Transformer Ratio Meter

[SurreyNick]

For my latest project I am assembling this Transformer Ratio Meter (see pic), which is an emulation of the one by Terry Dayton of D-Labs (https://www.youtube.com/watch?v=2ni_5D3pLbo) and adapted for UK mains. Terry was kind enough to share his circuit with me and I thought it would be interesting to compare its operation and efficacy to another Transformer Ratio Analyser circuit suggested by 'Yorkie' of this forum. I have quite a few AF transformers which are absent of all markings and I can put these meters through their paces to help identify which models they are.

As can be seen from the picture I have all but one of the surface mount components in place and now it's time for some wiring. First stage for me is to convert the circuit diagram to a wiring diagram as I find one of these much easier to follow and I was wondering if there is someone on this forum who would be willing to check I have correctly interpreted the circuit when drawing the wiring diagram? Being a relative novice I still find circuit diagrams a struggle and as this is the first a.c. device I will have made I don't want to make any mistakes.

I don't want to just post the circuit here as I haven't asked Terry for permission to publish his circuit, so it would have to be done via PM or email. If there's a willing soul would you let me know?

Many thanks

Nick

[Radio Fixer]

Well it to me would be another box to have to find room for Nick. But its always nice to build something.

'Old timers' just use a signal generator and a scope for audio transformers. It could also claim to be a better way of doing it as its easy to check frequency response at the same time. Something that can be forgotten when doing this is to include a suitable resistor to mimic the Ra of the valve driving the transformer. Without it the low frequency response will look fantastic. But with it the amount of primary inductance will show up and the response tail off as the frequency from the generator goes down. My scope even has a dB scale for easy measure of the 3dB down points if comparing transformers.

For mains transformers I simply hook them up to the supply and measure the unloaded windings (even the primary taps can be checked if they are easy to get at). The primary current should be minimal when doing this, if not its an indicator of shorted turns. In rare occasion I might load the secondary windings with resistors, if its an unknown transformer that I intend to use in something. If it runs cool at the sort of currents I might need then it could do the job. Normally of course it will be out of a radio and would just go back there and see what happens. If I can keep my fingers pressed firmly on it after its been on an hour then OK, if not its over 50C and I would do something about it. Its becoming usual to me to have to add metal clad resistors (bolted to chassis underneath and out of sight if possible) in the primary as the mains voltages are running here in the high 240s. Of course the Test Set would be safer for the less experienced and measuring anything directly connected to the mains then care is a must. An isolation transformer can be used.

Have fun with your build. If you don't have them yet then look out for a quality scope and a couple of generators (an audio and an RF are vey useful with FM on the latter if you think you will work on those radios a lot. For the odd occasion than an AM genie can be made to do the job).

Gary

[Radio Fixer]

Oh! dear, seems I might have driven Surrey Nick into a silent corner, putting down his project, and earned the censure from everyone else for spoiling his fun. This wasn't the intention, just showing that there are other basic ways that have been used for decades.

Gary

[AlanBeckett]

I'm with you Gary, that's how I do it, but each to his own.

Alan

[pwdrive]

Oh! dear, seems I might have driven Surrey Nick into a silent corner, putting down his project, and earned the censure from everyone else for spoiling his fun.  This wasn't the intention, just showing that there are other basic ways that have been used for decades.

Gary

Can't see that you've put down Nicks project, describing other methods is good.

Looks like he's doing a neat job and learning about the various bits of circuit/construction etc.

Would I build one for my own use, probably not, I'd just do a visual and ohms test to try and establish primary/secondary(s) connect up and see what comes out.

Lawrence.

[SurreyNick]

Sorry Guys, you've misinterpreted my silence. I have just been busy getting on with the project. I'm sorry I should have acknowledged your post Gary. I read it and simply parked it for another day, when I could ask you certain questions regarding the methodology you propose. I have a thirst to know many things, but I didn't want to get distracted from the assembly of the ratio meter. I feel a bit bad now having left you worrying you drove me away. I can assure you, it would take a little bit more than that!

Purile criticism or just trying really hard to find a fault, even a tiny one, is the only thing that puts me off. I got it recently on another forum when I posted the instructable on my series lamp limiter. Someone took a magnifying glass to the picture of the wiring and spotted I hadn't left the right wire lengths in the plug for best practice and then lectured me on my irresponsibility posting an instructable! Funny enough, following the criticism, I went on the ROSPA website and checked their instruction for wiring a plug and even they don't advise this gentleman's method. I'm not saying he's wrong. In actual fact he's right and it's very sound advice. It's just he could have simply pointed out that it might be better to wire the plug this way... Oh look, I'm bitching. Shut up Nick. Stand on a pedestal and you should expect someone to heckle you   

Anyway, back to my Ratio Meter. Hugh has very kindly been checking over my conversion of the circuit diagram into a wiring diagram, identifying and helping me correct the odd mistake, and today I have wired up the various resistors on a perforated board. I just need to track down a 5mm incandescent bulb with holder and I should have the meter finished in a few hours.

It was its simplicity of use that attracted me. That and (call me a tart by all means) it looked like a handsome device.

Sig gen and scope? Phew, that's still a bit too advanced for this poor old novice guys.

Nick.

[Radio Fixer]

Hello Nick

Sig gens often turn up at vey low prices . May need a little repair but normally this isn't too difficult, certainly for valve units. Advance made some good ones and I have a BVWS article on the one I sorted (PDF), PM me an e-mail and I will let you have it. Give you an idea.

Scopes are a bit more tricky and it depends what you intend to do. High spec ones aren't needed if the aim is just to do radio work. Ask on here what to look out for and someone may even have a working unit.

You will have a lot of fun and education on learning to drive them. I'm sure you will enjoy it and its the way to go if you want to go further in the hobby.

Building things is great, its how many of us learnt, so I'm glad my post wasn't discouraging. Improves your soldering and use of hand tools as well as electronics.

Gary

[Radio Fixer]

Well coincidence: http://www.ebay.co.uk/itm/VINTAGE-ADVANC...ltDomain_3&hash=item1c557bc1ff

I have the RF equivalent of this (that's what the article is about). It looks a good unit, I will have a close up gander in a mo and report back if I see any warts. Almost certainly valve but I will see if I can find out. Small, don't take up much bench space and well made.

Price? ... I know what my limit would be (PM me if you like)

Yep! two valves (triodes). Looks good.

Gary

[SurreyNick]

Not discouraged at all Gary.

That kind man Yorkie gave me a little sig gen some time back, but I will come back to you a future day regarding questions about scopes etc.

In the meantime, here's my attempt at the soldering. I know it's nowhere near as professional as many will do, but I was quite pleased with the outcome. I could have paid more attention to the lead-in and lead-out wires, making sure I properly poked them through the perf board so no bare wire is showing and I should also have had the resistors all aligned with their bands the same way around, but those are things I will remember for next time. The joints are all nice and tight though and continuity is steady.

Nick

Note: Actually, it might have been a wide range oscillator he gave me - or both! Blooming memory is rubbish these days and everything is packed up in the garage for the move!

[pwdrive]

Looks ok to me Nick.

Lawrence.