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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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6th Jun 2017, 2:20 pm | #1 |
Triode
Join Date: Jun 2017
Location: Northampton, Northamptonshire, UK.
Posts: 28
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Avo MkIV Valve tester problems
Hi, I have an Avo MKIV valve tester that works fine until I get to the "test" part of the checks. The meter then tries to swings hard left instead of showing a positive reading. Is this a common problem? Do the back off controls on this meter work the opposite way to the MKIII?
Thanks in advance. |
6th Jun 2017, 3:13 pm | #2 |
Octode
Join Date: Nov 2010
Location: Ross-on-Wye, Herefordshire, UK.
Posts: 1,648
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Re: Avo MkIV Valve tester problems
On the Mk.IV you set the two backing off controls fully clockwise. I don't know what the Mk.III does - but the user manual for the Mk.IV is totally clear on the point (page 16), and I am pretty sure that's what my own Mk.IV does too.
That assumes, of course, that your Mk.IV isn't faulty and someone hasn't been messing with the wiring! But there's no point in worrying about that until a quick twiddle with the backing off controls sees if that clears your problem. Richard |
6th Jun 2017, 3:20 pm | #3 |
Nonode
Join Date: Mar 2008
Location: Virginia Water, Surrey, UK.
Posts: 2,872
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Re: Avo MkIV Valve tester problems
Backing off control at fully clockwise should always give (positive) anode current display on the meter. Negative deflection means a bust control, damaged diode or similar, putting negative offset into anode load even when control is clockwise. Check if anode volts across load resistor make sense. Then track back down the offset circuitry.
Good luck Jeremy
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Jeremy, G8MLK, BVWTVM Friend, VMARS, BVWS Secretary. www.pamphonic.co.uk www.bttt.org.uk |
6th Jun 2017, 6:28 pm | #4 |
Triode
Join Date: Jun 2017
Location: Northampton, Northamptonshire, UK.
Posts: 28
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Re: Avo MkIV Valve tester problems
Thanks for your quick reply. I had not used the tester for a number of years, and the manual I have is for a MKIII tester which states that the back-off controls should be fully anti-clockwise. so, it looks like the MKIV reversed these controls. I will have another try, and see if there are any other faults! Thanks again.
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