Murphy V136C (1948)

[Heatercathodeshort]

Looks good so far Mark. The display appears to be well out of focus and I would suggest a look around the focus circuit to see why it is either passing too much or too little current.

It appears to be a frame collapse under that disguise, not surprising looking at that odd circuit.

The sound should be an easy one with the aid of your generator. Audio amp first at audio then work back at 41.5mc/s from the sound RF stage. Remember it is not a superhet as were all other Murphy models.

I hope you don't have to reinstate all the bodges to get it working again....

Good luck with it. John.
[PS I wonder if someone tried to retune the RF strip for another channel? I wonder where it came from.]

[mark pirate]

Hi John,

It appears to be a frame collapse under that disguise, not surprising looking at that odd circuit.

I tend to agree, sorting out the focus problem is next on the list. The audio problem has happened since all the bodges were removed, but it is all wired as per the manual. I have checked my work again, but it is fine.

I will have another read through the service info, I am still trying to get my head round the odd circuitry

I still have that V150 looking at me from a dark corner....

Mark

[mark pirate]

After another few hours in the workshop, I am getting there
John was correct in thinking that there was frame collapse hiding under the image on the screen, the cause was a missing connection to ground on the height control. With this reinstated a full screen raster appeared!

The previously high voltages are now around what they should be, the audio stage is now working again as well. The focus is also working and the frame hold is sort of working, but seems to be interdependent on the height and linearity controls.

Another problem is the racket made by the frame output, which is part of the scan coils?

I dug out the Aurora, and there was feint signs of an image on channel 1.
A bit of fiddling shows there is video getting through as there is part of test card C trying to get through

There is no sound getting through, so I suppose I will have to tackle the alignment next. Any tips would be most welcome.
There is also a missing ferrite core to find, hopefully the junk box may contain one.

I just hope the IFT's have not been damaged by the bodger....

Mark

[Freya]

Amazing, your doing really well on this considering the mess. Does the sensitivity control work well, have you tried bypassing the preamp and supplying the signal directly to the sensitivity control ?
At this stage, maybe leave the alignment, have you been through the aurora channels.

[mark pirate]

Hi Stephen,
I must admit to being well chuffed with it so far, looking back to the state it was in when I got it, I did think It was beyond hope!

Although a total rewire was called for, it was pretty straightforward job.
The fact that I took my time over it resulted in no wiring errors other than missing the wire to chassis from the height control

In answer to your questions. The sensitivity control works fine, it had been disconnected by the bodger.
I have tried bypassing the preamp, the signal is much weaker without it, so it is doing it's job.
I have been through all the channels on the Aurora, the only sign of life is on channel 1.

I don't relish the thought of realignment, but as it is probably miles off I don't have much choice.
It is obvious that the bodger has removed the cores and put some manky old string down the centres before screwing them back in

It may have been the reason for all the bodged modifications, in a vain attempt to get it to work!

I will have a good read of the manual's alignment instructions and follow it to the letter.

Mark

[Freya]

With the considerable output of the Aurora it should be belting through even with out the preamp, which leads to alignment once the missing core is located.

[brianc]

Just a point, Marc, "Manky old string" was often used in adjustable coils to prevent the cores from moving - temperature changes, audio vibration etc. Another method was very thin rubber strip, rather like miniature catty elastic!
I must say that I prefer string to gunge as it doesn't set hard or clog up.

[Stylo N M]

Hi
that really is amazing mark, i wish i could do what you do well done.

paul.

[MonochromeMarc]

This is all getting really good Mark
Excellent job so far !

Marc.

[Heatercathodeshort]

Don't be apprehensive if it needs alignment Mark. A signal generator helps working back from the detectors but it is a simple TRF and with care, 100% results can be achieved without one.

It's simply a matter of peaking the vision RF transformers and then 'staggering' them to obtain a nice bandwidth. Peak up the sound coils to maximum on the Aurora signal. That should give you a decent picture.

A combination of manual and generator should do the trick. Most bench type signal generators are not too well calibrated or the scale is too cramped to obtain the accurate frequency required in the manual.
I was puzzled a few years back with very low gain from an Ekco TS88 series chassis.
After a lot of headscratching I discovered a number of RF cores that had simply screwed themselves down over the years to the extent that a couple of them were actually loose in the can. John.

[ct92404]

I haven't been on the forum in several days, but I just had to say I admire the superhuman patience you seem to have, Mark! I'm familiar with basic electronic parts - transformers, capacitors, resistors, etc, but I don't know very much about how tuning circuits work in televisions and radios. So I admit I don't understand some of the terminology you guys are using. But still, I can follow along well enough, and you're doing awesome work! It's exciting to see whenever you make a new post and give an update on your progress. Considering the shape that antique television was in, it's amazing that you got the tube even lighting up again! Please keep up the good work. You should have a party to celebrate when you finally get a picture on the tube!

