AVO 7 Repair - UK Vintage Radio Repair and Restoration Discussion Forum

Andrewausfa · 28th Aug 2017, 10:38 pm

I picked this up, my first '7', for £3 from the MKARS rally on Sunday. While the meter was dirty and most of the lettering had flaked off, the movement seemed to be fine so it came home with me.

On testing I found this 1951 made meter worked on the 1V DC volts position but not on any higher ranges so I assumed an open circuit resistor above that range. On testing the 10V 4500 Ohm bobbin I found it read in the megohms, clearly that was one culprit. I went through my resistors and paired up couple of resistors for a total of 4493 Ohms, good enough. On soldering these into place everything now worked. All other ranges seemed fine and given a quick test with my AD584 voltage reference the 10V range was quite accurate.

The remaining engraved lettering was picked out, the front panel given a scrub and then the lettering roughly repainted with white acrylic. When dry, a coat of car wax was applied over the lettering. I then used a plastic bank card carefully to scrape all excess paint off. I removed the dial mirror and very carefully cleaned off some mould on inside of the glass with a damp cotton bud. While in there I lubricated the P. Q and R wirewounds with some Vaseline. The front panel was then given a polish with a vinyl care product which will dull down a bit. Lastly the stiff strap was cleaned and given some suppleness back with some leather cream

So another old instrument brought back into use.

Andrew

karesz* · 28th Aug 2017, 10:54 pm

Excellent work Andrew, congratulation!

Regards, Karl

Phil G4SPZ · 29th Aug 2017, 7:29 am

That looks wonderful. It even has a pair of matching blanking plugs in the PF sockets. Should be a Success Story! Well done.

The Philpott · 29th Aug 2017, 6:22 pm

Nice one. Don't trust that leather strap just yet; pinch it in a few places to check it genuinely has been reanimated!

deliverance · 29th Aug 2017, 8:15 pm

Excellent looks great

Andrewausfa · 29th Aug 2017, 10:03 pm

Thanks gents. I've tried to unsucessfully repair a couple of AVO 8s in the past both of which ultimately turned out to be faults with the movement so I'm quite pleased to get this one back working. The only remaining fault is that the case gasket was in bits. I'll see if I can get some rubber O ring to replace it.

Phil, I didn't notice the blanking plugs until I saw your message

Regards - Andrew

Tim · 29th Aug 2017, 10:07 pm

Quote:

Don't trust that leather strap just yet; pinch it in a few places to check it genuinely has been reanimated!

I agree. I was carrying my AVO8/2 yesterday and the strap snapped. It landed on a rug, and seems to be OK. I was a bit worried at first as Ohms wasn't working but it was just the battery had been dislodged.

Andrewausfa · 29th Aug 2017, 10:23 pm

I could use some harness stuff aka Neatsfoot oil on it. And risk a good old moan from the missus from the smell

The leather creme/restorer (evidently packed with essential oils for revitalising dry leather) I used works fine, it's not a polish.

There's no dry rot and the strap's about as supple as I am. Hmmmmm....

Andrew

28th Aug 2017, 10:38 pm	#1
Andrewausfa Octode Join Date: Dec 2010 Location: St Ives, Cambridgeshire, UK. Posts: 1,180	AVO 7 Repair I picked this up, my first '7', for £3 from the MKARS rally on Sunday. While the meter was dirty and most of the lettering had flaked off, the movement seemed to be fine so it came home with me. On testing I found this 1951 made meter worked on the 1V DC volts position but not on any higher ranges so I assumed an open circuit resistor above that range. On testing the 10V 4500 Ohm bobbin I found it read in the megohms, clearly that was one culprit. I went through my resistors and paired up couple of resistors for a total of 4493 Ohms, good enough. On soldering these into place everything now worked. All other ranges seemed fine and given a quick test with my AD584 voltage reference the 10V range was quite accurate. The remaining engraved lettering was picked out, the front panel given a scrub and then the lettering roughly repainted with white acrylic. When dry, a coat of car wax was applied over the lettering. I then used a plastic bank card carefully to scrape all excess paint off. I removed the dial mirror and very carefully cleaned off some mould on inside of the glass with a damp cotton bud. While in there I lubricated the P. Q and R wirewounds with some Vaseline. The front panel was then given a polish with a vinyl care product which will dull down a bit. Lastly the stiff strap was cleaned and given some suppleness back with some leather cream So another old instrument brought back into use. Andrew Attached Thumbnails __________________ Invisible airwaves crackle with life. Or they should do. BVWS Member

28th Aug 2017, 10:54 pm	#2
karesz* Heptode Join Date: Jun 2010 Location: Zurich, Switzerland Posts: 538	Re: AVO 7 Repair Excellent work Andrew, congratulation! Regards, Karl

29th Aug 2017, 7:29 am	#3
Phil G4SPZ Dekatron Join Date: Apr 2005 Location: Bewdley, Worcestershire, UK. Posts: 4,748	Re: AVO 7 Repair That looks wonderful. It even has a pair of matching blanking plugs in the PF sockets. Should be a Success Story! Well done. __________________ Phil Optimist [n]: One who is not in possession of the full facts

29th Aug 2017, 6:22 pm	#4
The Philpott Dekatron Join Date: Aug 2016 Location: Colchester, Essex, UK. Posts: 4,108	Re: AVO 7 Repair Nice one. Don't trust that leather strap just yet; pinch it in a few places to check it genuinely has been reanimated!

29th Aug 2017, 8:15 pm	#5
deliverance Heptode Join Date: Apr 2015 Location: Manchester, UK. Posts: 711	Re: AVO 7 Repair Excellent looks great

29th Aug 2017, 10:03 pm	#6
Andrewausfa Octode Join Date: Dec 2010 Location: St Ives, Cambridgeshire, UK. Posts: 1,180	Re: AVO 7 Repair Thanks gents. I've tried to unsucessfully repair a couple of AVO 8s in the past both of which ultimately turned out to be faults with the movement so I'm quite pleased to get this one back working. The only remaining fault is that the case gasket was in bits. I'll see if I can get some rubber O ring to replace it. Phil, I didn't notice the blanking plugs until I saw your message Regards - Andrew __________________ Invisible airwaves crackle with life. Or they should do. BVWS Member

29th Aug 2017, 10:23 pm	#8
Andrewausfa Octode Join Date: Dec 2010 Location: St Ives, Cambridgeshire, UK. Posts: 1,180	Re: AVO 7 Repair I could use some harness stuff aka Neatsfoot oil on it. And risk a good old moan from the missus from the smell The leather creme/restorer (evidently packed with essential oils for revitalising dry leather) I used works fine, it's not a polish. There's no dry rot and the strap's about as supple as I am. Hmmmmm.... Andrew __________________ Invisible airwaves crackle with life. Or they should do. BVWS Member