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Old 10th Jul 2022, 10:28 am   #1
HBWOODY
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Default Avo VCM Mk 3 NEG GRID POT

Does anyone know of a suitable replacement of a failed Avo Mk3 neg grid volts potentiometer?
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Old 10th Jul 2022, 11:16 am   #2
Craig Sawyers
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Default Re: Avo VCM Mk 3 NEG GRID POT

https://uk.rs-online.com/web/p/potentiometers/8427002

etc.

There is nothing fancy about the pot in the Mk3 - it is just a linear wirewound pot 10k. Mine was open circuit too - so I just bought one from RS/Farnell/Blore Edwards (forget where; probably RS.

Craig
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Old 10th Jul 2022, 11:23 am   #3
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Default Re: Avo VCM Mk 3 NEG GRID POT

Mullard Magic have Colvern 10k WW NOS for £2

https://mullard.org/collections/comp...ntiometers-nos

Larger diameter 10k ones here https://mullard.org/collections/comp...5k-50000-ohm-1
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Old 11th Jul 2022, 10:10 am   #4
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Default Re: Avo VCM Mk 3 NEG GRID POT

Craig
Thank you for that information. Thought that it may have been a special pot so relieved to know it is a standard linear 10k WW.
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Old 11th Jul 2022, 7:09 pm   #5
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Default Re: Avo VCM Mk 3 NEG GRID POT

The truly tricky one is on the CT160. That covers the range 0 to -40V in a single control, but with the lower voltage ranges expanded. So 0 to -5V is about a third of the rotation, -5V to -15V the second third and -15V to -40V in the final third. The control has three different wirewound resistance sections to achieve that.

There are a number of tricks that people have done if the original and very custom control has failed.

But the Mk3 and I think the Mk4 are linear. The voltage markings are equal with angle from 0 to -22V, and there is a separate switch to add -20, -40, -60 and -80V.

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