Old Bridge Megger - UK Vintage Radio Repair and Restoration Discussion Forum

David Simpson · 11th Jun 2010, 12:25 pm

Just aquired an old Series1 Bridge Megger. Wooden cased - identical to the one disscussed by russell w b & others back in 2008. Going by the suffix lettering at the bottom of the instructions inside the meter lid - I'd assumed that 1.45 might mean that it was made in Jan 1945. However, inside the hinged wooden top is a calibration card with the date(so it appears in pencil) of 9/9/12. The twelve is very clearly written.
Just how old are these testers ?
Originally, before receipt, I'd been told it was a 5KV Megger, but its definitely a 250V one, although only a few volts appear at the terminals.
No resistance box with it, but thankfully I have an old GPO decade box similar to the one discussed in the 2008 posts.
Any advice on restoration would be most appreciated.
The case looks like laquered Mahogany, rather than brown stained Oak.

Regards, David

russell_w_b · 11th Jun 2010, 1:00 pm

Quote:

Originally Posted by David Simpson

Just how old are these testers ?

David,

Although not quite your model, I have attached a couple of line drawings from 'Modern Electrical Engineering', written in 1918. The implication in the book is that Evershed's 'Megger' has been around for some time, and was derived from research by Professors Ayrton and Perry.

If your model looks like this, it could well date back to 1912.

David Simpson · 11th Jun 2010, 2:37 pm

Hello Russell, Thank you for the further pictures. Mine is definitely identical to the lower drawing on page 6 in your 2008 post.
It's scale plate is hand written, & the woodwork & brasswork are certainly of an Edwardian appearance. Moulded Bakelite & Aluminium were more in use in the 40's & 50's. Although they returned to wooden casing for their big Series2 2.5KV Hand Cranked/Motorised Meggers, in the 70's/80's, of which I have one.
Having gained another 30 years or so in antiquity, I'm really chuffed. My contact mentioned the possibility of another similar Megger needing TLC, so I'll soon have a number of them just about covering the whole century in my collection.
First things first, though - removing grime & renovating the badly scratched woodwork. Thankfully, the advice given last year by more experienced guys on my 1920'sTRF's woodwork restoration, should stand me in good stead.
The clutch still seems to work, and the meter movement glided smoothly to infinity.However, the "Index Adjuster" failed to make any fine adjustment.
Wonder if anyone else has delved into the innards of such an old Megger ?

Regards, David

russell_w_b · 11th Jun 2010, 5:56 pm

David,

According to t'internet, Sydney Evershed's 'Megger' was registered as a trademark on 25 May 1903. Of my own books, I found a reference in my 1914 'Instruction in Army Telegraphy and Telephony' that says:

'An instrument called the 'Megger' has recently been introduced for the purpose of measuring resistance from 50,000 Ohms to 100 Megohms, and this instrument should be used whenever possible, as it is simpler to use and more accurate for high resistances than Wheatstone's bridge...'

So there you have it: an antique!

11th Jun 2010, 12:25 pm	#1
David Simpson Nonode Join Date: Mar 2008 Location: Aberdeen, UK. Posts: 2,853	Old Bridge Megger Just aquired an old Series1 Bridge Megger. Wooden cased - identical to the one disscussed by russell w b & others back in 2008. Going by the suffix lettering at the bottom of the instructions inside the meter lid - I'd assumed that 1.45 might mean that it was made in Jan 1945. However, inside the hinged wooden top is a calibration card with the date(so it appears in pencil) of 9/9/12. The twelve is very clearly written. Just how old are these testers ? Originally, before receipt, I'd been told it was a 5KV Megger, but its definitely a 250V one, although only a few volts appear at the terminals. No resistance box with it, but thankfully I have an old GPO decade box similar to the one discussed in the 2008 posts. Any advice on restoration would be most appreciated. The case looks like laquered Mahogany, rather than brown stained Oak. Regards, David

11th Jun 2010, 2:37 pm	#3
David Simpson Nonode Join Date: Mar 2008 Location: Aberdeen, UK. Posts: 2,853	Re: Old Bridge Megger Hello Russell, Thank you for the further pictures. Mine is definitely identical to the lower drawing on page 6 in your 2008 post. It's scale plate is hand written, & the woodwork & brasswork are certainly of an Edwardian appearance. Moulded Bakelite & Aluminium were more in use in the 40's & 50's. Although they returned to wooden casing for their big Series2 2.5KV Hand Cranked/Motorised Meggers, in the 70's/80's, of which I have one. Having gained another 30 years or so in antiquity, I'm really chuffed. My contact mentioned the possibility of another similar Megger needing TLC, so I'll soon have a number of them just about covering the whole century in my collection. First things first, though - removing grime & renovating the badly scratched woodwork. Thankfully, the advice given last year by more experienced guys on my 1920'sTRF's woodwork restoration, should stand me in good stead. The clutch still seems to work, and the meter movement glided smoothly to infinity.However, the "Index Adjuster" failed to make any fine adjustment. Wonder if anyone else has delved into the innards of such an old Megger ? Regards, David

11th Jun 2010, 5:56 pm	#4
russell_w_b Dekatron Join Date: Jul 2007 Location: Penrith, Cumbria, UK. Posts: 3,687	Re: Old Bridge Megger David, According to t'internet, Sydney Evershed's 'Megger' was registered as a trademark on 25 May 1903. Of my own books, I found a reference in my 1914 'Instruction in Army Telegraphy and Telephony' that says: 'An instrument called the 'Megger' has recently been introduced for the purpose of measuring resistance from 50,000 Ohms to 100 Megohms, and this instrument should be used whenever possible, as it is simpler to use and more accurate for high resistances than Wheatstone's bridge...' So there you have it: an antique! __________________ Regds, Russell W. B. G4YLI.