Intervalve Transformer Rewind? - UK Vintage Radio Repair and Restoration Discussion Forum

ms660 · 30th Dec 2015, 5:11 pm

If I had an intervalve transformer rewound professionally could the original laminations and shrouds be used?

Any rough idea of the cost?

I have an early (1920's) receiver with two of them, one for sure has no continuity on either primary or secondary, not sure about the other one yet.

The exposed edges of the laminations have surface rust, not too worried about that cosmetically but would it affect a rewind job?

Just trying to get an idea regarding a rewind if it turns out that it needs one, the receiver is worthy of a proper job.

Lawrence.

kalee20 · 30th Dec 2015, 11:18 pm

Almost certainly.

It will be a very labour-intensive job. If it's 1920's then the laminations probably will not be exotic and stress-sensitive alloy, so while they obviously shouldn't be bent etc, they won't need handling with kid gloves.

The trouble is, a lot of the hard work and cleaning up is something you could do yourself, leaving the winding to the experts. But the experts will want to assess the whole thing first, make inductance measurements on an intact winding first before stripping, perhaps wind a test winding on top for turns ratio measurements - and sending it backwards and forwards is just messy and cumbersome.

The winding may need a bobbin or former made up, and possibly a winding mandrel tool to support it, depending on the lamination dimensions. It all adds to the cost of a small quantity oa a one-off. But modern wire enamels and materials should mean that it will last for almost ever.

Best people to ask will be Mike Barker (Murphymad) and Ed Dinning, who both do winding.

trh01uk · 31st Dec 2015, 10:23 am

Lawrence,

its unlikely that any professional winding company will even get out of bed for less than £75. Expect to be charged at least that - and probably considerably more.

You don't say what size the transformer is, but if its anything close to currently available lamination sizes, then it will be a lot cheaper to get a modern replacement wound using readily available parts. Transformers that have been potted in pitch or have been varnished are a bit of nightmare to get sufficiently clean to be able to recover the original laminations - and obviously taking on that job will bump the cost up a lot - unless you decide to do that your self.

If you don't know the original spec of the transformer, and your original is open circuit on at least one winding, then measurements aren't going to produce a specification. Someone will have to sit down and design a replacement - again a chargeable activity - unless someone on here can suggest "typical" specs for such a transformer.

Most of the UK transformer industry is now dead - with just a few specialists remaining - since most of the once vital circuit positions demanding transformers have been "designed out" - by switch mode power supplies and the like.

If I were you, I would start by posting photos of the transformer on here. Someone might even have a direct replacement sitting in their junk box!

Richard

ms660 · 31st Dec 2015, 10:56 am

Thanks for everyone's input so far, ideally the transformers need to maintain as much of there originality as possible as the receiver they are in looks to be a bit of a rare beast at the moment (more research to do)

The receiver I suspect, might have been originally fitted with TM valves, the receiver came to me with Mullard PM valves (2 volt) so I think the transformers were just standard jobies for the day, they appear to be Identical but so far no ID on the manufacturer.

Lawrence.

julie_m · 31st Dec 2015, 12:19 pm

If they are from France, then they will almost certainly be using metric sized laminations and bobbins.

ms660 · 31st Dec 2015, 12:28 pm

A pic of one of the transformers, only markings are PRI, SEC and a number, punching the number in the Googlatron hasn't resulted in any ID.

The pic doesn't show this but the shrouds appear to be held on with two rivets that appear to be only lightly peened over....hopefully.

Lawrence.

kalee20 · 31st Dec 2015, 10:54 pm

Hmm... Laminations with rounded corners? New to me! Unlikely to be a size still in fashion! But very unusual... Yes I'd want to recommission those transformers!

PJL · 31st Dec 2015, 11:19 pm

About 1/3rd of the 1920/30's transformers I have had o/c windings and it does not seem to be specific to manufacturer nor wire gauge as even 50K+ resistance windings can be OK.

Intervalve transformers of the period were very simple and are nearly always rough wound. You can rewind them yourself if you set up a simple jig (I use a pedometer for the counter). You can find the gauge of the wire by measuring the resistance of a metre length and comparing with a chart. Count the turns off as you unwind.

If you are lucky it may be a poor connection to the terminals or possibly a failure in the connection to the leadout wire on the outer winding.

