Simple Transformer Ratio Analyser

[Yorkie]

'Surry Nick' constructed a splendid home-brew radio analyser, which he wrote about in the thread below, prompting many interesting and wide-ranging posts:

http://golbornevintageradio.co.uk/forum/...p?tid=4797

In tidying up a heap of papers of circuits and home-brew projects that I've accumulated I came across a simple ratio analyser which featured in Nov 1974 Radio & Electronics Constructor. I can't say I've ever felt a pressing need to have such an instrument, but that said, I do have quite a lot of audio transformers about which I know little, especially transistor ones with no markings on them, and some 30s inter-valve transformers.

In looking at the circuit, it dawned on me that I have all the bits to hand to make one. Although the author states that due to the limitations of this simple instrument it doesn't warrant the expense of a permanently installed 50uA meter, I have one to hand anyway. I've even got a comb-joined mahogany box in which to house it! No idea how well it will work, but not a great deal of time to invest in building it, and no expense. I've designed a little tag-board layout so that it doesn't look too much of a 'rat's nest', and a front panel to fit the box that I have. The potentiometer will need to be calibrated on the front panel when built.

Just a bit of fun really, to satisfy my compulsion to build yet another little home-brew  test-gear gizmo which will probably find little use in my workshop! 

Oh well - small things amuse small minds

[AlanBeckett]

I've even got a comb-joined mahogany box in which to house it! 

That will a splendid Gadget. I trust Pictures will follow.

One day, long in the future, when we're all dead and gone people will say 'I wonder why someone made these beautiful Wooden Boxes'.
Mind you, I always wondered that with old Instruments in general.

Good luck with it.

Alan

[Ed_Dinning]

Hi Gents, a useful bit of kit. I must admit that I normally just use a scope and an LV mains supply, but I could be tempted. If the "master transformer" is made tapped it would be possible to have both course and fine pots to improve accuracy.
I may have a transformer from an old bridge about somewhere that could be pressed into service.
Not yet decided if mains powered or an oscillator running at 1.5KHz would be the best source; it would also be useful if phase could be indicated so the relative starts and finishes can be detected.

I see a project coming on.

Ed

[Yorkie]

Thanks for reading and for your encouraging comments Alan and Ed - I'll add some pics when it's finished (assuming that it works!). As to indicating the starts and finishes of the windings are connected will differ depending on the ratio of the transformer (less/greater than 10:1) or whether tapped, the terminals to which the starts of the windings will differ, which is why I added 'Refer to Data' on the front panel. (See fig 3 on page 3 of the article).

I found a small 6V transformer to press into service - the only thing I didn't have was a 1K wire-wound pot, so I splashed out on ebay for that!:

http://www.ebay.co.uk/itm/121723449171

This little project is running in parallel with the transistor curve tracer which I made the PCB for in 1982!

As to Alan's remark "One day when we're all dead...", to drift off into irrelevancies,  last week I attended the funeral of a fellow woodturning club member who was very fit and active until two months ago. He was a bachelor in his late 70s and had entered every monthly competition since joining the club fifteen years ago. I'd thought to myself 'I wonder what will happen to all of Ivor's turned items?' That question was answered at his wake - there were about 100 people, and every table had a dozen  items on it.  His brother announced: 'please take any of the items that you like, as a memento of Ivor's life'.

Rather a nice touch I thought. All of the items were nicely turned as they were competition pieces. I chose a little turned box about 3 inches high and two inches diameter. Cleverly done - the ring around the lower part isn't a layer of contrasting wood, which would have been easy to do. It's an accurately cut ring of veneer let into a groove. The ring in the top is just that  an accurately turned ring let into a groove.

As an aside, as he lived close by, I used to give him a lift to and from the club in a nearby village where parking is diffcult. He was Chief Examiner and President of the local branch of the IAM, so each time he sat alongside me it felt like I was sitting my driving test again!  He never turned down a lift, so I assume that he must have considered me up to scratch, but sadly, now I'll never know. 

[AlanBeckett]

http://www.ebay.co.uk/itm/121723449171

That's dreadful young David, it hasn't got Colvern written on it

Sadly that's a Value I haven't got.

Alan

[ppppenguin]

Unless I had an awful lot of transformers to check I wouldn't feel it worth a specialist bit of kit. Signal generator, DVM and possibly scope are all that's needed. Oh yes, and a few croc clip leads.

For audio transformers, measuring around 1kHz seems sesnsible. DVM and sig gen will quickly give you the ratio. Scope only needed to determine phasing though it can also be used to see gross distortion and see when the transformer starts to saturate as you wind up the voltage.

For power transformers then the standard open circuit and short circuit tests tell you most of what you need to know. I'm sure that Ed will explain them rather better than I. A reminder that the short circuit test is not done with full voltage applied

[Radio Fixer]

I'm a scope and signal gen user as well but if you like making things why not?

The box is beautiful; the inner rim is so thin and that must have taken real skill. What wood would that be? its very fine grained

Gary

[Refugee]

I can remember visiting a guy that did wood turning as a teenager. I never really got into it due to a lack of a workshop and funds for a lathe.
There may well still be a piece of two about from all that time ago.

I use a dual beam scope and sig gen for transformers and just read the ratio off as a ratio of amplitudes..

[Yorkie]

Done a little bit more at this analyser project. I've made a front panel, have positioned the various components and tag-board ready to wire up and have calibrated the pot.

A couple of pics of where I've got to so far.

The front panel is a bit cramped because I wanted to use a box that I already had to hand, but it should be functional (assuming that it functions!).

[pwdrive]

So far so good, looks neat.

Lawrence.