Avo Ct160 Help Needed - UK Vintage Radio Repair and Restoration Discussion Forum

AvoFan · 17th Jul 2005, 3:57 pm

Hello to all,
I'm new to this forum and this is my first post.
I recently purchased an Avo 160 tester without a chance to test it first ( no power cord) with the asurance that it worked fine. When I got it home I made up a power cord and plugged it in. While trying to calibrate it for line voltage of 240v I noticed that the meter doesn't respond like it should according to the manual. In fact it remains quiet still, refusing to move at all.
I've checked all voltages and they test fine, all inline with the manual specs.
I put a DMM across the meter (200k setting) and the meter moved half way up the scale.
Would anyone on this forum know if this meter is faulty and needs replaced?
Is there any tests I can do to find out if the meter is good/bad?
Thanks for any help

Wayne

Station X · 17th Jul 2005, 4:23 pm

Wayne.

The meter has a Full Scale Delection of 30 microamps and an internal resistance of 3250 ohms.

Connect a 330K resistor in series with it giving a total of 333250 ohms. If you now apply 9 volts from a battery to the series combination a current of about 27 microamps should flow. If the meter is OK it will have almost full scale deflection.

Repeat with bigger resistors which should give lower readings in accordance with ohms law.

Graham.

Mike Phelan · 17th Jul 2005, 8:04 pm

Hi Wayne
Make sure the Vg pot is intact - they get fried if the valve has excessive grid current.

retailer · 18th Jul 2005, 10:08 pm

Hi
The screen supply is half wave rectified DC and will appear to measure at about the set value. You need to check it at the pins of the 6AL5 rectifier.

17th Jul 2005, 3:57 pm	#1
AvoFan Retired Dormant Member Join Date: Jul 2005 Posts: 1	Avo Ct160 Help Needed Hello to all, I'm new to this forum and this is my first post. I recently purchased an Avo 160 tester without a chance to test it first ( no power cord) with the asurance that it worked fine. When I got it home I made up a power cord and plugged it in. While trying to calibrate it for line voltage of 240v I noticed that the meter doesn't respond like it should according to the manual. In fact it remains quiet still, refusing to move at all. I've checked all voltages and they test fine, all inline with the manual specs. I put a DMM across the meter (200k setting) and the meter moved half way up the scale. Would anyone on this forum know if this meter is faulty and needs replaced? Is there any tests I can do to find out if the meter is good/bad? Thanks for any help Wayne

17th Jul 2005, 4:23 pm	#2
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,287	Re: Avo Ct160 Help Needed Wayne. The meter has a Full Scale Delection of 30 microamps and an internal resistance of 3250 ohms. Connect a 330K resistor in series with it giving a total of 333250 ohms. If you now apply 9 volts from a battery to the series combination a current of about 27 microamps should flow. If the meter is OK it will have almost full scale deflection. Repeat with bigger resistors which should give lower readings in accordance with ohms law. Graham.

17th Jul 2005, 8:04 pm	#3
Mike Phelan Dekatron Join Date: Nov 2003 Location: Near Leeds, West Yorkshire, UK Posts: 4,609	Re: Avo Ct160 Help Needed Hi Wayne Make sure the Vg pot is intact - they get fried if the valve has excessive grid current. __________________ Mike.

18th Jul 2005, 10:08 pm	#4
retailer Heptode Join Date: May 2005 Location: Adelaide, South Australia Posts: 541	Re: Avo Ct160 Help Needed Hi The screen supply is half wave rectified DC and will appear to measure at about the set value. You need to check it at the pins of the 6AL5 rectifier.