Murphy U198M help.

[AmateurRepairer]

I have partially recapped and resoldered some of the joints on this radio (I’m no artist at it)

The original sound output had gone open circuit so a local member gave me a spare one he had lying around as well as a dozen magazines, you know who you are, thanks a bunch

I still can’t figure out where this black wire needs to go to. I believe it went inside the original transformer but I can’t do that on this eht as it is a completely different type. Also do I need to refit a resistor and also a capacitor as per the original set was.

This is going to be my bedside table set so it’s got to be right.

Thanks all

[AmateurRepairer]

P.s white wire I know where that goes. It’s the black one on the other side of the valve I am unsure about.

[paulsherwin]

Aren't the black and white wires the transformer secondary which goes to the speaker?

[AmateurRepairer]

Originally Posted by paulsherwin

Aren't the black and white wires the transformer secondary which goes to the speaker?

They are attached at the top of the picture.

The white wire is shrink wrap I have put on a above chassis capacitor wire which is being replaced as the insulation was like weetabix

As was most to fit on this set....

[cathoderay57]

Start with the audio output transformer. There are 5 connections. The 2 wires coming directly out of the bobbin go to the speaker terminals; from your first image you appear to have already connected these using one white and one black wire. There is no extension speaker socket and so no more wires to worry about on the speaker circuit. The other 3 connections (blue, red and yellow wires) go to the tags on the top of the transformer. If you haven't done so already you will need to measure the dc resistances between the outer 2 tags and between each outer tag and the centre, which logically should be the "centre" tap, but not necessarily. The resistance from one tag to the centre tag should be 6.3 Ohms, and from the other tag to the centre tag should be 185 Ohms. If the transformer is not an exact replacement the resistances might be a bit different, and also you might in any case see slightly different resistances on account of using a modern ohmmeter. The important thing is that one resistance should be very low and the other much higher. The centre tap goes to the cathode of the rectifier via a fuse. It should have a 0.01uF (10nF) capacitor rated at least 630v connected between the centre tap and the tag showing high resistance to centre. This tag also needs to be connected to the anode of the audio output valve, UL41, pin 2. The resistor definitely also needs to be refitted. It goes between the low resistance end tag of the transformer and the second half of the 32-32uF smoothing capacitor. Which of these is your mystery black wire who knows? You'll have to trace where the other end goes to and work it out. Hope that helps. P.S. One side of the speaker is connected to the chassis so there could be a wire hanging about from that. Cheers, Jerry

[AmateurRepairer]

Thanks Jerry, much appreciated. I’ll take a look properly in the morning eyes are gone now lol.

[AmateurRepairer]

Black wire goes to UY41 valve holder.... sound output valve?.

[AmateurRepairer]

Wait so if the capacitor needs to go to a wire onto UY41 valve holder, that’s it? But there’s only 3 tabs and they are all connected?

[cathoderay57]

The UY41 is not the sound output valve, it is the rectifier. Which pin number does the black wire go to, counting clockwise underneath the valveholder from the valve's side pip? There should be a single connection between the cathode of the UY41 rectifier pin 7 and a fuse underneath the chassis. It is possible that somebody has removed the fuse from your set. If it is there, the other side of the fuse should go to one tag of the 32+32uF capacitor. This same tag needs to be connected to the centre tap of the audio output transformer. In your last post I do not understand which 3 tabs you are talking about. Where are they? Jerry

[Radio_Dave]

My guess, and it is a guess is that the black wire connects the OPTx secondary/voice coil to the chassis. Please check against the circuit diagram

David

[AmateurRepairer]

Three tabs on the transformer cathoderay.

Here’s some pics. Fuse goes to UY41 via a replaced capacitor.

[Station X]

The circuit diagram is your friend.

A wire should go directly from pin 7 of the UY41 rectifier to the fuse.

From the other side of the fuse a wire should go to C32 32uF, C28 0.01uF and the centre tap of the output transformer primary.

[cathoderay57]

Sometimes it is easy to lose track of where you have got to. It might help to print a copy of the circuit then highlight with a marker pen each wire and component between the rectifier, HT capacitors and the output transformer, as you check it off. Unlike a flatpack cupboard you shouldn't end up with any missing or surplus parts at the end! Jerry

[David G4EBT]

Originally Posted by cathoderay57

Sometimes it is easy to lose track of where you have got to. It might help to print a copy of the circuit then highlight with a marker pen each wire and component between the rectifier, HT capacitors and the output transformer, as you check it off. Unlike a flatpack cupboard you shouldn't end up with any missing or surplus parts at the end! Jerry

Wise advice.

On 18 Feb the OP started a thread about this radio entitled 'Have I missed anything to get this set working?'.

https://www.vintage-radio.net/forum/...d.php?t=176760

In that thread (which is still live and to date has had 19 posts), six experienced forum members proffered helpful advice.

At post #11 of the thread I suggested:

Quote:

With any radio which is to be restored - especially of unknown provenance which has passed through several hands, it's always wise to print off the circuit and parts list, check resistors to see if any are more than say 20% out of tolerance, and to check the wiring of the chassis, and as you go, to mark the circuit with a highlighting pen so that you know you've checked that everything is wired correctly and nothing is missing. It goes without saying that when you're satisfied that everything appears to be as it should, you should first power it up through a lamp limiter so if there's anything untoward, it will become immediately obvious.

