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Old 5th Nov 2017, 10:07 pm   #1
sobell1980
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Default Murphy A188C repair.

Well it's a been a while since I last posted but that doesn't mean I've not had a little wireless project on the go here and there. So, this lovely old console wireless hit the bench a few months ago. I've recapped it and have the electrolytics still to do. Today I attempted to restring the tuning gang but I've failed. Partly due to the fact the tuning gang was part seized so no amount of attempts of replacing the drive cord would have worked. I have struggled like you would not believe to tie the cord to the spring on the drum and keep the right tension at the same time. If anyone has any pointers on a procedure for this? This is my first attempt at this . I measured the correct length and used the correct type cord. I think its a technique im falling down on. Any help as ever greatly appreciated.
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Old 5th Nov 2017, 10:10 pm   #2
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Default Re: Murphy A188C repair.

Quote:
Originally Posted by sobell1980 View Post
I have struggled like you would not believe to tie the cord to the spring on the drum and keep the right tension at the same time. If anyone has any pointers on a procedure for this?
Hello Dave,

I don't know this particular set, but the usual procedure is to tie the correct length of cord to the spring, then install the lot on the radio, i.e. you tie the cord with the spring slack, then tension the spring.

HTH,

Nick.
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Old 5th Nov 2017, 10:19 pm   #3
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Default Re: Murphy A188C repair.

I thought that might be what you suggest. Effectively tieing the spring to the cord first you end up with a loop of cord. In the diagram I have it needs to leave the tuning drum separately in opposite directions.
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Old 5th Nov 2017, 10:31 pm   #4
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Default Re: Murphy A188C repair.

I have one on the go at the moment. A proper sized set, everything is to a large scale, including the cord drives.

I thread them as per the diagrams, holding the cords in place on the pulleys with masking tape, without the springs, until I have everything in place and thread the ends into the tuning drum.
Taking all slack out, I tie ends to the spring as close as possible before hooking the spring on.
If you have problems getting the tension, tie temporary knots to the springs, hook it all up, adjust the tensions, then tie better knots. Rehook the spring.
Sometimes with long cords, I hook it all together with the cord off one pulley, resting on the pulley axle, and then lift the cord onto the pulley last thing.
This gives a bit more tension.
I use knitted Necklace Bead Cord, 1mm, from China and pre-stress a length over night by hanging it with weights, not that it stretches much at all, but it takes the curl out. Its cheap, it takes secure knots well and doesn't slip.
Nylon fishing line is a beggar to tie knots in that stay put.

Always remember that there is/was supposed to be a blind guy who used to re-cord sets!
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Old 5th Nov 2017, 10:49 pm   #5
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Default Re: Murphy A188C repair.

I used to tie to the spring last, spring in place and anchored, do the route with the cord so as to connect to the spring last, feed end of cord through the spring eye, pull cord back on itself until the spring is tensioned correctly, make a mark on the cord with a pen or whatever where the cord is in contact with the spring eye, remove spring, tie cord to spring eye as per the mark that was made (easy to do now as it's not under tension) refit/anchor spring with cord now attached (now under tension)

Lawrence.
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Old 5th Nov 2017, 10:56 pm   #6
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Default Re: Murphy A188C repair.

Picture shows how the cord should be routed.
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Old 5th Nov 2017, 11:09 pm   #7
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Default Re: Murphy A188C repair.

The other idea I use is not to tie knots at all. If space is tight try this.

Get to the point of connecting the ends to the spring with the cord correctly located on the pulleys and drum.
Thread the ends through small ferrules that are used for bead spacing, then through the spring and back on itself through the ferrule. Tighten everything up then crimp the ferrule, locking the cord. Its better than knots as its easier to get the tension right first time and with my fat fingers easier than macrame.
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Old 5th Nov 2017, 11:11 pm   #8
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Default Re: Murphy A188C repair.

That type in the picture is quite easy to do without the spring being under tension either for cord routing or tying off.

All that's needed is a small loop of wire....

Lawrence.
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Old 6th Nov 2017, 8:09 pm   #9
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Default Re: Murphy A188C repair.

Good evening folks.
I started today by ordering more 1mm tuning cord. The correct stuff so shouldn't stretch. I'm very much liking Sams idea of using ferrules. Would be much easier to to do this than tie two knots extremely close together onto the end of a tiny spring. Is there a certain type of ferrule you recommend. I've looked online and found ones for 0.8mm steel rope that could be cut shorter to fit between the inner drum edge and spring. Please see photo.
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Old 7th Nov 2017, 3:41 pm   #10
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Default Re: Murphy A188C repair.

