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Old 14th Jul 2019, 2:46 pm   #1
Beardyman's Avatar
Join Date: Jan 2018
Location: Portsmouth, Hampshire, UK.
Posts: 216
Default Murphy U198H back to work

Good day to one & all.
Having just had a week off work with no particular plans in mind I had some time to look at a Murphy U198H. Quite an unassuming little set at first glance. Needless to say it had time related damage. A small piece of the cabinet was gone, the back card near the dropper was very toasty with some pieces missing. The dropper looked as if it had had a hard life but initial resistance checks showed all sections to be intact. The insulation of the wiring had suffered long term heat exposure crumbling away at the lightest touch.
I was pleased to see the wave change lever had more or less survived, only a small piece at the end was missing. Another feature of this set is that is doesn't have a pilot light, just a red plastic tag that pops up from behind the volume control, unfortunately one pin is missing so it no longer pops, I may well add a mains neon somewhere, we shall see if a repair can be done.
I think this set was in a kitchen for quite a while as there was condensed fat over everything, as soon as the heat of a soldering iron touched it the smell was very reminiscent of our local chippy! So much so that my better half poked her head into the workshop while sniffing the air & asked, "Have you got chips in there?"
After having shown her that it was, in fact, the radio her response was "Ewww, sticky". That combined with a liberal amount of dust made for a delightfully nasty mess, a few hours with various solvents & brushes/rags/cotton buds revealed a chassis in good conditon. The grease appeared to have some preservative qualities!
A quick check of the valve filaments was disappointing, the UL41 was open, luckily I had a new one left over from another project, a CV1977. All the rest were ok although the UCH42 had a white halo at the top but it was barely visible without magnification. As these valves are the rimlock type I inspected them all at the base for hairline fractures. Lo & behold it had such a fracture, not having one to hand I ordered one, odd that it was £2 more expensive direct from the supplier than through their outlet on a well known auction site.
There are a number of Hunts moulded capacitors in these sets & all were split and/or crumbling. C28 (trader sheet) was replaced with a 0.1uF X2 type, a 0.05uF was originally fitted but with the amount of mains hash these days it could do no harm. With the handful of wax caps there was a relatively small amount to be changed. All the previously mentioned capacitors were checked before replacement, all were leaking badly or were way off their stated value. I have learned that the small value silver mica caps hardly ever go west so these were left well alone. The HT capacitor (two in one can each of 32uF) looked in good shape, no leaks or bulges. It reformed very well indeed, less than 50uA leakage which for a part that old I thought remarkable & the value was within 1uF of nominal. The tuning cord had snapped a long time ago but the pointer was still there, with a relatively simple run it was re-strung in under an hour. The thing I struggle with is making off the knot to the spring, I have quite large hands which really doesn't help! Some of the resistors were off by 50% or more, I've noticed this seems to be prevalent with values over about 100K. There is a 10M in the grid circuit for the 10LD3, this was reading all over the place, it started at 8.7M & after about 2-3 minutes it was up over 18M! A tad unstable methinks? There were no signs the set had been previously "got at" or that the twiddler had been at large. The HT fuse was checked & found to be intact, I added a mains fuse as well in a holder mounted on the chassis well out of harms way. O/P transformer readings matched the trader sheet, all good. Came the fateful moment to apply power. I'm very fortunate to have an adjustable DC PSU (0-630VDC & 0-2.7A) at my disposal & it is ideal for AC/DC sets. Set for 220VDC & current limited to 150mA the filaments came up, current dropped back to about 100mA & slowly came forth the dreaded sound of "motorboating"! Back to the drawing board! A close look showed a "hidden" Hunts! It was C5, part of the screen grid circuitry for the UCH42. Instead of it being 0.04uF it was closer to about 100pF hence the "motorboating". Once replaced I was quite taken aback by this set. It sounds much bigger! A really nice tone with plenty of volume. Good selectivity despite it having an underslung ferrite rod aerial. I was concerned with how hot the dropper would run given the state of the back card but it isn't excessive, the top of the cabinet gets only hand warm with the heat deflector in place. I repaired the back card with some baking mesh, it can stand oven temperatures so this should be no problem, it's available in most pound shops. The case has cleaned up quite well with liberal applications of polishing paste No:5. All in all a thoroughly enjoyable project to while away the afternoons when its been too hot to do anything else & a surprisingly sensitive, good sounding set to boot.
PS Only 5 photos attached, more to come.
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The difference between stupidity and genius is that genius has its limits. (Einstein)
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Old 14th Jul 2019, 2:48 pm   #2
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Default Re: Murphy U198H back to work

More photos as mentioned above:
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The difference between stupidity and genius is that genius has its limits. (Einstein)
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Old 14th Jul 2019, 3:00 pm   #3
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Location: Oxford, UK
Posts: 20,496
Default Re: Murphy U198H back to work

These are good no nonsense 'second sets' and perform well. I have the wooden cased variant, the U598.
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Old 14th Jul 2019, 6:31 pm   #4
bobbyball's Avatar
Join Date: Jul 2011
Location: Stockport, Greater Manchester
Posts: 1,138
Default Re: Murphy U198H back to work

Good to see another set saved, nice job. I had a similar Ferranti set some years ago and added a neon lamp behind the dial to show it was "on". It was our kitchen radio for years.

Murphy sets were always slightly "different"...
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Old 14th Jul 2019, 10:28 pm   #5
stitch1's Avatar
Join Date: Jan 2008
Location: Durham, County Durham, UK.
Posts: 620
Default Re: Murphy U198H back to work

Good job and a nice write up I repaired a back in a similar way, I think itís in a thread here somewhere.
I also have the wooden version, it's awaiting attention, the rear knob is missing and all the glue in the cabinet has dried out so it has collapsed but otherwise in good condition.

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