UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Television and Video

Notices

Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

Closed Thread
 
Thread Tools
Old 17th Jan 2023, 10:33 pm   #1
Niechcial,Steve
Hexode
 
Join Date: Jan 2007
Location: Beckenham, London, UK.
Posts: 373
Default Murphy V310 LOPT rewind

The LOPT failed on a Murphy V310 while I was working on it. I am just a rank amateur when it comes to transformer winding, but a couple of Bush ones I did last year are holding up well so I thought I would have a go at the 310. The surgery worked so here are some of the details for anyone who fancies a go. It is only possible using basic kit to rewire the main coil. If the EHT overwinding has failed that is a specialist job. But that it is not necessarily a problem as you can replace it with a simple tripler as described below.

The main coil bobbin is fairly easy to rewind as the core comes apart quite easily, there is plenty of room on the bobbin for the turns required, and the wire is quite thick. The main complication is that the trannie lives in a can full of oil and will have to go back into the can with fresh oil to work. There is no need to cut or file the can to dismantle. Simply lift the lip of metal with a screwdriver all the way round, then straighten it fully with pliers (pic 1). The transformer then slides in and out easily. Pic 2 shows the contents- main coil is on the left limb of the core in the picture, EHT overwind and space for rectifier heater winding are on the right (heater winding already removed in this pic). In between the two coil bobbins is the dropper resistor for the rectifier heater. Beware the oil in the can may contain toxic PCBs so avoid excessive hand contact with it.

Having got the transformer out the can, you will see how undoing two brass clips allows the two U-shaped pieces of the core to be pulled apart. Be careful not to lose the two plastic insulating discs that sit between them . After careful unsoldering of all the lead out wires, both bobbins can be lifted off the core.

To rewind I used a simple £25 coil winder which has a mechanical counter (Pic 3). Pic 4 shows the main coil bobbin. Before I had got to this point I had used a simple ‘ringer’ to confirm the EHT winding was ok, and the fault was on the main coil somewhere. Every winding, on the main coil rang poorly, but that did not mean they were all faulty as a short on one winding is often enough to damp the whole transformer. I started where you have to, by pulling off the top winding on the bobbin using the winder to count the turns. This is the ‘hot’ winding which runs between valve top caps. I then used the ringer again. This time all coils rang well indicating the fault was on the winding removed. At this point I could have continued and taken off the rest of the windings and done a thorough job by re-winding the whole thing. However this would amount to about 3 times the amount of winding, and as I am slow at it I decided just to replace the failed winding. This is a decision I may later come to regret! Working from the inside out, this winding’s turns are 35-55-55-55-55-30. 285 turns in all over 6 layers each separated by Mylar tape (insulating tape will not substitute). I gauged the wire with a micrometer as 0.225 mm. I got fresh oil from a radio ham supplier- they do it in two litre bottles.

You can test the main coil of the transformer outside of the can and oil but if you do, leave the EHT overwind off the core. I didn’t and running it in the air it arced everywhere and was damaged before I could switch off . The EHT overwind has no extra insulation on it and needs immersion in the oil to survive. Inside the can, all the transformer contacts are within a few mm of the metal can, hence the need for the oil which forms an insulating barrier. I built a 3 diode 3 cap tripler in the can in the space where the overwind had been and this works well. I guess instead of oil you could use other potting compounds, but these expensive, and once embedded you will never get the transformer out again if it fails again.

The thing has been running stably for several hours now producing plenty of width, an EHT of 13 KV and a boost voltage of 440V. This compares with 14KV and 470V as given in the manual. I could probably get boost up by a tuning cap across the coil, but it works well enough. I’m guessing that the oil filled LOPTS on other Murphy models are probably very similar so similar rewinding may work.
Attached Thumbnails
Click image for larger version

Name:	Transformer Can.jpg
Views:	309
Size:	41.2 KB
ID:	271733   Click image for larger version

Name:	Main Coil Bobbin.jpg
Views:	302
Size:	23.0 KB
ID:	271734   Click image for larger version

Name:	Coil Winder.jpg
Views:	332
Size:	31.1 KB
ID:	271735   Click image for larger version

Name:	V 310 Transformer.jpg
Views:	311
Size:	75.6 KB
ID:	271736  

Last edited by Station X; 18th Jan 2023 at 10:34 am. Reason: Added some white space.
Niechcial,Steve is offline  
Old 18th Jan 2023, 12:01 am   #2
high_vacuum_house
Octode
 
high_vacuum_house's Avatar
 
Join Date: May 2003
Location: Belper Derbyshire
Posts: 1,906
Smile Re: Murphy V310 LOPT rewind

That’s a smart looking coil winder especially for £25! Where was it acquired from.
I have a couple of oil immersed LOPT’s . I think they are usually quite reliable as the can is hermetically sealed unless the oil is contaminated or leaks out.

