Murphy V310 Lopty Rewind or Replace - UK Vintage Radio Repair and Restoration Discussion Forum

Mikey405 · 5th Mar 2017, 3:09 pm

Hi all.

A pal of mine in Wales (non technical) has for many years used a Murphy V310 as his everyday set (at least a couple of hours per day). He has 3 spare sets which have, up to now, provided a wealth of spare tubes, loptys and other bits and bobs whenever his main set has failed. Unfortunately it now looks as though the last lopty has failed with a shorted turn and replacement from stock is no longer a possibility. I've been told, although I haven't heard it from the good Mr Barker's or Mr Dinning's mouth, that these transformers are next to impossible to rewind reliably due to issues with arcing overwinds etc.

I had a few ideas myself:

1. Find another derelict V310 / V320 and use the lopty out of that.
2. Modify the circuit to suit another kind of transformer from a different set.
3. Get the primary of one of the existing transformers rewound with a doubler on the line output valve anode.
4. Get the primary rewound with a half-voltage secondary and then use a solid state doubler circuit built in to the lopty can.

My preferred method would be the last one but I don't whether this is a practical proposition, or whether anyone had the same problem with their V310 and solved it in a different ingenious way.

Thanks everyone.

Kind regards.

From Mike.

FERNSEH · 5th Mar 2017, 11:39 pm

Hi Mike,
I'd go for option No.2, replace the oil filled line output transformer with a "dry" one. Has the set in question been modified for a separate line oscillator? This modification was introduced to solve the line frequency drift problem inherent in the self oscillating line output stage.

DFWB.

Radio_Dave · 6th Mar 2017, 10:37 am

I don't know if this is relevant to your problem but because I'm trying to fix one of these sets I've been reading lots of old treads about them

.

It's seems that a very common fault of the LOPTx is failure of the U26 heater winding. The simple fix is to fit an EHT rectifier stick where the U26 should be. http://www.vintage-radio.net/forum/s...ad.php?t=44907

David

Heatercathodeshort · 6th Mar 2017, 5:18 pm

In the 1960's a 'dry' transformer was available from Direct TV Replacements of Lewisham.
It was a very good replacement but would be difficult to reproduce today.
David's approach I feel would be a permanent cure. RadioDave is certainly correct reference the U26 heater winding. It used to go down to the core or simply O/C. Wretched things these oil filled nasties. The odd thing is Murphy could produce really good dry transformers such as the ones in the V230 and V350. They never failed. The oil slicks went on for far too long. John.

FERNSEH · 6th Mar 2017, 6:46 pm

I believe British Relay Wireless had specially made "dry" line output transformers for certain rental Murphy TV sets. Not so sure about the V310 but certainly the V659 series.
Before condemning the line output transformer why not build a proper line oscillator in order the line output stage has the correct line drive waveform.
The circuit used in the V310A models could be copied.

DFWB.

5th Mar 2017, 3:09 pm	#1
Mikey405 Octode Join Date: Jul 2006 Location: Solihull, West Midlands and Beaford, Devon Posts: 1,626	Murphy V310 Lopty Rewind or Replace Hi all. A pal of mine in Wales (non technical) has for many years used a Murphy V310 as his everyday set (at least a couple of hours per day). He has 3 spare sets which have, up to now, provided a wealth of spare tubes, loptys and other bits and bobs whenever his main set has failed. Unfortunately it now looks as though the last lopty has failed with a shorted turn and replacement from stock is no longer a possibility. I've been told, although I haven't heard it from the good Mr Barker's or Mr Dinning's mouth, that these transformers are next to impossible to rewind reliably due to issues with arcing overwinds etc. I had a few ideas myself: 1. Find another derelict V310 / V320 and use the lopty out of that. 2. Modify the circuit to suit another kind of transformer from a different set. 3. Get the primary of one of the existing transformers rewound with a doubler on the line output valve anode. 4. Get the primary rewound with a half-voltage secondary and then use a solid state doubler circuit built in to the lopty can. My preferred method would be the last one but I don't whether this is a practical proposition, or whether anyone had the same problem with their V310 and solved it in a different ingenious way. Thanks everyone. Kind regards. From Mike. __________________ G7TRF Last edited by Mikey405; 5th Mar 2017 at 3:26 pm. Reason: Speeling.

5th Mar 2017, 11:39 pm	#2
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Murphy V310 Lopty Rewind or Replace Hi Mike, I'd go for option No.2, replace the oil filled line output transformer with a "dry" one. Has the set in question been modified for a separate line oscillator? This modification was introduced to solve the line frequency drift problem inherent in the self oscillating line output stage. DFWB.

6th Mar 2017, 10:37 am	#3
Radio_Dave Nonode Join Date: Jun 2004 Location: Norwich, Norfolk, UK. Posts: 2,543	Re: Murphy V310 Lopty Rewind or Replace I don't know if this is relevant to your problem but because I'm trying to fix one of these sets I've been reading lots of old treads about them . It's seems that a very common fault of the LOPTx is failure of the U26 heater winding. The simple fix is to fit an EHT rectifier stick where the U26 should be. http://www.vintage-radio.net/forum/s...ad.php?t=44907 David __________________ http://www.youtube.com/ My Nixie Clocks

6th Mar 2017, 5:18 pm	#4
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Murphy V310 Lopty Rewind or Replace In the 1960's a 'dry' transformer was available from Direct TV Replacements of Lewisham. It was a very good replacement but would be difficult to reproduce today. David's approach I feel would be a permanent cure. RadioDave is certainly correct reference the U26 heater winding. It used to go down to the core or simply O/C. Wretched things these oil filled nasties. The odd thing is Murphy could produce really good dry transformers such as the ones in the V230 and V350. They never failed. The oil slicks went on for far too long. John.

6th Mar 2017, 6:46 pm	#5
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Murphy V310 Lopty Rewind or Replace I believe British Relay Wireless had specially made "dry" line output transformers for certain rental Murphy TV sets. Not so sure about the V310 but certainly the V659 series. Before condemning the line output transformer why not build a proper line oscillator in order the line output stage has the correct line drive waveform. The circuit used in the V310A models could be copied. DFWB.