B&W TV Going through my sets in storage .

Posted by: @jayceebee

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The PY88 as most of us know was used in the A640 styles of chassis. I had thought it was used in that style also, maybe in the versions with the transistor IF?.

Quick look at the Bush TV14x series manuals shows that a PY800 was used in the versions with both the valve and germanium transistor IF panel - these being chassis types A543, A571 and A591.

Oh dear, looks like I'm losing it 🙃 but it is 50 years since I last had the back off one of those. Must haul my A640 up onto the bench, last time I tried it the IF strip was dead.

For the record I thought it should have been a PY88 as well until I checked the circuit I have which is good old LLJ's "Servicing Television Receivers" series. Yes! Itza Mazda! Goldstar, the original 'silvery screen' 😎 Just goes to show, they weren't all bad!

It reminds me of when I used to get old sets from TV shops and the tip. I was looking for a 'Push through' Panarama type 19" tube for a 1400 (trans)portable I had that had a very very flat tube, (Probably been boosted to death before I got the set)  At the time most of the sets I was getting were older types, 950s Pye 11Us - that type of age, so a 1400 was highly prized especially a 'Portable'!

My mate and I had a look at the tip we found a few old radios, got some valves and speakers but no TVs, Not today!  Just as we were leaving I spotted the remains of a 1400 against the chain link fence, it was pretty destroyed the cabinet in bits, the PCB broken and rusty, spattered with mud, it had obviously been there a long time and had been narrowly missed by the bulldozers as it was against the fence. It had an intact tube! But oh dear! A Mazda Goldstar! The 'dag was bubbling from the damp. I nearly didn't bother but as I was desperate  I disconnected the remains of the chassis and put the tube complete with the front of the cabinet on my specially made in metalwork at school bike rack! The rack was removable and like the sort of thing usually on a trade bike...

Both me and the tube survived the 5 mile ride home and was swiftly fitted to the 1400. It was absolutely perfect! I was amazed! 

The next set I have put on the bench is a Bush TV125 convertible but in this case not fitted with a UHF tuner. Chassis 336. The Circuit I have is for the Murphy equivalent models and lo and behold what does it state is the boost diode? A PY88! @jayceebee It seems the earlier chassis did use the PY88.  I see that the heater plug for the UHF tuner is just linked across so I assume the dropper setting had to be adjusted to accommodate the UHF tuner valves? Or did you just remove the PY88 and fit a PY800/801 ? 

This set came to me from another collector years ago when I looked inside it looked as if it had been a parts mule. Every plug was out the top cap of the DY disconnected and the two screws missing holding the IF chassis in place the tube also looked suspiciously clean compared with the chassis. it also had two capacitors lashed in the line stage one of which is the boost cap... Hmm... This set has been "looked at".

I decided to see how bad things were so in the first instance I connected the LOPT overwind across a power supply and left it cooking for a few days while I played with the other sets.

First I checked the tube heaters had continuity then I put the plugs back in left the heater chain broken and reformed the smoothers. When I was happy that they were OK I reconnected the heaters and gave it some mains. Smoke poured from the dropper while it burnt of the cr4p then the line stage spluttered into life the line hold control was very intermittent but after a while things settled down and I got a blank raster. I connected the converter and after tuning around got good sound and a very washed out picture that came and went the contrast control having no effect. 

All of the If chassis valve holders were very intermittent, giving them and the system switch a clean and a wiggle settled things down and I had a grey flat but stable picture.

At this point there was a squark from the timebase and the picture went off! The PL36 then clinked and started to overheat... Oh dear ! enough for today!  Has the LOPT died will the set go back in the spare room for another decade?....

Enjoying this thread Rich, and the walk through all the TVs from your store.

With regard to the TV125, I have just two B&W TVs left in my collection, both Bush, one being a TV125CU I got it this very month, in fact on this very day 10-years ago! Lovely set, I've also not switched it on for those 10-years, since repairing it. I'd fully expect the LOPT to complain despite it recovering itself, as detailed in my thread. Amazing how the years just flash by.

@slidertogrid 

I don’t recall any heater changes when fitting a UHF tuner, the difference was relatively small with both valves having 3.8v heaters.

Then again we fitted very few to the TV125 range. 
I found the PY88 a more reliable valve than either PY800/801.

I will have to have a look at the heater circuit as they look a little on the bright side there is also a RS 'polo' dropper section tacked in and then bypassed that needs looking at. Luckily I have another set pretty much untouched same chassis so I can compare that. I have just re read Chris's thread on his set My LOPT certainly seemed to 'foam' some moisture out of the top of the overwind when I cooked it so when you run your set up again Chris it may be a good idea to give the LOPT a heat up first?

The reason the EHT had failed was easy to find another dodgy valve holder, When checking voltages around the PCF80 line osc the set spluttered and tried to work rocking the PCF80 the set sprung into life again, so I cleaned the holder and valve pins, so far so good....