Christopher Capener
__________________
Interests in the collection and restoration of Tefifon players and 405 line television
high_vacuum_house is online now  
Old 18th Jan 2023, 8:13 am   #3
Niechcial,Steve
Hexode
 
Join Date: Jan 2007
Location: Beckenham, London, UK.
Posts: 373
Default Re: Murphy V310 LOPT rewind

That particular one seems no longer available for under £42 but here is what looks like a similar one for £24.99

https://www.ebay.co.uk/itm/282054552715
Niechcial,Steve is offline  
Old 18th Jan 2023, 10:13 am   #4
Rich Woods
Pentode
 
Rich Woods's Avatar
 
Join Date: Sep 2017
Location: Ceredigion, Wales, UK.
Posts: 243
Default Re: Murphy V310 LOPT rewind

Quote:
Originally Posted by high_vacuum_house View Post
That’s a smart looking coil winder especially for £25! Where was it acquired from.
I have a couple of oil immersed LOPT’s . I think they are usually quite reliable as the can is hermetically sealed unless the oil is contaminated or leaks out.

Christopher Capener
I must have been very unlucky back in the 70’s as every Murphy I got hold of back then had a duff LOPT, bar 1 console set, which also eventually failed. Back in those days sadly that was curtains for the set which was then broken for spares.
__________________
It’s all about the music…….
Rich Woods is offline  
Old 18th Jan 2023, 10:54 am   #5
murphyv310
Dekatron
 
murphyv310's Avatar
 
Join Date: Sep 2006
Location: Kilmarnock, Ayrshire, UK.
Posts: 5,420
Default Re: Murphy V310 LOPT rewind

Hi.
Great job indeed. The can incidentally is the same size as a Heinz tomato soup or beans tin which I've used successfully in LOPT rebuilds.
__________________
Cheers,
Trevor.
MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member
murphyv310 is offline  
Old 18th Jan 2023, 1:16 pm   #6
Niechcial,Steve
Hexode
 
Join Date: Jan 2007
Location: Beckenham, London, UK.
Posts: 373
Default Re: Murphy V310 LOPT rewind

Thanks Trevor. Have you rewound other Murphy LOPTs?

The tube cover on the back of my V310 is missing. Any chance you could measure yours for me please so that I can fabricate a replacement? Thanks in anticipation
Niechcial,Steve is offline  
Old 18th Jan 2023, 1:19 pm   #7
Niechcial,Steve
Hexode
 
Join Date: Jan 2007
Location: Beckenham, London, UK.
Posts: 373
Default Re: Murphy V310 LOPT rewind

I think the LOPT failure rate on Murphys is very high Rich. It seems to be something to do with the oil absorbing moisture over the time. Also the materials of the time of which they are made (including paper between the windings) , were not durable for prolonged soaking in oil.
Niechcial,Steve is offline  
Old 18th Jan 2023, 1:47 pm   #8
Welsh Anorak
Dekatron
 
Welsh Anorak's Avatar
 
Join Date: Apr 2005
Location: North Wales, UK.
Posts: 6,882
Default Re: Murphy V310 LOPT rewind

Steve - don't forget the plastic pudding bowl 'modification', though you may get some funny looks in the supermarket...
__________________
Glyn
www.gdelectronics.wales
Welsh Anorak is online now  
Old 18th Jan 2023, 3:37 pm   #9
Niechcial,Steve
Hexode
 
Join Date: Jan 2007
Location: Beckenham, London, UK.
Posts: 373
Default Re: Murphy V310 LOPT rewind

Blimey Glyn, what's that?
Niechcial,Steve is offline  
Old 18th Jan 2023, 3:52 pm   #10
peter_scott
Dekatron
 
peter_scott's Avatar
 
Join Date: May 2003
Location: Edinburgh, UK.
Posts: 3,273
Default Re: Murphy V310 LOPT rewind

Very well done!

Peter
peter_scott is online now  
Old 18th Jan 2023, 6:21 pm   #11
Rich Woods
Pentode
 
Rich Woods's Avatar
 
Join Date: Sep 2017
Location: Ceredigion, Wales, UK.
Posts: 243
Default Re: Murphy V310 LOPT rewind

Quote:
Originally Posted by Niechcial,Steve View Post
I think the LOPT failure rate on Murphys is very high Rich. It seems to be something to do with the oil absorbing moisture over the time. Also the materials of the time of which they are made (including paper between the windings) , were not durable for prolonged soaking in oil.
It just grieves me that I scrapped so many of the sets back in the day as they are, I guess, potentially much easier to rewind compared to pitch covered LOPTS. Also when they are working properly they have one of the best pictures of all the 405 line sets. These days in many ways we are spoiled. Valves & components next day from eBay, etc, technical data available from the forum & other on line sources. It’s easy to forget how difficult technical info and valves were to come by back in the 70’s as a teenage amateur. No internet & no interest from the trade (with a few honourable exceptions).
__________________
It’s all about the music…….
Rich Woods is offline  
Old 18th Jan 2023, 6:24 pm   #12
Rich Woods
Pentode
 
Rich Woods's Avatar
 
Join Date: Sep 2017
Location: Ceredigion, Wales, UK.
Posts: 243
Default Re: Murphy V310 LOPT rewind

Quote:
Originally Posted by Welsh Anorak View Post
Steve - don't forget the plastic pudding bowl 'modification', though you may get some funny looks in the supermarket...
The plastic bowl that comes with supermarket treacle sponge pudding works well too!
__________________
It’s all about the music…….
Rich Woods is offline  
Old 18th Jan 2023, 6:40 pm   #13
Radio_Dave
Nonode
 
Radio_Dave's Avatar
 
Join Date: Jun 2004
Location: Norwich, Norfolk, UK.
Posts: 2,543
Default Re: Murphy V310 LOPT rewind

Quote:
Originally Posted by Niechcial,Steve View Post
The tube cover on the back of my V310 is missing.
There is no cover attached to the back of a V310, just a hole where the focus control passes through.


