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A Marconi 707 added to my collection

 
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Re: A Marconi 707 added to my collection

Post by Briancuff » Sun Aug 02, 2015 3:22 pm

Yes Mike. That's what I will do. Meantime, I'm trying to find some suitable eyelet tags to replace the brittle ones. If I'm going to re-build, I might as well go the whole hog (I said it was a pig in a poke :bba :bba )

 
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Re: A Marconi 707 added to my collection

Post by Briancuff » Thu Dec 03, 2015 5:36 pm

I didn't realise that I hadn't posted about the manufacture of new tags on this forum so here goes:
I needed to replace loads of the tags on the strips because of the aforementioned dezincification. Looking through the tag makers' websites, there was nothing even similar so I drew a development of the tag and asked a couple of pressing companies on the web to quote their price for a minimum order quantity of tags and the tooling charges.
I was pleasantly surprised at the offer and went ahead. I finally got the finished tags today (the makers forgot to tin-plate them so I got it dome locally, saving £27!).
I had already made a special square punch and punched some trial Tufnel strips so I was able to try the tags straght away. The picture shows the result - I'm pleased but they were quite expensive but the 707 is worth it.
Final-Tagstrip.jpg
The Tufnel is a bit light in colour but the dark (Whale) stuff they do is too brittle.

 
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Re: A Marconi 707 added to my collection

Post by Katie Bush » Thu Dec 03, 2015 7:15 pm

I always am amazed by the ingenuity of forum members, and this is one such occasion.. I am well impressed with those results!

Just out of curiosity, does Tufnol have the same insulation characteristic as Paxolin? Or maybe even better?

Tufnol is an amazingly versatile material, and I can remember it being used by David Brown to manufacture the timing gear trains used in their mid 50's range of tractors (DB25, DB30, DB900 and DB950) 0 I have no idea how successful they were, but I do remember Tufnol couplings being used in the diesel injection pump drives on some tractor engines. :aad

Marion

 
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Re: A Marconi 707 added to my collection

Post by Doz » Thu Dec 03, 2015 7:41 pm

Katie Bush wrote:I always am amazed by the ingenuity of forum members, and this is one such occasion.. I am well impressed with those results!

Just out of curiosity, does Tufnol have the same insulation characteristic as Paxolin? Or maybe even better?

Tufnol is an amazingly versatile material, and I can remember it being used by David Brown to manufacture the timing gear trains used in their mid 50's range of tractors (DB25, DB30, DB900 and DB950) 0 I have no idea how successful they were, but I do remember Tufnol couplings being used in the diesel injection pump drives on some tractor engines. :aad

Marion


Used to maintain a modulator which had 60KV on tufnol insulators. Never saw one fail.

 
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Re: A Marconi 707 added to my collection

Post by Briancuff » Thu Dec 03, 2015 7:57 pm

Thanks for your comments, Marion.
There are several grades of Tufnel with characteristics chosen to suit various tasks such as insulation, mechanical wear and good machining properties. Some grades are made from paper (Whale for example) but most are cloth based. I would recommend visiting the Tufnel website for interesting details of the various grades.

 
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Re: A Marconi 707 added to my collection

Post by Rebel Rafter » Thu Dec 03, 2015 8:47 pm

Hi, from RR. I thought I'd done some restorations in my time but nothing like this one. That's real restoration. Dezincification is a problem with some brass plumbing fittings which is why some are now made from a special blend of metal. Couldn't those old valves be suspended over an ultrasonic cleaner so that just the pins are in the solution? It looks like you'll have to take lots of careful pictures of the old chassis to see where all the connections go afterwards, as well as drawing various diagrams, have you got a circuit diagram? I've never had a chassis that rusty. Has anyone on here ever seen the book about electronic classics? I can't remember the exact title but I've got it somewhere, amongst all the others. There's lots of suggestions in there for restoring bits of really old stuff. I used to completely strip down old sets with plastic cabinets and back covers and then stick the cabinets and backs in the bath and drench them in foam cleanser and get them looking like new, I thought that was restoration but it's nothing like stripping out all those hardwired bits and then trying to put them all back exactly as they were. And I thought rebuilding a 1000 watt stage PA amplifier was a big job. It had 20 TO3 o/p transistors which all had to be replaced. I might write a post about that some time in another section. Where do you get your little tags? RR.

 
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Re: A Marconi 707 added to my collection

Post by Briancuff » Thu Dec 03, 2015 9:29 pm

Hi RR
I will try replacing the whole base on the valves that are past cleaning. I have tried my ultrasonic bath with this sort of corrosion and it didn't touch it so it will be replace or scrape!
I have the full manual for the 707 and I have already restored my 706 which is almost identical but you're right about lots of notes and pictures!

 
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Re: A Marconi 707 added to my collection

Post by Briancuff » Sat Dec 05, 2015 8:27 pm

I have constructed a replica EMI tagboard for someone on another forum and I might well reconstruct all the boards and strips on my 707. The picture shows the new tagboard.
707 Short Tagboard (Large).jpg

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