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Old 13th May 2022, 11:55 am   #1
Techman
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Default Megger. Evershed & Vignoles hand crank - series 2?

This is another sale room bargain, obtained sometime last year. I'd spotted it and I got a strong feeling that nobody in the room would be interested in it, or even know what it was, and I was right, I was the only bidder at a quid! It's exactly the same as the one I used to use occasionally at work many years ago and I'd always wanted one. I think this is what may be called a 'series 2', although someone may correct me if I'm wrong on that one.

It does work and I've used it a number of times, but I've read somewhere about a capacitor used for the smoothing of the generator DC output that tends to become leaky and reduces the output voltage, also making cranking harder. I did a test with it on two different DVMs and on a 1 meg meter the output measured a maximum of around 320 volts with the resistance of the meter coming out at just under 1 meg. On a 10 meg meter the output voltage measured a maximum of 355 volts with the meter measuring around 10 meg. I believe that the voltage output should be around 500 volts.

The pictures below show the instrument and it looks as if the end screws are sealed, perhaps indicating that it has never been opened. The question I'm asking is does anyone know the correct method of disassembly before I start, and what am I expecting to find regarding this capacitor? There seems to be very little information on this particular model on-line.
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Old 13th May 2022, 12:55 pm   #2
The Philpott
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Default Re: Megger. Evershed & Vignoles hand crank - series 2?

Mine is an earlier Bakelite 500v version of different appearance, but i do recall the screws were under waxy anti-tamper plugs, which dug out quite easily. Undisturbed since 1941, presumably!

Its voltage was found to be half that of the rated output, and it was largely (if not completely) down to the capacitor, a Dubilier. Half the size of a matchbox, fixed with a metal flange.
I think I replaced it with a polypropylene one (I had better check that) and also replaced a resistor while I was in there.

On completion I had about 455v versus the rated 500v.

Refer Richards Radios, i think he has a page on Evershed & Vignoles. Approximate year of manuf. can be gleaned from your serial number.

Dave
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Old 13th May 2022, 1:32 pm   #3
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Default Re: Megger. Evershed & Vignoles hand crank - series 2?

viz:

https://www.vintage-radio.net/forum/...d.php?t=145767
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Old 13th May 2022, 1:49 pm   #4
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Default Re: Megger. Evershed & Vignoles hand crank - series 2?

Thanks for that, Dave. I'll have a read through your thread.

I'd seen the Richards Radios site the other day and bookmarked it - that's where I got the 'series 2' reference from.
http://www.richardsradios.co.uk/meggers.html
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Old 13th May 2022, 2:11 pm   #5
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Default Re: Megger. Evershed & Vignoles hand crank - series 2?

I think I may have read through your thread and some others when I was doing a bit of research a while back, but couldn't find anything specific on the model that I have. Surprisingly, I seem to remember that I found reference to the Chinese at one time making a modern replica of this megger.

Mine doesn't read down to infinity when cranking with nothing connected and always gives a small reading down that end of the scale, which leads me to suspecting this capacitor issue. It didn't do this when I first got it, so looks like it hadn't been used in many years and once put to use it had set the capacitor off leaking, as you might expect.
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Old 16th May 2022, 10:20 pm   #6
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Default Re: Megger. Evershed & Vignoles hand crank - series 2?

I had a look at it this evening and took it apart - now all put back together again.

So it looks like there's no one left in living memory that knows anything about this particular model. Even good old YouTube had nothing, other than a couple of demonstrations of the Chinese clone version. These seem to be particularly rare, which surprises me, as there was at least one of this type where I used to work, and also the fact that the Chinese chose this particular model to remanufacture not that long ago. It's a shame that there was no video showing one of the Chinese new ones being stripped down, as that would have been interesting to see for a comparison.

There's three screws (well slotted nuts) on the back and a screw on the top, all sealed with proper 'old school' sealing wax (by the look of it), but it turned out that the single screw on the top just covers the meter adjustment screw beneath.

This is yet another piece of test gear that I've acquired recently that's turned out to be a lot older than I originally thought, which I'm more than happy with - the older the better!

There's not a lot to say, other than where's the capacitor that I've read about? Probably too old to have had one ever fitted, is the likely answer. So I'll let the pictures tell the story over this and the next post:-
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Old 16th May 2022, 10:24 pm   #7
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Default Re: Megger. Evershed & Vignoles hand crank - series 2?

The two resistors that were all taped up were 33K and 15K in series.

So it's pre 1949.
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Old 17th May 2022, 9:47 am   #8
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Default Re: Megger. Evershed & Vignoles hand crank - series 2?

Not the first time i've come across a dearth of data about one of the early hand-cranked testers:

I found the date 1943 inside a 'Record Minor', this is a design that also lacks a capacitor, and it's low on output. In the end i put it back together on the assumption that struggling to get 50v out of it was probably symptomatic of shorted windings. Nicely made and good to work on, loads of room inside, but ultimately demoted to curio/paperweight status. I was in the dark with this model, no information data or advice came forward.

Dave
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Old 17th May 2022, 11:55 am   #9
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Default Re: Megger. Evershed & Vignoles hand crank - series 2?

Quote:
Originally Posted by The Philpott View Post
Refer Richards Radios, i think he has a page on Evershed & Vignoles. Approximate year of manuf. can be gleaned from your serial number.
The thing I omitted to mention was that it wasn't until I removed the movement that I could see the serial number on the scale plate and since putting it back together I've also now found the same number stamped in a tiny font on the bottom of the case. Looking this number up as in the above site reference puts it earlier than 1935, but later than 1928, so guessing probably early 30s.

