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 Post subject: Vintage Lamps
PostPosted: Thu Dec 24, 2009 4:04 pm 
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Over the last couple of months I had bought some vintage 250W MBF lamps off Ebay. One was a MBF from either the 70s or 80s, the other was MBU from the 60s. Annoyingly neither of them worked.

For those who don't know, mercury lamps have an auxiliary 3rd electrode near one of the main electrodes. This 3rd electrode is supplied via a resistor. As mercury gear contains no ignitor (unlike SON), and as the mains voltage isn't high enough to strike between the main electrodes, the arc is started between the main and auxiliary electrode. This creates a small arc which then produces enough ions to allow the main arc to strike.

Since my lamps weren't starting I assumed the resistor must have gone open circuit....Bother.

However I noticed that I had a Thorn 250W ballast that would run either SON or MBF. Hmm, an idea springs to mind. What if I wire it as SON but fit a MBF lamp? The SON ignitor should strike the lamp and if it does the main arc tube must be ok. A few 10s of seconds won't cause any harm to the lamp as being cold, current will be limited.

So, flick switch, hey presto, both light. I then tried both lamps on my other 250W MBF gear and they are both ok, and start from cold.

So I wonder if the long term storage had caused the mercury to collect at the end of the arc tube causing it to short out the starting electrode? The use of ignitor gear would have made the starting electrode redundant and also vapourised the mercury away from the auxiliary electrode - certainly the MBU lamp had a lot of mercury at one end.

I have never heard of this "problem" with old mercury lamps. I knew of the problem with old SOH lamps which must be run for several hours when they come out of storage - see Lamptech.


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 Post subject: Re: Vintage Lamps
PostPosted: Sat Dec 26, 2009 2:21 am 
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Phosco152 wrote:
Over the last couple of months I had bought some vintage 250W MBF lamps off Ebay. One was a MBF from either the 70s or 80s, the other was MBU from the 60s. Annoyingly neither of them worked.

I'm glad you got them both working in the end!

If the MB/U lamp was from the same seller that I bought mine from (the one who is selling off a batch of them one at a time), the only fault I found was with the metallic end cap, which had a few small splits in it where it joins the glass. I checked this wouldn't be a problem with my Dad before powering it up, and he said it was simply the lamp showing its advanced age.

The lamp powered up fine with the 250w MBF/U gear sold to me by Harrison Lighting. To be honest, I wouldn't have a clue what to do if it hadn't!


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 Post subject: Re: Vintage Lamps
PostPosted: Sat Dec 26, 2009 8:18 am 
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Yep my MBU lamp has the same problem - splits in the cap and also the cement has gone weak holding the cap on, so it moves. I will have to unsolder the cap and the refit it using some high temperature epoxy I have. I have done this on 3 BC MBF lamps before.


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 Post subject: Re: Vintage Lamps
PostPosted: Mon Dec 28, 2009 11:48 pm 
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When thin-gauge brass is stretched and formed to make the caps, it becomes worked-hardened in the process. With the passing of the years, this evetually shows up as stress fractures, but is quite normal.


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 Post subject: Re: Vintage Lamps
PostPosted: Tue Dec 29, 2009 2:49 pm 
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If only this mercury lamp tester really could test mercury lamps!


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 Post subject: Re: Vintage Lamps
PostPosted: Tue Dec 29, 2009 3:15 pm 
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Ha, Ha, yes I've seen that before and thought what a load of rubbish. Description should read Mercury Brand Lamp Tester.


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 Post subject: Re: Vintage Lamps
PostPosted: Sat Feb 05, 2011 4:21 pm 
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mazeteam wrote:

my finds:
35w SOX lamp, possibly vintage
http://cgi.ebay.co.uk/35w-sox-lamp-sodi ... 20b6d90173


Phosco152 wrote:
If you zoom in on the Philips paper label for that 35W SOX lamp, you will see it has an 01 for London dialling code which therefore dates it to being manufactured pre 1990 - assuming of course Philips updated the number. Given the change over to 071/081 was publicised around 18 months before the change, it could be older.

Note also the different Philips font in the logo and the brown Bakelite cap. Around 1994 the red cap SOX Plus was introduced and this became the standard production lamp from Philips. At the same time the lead wire seals were improved and the ceramic sleeve on the wires deleted. The lamp on Ebay still has the sleeves.


Well my one arrived yesterday.

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The date code gives October 1989 as the date of manufacture.


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 Post subject: Re: Vintage Lamps
PostPosted: Wed Feb 16, 2011 6:29 pm 
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My latest lamp is a vintage Crompton MA mercury lamp.

Image

It came from Ebay and I didn't think I would win it - I put a last minute bid in and won. I didn't look that closely at the listing and it wasn't until it arrived that I realised it was a low pressure MA lamp - which means it must be run cap up. The dark coating on the cap threads are a graphite coating to prevent it binding in the lamp holder.

The box is in very good condition, but there are a couple of very interesting things about it.

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The Royal crest refers to the "late King George VI" which means it has to be post 1952 following the death of the King.

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However, the end of the box carries a Nato Stock Number (NSN).

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This form of NSN didn't exist before 1975, so it looks like old stock on the shelf was "codified" with a NSN. By 1975 the MA lamp was well and truly obsolete, so I am pretty certain it predates that. The 996 6738 part of the NSN is reproduced on the lamp cap.

The lamp has a date code which translates to May 1957 or May 1965. Given the reference to King George VI, I am pretty sure it would be the former. By 1965, MB lamps were well established, so again it would suggest the earlier date. The lamp is also engraved with "Property of HM Government". This appears to have been etched on at a different time to the logo which would back up the theory of old stock being codified.

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Further evidence of this being a May 1957 lamp is provided by the brilliant Lamptech site. That lists a practically identical lamp - only the logo is different - the date of that lamp is June 1959.

The box is also the same, the crest appears to be the same, but unfortunately the text is too blurred to read. The text layout is slightly different but I can just make out what looks like George VI.


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 Post subject: Re: Vintage Lamps
PostPosted: Wed Feb 16, 2011 7:42 pm 
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Very nice but the most important thing - does it work?


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 Post subject: Re: Vintage Lamps
PostPosted: Wed Feb 16, 2011 11:26 pm 
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That lamp type must be pretty rare now! Are these the lamps with the very green glow used in the likes of GEC Viatrons back in the day?


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