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Old 28th Oct 2019, 4:38 pm   #1
Niechcial,Steve
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Default Murphy V659/759 restoration

I have just started work on this set I picked up on Ebay. It is in pretty poor condition showing signs of possible damp damage with the cabinet coming apart and the aquadag flaking off. Fortunately no signs of worse corrosion and the tube emission is at the bottom end of green on the tester.
I was attracted to this set because it is one of the earliest dual standard sets and this one has the optional uhf adapter kit fitted. This consists of a complete duplicate receiver up to and including the sound and vision detectors. When you change standards the system switch switches out one set of signal and IF valve heaters and switches in the others so there is always a pause while the valves you are switching to warm up. This set has its system switch locked on 625.I am not sure whether it is a 659 or 759 as the label is missing.
So first checks- after visual inspection -no continuity across mains lead turns out to be o/c mains switch. Doing a temporary bridge brings heaters but nothing more- HT fuse O/C. Measuring across ht line gives a resistance of 245R! Pulling out the plug which links the UHF converter to the main chassis causes the resistance to return to normal. So fault is obviously on UHF module. Taking the base of that module reveals that the HT feed resistor to the UHF tuner is cooked. The resistance of the HT feed point on the tuner to chassis is about 25R! Now I have never come across an inter electrode short on a UHF valve before but there's always a first time and it's an easy thing to check- or would be if the tuner wasn't wedged into such a small place that it's virtually impossible to pull a valve out. I do eventually pull out the PC88 and the resistance to earth leaps up to the Ks. Put a new PC88 in and 25R reappears, Interesting! far too much effort to get the tuner out at the moment so settle for snipping the HT to it for a trial run.
New HT fuse but still no raster. Turns out to be dodgy connection on one pin of the PY. So now have full width but low height non-linear raster which blooms out into a black hole when the brightness is advanced. I don't have a new U26 but I suspect the problem is low heater volts on the U26.The width was full at low brightness so hopefully not a line problem. Meanwhile the resistor feeding the HT rectifier at the front of the chassis is smoking profusely so time to take break.
I think my strategy will be to get this set running on 405 and take it from there. I've seen on the forum advice that it's a good idea to drain, flush and refill the transformer. can anyone advise me how to do that please- especially what to flush with?

Thanks,


Steve
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Old 28th Oct 2019, 5:15 pm   #2
dazzlevision
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Default Re: Murphy V659/759 restoration

The Murphy Astra recently on Ebay, with the UHF plinth fitted was a V659X model. The easy way to tell a Mark 2 Astra is that it has seven grey, circular channel selector pushbuttons. The Astra V6xx models (excluding the ultrasonic remote control ones) had cream coloured, “scalloped” pushbuttons.

See this thread for a photo of an Astra Mark 1 set: https://www.vintage-radio.net/forum/...d.php?t=146631

and a Mark 2 here: https://vintage-radio.net/forum/show...t=39287&page=2

Last edited by dazzlevision; 28th Oct 2019 at 5:20 pm.
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Old 28th Oct 2019, 5:48 pm   #3
Niechcial,Steve
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Default Re: Murphy V659/759 restoration

Many thanks Dave. I hope I wasn't bidding against you for it!

Stephen
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Old 28th Oct 2019, 5:50 pm   #4
dazzlevision
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Default Re: Murphy V659/759 restoration

No, I wasn’t after it.
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Old 28th Oct 2019, 6:30 pm   #5
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Default Re: Murphy V659/759 restoration

I did eye it up but was put off by the cabinet and the fact I couldn't afford it so never bothered bidding.

Cheers
Neil.
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Old 28th Oct 2019, 7:41 pm   #6
akuram1
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Default Re: Murphy V659/759 restoration

They were really beautiful sets.
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Old 29th Oct 2019, 9:46 am   #7
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Default Re: Murphy V659/759 restoration

Quote:
Originally Posted by dazzlevision View Post

See this thread for a photo of an Astra Mark 1 set: https://www.vintage-radio.net/forum/...d.php?t=146631
It doesn't seem 18 months since I got that set.. it is sitting on my workshop floor still awaiting attention.
I am following your thread with interest!

