5th Oct 2018, 10:54 am | #101 |
Octode
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Re: Help needed restoring a Murphy V310
Is that EHT measurement taken with the brightness down, it should be.
Did you try tapping around to see if you can get it to come back, suggesting a loose connection. Your previous comment on the loose wire on the frame transformer is not relevant to this fault, any suspicion should be around the line components. Also we need to know if the line collapse appears instantly or gradually.
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5th Oct 2018, 11:19 am | #102 | |||
Nonode
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Re: Help needed restoring a Murphy V310
Quote:
Quote:
Quote:
Regards David
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5th Oct 2018, 11:29 am | #103 |
Octode
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Re: Help needed restoring a Murphy V310
It sounds like a bad joint or connection, it could be inside the transformer. If it had collapsed slowly it may indicate a component breaking down.
The EHT is inconsequential at this stage and is probably ok, your biggest issue is the collapse. John or others may have some ideas about where to go from here. Maybe a transformer from an alternative set could be used assuming a direct replacement cannot be found.
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5th Oct 2018, 12:34 pm | #104 |
Dekatron
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Re: Help needed restoring a Murphy V310
The line oscillator is stopping but seeing as this is a self-oscillating design, it could be anything. Have you checked all the R's and C's around the 30P4 that set the bias and hold? Has MR2 been replaced?
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6th Oct 2018, 6:26 pm | #105 |
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Re: Help needed restoring a Murphy V310
OK let's have a gathering of suggestions.
The line output stage is self oscillating. If it stops the EHT will collapse and cannot leave a vertical line. We must therefore conclude that the wiring from the transformer to the scan coil lead out wires is highly probable. I would not suspect the actual windings themselves but it's not set in stone. Does the line fade after 10 seconds [as the EHT fades to zero] after appearing or does it remain? If it remains I would agree with Stephen. It's my long arm suspicion that there is an internal intermittent connection within the transformer. This is most likely to be where the thin wires from the windings are jointed [soldered ] to the lead out wires that exit from the top. The chances are they have rotted due to oil contamination. They may even have arced through at a possible pinch point within the can.This is all calculated guess work. It would be nice to open the can and have a look what is actually happening. I have my own method of opening the can that does not involve smashing open the top seal but this, if necessary can be explained. Some care, patience and a hacksaw are required. The EHT is low due to the incorrect loading when the connection [s] fail. I think that is about all I can advise but it is certainly not the end of the end. John. PS I would set the voltage selector to 240V unless your mains is much lower than this. |
6th Oct 2018, 7:56 pm | #106 |
Nonode
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Re: Help needed restoring a Murphy V310
Thanks for all the replies.
Ok, I'll spend some time checking C & R's and all the soldered joints. If nothing improves I'll open up the LOPTx. The vertical line did disappear completely the last time I powered it up but that was with the EHT meter connected, which must be loading the transformer? Regards David
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7th Oct 2018, 8:50 am | #107 |
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Re: Help needed restoring a Murphy V310
The EHT meter will not load the system to such an extent. The actual loading is tiny. How long did it take to fade after the line appeared? Do the test with the meter disconnected.
Opening the transformer must be carried out in a safe, clean, and neat manner. A supply of rags, a hacksaw and disposable rubber gloves are required. Failing this it will be impossible to obtain a reseal. Put a layer of insulating tape around the top of the can and use this as a guide to cut through the can about an inch from the top. Turn the can as you cut through taking great care. Oil will run out and must be soaked up. Just my way as resealing is easy with Araldite but you may have your own method. J. |
7th Oct 2018, 9:53 am | #108 |
Octode
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Re: Help needed restoring a Murphy V310
Hi John,
Do you have any pictures of the insides of one of these oil filled transformers? What do you refill it with when you put it back together? I assume you wouldn't re use the old oil, if there was any left, due to possible water contamination? I think the conclusion was that the oil used was unlikely to contain PCB's but I guess we ought to take sensible precautions, just in case! Do you think the oil filled transformers were more or less reliable than conventional ones when they were new? Cheers Nick |
7th Oct 2018, 10:32 am | #109 |
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Re: Help needed restoring a Murphy V310
I believe best quality cooking oil is very satisfactory. I was given this tip by 'MURPHY V310' who unfortunately is no longer a member of this Forum. He worked for BRW who at that time had many thousands of V310 models out on rental.
