You may have seen this set on ebay. I have long fancied a nice small screen example of the A640 chassis and this would appear to be such a set, if the vendor's photo's are anything to go by. See below and I think it is fair to say that this set may not have had mega-hours worth of use in it's lifetime. It is not a silly distance away and I go to collect it this Saturday. I was fortunate enough that the vendor kindly accepted an offer of £185, it was up for £250. Yes, I know.... but tell me where such a good example of this set can be easily obtained today? It is a very long time since these were ten-a-penny......
@pye625
A long time since I had the back off one of those, they had a few stock faults but a decent set from what I remember.
Of course the LOPTX, then silicon HT and heater rectifiers, mains dropper, occasional valves, the last vision IF amp, a BF173 if I remember correctly, and those black user controls.
I do believe I did spot that one. Well done on getting it. I have to confess, I haven't bought in any 'new' sets for quite a while now, and none during the Covid crisis - Except for the 42" Samsung LCD which was going for a song, and only 10 miles away, March of last year.
Of course the LOPTX
Oh yes indeed Frank.... The lovely tar covered overwind (if that type was still being used at the time of this set). Well, I am not expecting any miracles here but we shall see.
In the set's favour, it has not been powered up and seems to have been stored in good dry conditions.
I'm almost certain that set will have the Plessy LOPT with the white plastic overwind, doesn't mean a lot though as we all know with these. There were also two single standard versions of the V2015, suffixes SS using the infamous A774 and S using the single standard version of the A640 known as Z146. The latter had one instead of two smoothing cans relocated to behind the chassis.
Of course the LOPTX
Oh yes indeed Frank.... The lovely tar covered overwind (if that type was still being used at the time of this set). Well, I am not expecting any miracles here but we shall see.
I had what I think was the Bush version about 40 years ago (EEEEK!) - the TV183D. 19 or 20" tube? Anyway, it had the tar-covered tranny.
Wot wuz ded. Along with the CRT and the 2.2/68 ohm dropper.
Crikey Andrew you certainly pushed the boat out for that one, but it does look very smart indeed. Usually the 'OFF-VOL' marking above the user control is worn right away on surviving examples but it looks pristine on yours. Hopefully a low hour crt too. Fingers crossed for the LOPT- I reckon it may work after the usual precautionary drying out process, but will it keep on working?
It should be an excellent performer, so well worth the effort.
Looking forward to this!
Steve 😀
Hi Steve, yes I did and perhaps should have waited to see if the price came down to something more sensible. But on the other hand, what's done is done and if I waited, I probably would have missed it completely. I think the worst thing is discovering after I bought it that this set was sold at an auction last December for only £8. But again on the other hand, some time back I did only pay 20 odd quid for a Baird M702 and later sold it for considerably more after I had the pleasure of restoring it to working order. But it is a much rarer set than the Murphy.
Win some, loose some I guess. So can't really grumble I suppose.
The golden rule is to remember your ABC with any sale....
Assume nothing, Believe nothing, Check everything !
I had a very similar model, the 1969 V1914, using the A640 chassis, when I got rid of my B&W collection I gave it to John. It, too, was in remarkable condition.
https://www.radios-tv.co.uk/1969-murphy-v1914/#main
p.s.
Service data for yours is now in the library.
Thanks Chris, I will download that data and make any circuit references to it if needed as we go along.
I had a very similar model, the 1969 V1914, using the A640 chassis, when I got rid of my B&W collection I gave it to John. It, too, was in remarkable condition.
https://www.radios-tv.co.uk/1969-murphy-v1914/#main
p.s.
Service data for yours is now in the library.
For the last year it’s been residing in my lockup. It will be making its way to the workshop in the next couple of weeks.
The last time I tried it there were no problems at all although the dropper has previously had attention with an untidy repair before it even came into Chris’s ownership. The 680 ohm in the cathode of the audio output looked a little discoloured, we always checked the value and replaced if needed on any A640 that came in.
Looking forward to seeing how you get on with yours.
Hello, well the set is now on the bench and initial investigations are as follows...
The CRT looks to be of reasonable emission.
The PY88 has a cracked base and is down to air. The reason for this could be that it overheated due to possible shorted turns in the EHT overwind placing an excessive load on the line stage. This possibility is further evidenced by the fact that 3R57 is open circuit on the 250 ohm section, the left section shown below. This should supply HT1 which goes to the PY88 anode, among other things. I don't have a replacement resistor.
The LOPT when tested with my "skantest" oscillator kills oscillation when the overwind is connected. A good overwind usually increases the oscillation with the neon glowing brighter and with a slight buzz from the LOPT itself. I don't have a LOPT to replace it with, but that may not be of any great surprise!
Some futher investigation is needed before I can reach a firm conclusion however. For instance, the DC resistance of my overwind is approx. 250 ohms and it looks like it should be around 220 ohms according to the data. But of course, all it takes is one shorted turn to stop it working.
Removing the overwind from the LOPT (very easy in this case) and some temporary rather horrendous lash up's to substitute the open circuit 3R57, not to mention the careful installation of a Thorn EHT tray, it may be possible to establish if we have a basic functional set.
Careful study of the first photo below will reveal what was done and I must stress that this was only for a brief test before it was all dismantled. Far too dangerous to leave for any further testing !
So, after reforming the main HT capacitors and a new PY88, plus snipping out the mains RF bypass capacitor, we now can see the possibilities unfold.....
It looks like that set is definitely "working outside the box"..!
All I need now is a nice new LOPT overwind and a mains dropper. Simple eh?
What are the dropper section values?
Hi Chris, the dropper is physically one item and the value's are 250 plus 14 ohms, and an electrically seperate 156 ohm.
(It is the 250 ohm section that is open, seen here below on the left).
Thought so, I've got one but guess what? The 250R section is open, must be a common fault. I'll have a further look as I've a huge box full of all manner of droppers.
Haha ! Blimey, yes because that section sufferes if the boost cap goes short, or worse things happen in the line stage.... and of course, we all know what. Mr sweet innocent LOPT's that they are !
Thanks Chris 🙂