however good the work performed, it will require calibration standard valves to measure to demonstrate compliance, which are not available, except from those techs/hobbyists who have kept their equipment as well fettled as possible, and this is still not independently verifiable. I personally use various valves tested on a calibrated Amplitrex to assess my testers accuracy. It's within 5%, this is accurate enough for my needs, it is not by any means calibrated.

    So I'd say it might be time to stop banging on about something which can't happen and messing up someone else's fun. He's so fed up he's got it all for sale now. We all know eBay sellers claim all sorts and are often 'mistaken', here is an AoS member who is trying to do the right thing and maybe make a few quid selling some rare and potentially valuable valves, and is in no way pulling a fast one, albeit it's turned out more challenging than he was expecting.

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  4. #24
    Join Date: Sep 2014

    Location: brighton uk.

    Posts: 4,328
    I'm jamie.

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    My System
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  5. #25
    Join Date: Nov 2015

    Location: Wolverhampton

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    I'm Oliver.

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    Quote Originally Posted by karma67 View Post
    You've been busy!
    Lol
    Analogue: Technics SP10 MK2 > Phonomac AT-1010 MK6 tonearm > Ortofon Kontrapunkt b > Bigbottle Jfet MC Valve Phonostage (Telefunken Valves)
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    Price List For SPOTFIRE Cables here:https://bit.ly/2Uxiv3j

    Alternative reading: http://www.audioaddictsforum.com

  6. #26
    Join Date: Sep 2014

    Location: brighton uk.

    Posts: 4,328
    I'm jamie.

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    yep,the search function is a wonderful tool
    My System
    John Wood KT88 Amp.
    Paradise Phono Stage
    Sony TTS-8000 Turntable.
    PMAT-1010 MK6 Tonearm.
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    Yamaha NS1000m Speakers
    KARMA Interconnects & Tonearm Cable

  7. #27
    Join Date: May 2019

    Location: Co.Durham

    Posts: 16
    I'm Frank.

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    Having looked at the ad, the seller does say that it was "calibrated" (in whatever sense you want to use) some years ago *when he first got it*, and that he recommended having it "calibrated" (in whatever sense you want to use) by the buyer. So, the question as to whether or not it has been, is a pretty valid one, especially if it were to be used commercially.

    If I were to buy a valve oscillascope and the seller advised having it calibrated, the first thing I'd do would be to have it calibrated. Old resistors go high, capacitors leak; valves age. If I didn't have it calibrated, how confident could I be in how accurate the readings from it would be? I couldn't.

  8. #28
    Join Date: Jun 2015

    Location: London/Durham

    Posts: 3,046
    I'm Lawrence.

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    Quote Originally Posted by karma67 View Post
    No I didn't ask for readings nor did I give readings when I sold some valves. My point earlier was not that valves should not be sold without readings from a calibrated valve tester but that if readings are given from a valve tester it should have been tested beforehand so that those readings are within a known tolerance of actual (or close to actual) figures. By calibrate I did not mean that it should be calibrated according to the manufacturer's specification but that some work is done to check it is within reasonable tolerance of a reasonably close reading. I'm sure with some advice and access to some accurately measured valves Andy could have done it himself.

    The reason I gave this advice is that Andy had just bought a stash of old and possibly rare and valuable valves and shortly afterwards bought a valve tester. It was a reasonable assumption that his intention was to test the valves with the tester ("calibrated" or "uncalibrated") and sell them. I was concerned that he might find himself in a situation where a professional bought say a matched quad of GEC KT66s to sell on then tested then himself on a serviced machine and found they were out by a significant margin and demanded his money back. Not wanting to see Andy get into this situation and possibly effecting his reputation on here, I sought to give him some advice to avoid this. Clearly some think this was a bad thing to do. I still haven't worked out why.

    I'm sorry if Andy has in the light of this advice decided to sell the lot on, as I said I.didn't think it would be that hard to check the tolerance of his machine with some help from experienced forum members.

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  9. #29
    Join Date: Feb 2008

    Location: Middlesex, UK

    Posts: 4,020
    I'm Alex.

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    One of my main responsibilities at GEG Marconi (later to become BAE Systems), was the calibration of all the equipment in the Advance Technology Department. This included the new (then), technology of X-Ray fluorescence thickness and composition measuring equipment. I had to make the standards for calibration.

    However, we did not have a valve tester in the department.

    I would think it likely that someone on this forum could help.

    https://www.vintage-radio.net/forum/index.php?
    Spendorman

  10. #30
    Join Date: Apr 2012

    Location: London

    Posts: 556
    I'm James.

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    Quote Originally Posted by spendorman View Post
    One of my main responsibilities at GEG Marconi (later to become BAE Systems), was the calibration of all the equipment in the Advance Technology Department. This included the new (then), technology of X-Ray fluorescence thickness and composition measuring equipment. I had to make the standards for calibration.

    However, we did not have a valve tester in the department.

    I would think it likely that someone on this forum could help.

    https://www.vintage-radio.net/forum/index.php?
    From my reading I find that there were plenty of testers in MOV factories (eg. Hammersmith) in the 50s up to early 70s, but not AVOs by any stretch of the imagination! Every large receiving valve and all batches of miniatures were tested prior to batching, packing and dispatch, hence the simple selection for the Gold Lion series. Sounds like you're too young for those days

    There are plenty of people who can fettle AVOs to minimise their accumulated errors, and vintage-radio.net is one good source for such help.The well known ones can be found if one can be bothered to dig a little, you can still get the movement re-magnetised should it be necessary, what you can't do is get one calibrated to a recognised standard with a certificate to prove it meets an accepted standard. So it won't be calibrated, period. Wrong word, and although Lawrence pleads in post #28 that it makes no difference, it isn't splitting hairs - he's just been careless. Andy can't get his tester calibrated so why go on about it. He can get it serviced and checked for accuracy but that is altogether a lower hurdle. I accept that this is what was originally meant, and the irritation felt by some of us comes from the unfortunate use of the wrong word. Just a storm in a teacup, lets move along Sirs.

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