- Chris

[mark pirate]

I will hunt through the junk box today to see if I have a suitable core to replace the missing item. I have noticed from the circuit diagram that there are some components hiding in the IFT's, namely R60, R70 and C5.

I hope these components are ok, as I don't really want to start removing the IFT's at this stage.

I will attempt a realignment today, I have included a couple of pages from the manual showing details of the receiver for those playing along at home

Just a point, Mark, "Manky old string" was often used in adjustable coils to prevent the cores from moving

The 'string' in this set is definitely not original, some of the IFT's have some type of plastic tape and was obviously what the bodger had lying around at the time!

Mark

[beery]

Hi Mark,

Don't be too worried by the components hidden in IFT cans.
The capacitors across the coils will be either mica or ceramic types so very reliable.
The resistors across coils are there for damping, to give the IF a broad response. Even if they were to go up in value by 50% you would probably not notice any difference in performance.
Best to always leave covers on IFTs until a genuine fault is suspected.

I remember the first time I had to realign a TV it was indeed daunting. The alignment is generally something you never have to touch. In this case, not only is it necessary, but also you can't make it any worse. I think you will be pleasently suprised by the results.

Alignment instructions often call for a vision output meter or audio watt meter. You don't need those, just a scope.
Do the alignment using an RF sig gen which has a modulated output (such as a 600Hz sine wave). It will be more accurate if you use a frequency counter to check the output of the sig gen, but remember to switch the modulation off when you check it as it will throw off the reading.

When not using the aerial socket, connect the sig gen with a couple of Ycaps of about 470pF.

I also assume you are using an isolation transformer with the V136C as the chassis is always at half mains

Some alignment instructions call for a damping resistor to be put across the other coil in the can of the one you are adjusting. Take a 1/4 resistor of the value specified (actually 470 ohms works ok generally). Heat shrink the resistor leaving just the last 3mm of each lead exposed and solder on an insulated croc clip at each end. The resistor should be such that you can clip it on to an HT rail without getting a belt...

Hope this helps...

Cheers
Andy

[beery]

Hi all,

I should point out for safety that here:-
"Heat shrink the resistor leaving just the last 3mm of each lead exposed"
I meant to say heatshrink the whole resistor including the body, because the insulation of the resistor itself cannot be relied upon.

Cheers
Andy

[Heatercathodeshort]

Remember the interstage transformers are stagger tuned to the actual vision and sound frequencies. They are not IF transformers. It is much easier to align a TRF such as this Murphy V134/136 compared to a superhet. J,

[mark pirate]

I had a rummage through my junk boxes to no avail, but managed to rob some aluminium cores from a scrap Pye LV20 chassis.
I found fitting this to L7, which was missing it's core, peaked up nicely with the signal generator connected via the aerial socket.

I ended up having to remove L8/L9 as it had obviously been got at, the core was bent away from the access hole on the top of the can.
On removal I found that it had certainly been off before
The tabs on the can were bent back, and the brown spacer that locates the top of the coil former to the top of the can was missing. I managed to reassemble the unit so the former was now in line with the access hole.

I did have a bit of a twiddle, and managed to increase the video gain somewhat.
There are two types of cores fitted originally, some are brass while others are ferrite. Luckily the parts list (below) shows which type are fitted to each coil.

I think the bodger has fitted the brass type where it should be ferrite, hence the missing core from L7.

Some of the ferrite cores are physically damaged where the adjustment slot should be, so replacements are needed before any more progress can be made.

I had a feeling that this would turn out to be a pain to sort out, I was not wrong!

Mark

[Freya]

Are the ferrite cores not double ended ? I have added slots in blank ended cores before (using dremel cutting disc), turning them end for end.

[brianc]

I might well have some spare iron dust/Ferrite cores of the right type, Mark. Measure the diameter and length and I'll have a look. I also have some formers like that too.

[Heatercathodeshort]

I think someone has definitely attempted to change the channel possibly from 1 to 4. The brass cores in place of the iron dust seem to confirm this.
Looks good, it should not be too difficult to reinstate the broken formers and coils.
It may have originated from somewhere in the region of Northamptonshire where the channel 4 signal was stronger in most cases. J.

[mark pirate]

Hi Brian,
I will measure the cores and let you know, they are the single ended type.

I think someone has definitely attempted to change the channel possibly from 1 to 4. The brass cores in place of the iron dust seem to confirm this.

It certainly is a possibility, but I think more likely that the brass core was subbed due to the bodger breaking one of the ferrite cores. When I got the set there was a capacitor inserted in L7 in place of the core
Just for fun I reinserted it and the sound came up!

The Murphy parts list shows three types of cores are used, two are different types of brass cores, sadly no length is quoted....

Mark