David
Radio_Dave is offline  
Old 18th Jan 2023, 8:10 pm   #14
Ed_Dinning
Dekatron
 
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,171
Default Re: Murphy V310 LOPT rewind

Looks a good coil winder for the money and adequate for many jobs if a bit tedious on big rewinds

Ed
Ed_Dinning is offline  
Old 19th Jan 2023, 1:21 pm   #15
Niechcial,Steve
Hexode
 
Join Date: Jan 2007
Location: Beckenham, London, UK.
Posts: 373
Default Re: Murphy V310 LOPT rewind

Is there a little bump or something then David, because the tube does potrude beyond the back?
Niechcial,Steve is offline  
Old 19th Jan 2023, 1:29 pm   #16
dazzlevision
Dekatron
 
Join Date: Sep 2003
Location: Near Swindon, North Wiltshire, UK.
Posts: 3,595
Default Re: Murphy V310 LOPT rewind

IIRC, on the V310, the focus control was actually the moulded brown cup shaped cover (phenolic material) that covered the CRT base connector and was screwed to the focus magnet assembly.The three fixing flanges of which often broke, due to rough handling.

Photo here:https://www.radiomuseum.org/r/murphy_v_310v31.html
dazzlevision is online now  
Old 20th Jan 2023, 9:39 am   #17
Niechcial,Steve
Hexode
 
Join Date: Jan 2007
Location: Beckenham, London, UK.
Posts: 373
Default Re: Murphy V310 LOPT rewind

Thanks for that Dave. Yes the focus flanges on mine are broken. So that whole thing on the back twists to control the focus?
Niechcial,Steve is offline  
Old 20th Jan 2023, 9:42 am   #18
dazzlevision
Dekatron
 
Join Date: Sep 2003
Location: Near Swindon, North Wiltshire, UK.
Posts: 3,595
Default Re: Murphy V310 LOPT rewind

Quote:
Originally Posted by Niechcial,Steve View Post
So that whole thing on the back twists to control the focus?
Yes.
dazzlevision is online now  
Old 20th Jan 2023, 1:42 pm   #19
German Dalek
Hexode
 
German Dalek's Avatar
 
Join Date: Jan 2011
Location: Düsseldorf, Germany.
Posts: 367
Default Re: Murphy V310 LOPT rewind

Hi Steve,
Please discribe your tripler with used values.
How do you seal the can after servicing?

Many thanks in advance!

German Dalek
__________________
And now something completly different:

MARC BOLAN, he was/is the real king of Pop Music!
German Dalek is offline  
Old 21st Jan 2023, 8:56 pm   #20
Niechcial,Steve
Hexode
 
Join Date: Jan 2007
Location: Beckenham, London, UK.
Posts: 373
Default Re: Murphy V310 LOPT rewind

Greetings German Dalek! I used a 3 silicon diode, 2 ceramic capacitor tripler. Here is the source for the diodes: https://www.ebay.co.uk/itm/283196488...Bk9SR8bT5dy6YQ
I used 1000pf 6Kv capacitors because I had them in stock, but 500pf at 5 Kv or greater would be fine. The circuit is simply that as used in the Thorn 1500 and similar sets. I attach a photo. The input is from the feed to the top cap of the line output valve. I took the EHT out on a new piece of cable which I joined onto the existing EHT cable inside the insulated base cover of the now –not- required EHT rectifier valve.
The ends of transformer windings are soldered to brass eyelets in the cardboard fixings on the transformer. Once you have removed the EHT overwind, rectifier heater winding and dropper resistor, that frees up enough brass eyelets to mount your diodes and capacitors. They fit in space where the overwind coil was. By judicious bending of leads I did just about get the tripler to work in air without arcing across, but it really needs to be in the oil where it’s fine. Getting the transformer in and out of the can is a bit fiddly with a slight risk of damage, so for test purposes you might like to run the whole assembly in a glass jam jar of oil first.
I haven’t bothered to try and seal the can. I think it is generally reckoned hard to seal perfectly because the rubber by now has usually hardened and distorted. This means of course I can’t tip the set on its face to get the case back on. If I did want to seal it a bit I would just tap down the edge of the can lip again with a small hammer and a metal drift
Good luck. If you try it I’d be interested to hear how you get on
Attached Files
File Type: pdf 1500 Tripler.pdf (611.3 KB, 80 views)
Niechcial,Steve is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 11:03 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.