You can also see what looks like another repair date pencilled on the works in two parts in the second picture in post #6, of 'TW 59'. At the top and in the background of the same picture can be seen some of the crumbled red sealing wax that had gone rock hard. So it looked like from the hardness of that sealant that the unit hadn't been apart for a very long time, although I don't think that the black tape around those replacement resistors dates from as far back as 1949 or even 1959. The two green resistors have replaced one of those wound bobbin type bolted on resistors that would have originally been in their place. There would originally have been four of them, but now only three original ones. The problem is that there's nothing to go on as to whether those resistors are the correct value, also all the available circuits of other units only show three resistors as a maximum used.

It does work and is giving an 'indicated' 360 volts maximum on a 10 meg/volt DVM. Measuring a few random resistors it's near enough reading correctly. Short circuit is on the line on the scale, but with nothing connected to the terminals it only reads to 100 meg and not infinity at the other end of the scale. There was a recent thread describing slightly conductive bakelite on an Avometer, so it could be something like this with the terminal insulators on this unit. I thought that I'd originally had it go right down to infinity, but I'm now wondering if I just imagined this.
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Old 17th May 2022, 1:42 pm   #10
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Default Re: Megger. Evershed & Vignoles hand crank - series 2?

Quote:
Originally Posted by The Philpott View Post
Not the first time i've come across a dearth of data about one of the early hand-cranked testers:

I was in the dark with this model, no information data or advice came forward.
Yes, it's surprising. I thought that this alloy cased version was as common as muck, as I've seen several over the years and not particularly seen any of the other hand cranked versions.
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Old 17th May 2022, 1:51 pm   #11
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Default Re: Megger. Evershed & Vignoles hand crank - series 2?

If the tester is showing an honest 100meg o/c i assume the terminals are OK..but easy enough to check.. I suppose that if only one terminal was leaking to the (mazak?) casing your hand could be diverting a small amount of current to earth.
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Old 17th May 2022, 4:28 pm   #12
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Default Re: Megger. Evershed & Vignoles hand crank - series 2?

If this is a 500v Megger, but only giving 350 into an O/C (well, VERY high resistance test meter, VTVM better, then does this not suggest the magnet is losing strength. For use in the real world (and why not?) then you must have the full 500v. Would neodymium add-ons help?
Les.
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Old 17th May 2022, 11:25 pm   #13
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Default Re: Megger. Evershed & Vignoles hand crank - series 2?

Measuring the O/C voltage (ie. with known meter input resistance) at the crank generator terminals (when one wire to remaining circuitry is disconnected), may be insightful.
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Old 18th May 2022, 12:51 am   #14
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Default Re: Megger. Evershed & Vignoles hand crank - series 2?

I found my low output was improved greatly by cleaning the rotor and brushes. The blue bit in your photographs looks very much like the blue bit on mine. Some pictures over on that thread for comparison. https://www.vintage-radio.net/forum/...d.php?t=187826

I'm in the process of discussing with Ed Dinning whether it's worth rewinding the bobbin resistors, or whether putting some modern ones in is the way to go. I've got two O/C.
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Old 18th May 2022, 5:06 pm   #15
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Default Re: Megger. Evershed & Vignoles hand crank - series 2?

I must admit i generally leave o/c bobbins in place, snip one end out of circuit just in case, and replace with a component resistor. Once or twice, having removed a bobbin i regretted it due to flakes of dust and shellac being released to float around inside, unerringly settling on the glass or scale plate.. (This was on avos, not insulation testers)

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Old 18th May 2022, 5:18 pm   #16
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Default Re: Megger. Evershed & Vignoles hand crank - series 2?

I think that's what I'll do, Dave (the new resistors, not go looking for flakes of shellac...). Would you advise using some particular high-voltage, high stability types?

Edit: I'm sorry, Techman. I thought this was the thread about my Megger! Perhaps you're interested in this question too, so I'll leave it up.
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Old 20th May 2022, 9:04 pm   #17
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Default Re: Megger. Evershed & Vignoles hand crank - series 2?

-Not sure what the spec. of the resistors should be, i assume HV high stability as you say.

I'm not sure quite why, but my aforementioned 'Record Minor' tester perked up on test today...perhaps it had been kept somewhere damp and idle in it's previous slumber.

All readings taken from a 20kohm/volt meter- all of a sudden 50v became 125v. Had another extended go and the torque required to turn the crank suddenly reduced and the output was 190v. Next time still easier to crank and 280vDC obtained. Not too concerned about noises from inside as the gears are brass, not composition, and i did inspect them years ago. All very curious.

Sorry to thread hi-jack again, but thought you might be interested.

Dave
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Old 28th May 2022, 1:33 pm   #18
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Default Re: Megger. Evershed & Vignoles hand crank - series 2?

No problem re any hijack chaps, all information related to the technology is very welcome!

I've been side tracked on various other things, so not done any more with it, but removing the generator and cleaning the rotor/commutator and brushes may be worth while, although the voltage output is so stable when it gets there that I wouldn't have thought that it would be caused by this, but you never know. Loss of magnetisation mentioned is another possibility. It's a shame the original faulty bobbin has been removed to make space for those resistors - I'm sure there would have been room to leave it in place, but let's face it, it would have just been a repair at the time to get it going again and not to preserve the original innards a vintage item.

It's still very useful at 350 odd volts, as it's ideal for testing most vintage capacitors etc...and I like preserving vintage components such as those if at all possible.
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Old 28th May 2022, 7:52 pm   #19
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Default Re: Megger. Evershed & Vignoles hand crank - series 2?

Indeed, and (some of) the asking prices are starting to get silly, so a working example is certainly something to hang onto. Always nice to have things that don't have batteries so can safely be forgotten about until needed.
Dave
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