Rich
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Old 30th Oct 2019, 4:51 pm   #8
Niechcial,Steve
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Default Re: Murphy V659/759 restoration

I started out today on Plan A which is to get this set working on 405 first. I thought this made sense because:
a) The UHF tuner has an internal HT S/C
b) By running on 405 I could avoid having the UHF module in the way on the work bench.
Now it is clear that on the V759, switching to 405 and unplugging the UHF module leaves you with the original working 405 receiver. But as Dazzlevision kindly pointed out, this is a V659XA- very similar to the 759 but with some significant differences as I was about to find.
Unplugging the UHF module broke the heater chain continuity, even when switched to 405,so I then set out to trace this through. I have the circuits for both the 659 and 759 and after about half an hour I had the belated sense to see if the heater chains are different- they are- some valves are in a different order. On checking further, this heater chain corresponded to neither. It may be that that the modification from V659 to V659X involved further changes to the heaters. Unfortunately, those instructions I don't have as they would have come with the UHF module kit.
I now did what I should have done in the first place, which was to plug in the UHF module and operate the systems switch to see if it made any difference to the heater chain. It didn't- heater continuity was restored but it didn't vary at all when operating the switch. There is no obvious bodging around the system switch, but somewhere this set has been hardwired 625 only.
I don't know what other changes may have been made so for now I will resort to Plan B- fix the UHF tuner and try and get it working on 625 first.
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Old 30th Oct 2019, 5:30 pm   #9
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Default Re: Murphy V659/759 restoration

Murphy Radio issued instructions on how to maintain the heater chain on both systems. The data is in the Murphy Service news. It will take a day or two to find it if you need it.
Very unusual to have an HT short in the tuner. I suppose the PC86 and PC88 are in the correct sockets? The feed through capacitor on the HT tag might well have broken down to chassis. The Pye 11U tuner used to do this on one of the heater feed troughs putting out the last few valves and CRT heaters. Good luck with it. John.
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Old 30th Oct 2019, 6:08 pm   #10
Niechcial,Steve
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Default Re: Murphy V659/759 restoration

Thanks John. If you could find that Murphy News I would be grateful, but absolutely no rush.

Yes I thought probably lead through cap too. We will see. I am pretty sure valves are correct way round but will check again. Steve
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Old 31st Oct 2019, 10:41 pm   #11
Niechcial,Steve
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Default Re: Murphy V659/759 restoration

Some progress tonight. Once I got the UHF plinth off the cabinet the UHF tuner cover was easily removable without having to remove the tuner from the plinth. You were on the right lines thanks John- somebody had fitted two PC86s instead of a PC86 and a PC88. That was causing the HT short. Unfortunately, as well as burning up the external 1.8K HT feed resistor the short also burnt up a little internal 0.25W 1.8K resistor which forms part of the oscillator anode load. I replaced this as carefully as I could, but it involved unsoldering another coil and moving it to one side. I just hope it still oscillates. Some of these valve tuners were reluctant to oscillate at the best of time and were choosy on valves. A friend of mine who used to work for RR at that time told me he always carried a rare version of the PC86 with gold plated pins for the really stubborn sets.
Switching the set on, it proved difficult to get the line output running. I traced the fault to a bad connection on the anode pin of the PY. No amount of cleaning helped and I could see sparks actually from inside the pin mounting. The only way I could get it to run was by unplugging it,dangling it from its cathode lead and connecting the valve pins with jump leads. Unfortunately the PY only has one pin connected to the anode internally so I am going to have to change the valve base.

The HT is low at about 140 volts with the rectifier surge resistor smoking.HT current is 350mA. HT resistance to chassis cold is fine. That will be the next thing to tackle.
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Old 31st Oct 2019, 10:47 pm   #12
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Default Re: Murphy V659/759 restoration

A couple of pics
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Old 3rd Nov 2019, 7:25 am   #13
Niechcial,Steve
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Default Re: Murphy V659/759 restoration

I replaced the PY valve holder with a nice new ceramic one pot rivetted into place and got rid of the dangling PY (pic attached), and when I plugged in a UHF signal and switched on up came a picture (pic attached). The frame and line hold controls were both at the extremes of travel, the contrast was reasonable, but the contrast control inoperative, there was very poor frame linearity and low width with an HT voltage of around 180V instead of 215V. I haven't got a speaker plugged in at present to check the sound.
What does not come over from the thumbnail is that the picture definition is excellent, with no ringing or over shoot etc. It is a relief that the UHF tuner does oscillate over the whole band. The tuner gain is also good as judged by the fact that I get some signal pick-up with the aerial plug removed, so I seem to have avoided disturbing the tracking too much when I replaced that internal resistor.
I spent the rest of the session replacing Cs and some Rs around the Frame stage, including the cathode resistor (which had gone high) and the cathode electrolytic. None of that made much difference to the frame lin. so I must look further. The frame hold is in the centre of travel now with a good lock.
Has anybody got any ideas on the low HT? Total consumption is about 340mA, dropping to 220mA with the line stage disconnected. The metal rectifier has of course been replaced with a silicon diode and additional series resistor. I would have expected around 310mA for the whole set. Does anyone think 120mA for the line stage is excessive?
Thanks, Stephen
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Old 3rd Nov 2019, 1:08 pm   #14
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Default Re: Murphy V659/759 restoration

