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Old 24th Dec 2016, 10:59 pm   #1
oceanobsession1
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Default AVO MK2 help with testing valves.

Hi folks, can anyone help with mutual conductance reading?

First you need to find the mutual conductance of the valve let's say EL84 which is 8.75. So you set the meter selector at 10 and zero the meter then press the mav button, do you then read the mu reading at the top to get the mutual conductance? It's very confusing.

Also when say testing an EL84 you have 50mA, you then zero the meter and press mav. Do you read the mA scale or mav scale for mA/V?

THANKS PHIL.
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Old 25th Dec 2016, 12:04 pm   #2
ms660
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Default Re: AVO MK2 help with testing valves.

I've not used one of those testers so I'm not familiar with one but here's my guess rightly or wrongly....There's two scales, 0 to 100m/A and 0 to 25m/A those show the standing anode current before the meter is backed off to zero, for instance if during the set up the valve's anode draws 40m/A then reading off the top scale of those two should indicate 40m/A, but if for instance the current draw is only 1.5mA then read off the bottom scale.

Moving on to the ma/V test you will already know what reading to expect from a good valve by reference to the ma/V figure in the Avo valve data book, I think the scales then should be divided by ten to represent m/A's per volt, ie: top scale = 0 to 10mA/V, bottom scale = 0 to 2.5mA/V so if for instance you're expecting a figure of say 6mA/V then take a reading from the top scale, if the expected figure was say 1.5mA/V then take a reading from the bottom scale.

So far as I can make out, the selection of which of those two scales to use is governed by the initial setting of the switches as per the valve data/instructions etc.

With a bit of luck someone else can confirm as to what's what for definite.

Lawrence.
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Old 25th Dec 2016, 5:24 pm   #3
mole42uk
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Default Re: AVO MK2 help with testing valves.

Thanks Lawrence, I had no idea that "the mav button" meant the ma/V switch!!
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Old 15th Jan 2017, 11:05 am   #4
Phil G4SPZ
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Default Re: AVO MK2 help with testing valves.

On the Mk III, which may be different, after backing off the anode current to zero and switching to mA/V, the actual value of mA/V is found by rotating the mA/V control to bring the meter pointer up to the line marked in the middle of the green sector at about 70% of FSD. Then read off the gain from the rotary mA/V control.
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