30th Dec 2015, 5:11 pm	#1
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Intervalve Transformer Rewind? If I had an intervalve transformer rewound professionally could the original laminations and shrouds be used? Any rough idea of the cost? I have an early (1920's) receiver with two of them, one for sure has no continuity on either primary or secondary, not sure about the other one yet. The exposed edges of the laminations have surface rust, not too worried about that cosmetically but would it affect a rewind job? Just trying to get an idea regarding a rewind if it turns out that it needs one, the receiver is worthy of a proper job. Lawrence.

30th Dec 2015, 11:18 pm	#2
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,087	Re: Intervalve Transformer Rewind? Almost certainly. It will be a very labour-intensive job. If it's 1920's then the laminations probably will not be exotic and stress-sensitive alloy, so while they obviously shouldn't be bent etc, they won't need handling with kid gloves. The trouble is, a lot of the hard work and cleaning up is something you could do yourself, leaving the winding to the experts. But the experts will want to assess the whole thing first, make inductance measurements on an intact winding first before stripping, perhaps wind a test winding on top for turns ratio measurements - and sending it backwards and forwards is just messy and cumbersome. The winding may need a bobbin or former made up, and possibly a winding mandrel tool to support it, depending on the lamination dimensions. It all adds to the cost of a small quantity oa a one-off. But modern wire enamels and materials should mean that it will last for almost ever. Best people to ask will be Mike Barker (Murphymad) and Ed Dinning, who both do winding.

31st Dec 2015, 10:23 am	#3
trh01uk Octode Join Date: Nov 2010 Location: Ross-on-Wye, Herefordshire, UK. Posts: 1,654	Re: Intervalve Transformer Rewind? Lawrence, its unlikely that any professional winding company will even get out of bed for less than £75. Expect to be charged at least that - and probably considerably more. You don't say what size the transformer is, but if its anything close to currently available lamination sizes, then it will be a lot cheaper to get a modern replacement wound using readily available parts. Transformers that have been potted in pitch or have been varnished are a bit of nightmare to get sufficiently clean to be able to recover the original laminations - and obviously taking on that job will bump the cost up a lot - unless you decide to do that your self. If you don't know the original spec of the transformer, and your original is open circuit on at least one winding, then measurements aren't going to produce a specification. Someone will have to sit down and design a replacement - again a chargeable activity - unless someone on here can suggest "typical" specs for such a transformer. Most of the UK transformer industry is now dead - with just a few specialists remaining - since most of the once vital circuit positions demanding transformers have been "designed out" - by switch mode power supplies and the like. If I were you, I would start by posting photos of the transformer on here. Someone might even have a direct replacement sitting in their junk box! Richard

31st Dec 2015, 10:56 am	#4
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Intervalve Transformer Rewind? Thanks for everyone's input so far, ideally the transformers need to maintain as much of there originality as possible as the receiver they are in looks to be a bit of a rare beast at the moment (more research to do) The receiver I suspect, might have been originally fitted with TM valves, the receiver came to me with Mullard PM valves (2 volt) so I think the transformers were just standard jobies for the day, they appear to be Identical but so far no ID on the manufacturer. Lawrence.

31st Dec 2015, 12:19 pm	#5
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Intervalve Transformer Rewind? If they are from France, then they will almost certainly be using metric sized laminations and bobbins. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

31st Dec 2015, 12:28 pm	#6
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Intervalve Transformer Rewind? A pic of one of the transformers, only markings are PRI, SEC and a number, punching the number in the Googlatron hasn't resulted in any ID. The pic doesn't show this but the shrouds appear to be held on with two rivets that appear to be only lightly peened over....hopefully. Lawrence. Attached Thumbnails

31st Dec 2015, 10:54 pm	#7
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,087	Re: Intervalve Transformer Rewind? Hmm... Laminations with rounded corners? New to me! Unlikely to be a size still in fashion! But very unusual... Yes I'd want to recommission those transformers!

31st Dec 2015, 11:19 pm	#8
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Intervalve Transformer Rewind? About 1/3rd of the 1920/30's transformers I have had o/c windings and it does not seem to be specific to manufacturer nor wire gauge as even 50K+ resistance windings can be OK. Intervalve transformers of the period were very simple and are nearly always rough wound. You can rewind them yourself if you set up a simple jig (I use a pedometer for the counter). You can find the gauge of the wire by measuring the resistance of a metre length and comparing with a chart. Count the turns off as you unwind. If you are lucky it may be a poor connection to the terminals or possibly a failure in the connection to the leadout wire on the outer winding.