I will contact him and confirm the solution. Oil filled transformers, if hermetically sealed were incredibly reliable. The mains EHT transformer employed in the Ekco TC165/TC113 were reliable together with the Ferguson 968T. There were others such as the Philips 385 series that held up well. The problem comes when the seal becomes compromised. The Murphy transformers were OK when new but leaked usually due to the decomposition of the rubber seals at the point of exit of the lead out wires. Add to this the chemical reactions of the plastic, rubber and oil and you have a problem as the years pass. Air enters and contaminates the insulation properties of the high grade oil. Remember of course that they had a design life of 10 years and we are now over 60 years past their design life! Saying that they did give problems with the U26 heater winding breaking down to the core and rotting where it exited from the transformer. Some transformers had an aluminium rivet plugging one of the lead out exit points. This may have been the oil filler and it may be possible to drain the oil if the rivet can be removed easily. It would probably take a few days to drain if inverted into a jam jar. Now there's a thought. Glass pot, oil..I'll leave the rest to your ingenuity [if you dare] I opened one many decades ago. It's a faded memory now but it's only a normal LOPT inside. There were open type transformers [not supplied by Murphy] obtainable as replacements. As far as I know there were only two Murphy models produced 1950-1963 that did not use an oil filled LOPT. The 12" V230 portable and the 14" V350 portable. It did cut down the 10kcs line whistle but I think it was more of an expensive quirk, one of many that led eventually to the collapse of Murphy Radio about 1962/3. John. |
7th Oct 2018, 11:38 am | #110 | |
Nonode
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Re: Help needed restoring a Murphy V310
Quote:
I did intend to un-pein the lip of the lopt, like I've done many times with electrolytic cans, will this work? If I do open up the lopt what should I do with the U26 heater winding with insulation breakdown? There's also the unused line output winding, which is currently connected to the chassis, maybe it's breaking down as well? Regards David
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7th Oct 2018, 4:16 pm | #111 |
Heptode
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Re: Help needed restoring a Murphy V310
Out of interest, would it be possible to post a couple of photos of this oil filled LOPT?
Jac |
7th Oct 2018, 5:28 pm | #112 | |
Dekatron
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Re: Help needed restoring a Murphy V310
Quote:
Best to remove the heater winding altogether. It will be virtually impossible to reseal the can if you open the top but if you feel you can manage this then by all means have a go. I cut the can around 1" from the top with a fine hacksaw taking great care not to damage the inside windings. Then upon reassembly, clamp the two halves together then run a ring of Araldite around the join. Of course it has to be clean and oil free. This is only a suggestion and your method may well be a better solution. John. |
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7th Oct 2018, 6:16 pm | #113 | |
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Re: Help needed restoring a Murphy V310
Quote:
DFWB. |
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7th Oct 2018, 6:16 pm | #114 |
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Re: Help needed restoring a Murphy V310
Hello Jac,
I don't have to hand a V310 transformer but this is the one for the earlier V240/250. The V310 is taller and thinner. This is even more crazy due to the fact that it has the U25 EHT rectifier enclosed within the oil can and cannot be replaced! This requires replacement of the complete unit when the wired in type U25 fails. It is the Mazda 2v version of the Mullard EY51 but nothing like as reliable. You can see the aluminium rivet that I presume plugs the whole where it was filled, on the left. To be fair to Murphy the whole assembly did not cost much more than the rectifier and for a number of years Murphy would carry out a 'reconditioning' service for around 30/- [£1.50]. The top is soft squashy rubber. John. PS I hope you cooked your eggs to go with the baked beans in the transformer oil David. I do hate food waste.. |
7th Oct 2018, 7:49 pm | #115 |
Heptode
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Re: Help needed restoring a Murphy V310
Thanks David and John for the photos.
Quite different from the Philips 385-like can and the 25kV (and 7kV) square cans. Jac |
8th Oct 2018, 8:46 am | #116 |
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Re: Help needed restoring a Murphy V310
As the EHT collapses instantly the most likely break would be one of the internal connections to the 30P4 or U191 valves. These are at the highest potential and most likely to decompose. J.
Just to add, this picture shows how the leads exit the supple rubber top. It may be synthetic rubber but it makes little difference. The leads pass through tight sleeved holes but not absolutely oil or air tight over years of heating and cooling. Last edited by Heatercathodeshort; 8th Oct 2018 at 8:54 am. Reason: Added info. |
8th Oct 2018, 8:59 am | #117 |
Heptode
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Re: Help needed restoring a Murphy V310
Thanks John,
That illustrates the top seal clearly. From David's photo and your text I understand that it basically is a normally constructed LOPT inside the can. I hope I'm not too much digressing from the topic, but I was wondering what the LOPT inside the can of a Philips 385U looks like.... Jac |
8th Oct 2018, 11:16 am | #118 | |
Nonode
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Re: Help needed restoring a Murphy V310
Quote:
Regards David
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8th Oct 2018, 11:30 am | #119 |
Dekatron
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Re: Help needed restoring a Murphy V310
This is a self-oscillating design so as soon as there is insufficient feedback to maintain the oscillation, it will stop and the line will collapse. The 30P4 will then run at very high anode current.
The white stuff may be the cathode coating. |
8th Oct 2018, 5:36 pm | #120 |
Dekatron
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Re: Help needed restoring a Murphy V310
Agree. [I thought we had eliminated the 30P4?] J.
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