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| Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
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22nd Nov 2025, 9:55 am
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#1 |
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Heptode
Join Date: Nov 2018
Location: Staffordshire Moorlands, UK.
Posts: 659
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AVO 8 MK 3 Terminal Query
Good morning all,
Just a quick query. You will note that the AVO Mk3 has the left input as Common Terminal DC + & AC and the right terminal as DC- & AC switch ranges. The AVO Mk5 has the left terminal as DC+ & AC and the right terminal as common. Please explain why the common terminals are are reversed and please confirm that the red test lead should be connected to the lefthand terminal on the older Mk3. Thank you. Brian |
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22nd Nov 2025, 12:34 pm
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#2 |
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Heptode
Join Date: Mar 2020
Location: Rochdale, Greater Manchester, UK.
Posts: 766
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Re: AVO 8 MK 3 Terminal Query
Hi Brian - confirming that "it does what it says on the tin" for the older Model 8 Mk3 (and others) the bottom left-hand terminal is indeed the DC+ terminal, as marked. I'm looking at a pair of them on the bench right now. Those plastic caps do come up from time to time on EBay.
Cheers Chris |
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22nd Nov 2025, 1:53 pm
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#3 |
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Heptode
Join Date: Nov 2018
Location: Staffordshire Moorlands, UK.
Posts: 659
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Re: AVO 8 MK 3 Terminal Query
Thanks Chris, so the red test lead on the Mk 3 does actually connect to the common DC+ & AC?
Thanks, Brian |
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22nd Nov 2025, 2:03 pm
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#4 |
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Heptode
Join Date: Mar 2020
Location: Rochdale, Greater Manchester, UK.
Posts: 766
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Re: AVO 8 MK 3 Terminal Query
Yes, that's correct Brian. Why not give it a try on a 1.5V battery to give you confidence?
It may help you to get it straight in your head if you think of it as it's actually marked on the Avo, "DC+ and A.C. Common Terminal" rather than as you have written here twice "Common Terminal DC + & AC" So for DC measurements it is always the +ve terminal. Cheers Chris |
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22nd Nov 2025, 2:08 pm
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#5 |
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Heptode
Join Date: Nov 2018
Location: Staffordshire Moorlands, UK.
Posts: 659
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Re: AVO 8 MK 3 Terminal Query
Thanks Chris, will do as you say.
Thanks. Brian |
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22nd Nov 2025, 2:33 pm
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#6 |
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Heptode
Join Date: Nov 2018
Location: Staffordshire Moorlands, UK.
Posts: 659
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Re: AVO 8 MK 3 Terminal Query
OK Chris, got it now.
Cheers. Brian |
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22nd Nov 2025, 5:34 pm
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#7 |
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Octode
Join Date: Jul 2004
Location: Dundee, Scotland, UK.
Posts: 1,913
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Re: AVO 8 MK 3 Terminal Query
Replacement terminal caps can be successfully 3D printed. A search should find a link to the data for this which I posted during the last year or so.
PMM |
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22nd Nov 2025, 6:33 pm
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#8 |
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Heptode
Join Date: Nov 2018
Location: Staffordshire Moorlands, UK.
Posts: 659
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Re: AVO 8 MK 3 Terminal Query
Thank you PMM, will have a search.
Brian |
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25th Nov 2025, 8:43 pm
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#9 |
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Dekatron
Join Date: Aug 2016
Location: Colchester, Essex, UK.
Posts: 4,430
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Re: AVO 8 MK 3 Terminal Query
Carefully warm them up before fitting to avoid cracking, as the splines have to cut into the plastic as they're installed. Repro ones may be less vulnerable depending on the material used.
Dave |
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2nd Dec 2025, 2:51 pm
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#10 |
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Heptode
Join Date: Feb 2010
Location: Heysham, Lancashire, UK.
Posts: 731
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Re: AVO 8 MK 3 Terminal Query
The “COMMON” engraving only applies to the kV ranges, which use the top terminals and one of the bottom terminals, the one marked COMMON.
In the Mk3, for the 2.5kV DC range the bottom left terminal is the positive terminal and the top left terminal is the negative terminal. In the Mk5, for the 3kV DC range the bottom right terminal is the negative terminal and the top left terminal is the positive terminal. So for kV ranges only, the common terminal has swapped sides, and the top terminal has changed from negative to positive. Stuart |
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