Did you reform the main reservoir and smoothing can electrolytics (C1 and C2) before applying full mains to the TV?

It might be that you have low capacitance there, reducing the available HT and increasing ripple....?

Have you checked that those two Radiospares power resistors on each mains dropper resistor are the correct values?

If you have no speaker connected, or dummy load, make sure the volume control is set to minimum, otherwise it could damage the audio output transformer.

Before proceeding further, I’d certainly replace the line drive coupling capacitor to the 30P19 (C314), the boost HT reservoir capacitor (C43), the CRT’s A1 decoupler (C317) and the 625 S correction capacitor (C45). Component references are from the Murphy service manual.

I’ve restored several Astra models and every one has exhibited the “moisture in the line output transformer syndrome”. In addition, the oil in the LOPT can has probably absorbed moisture over the years that the set has hasn’t been in daily use.

Last edited by dazzlevision; 3rd Nov 2019 at 1:17 pm.
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Old 3rd Nov 2019, 1:14 pm   #15
Niechcial,Steve
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Default Re: Murphy V659/759 restoration

Thanks Dave. Yes I agree- my thoughts are line coupling cap and/or S-bend causing excess current through the line stage. I have already changed the boost cap. If the main smoother were down I think I would be seeing much more hum than I am, but if all else fails, I will give it a go.
Stephen
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Old 3rd Nov 2019, 1:53 pm   #16
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Default Re: Murphy V659/759 restoration

A word of caution Steve. Modifying the heater circuit to provide instant change over from 405 to 625 involved bridging the mains dropper with a high wattage resistor to compensate for the added valve heaters.
I have searched to find the mod sheet but I have filed it 'safely' away.. It will turn up when I least expect it! John.
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Old 3rd Nov 2019, 1:54 pm   #17
Niechcial,Steve
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Default Re: Murphy V659/759 restoration

PS. Do the LOPTs ever fully recover Dave? I have got some proper fresh transformer oil I could put in this one. Are they easy to drain?
Thanks, Stephen
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Old 3rd Nov 2019, 2:02 pm   #18
Niechcial,Steve
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Default Re: Murphy V659/759 restoration

Thanks John. When I flip the system switch on this set, the line sped changes but nothing else seems to- ie I get a UHF picture at 405 speed. Clearly there has been modification somewhere to render this set 625 only.
I need to take the tube out and paint some more aquadag on it as it has a tendency to fizz around patches that have come off. While it's out I will take a good look at the systems switch and also replace the 625 S capacitor which is hard to get to with the tube in.Stephen
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Old 3rd Nov 2019, 2:48 pm   #19
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Default Re: Murphy V659/759 restoration

Quote:
Originally Posted by Niechcial,Steve View Post
PS. Do the LOPTs ever fully recover Dave? I have got some proper fresh transformer oil I could put in this one. Are they easy to drain?
Thanks, Stephen
I only kept one Astra, a V789. Its in a room with a dehumidifier. Initially, after restoration, it would exhibit the typical damp LOPT syndrome if left running for more than ten minutes or so. However, after several months in a room kept at around 50% humidity, it now runs for an hour or more without fault. I guess the drier air and heat from the set (when running) has driven out/drawn off some moisture.

I have never tried draining and refilling the oil, but Im pretty sure other threads on this forum show how its been done successfully.

I also have the Murphy Service News that covered the no delay when switching between 405 and 625 mod. Ill look it out and email it to you.
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Old 3rd Nov 2019, 2:52 pm   #20
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Default Re: Murphy V659/759 restoration

IIRC, the 625 S-correction capacitor is a 75nF 750Vdc working axial leads TCC branded wax type.

I have used 68nF on my set, as 75nF caps like the original are not easy to come by.
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