I'm going to try these ferrules as above and will let you know how I get on.
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Old 7th Nov 2017, 4:27 pm   #11
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Default Re: Murphy A188C repair.

Recon they will do fine.
I use brass bead making ones from the ROC, they are smaller diameter and thinner, about 2mm long. I have to ovalise them to get 2 strands in.
I bought them originally for pigtailing components in, they crimp easily and solder beautifully. Can't remember exactly which.
Something like:

https://www.ebay.co.uk/itm/500-x-Bra...oAAOSwl8NVa1zY

Other suppliers and makers available, this is not a recommendation etc.

Sam.
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Old 26th Nov 2017, 8:10 pm   #12
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Default Re: Murphy A188C repair.

Good evening all. Sorry for the huge delay in updating the thread. I have however been deeply involved with the set, restringing the tuning drive (which took several attempts). I ended up using the ferrules as described earlier in the thread. I do not have the dexterity to tie small knots and get the tension correct. I recapped the set and changed all the hunts which were cracked and crumbling. I also replaced the electrolytics, some were bulged and the tops had cracked. So after all this I went for the switch on. I was met with silence. I noticed that all but two of the valve heaters were working. The two which were not working were the UU6 rectifier valve, heater tests open circuit and the same with one of the paired output valves a 6P25. Swopping the two 6P25's over confirmed this and the fault moved to where the other 6P25 was working and vice versa. A continuity test on my meter doubley confirmed the heaters are open circuit. Next question is, does anyone have these valves that I could purchase? I've now checked the working voltages to the dead valve bases and all appears ok. Or, do I need to make a separate request in the wanted section? Anyway that's where we are up to on this set.
Dave .

Last edited by sobell1980; 26th Nov 2017 at 8:16 pm.
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Old 26th Nov 2017, 9:03 pm   #13
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Question Re: Murphy A188C repair.

Well done for you persistence with the dial cord, Dave ; I feel happy for you that you have it sorted now.

Re the valves you’re looking for, yes, it’s probably worth posting a separate request in ‘parts and service information wanted’ - more people will likely notice there!

I hope you find what you need and can complete the restoration soon!
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Old 27th Nov 2017, 12:41 am   #14
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Default Re: Murphy A188C repair.

Before you toss those valves away, try resoldering the ends of the pins. I have had several 6P25 that have appeared to be O/C heaters but were recovered. Similarly with the rectifier, they draw a fair 1.1amps heater current and are known to lose contact with the wire inside the cap.
KT61 is nearly a 6P25. Pin compatible.
You could always hide 2 silicon diodes and a 120 ohm resistor under the rectifier base if the UU6 is definitely duff.
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Old 1st Dec 2017, 7:19 pm   #15
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Default Re: Murphy A188C repair.

Thanks Sam. When you say solder the pins on the uu6, do you simply mean re-tin them and hope it makes contact? Will I need to remove the base? Luckily Graham has an 6P25 on its way to me but I still have no luck with a uu6. I would like to put it back to original with a working UU6. They command eye watering prices. I could try the diodes for now just to get it up and running and on test. It's a Christmas present for my friends 'Great Hall' as I call it. It will be given a home and be well used and loved there.
Dave.
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Old 1st Dec 2017, 8:44 pm   #16
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Default Re: Murphy A188C repair.

The valve pin is hollow, and the leadout wire from the valve bulb is threaded through and soldered at the bottom of the pin. You can see this if you look from below. This joint can become dry resulting in a dead heater.
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Old 1st Dec 2017, 8:52 pm   #17
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Default Re: Murphy A188C repair.

Will give this a go tomorrow. If I check the heater with my meter. It flicks from open circuit to erratic various high resistance reading. This may indicate as you say a dry joint.
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Old 1st Dec 2017, 10:37 pm   #18
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Default Re: Murphy A188C repair.

Poor joints in valve bases are not new, I wouldn’t recommend it on rare valves but this tool was sold in the USA to save soldering the pin.
On sale in 1959.
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Old 2nd Dec 2017, 1:50 am   #19
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Default Re: Murphy A188C repair.

I desolder the pins with a sucker, you should be able to see the end of the wire, then re-flux with a pen and resolder. You usually only need to do the heater pins, 2 & 7.
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Old 2nd Dec 2017, 5:19 am   #20
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Default Re: Murphy A188C repair.

There is a UU6 for sale on ebay but not cheap. My A188 also had a duff one but it was dead short one anode to cathode. I may try blasting it to get it to go open circuit as the heater is OK.
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