By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Allendale Jan 24th

Fixing the AVO

All Topics | Latest Posts

Search for:  in Thread Title in  
Roger Hart07/12/2019 16:26:17
118 forum posts
27 photos


Roger Hart07/12/2019 16:35:47
118 forum posts
27 photos

p1040337.jpgAfter deciding to press on and rewind my AVO coil (see last posting) I took the coil apart and stripped off the wire and measured. Then built very simple coil winder for 50swg wire (a bit fine). Put on 1200 turns from calculated value plus 10%. Then made jig to re-glue bearing pivot plates and re-assembled. Disappointed to find read about 25%. Didn't fancy winding again so fitted some bigger neodymium magnets plus a bit of jiggy-pokery with shunts and swamp resistors. Now reads correctly. Was it worth it - no, cheaper and easier to visit eBay. But I've started so I'll finish...... Sorry about order of photos, not got the hang of that.p1040339.jpgp1040336.jpgp1040335.jpgp1040333.jpg

john fletcher 107/12/2019 18:31:00
602 forum posts

You will find a lot of information regarding AVO meters on Vintage Radio, it is free to join, and there are many pages of AVO info. I haven't heard of anyone carrying out movement coil rewinds before. Good for you and its now working. John

Phil Whitley07/12/2019 18:54:04
1222 forum posts
146 photos

You sir, are a hero! that is not an easy job to tackle! I have an avo service manual, if you would like one, but it is 5.9 meg so would have to use dropbox etc to get it to you, it may even be available at vintage radio as a download, thats probably where I got it from!


Roger Hart08/12/2019 10:30:57
118 forum posts
27 photos

Thanks for the responses. I looked at VintageRadio, very handy info. The bottom line is that I used 50 SWG wire which is 0.001 dia and requires 78,750mm for 2608 ohms resistance. This leads to 1078 turns approx. This IMHO turned out to be too few for the magnet block. Ampere-turns is what sets the sensitivity.

Had I used 49 SWG .0012 dia and requires 113,550 mm for 2608 ohms which leads to 1554 turns approx I would probably had the right result. But being a bit dim, although the wire sample I measured did measure a bit over 0.001 I took the extra to be the enamel. That 0.0002 makes a lot of difference - cunning chaps those AVO people.

old mart08/12/2019 16:29:19
1825 forum posts
148 photos

Have you balanced the needle?

Ian P08/12/2019 16:48:10
2406 forum posts
101 photos

You have my admiration for rewinding a moving coil meter!

When I've examined some meter movements (probably smaller than AVO size) the whole moving assembly looks to use watch sized components like tiny jewels held in microscopic collets held together with shellac or similar. I would never have thought they were repairable.

Ian P

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Support Our Partners
Allendale Electronics
Eccentric July 5 2018
Eccentric Engineering
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest