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The "small" restore....Murphy U198M
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April 20, 2017
8:27 pm
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marc
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Hi all,

After many failed attempts in the past I am now the proud owner of an unbroken little Murphy U198M and thanks must go to our very own Cathovisor for his help in finding it. thumb_gif

So initial impressions are very favorable as it's in pretty good condition even the wave change lever is still in one piece ! One valve is missing UCH42 and the dial drive cord is snapped other than that every thing looks untouched.

Marc.

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And now with dial drive cord replaced.....

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More to follow

Marc.

April 20, 2017
9:33 pm
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PYE625
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Hi Marc, well done for obtaining one  thumb_gif

Has it still got the little red plastic pip that rides up in the slot above the volume control to indicate power? 

Andrew.                                                                                   

                         

April 20, 2017
9:41 pm
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Katie_Bush
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Best not come near me with that one... It was one of those that I tried to 'tap gently' at about four years old (big fireside hammer). The radio never did work again after that!

If at first you don't succeed, try a new fuse!

April 20, 2017
9:45 pm
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PYE625
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Here is the plain brown version U198.

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Andrew.                                                                                   

                         

April 20, 2017
9:50 pm
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Katie_Bush
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PYE625 said
Here is the plain brown version U198.

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Thinking about it, ours might have been plain brown - but it was fifty five years ago!

If at first you don't succeed, try a new fuse!

April 20, 2017
10:00 pm
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PYE625
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And they don't 'arf run hot mum.  

Little hot bottles and the dropper slowly sizzle away mob_gif

Andrew.                                                                                   

                         

April 20, 2017
10:54 pm
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nuvistor
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I do like the small MW/LW AC/DC sets, nice and simple and generally gave a good account of themselves for what was inside them.

Frank

April 20, 2017
11:37 pm
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Hi all,

Andrew, I didn't even know they had a pip as a power indicator, you live and learn but sadly no I can't see one. I reckon I might have to hunt down it's brown brethren at some point. hmm_gif

Marion, tut tut, how to make an instant jig saw. eek_gif

Frank, I am developing quite an appetite for these little sets and have a few now including Bush DAC90, 90A, 70, ultra T401, R766, R656, Cossor CR1200U, a couple of Figaro's, Masteradio D121 plus a few battery portables Decca, Dynatron, Hacker, Roberts and a Bush MB60. There are probably more but I can't remember off hand.

Tomorrow I plan to introduce some volts to the Murphy providing I can lay my hands on a UCH42 valve.

Marc. 

April 22, 2017
1:18 am
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marc
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Hi all,

As luck had it I did have a UCH42 valve in stock and even better I actually managed to find it too ! So with that placed in the Murphy it was time to shove some volts in via the Variac.

At around 150v the heaters of each valve could be seen but as the voltage increased the set seemed dead not even a buzz on the speaker. A quick check of the HT showed a healthy 205v so not that, is the speaker O/C ? No, audio TX checked fine too. Was UL41 valve the problem, well it checked fine on the Mullard valve tester so what the heck would make the set appear dead ? hmm_gif

Looking at the wave change switch I thought it looked very 'dry' in a crusty sort of way so gave it a splosh of Servisol and guess what....we have life. grin_gif Now, I wouldn't have thought that a wave change switch would have killed the hum normally apparent at the speaker but hey ho we live and learn.

So the set is working well and giving quite a good account of itself pulling in plenty of stations. So all that's left is to give every thing a good clean and reassemble the wee little beasty but that's a job for tomorrow.

Marc.

April 22, 2017
8:00 am
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PYE625
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Considering the small size of set, I was surprised Murphy didn't use a Mazda 10P13 output valve instead of the UL41. The 10P13 has a lower rating and draws less anode current, therefore keeping the heat down a little. They are pin compatible and I use a 10P13 in my U198. HT rises a small amount due to lower current draw, but the set does run a little cooler.

Andrew.                                                                                   

                         

April 22, 2017
1:59 pm
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Hi all,

Andrew, that's handy to remember about the 10P13 valve should a replacement ever be needed.

As for the set, it's now resembled, polished and on soak test.

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This has been a 'hoot' of a restore.

Marc. 

