AVO glass replacement - UK Vintage Radio Repair and Restoration Discussion Forum

2E1CIH Mike · 16th Dec 2011, 8:37 pm

Hi,

I've bought an AVO 8 with a cracked glass (otherwise seems to be good), and another with a good glass (otherwise seems to be not good - the needle drifts about when the meter is inclined).

Before I take them to pieces (to fit the good glass in the otherwise good meter), and possibly do some harm, is there anything I should know?

I must admit to spending a very short amount of time seeing if the case would seperate on one of them, but it didn't, so I didn't try any more incase there is something I didn't know about.

Thanks.....Mike

Alistair D · 16th Dec 2011, 10:21 pm

There 5 screws round the rim of the back case. 1 may have pitch over it. Remove these and the 2 parts will separate.
PM me your email address and I will send you a copy of the service manual.

Al

Pamphonica · 17th Dec 2011, 9:06 pm

A few obvious points

work in a dust-free area, and especially with no possibility of metal dust
be incredibly careful not to hit or catch the needle. Bending or jarring may be very hard to repair.
don't tap or bang the magnet, you will lose magnetisation
try to work with non-magnetic tools if close to the magnet
wrap wire round the meter terminals (or Avo terminals on 50uA range) to shunt meter and minimise meter movement

I ws very nervous about replacing an Avo glass the first time. I took my time, made sure my sleeves were rolled up to avoid catching sleeves on needle, and achieved a great result.
Good luck and well done to be getting an Avo back on its noble feet.
Jeremy

WME_bill · 18th Dec 2011, 12:31 pm

Meter glass. You are quite right to stick to glass. Plastic / perspex collects static, and the needle will stick. Avo are very strong on this in their service notes. Have you considered getting a fresh piece. When I have had to replace meter glass, often with a small cut out for the zero screw, I have found my local glass merchant very helpful. They seemed to enjoy the challenge of curves and notches. And they would happily use 1/16 thick glass with no arguement. Have you tried replacing an old pane of glass - must be 4mm for safety reasons. So I always specify horticultural or for a picture. Bill m0wpn

Leon Crampin · 18th Dec 2011, 2:05 pm

Remember that if you remove the movement from the front panel (all due precautions needed) you will still need to set the cutout trip point. This is done by rotating the cutout base plate.

It's not a difficult job but I hate doing it as finding the trip overload point seems to be rather brutal to the meter. I usually set them to trip earlier rather than later to avoid hammering the movement. The only consequence of this in use appears to be the occasional random trip on mechanical shock with a slight reluctance to reset. This is not usually a problem in actual use.

Leon.

16th Dec 2011, 8:37 pm	#1
2E1CIH Mike Triode Join Date: Jul 2011 Location: Cambridgeshire Posts: 43	AVO glass replacement Hi, I've bought an AVO 8 with a cracked glass (otherwise seems to be good), and another with a good glass (otherwise seems to be not good - the needle drifts about when the meter is inclined). Before I take them to pieces (to fit the good glass in the otherwise good meter), and possibly do some harm, is there anything I should know? I must admit to spending a very short amount of time seeing if the case would seperate on one of them, but it didn't, so I didn't try any more incase there is something I didn't know about. Thanks.....Mike

16th Dec 2011, 10:21 pm	#2
Alistair D Nonode Join Date: Jan 2010 Location: Edinburgh, UK. Posts: 2,008	Re: AVO glass replacement There 5 screws round the rim of the back case. 1 may have pitch over it. Remove these and the 2 parts will separate. PM me your email address and I will send you a copy of the service manual. Al __________________ I won't tell you how I discovered that.

17th Dec 2011, 9:06 pm	#3
Pamphonica Nonode Join Date: Mar 2008 Location: Virginia Water, Surrey, UK. Posts: 2,877	Re: AVO glass replacement A few obvious points work in a dust-free area, and especially with no possibility of metal dust be incredibly careful not to hit or catch the needle. Bending or jarring may be very hard to repair. don't tap or bang the magnet, you will lose magnetisation try to work with non-magnetic tools if close to the magnet wrap wire round the meter terminals (or Avo terminals on 50uA range) to shunt meter and minimise meter movement I ws very nervous about replacing an Avo glass the first time. I took my time, made sure my sleeves were rolled up to avoid catching sleeves on needle, and achieved a great result. Good luck and well done to be getting an Avo back on its noble feet. Jeremy __________________ Jeremy, G8MLK, BVWTVM Friend, VMARS, BVWS Secretary. www.pamphonic.co.uk www.bttt.org.uk

18th Dec 2011, 12:31 pm	#4
WME_bill Octode Join Date: Oct 2007 Location: Exeter, Devon, UK. Posts: 1,554	Re: AVO glass replacement Meter glass. You are quite right to stick to glass. Plastic / perspex collects static, and the needle will stick. Avo are very strong on this in their service notes. Have you considered getting a fresh piece. When I have had to replace meter glass, often with a small cut out for the zero screw, I have found my local glass merchant very helpful. They seemed to enjoy the challenge of curves and notches. And they would happily use 1/16 thick glass with no arguement. Have you tried replacing an old pane of glass - must be 4mm for safety reasons. So I always specify horticultural or for a picture. Bill m0wpn

18th Dec 2011, 2:05 pm	#5
Leon Crampin Octode Join Date: Nov 2005 Location: Surrey, UK. Posts: 1,870	Re: AVO glass replacement Remember that if you remove the movement from the front panel (all due precautions needed) you will still need to set the cutout trip point. This is done by rotating the cutout base plate. It's not a difficult job but I hate doing it as finding the trip overload point seems to be rather brutal to the meter. I usually set them to trip earlier rather than later to avoid hammering the movement. The only consequence of this in use appears to be the occasional random trip on mechanical shock with a slight reluctance to reset. This is not usually a problem in actual use. Leon.