AVO Low resistance ohmmeter 1941

[Mike Watterson]

1289 : rear cycle lamp, 3 x B cells. (Grid bias and HT packs from 1920s). Still sold, but not as a 1289, but as a 3R12.
800: Front cycle lamp, 2 x F cells. (often used in 1.4V LT packs from 1939, sometimes 2, 4, 6 or even 8 in parallel!) Still four inside 996 packs, as cheap as €2 here! Also a 6R55

The 3R25 is amazing still available, it's an AD28
IEC R12 = B Cell
IEC R25 = F cell
See my site
http://www.blaukatz.com/tables/batteries-in-2014/

[The Philpott]

Yeah, as mentioned Richards Radios and also the other forum has images so I didn't hasten to attach any here. (The ones on RR are as good as my camera can manage, and he has cropped and processed them so better off looking at them)

And, yes, compartment not C cell size, slightly smaller, no doubt the one you have pictured.

This is indeed the unit that was on 'an auction website' but it did need some tlc. The glass was broken- and very very thin anyway, so redone with acrylic. A joint was loose inside - just needed more solder.

Needless to say AVO became Megger which is why I approached them.

The dial is handpainted in the factory style of the period. (black on ivory)

Thankyou for your comments, I will wait to see if any more details turn up!

[The Philpott]

Just by way of a) an update and b) a BUMP in case anyone has any more information on this..

In the thread starter i mentioned that the early HR DC Avominor did not appear to exist. Since then 3 of them have turned up in good hands. (2 of which have their boxes)
The serial numbers for 2 of them are predictably low, ie below 500. The serial number of the remainder has not been given (owner wasn't being awkward, he simply didn't have it to hand.)

My initial theory that the HR unit was requisitioned in full by the military seems to have no basis in fact- it was a guess after all.

As regards the LR Ohmmeter (the main subject of the thread starter) no other examples have 'come out of the cupboard' --unless you know differently.

[Excessive Leakage]

Hi Tim

I have just picked up a LR Resistance ohmmeter, number LR375-541.

It is not in very good condition but should be salvageable. It didn't help that the courier threw it over my back gate onto tarmac and the package that it was in sat out in the rain for a few days, while I was away for work  

Glass is still intact (not sure how) but an old battery was left inside which has leaked.

I'll let you know how I get on with repairing it.

Cheers

Adam

[The Philpott]

Oh, excellent, any pictures yet? Mine is No. 370-441. Hope yours is salvageable.

As i may have mentioned before pics of mine are on Richards Radios.

Dave

[Excessive Leakage]

Hi Dave

Sorry for calling you Tim earlier! I misread your username  

The meter is currently in bits. I have freed up the 'sticky' movement but the magnet has some surface rust which I am currently loath to do anything about (I know where all the rust will end up if I try to remove it, in the movement). Any suggestions as how best to approach that problem, without totally dismantling the movement, would be gratefully received.

Case is exactly as yours, save for my repair of the slight damage from the courier.

I'll make a concerted effort to reassemble in the next day or two and I'll send pics of it then. Meanwhile here are the pics of the poor thing, taken from the ebay listing (I must have seen it as soon as it was listed with a BIN option).

Cheers

Adam

[The Philpott]

Thanks for images. So it's had a bit of a hard life then!

As regards flakes of rust on the magnet i would have thought close co-operation between a toothpick and a blob of blu-tack would remove then secure the rust. Blu tack is stickier, i find, if you mash it a bit by hand before using it. I share your concern regarding flakes getting into the movement, the gap in there is tiny on these meters and easily bridged.

It looks like your movement may be out of balance judging by the position of the needle, i have re-balanced large AVO movements but not the small fiddly ones- but i imagine it is possible. Shout if it turns out you need a link to generic/general meter balancing instructions.

The hand painted dial is very nice on yours. The glass will be very thin, something around 1/16th.

My favourite way of getting grot off the front of the case is WD40 and a toothbrush- very therapeutic.

[Excessive Leakage]

Hi Dave

I'm pleased to advise that the meter is balanced now (gunge removed). The movement appears to be free.

I'll try the blutack on the rust and should have this back together tomorrow.

Singer sewing machine oil (in moderation) appears to do wonders for old AVO cases. I'm planning on cleaning the case and then treating to some oil.

Cheers

Adam

PS I wonder if there are any other of these little blighters out there?

[The Philpott]

Excellent, more stuff saved from obscurity. I think i will convert to sewing machine or airgun oil for cleaning frontages, they do sound more suitable.

On the images of mine you will notice the waxy woven insulation has almost all been changed for blue silicon sleeving- this seemed the obvious choice at the time as i had to disconnect several wires to take the movement out, renew the cracked glass, solder a loose joint on the shunt board, then reassemble! As a result of the loose joint i could quite easily have damaged the movement, as in use it banged over to FSD, but all was ultimately well. The brass clips that retain the glass aren't terribly well placed, one is (almost) in view from the front. I think i cropped a corner off it for aesthetic reasons! It originally belonged to an aircraft fitter in the RN, so may have been used for checking continuity in radio/IFF sets or bomb/torpedo switches/solenoids, all subject to problems in the salty atmosphere..

I also acquired a Low resistance range extension unit for AVOminor use, with period battery inside! It is pretty cumbersome to use though compared to the self contained LRO.

[The Philpott]

In the interests of full disclosure (and so you have a general idea) i can say i paid about £80 for the LRO. I really don't like bidding against other people for this stuff as i am generally bidding against collectors or engineers rather than traders, and it all goes a bit against the grain. Considering rarity i think that might be a little on the low side; it was in very good fettle overall.