April 22, 2017
2:21 pm
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nuvistor
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Looks excellent, these type of  sets were on the whole very well made, they were priced that most if not every home could have one, not cheap but within reach.

I was going to suggest it would make a good workshop radio but the cabinet has come up great so its too good for that task.

Frank

April 22, 2017
2:31 pm
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Hi Frank,

Yes it has come up well and too good for the workshop and also too fragile for in there, the cases were made from a very brittle form of Bakelite and took next to nothing to reduce them to a thousand pieces. I will try and find some paint at a later date to touch up the paint chips around the front edges.

This Murphy does put out a very good sound considering the size of the little thing, excellent. thumb_gif

Marc.

April 22, 2017
3:29 pm
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PYE625
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Hi Marc, it looks great and you were very "wise" to restore it. If it had say, been left in a "barn" and got all rusty, it could have stopped the restore in "mid flight". You may have felt a bit of a "twit-a-woo"  trying to get it to work. 

At least the "hunting" is over for a nice example of this set.

grin_gifgrin_gif

Andrew.                                                                                   

                         

April 22, 2017
4:13 pm
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marc
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PYE625 said
Hi Marc, it looks great and you were very "wise" to restore it. If it had say, been left in a "barn" and got all rusty, it could have stopped the restore in "mid flight". You may have felt a bit of a "twit-a-woo"  trying to get it to work. 

At least the "hunting" is over for a nice example of this set.

grin_gifgrin_gif  

Careful Andrew or you'll have me 'owling with laughter ! grin_gif

I reckon the hunt is on for the all brown 'Tawney' version to partner this one now. hmm_gif

Marc.

April 22, 2017
4:47 pm
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sideband
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marc said
Hi all,

Andrew, that's handy to remember about the 10P13 valve should a replacement ever be needed.

Yes they are pin compatible but if you are thinking of replacing a UL41 with a 10P13 you should check the anode current (by measuring the voltage drop across the cathode resistor and do Ohms Law). You may need to increase the cathode resistor to bring the anode current down to within the limits for the 10P13.

April 22, 2017
5:01 pm
turretslug
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ISTR the DAC90A can get away with a 10P13 as a straight swap for a UL41 because of the unusually low HT applied to the output valve screen grid and remaining signal valve anodes but with other sets where the screen grid volts are in the more usual 150-190V range, a bit of care is needed over anode current and biasing as mentioned by SB. There's an Eddystone 670A here with UL41 output, should it ever need replacing I'd opt for a 10P13- after all, it doesn't need to shake the walls!

April 22, 2017
5:32 pm
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sideband said

marc said
Hi all,

Andrew, that's handy to remember about the 10P13 valve should a replacement ever be needed.

Yes they are pin compatible but if you are thinking of replacing a UL41 with a 10P13 you should check the anode current (by measuring the voltage drop across the cathode resistor and do Ohms Law). You may need to increase the cathode resistor to bring the anode current down to within the limits for the 10P13.  

I once replaced the UL41 in an Ekco 'handbag' portable (U122/159/215) with a 10P13 in those days when UL41s were rapidly becoming unobtainium but did indeed have to adjust the cathode resistor to get the bias right. They might be pin-compatible, but they are not equivalent.

To know yet to think that one does not know is best; not to know yet to think that one knows will lead to difficulty. Lao Tzu
April 22, 2017
5:41 pm
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PYE625
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From memory, the conditions in my U198 were ok with a 10P13, but I will have to go and check just to satisfy myself.

Certainly, there is no way a 10P13 can be run at anything like the maximum ratings for the UL41.

Andrew.                                                                                   

                         

April 22, 2017
6:03 pm
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PYE625
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After a quick check in the U198H, I find 7.8v across the 220 ohm cathode resistor which equates to approximately 35mA of cathode current through the 10P13. This means the valve is more or less being run at maximum ratings. It would therefore be of benefit to reduce the screen voltage and or increase the value of the cathode resistor.

As I am unlikely to be using my set for long periods, I may as well re-fit a UL41 to keep it original as I don't want to go altering components needlessly to suit another valve type.

I've just spotted mine has a 10C1 fitted in place of a UCH42.

Marc, a Tawney version would look great next to pale-face  grin_gif

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Andrew.                                                                                   

                         

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