Taylor Transistor Tester Model 44 Meter Movement

[Colin]

I recently responded to a generous offer from AntLong and in due course received a rather sad looking Taylor Transistor tester. It had a pair of very corroded batteries inside which had damaged a few parts, but nothing that couldn't be replaced. It needed a new scale plate (corroded right through from the back), a pair of battery retaining brackets and a couple of plugs for the battery connections. Otherwise, a good clean and some TLC looked like it would return the unit to its former glory.

However, although the meter movement was free, the moving coil was found to be O/C.

Consequently I have a number of questions for the team ...

1. What are the chances of my successfully dismantling the movement, re-winding the coil and putting it all back together again ... yes, I thought not! Any advice if I decide there's nothing to lose and try it ... I may learn a lot even if I'm not successful.

2. Does anyone know if the meter movement from any other device (Taylor multimeter, Simpson etc.) be a suitable replacement for the M44? (the M44 has a 50uA f.s.d. meter with a swamp of 3465R )

3. Does anyone have a Taylor meter with a similar movement that they would be willing to sell to help with this project? I'm assuming it would have to be a 'donor', and other than having a functional meter, be beyond repair. Worth asking even if the chances of a 'result' are slim

I've attached a few pictures of the damaged movement and here's a link to a post from Mike Phelan with a picture of his restored tester.

https://www.vintage-radio.net/forum/...nsistor+tester


Thanks in advance for all help or advice.

Regards
Colin

[Brian R Pateman]

Originally Posted by Colin

What are the chances of my successfully dismantling the movement, re-winding the coil and putting it all back together again ...

It all depends how good your eyes are and how steady your hands are!

It also depends where the coil is broken.

It's worth having a really good look with a magnifying glass to see if the connections between the coil and the hairsprings are OK. I have known these to suffer from corrosion.

I've done repairs to meters before, although not for a while and it can be done. Put it this way, what have you to lose by having a go?

Failing that I may have a donor movement somewhere but I don't think there is anything in my boxes of meters with the same scale length or that long a pointer.

Regards and good luck,

[Colin]

Thanks Brian,

I spent ages with a X15 jewellers loupe under a very strong light looking at this. The moving coil winding looks in good shape but I'm certain it's O/C. Continuity tests from the soldered connections (coil to the hairsprings) produced no results across the winding so it must have corroded through at some point. I tried resoldering these to make sure they were good but with no success. There was a lot of corrosion on the scale plate which had been eaten right through back to front (0.75mm thick) in the area of the movement, so It's very possible that a section of the 0.0254mm (50 SWG) wire has gone too.

I fancy having a go at the repair, as you say 'nothing to lose', but some advice from those more experienced in these matters would improve my chances of success!

BTW, do you know where I can get hold of some 50 SWG enamelled copper wire?

Appreciate you looking in the spares box.

Regards
Colin

[pmmunro]

Colin,

The Taylor centre pole movement used in your tester is derived from the same design as the movement in the Mark V, VI and 7 versions of the Avometer Model 8. It may be worth comparing the specifications.

In principle, the centre pole movement cannot be dismantled without some loss of flux and ideally it would be best to demagnetise it before dismantling and then remagnetise it after effecting a repair.

You will probably find it quite difficult to get 50 swg enamalled copper wire and it may be worth trying US suppliers if you can find one willing to supply the small quantity you need in a near equivalent gauge.

Let us know how you get on.

PMM

[Colin]

Thanks for your input PMM, very interesting ...

Originally Posted by pmmunro

The Taylor centre pole movement used in your tester is derived from the same design as the movement in the Mark V, VI and 7 versions of the Avometer Model 8.

This would certainly be worth checking out. Are you suggesting it may be possible to effect a transplant?

Originally Posted by pmmunro

In principle, the centre pole movement cannot be dismantled without some loss of flux and ideally it would be best to demagnetise it before dismantling and then remagnetise it after effecting a repair.

Sounds complicated. Is it possible to do without specialised equipment and if so, how is it done? Also, you say 'some loss of flux' would this be significant and could it be accommodated through adjusting component values, i.e. the swamp resistor for example?

Finally, is it advisable to use brass or otherwise non-magnetic tools when workng on the movement?

Regards
Colin

[David Simpson]

Hello Colin, If your movement is the same as an 50 micro-amp fsd AVO 8, why not send it to "Mr AVO" - Bill Barton from Bolton. I can let you have his address, if you dont already know it.
He repaired an AVO8 Mk3 movement for me back in the spring & did a very good job. Cost about £20 or so + P&P. I also needed a replacement meter for my AVO CT446 Tr.Analyser, and was able to obtain a new item of similar dimentions & exact fsd requirements from - Benchmark Instruments in Ludlow, for about £60 or so + P&P. Mind you, I've seen old working AVO's for sale for approx £20, so you could remove it's meter & flog the rest of the case for spares for a tenner.

Regards, David

[Colin]

Hello Dave, thanks for your suggestion about Bill. I have emailed him with an enquiry but received a short note to say that he's not able to respond until January, when I should contact him again.

I'll continue with my search for a suitable donor movement and in the meantime hatch plans for a DIY re-wind!

rgds
Colin

[David Simpson]

Hello again Colin. I'll have a root around my wee w-shop. I think the older Megger BM series ins.tester has a similar movement, if I recall. And I've one or two lying somewhere. Shall get back in touch if I find one.

Regards, David

[Colin]

Hi David, that's useful to know and very good of you to try to help. I'm sure the movement was used in a number of devices, the trick is knowing which ones! I'll keep my fingers crossed.

Thanks
Colin

[WME_bill]

I have looked up the manual for the Taylor 44 transistor tester. It says it is a 50ua, 200mv meter. So almost any large 50ua meter should do. The Avo 8 used a 30ua meter, which was shunted to 50ua to give good damping of the movement. The Avo 7 was shunted to 1ma, so no help. I converted mine many years ago to a FET Tester, as Wireless World December 1971,exploiting the existing current range shunts. It has proved a very useful bit of test gear.
I have tried rewinding a meter coil in the past, but with persistent failures. The top of the winding has to be level to give a true base to cement on the top and bottom bearings. They have to be exactly central on the coil, as there is very little margin in the magnet gap for even slight misplacement. Then the gap always attracts a bit of iron from the air. That takes hours to poke out with a stainless steel needle.