End quote.

On 6 March, the OP started this second thread about to the same radio.

A further three experienced forum members to date have given advice. This is indicative that when new, enthusiastic and inexperienced would-be restorers join the forum (a road along which those of us who aren't professionally trained in electronics have travelled), every assistance and encouragement will be offered.

Several questions have been asked by the OP as to where a lose wire belongs, and the rectifier valve has been mistaken for the output valve.

The last thing I'd wish to do is to belittle the efforts or dampen the enthusiasm of a new member, or inhibit him or others from seeking help and advice. However, the answer to most of the questions would be self-evident by reference to the circuit. If - as suggested - a highlighter pen is used to mark off what has been checked - any missing or incorrectly wired connections soon become obvious.

Wires go from A to B and if a wire is attached to say a valve-holder tag, but is swinging free at the other end, its location can soon be identified from the circuit. In these two threads, I've not picked up whether the OP has the circuit data to hand, and if so, whether it's the maker's or Trader Sheet 1375. To say 'the fuse goes to UY41 via a replacement capacitor' (if it does, it shouldn't, as has been said), is an indication that a cross-check with the circuit diagram hasn't been made as that would clearly highlight a wiring error.

The Murphy U198 is a nice little radio which - though 'live chassis' with the need for additional caution. It's a simple commonplace AM radio with a low component count (19 resistors, 28 caps). It performs well and is an ideal 'starter' radio on which to learn basic diagnosis and fault-finding techniques. That said, though it's still 'work in progress' the OP has started another thread on a VHF 2D. AM/FM, long, medium and short-waves, push button wave-change, flywheel tuning and complex dial-stringing arrangements. (32 resistors and 66 caps).

I've no doubt that continued help will be forthcoming in response to any requests for advice and assistance, but unless a methodical approach to fault diagnosis by reference to makers' data, resistance, continuity and voltage checks are made, photos taken and notes made, it will be a long haul.

Many radios that come our way have been 'got at', modified, bodged etc. making diagnosis, rectification and restoration even more of a challenge. A mind-set can soon develop that simply replacing capacitors, resistors, valves etc en bloc will eventual cause a radio to burst into life. Not only are the odds stacked against that, there's the likelihood of introducing faults that weren't there in the first place. We know this is so because many of us have tried that approach in the early stages until the penny dropped.

I do hope the U198 is nearing completion and wish the OP every success with this any other radios.

[AmateurRepairer]

Thanks David for your kind words as well as others.

Love working on this little Murphy and it’ll be staying with me until a trusted person can be the new owner for it at cost.

I’ll not need to realign it as it was working well then went dead and was chucked in shed by previous owner. I think the issue was the top wire had snapped off the mains dropper. Then I resoldered it and the set started, then died again. Hissing sound and melted wax, main cap from fuse holder to first valve holder had gone pop. Made a right old mess.

Then I decided on a full resto.

[Station X]

Originally Posted by AmateurRepairer

main cap from fuse holder to first valve holder had gone pop. Made a right old mess.

Then I decided on a full resto.

There shouldn't be a capacitor in that position. The set could never have worked and never will work with a capacitor in that position.

I suspect that you've fitted a new capacitor in the wrong position. Several members have already advised as to how the fuse holder should be wired to the rectifier.

[Radio Tech]

Connor, Davids advice about the circuit diagram for the set is absolutely spot on, if you follow that and work progressively from one end to other you will get it right. Take you time and good luck with it, you know there is help here when you want it.

Best wishes

Ken

[telstar]

Originally Posted by AmateurRepairer

I have partially recapped and resoldered some of the joints on this radio (I’m no artist at it)

The original sound output had gone open circuit so a local member gave me a spare one he had lying around as well as a dozen magazines, you know who you are, thanks a bunch

I still can’t figure out where this black wire needs to go to. I believe it went inside the original transformer but I can’t do that on this eht as it is a completely different type. Also do I need to refit a resistor and also a capacitor as per the original set was.

This is going to be my bedside table set so it’s got to be right.

Thanks all

Hi. I have a Murphy U198 somewhere, so I will have a look for where the wires go.
Cheers
Mike

[telstar]

Originally Posted by AmateurRepairer

I have partially recapped and resoldered some of the joints on this radio (I’m no artist at it)

The original sound output had gone open circuit so a local member gave me a spare one he had lying around as well as a dozen magazines, you know who you are, thanks a bunch

I still can’t figure out where this black wire needs to go to. I believe it went inside the original transformer but I can’t do that on this eht as it is a completely different type. Also do I need to refit a resistor and also a capacitor as per the original set was.

This is going to be my bedside table set so it’s got to be right.

Thanks all

Hi. Here is a photograph of the o/p transformer on my U198 radio. It looks like the wire comes from the secondary of the transformer then up through the top to the speaker. Check for breakage in the wire.
Cheers
Mike

[AmateurRepairer]

Cheers everyone.