 I removed the IF panel and turned it around so I could measure some voltages the Bowden cable was already removed so it was fairly easy to prop it up on the bench while still connected. 

The problem was fairly straightforward a 6.8 meg resistor on the system switch to the 405 contrast control was open circuit. A new resistor and away we went plenty of Contrast! 

Next I plan to tackle the frame fault and have a look at the work that has been done previously and tidy things up a bit. Considering what the chassis looked like when I first took the back off it isn't as bad as I expected. I suspected that one set had been made out of two and this was all the 'bad' bits! Well if that is the case 'the bad' isn't so bad, really....

 Opps sorry wrong picture! I can't find out how to delete it ! Correct pic to follow...

Today I tided up the replacement capacitors near the LOPT. Cleaned the system switches and reconnected the Bowden cables. Then I dealt with the terrible frame linearity, frame jitter and intermittent width. Replacing capacitors cleaning pots and replacing the PCL805 which was slow to warm up. I replaced the two capacitors on the tube base which were very leaky. Each time I switched on there was improvement.

I am now fairly happy, the picture is stable fairly with good linearity and definition with a good range of adjustment on brightness and contrast. Considering the set has spent its whole working life on 405 I am lucky with the buttons as they all tune

none of the problems Chris had with his. There are also a fair few Mullard 'mustard' Capacitors so that has saved some time. There is still a green plastic capacitor on the frame transformer to replace and a knackered looking black and red Plessy 'Sellotape special' on the audio amp. 

Considering how got at and robbed the set seemed to be I think it has turned out fairly well. I think I am particularly lucky with the tube and (so far) the LOPT... 

I spoke too soon! The picture went really snowy flat and grey! I gave the tuner a tap and it jumped about all over - came back - went off. I removed the tuner, cleaned the band switch, lubricated the mech, cleaned the valve holders and pins. Then I fitted some felt washers to the knobs to replace the perished foam ones and gave it a try, Success! A nice stable picture...

Then the width went in jumped out again followed by fireworks in the PL36. So that went in the bin and I cleaned the valve holder. Back working again!  Now to watch 'Murder at the gallop' starring the formidable Margaret Rutherford... 😍 🤩 

@slidertogrid 
I had forgotten how well engineered and relatively easy to work on these sets were. Has the thermistor  modification been done on the set.

@nuvistor I think so I am going to check the chassis against the circuit later today. I think this may be what the disconnected 'Polo mint' RS section that is near the fuses may be about. Certainly some modification has taken place, But why someone would fit it and then bypass it leaving it in situ is a mystery...

@slidertogrid 

I don’t think the circuit shows the mod, it’s at the end of the manual in the modification section.

From memory swop the places over for the 68ohm and thermistor but replace the 68 ohm with a 10 ohm, but please check before taking my memory as correct.

It's detailed in my thread courtesy of TerryKC

https://www.radios-tv.co.uk/community/black-white-tvs/1963-bush-tv125cu-skip-find/#post-52534

I have a TV125 that I’ve not done anything with, got it ages ago from a guy in Coventry who had a load of RGD radiograms, it sort of works, but has a really wishy washy picture on both standards. Annoyingly, the finish on the top of the cabinet has begun splitting and cracking, it was perfect before! Maybe it’s too dry in my shed!

Regards,

Lloyd

It may be that it is too dry or it may be heat, some Philips sets had a similar finish but with a thin ply case. they often cracked badly especially if they were situated in a place where the sun could get to it. I never refinish TV cabinets I touch in chips and marks if possible and then leave it as part of it's history. 

These sets are one of my favourite, our local Murphy dealer was evicting them in the early 70's I had a load of barrel Murphy's followed by quite a few of the Murphy version of this model. if they were 405 only, unconverted there was usually little or nothing wrong, ones with the UHF tuner were less common but the occasional one would be plonked in the yard if I got lucky! Even back then the LOPTs were a weak spot with pitch droop on the overwind and the usual falling off of EHT as it got hotter.

I have had visitors today so I haven't been able to get any time on my set, It ran fine yesterday and Miss Marple was able to solve her mystery - murder...

Thanks Chris and Frank. I have it sorted now, the mod had been carried out but the person hadn't fitted a 10 ohm dropper resistor, the disconnected dropper section that had been bypassed was 68 Ohms. They must have found that it didn't work so just bypassed it. I checked the voltage across the tube heater with the variac set to 240v and it was over 7 volts!  I found a suitable high rated resistor that I temporarily lashed in that brought the heater volts to 6.4V, that's more like it.  The two or three ceramic standoffs are long gone, the Thermistor being mounted on a tag strip on the back of the dropper shield.

I found a bit of tag strip and with the aid of a couple of washers secured it through one of the holes left by one the ceramic stand offs. then I securely wired the dropper section to the tag strip and soldered it into place. The lower heater voltage then exposed another slow warming valve this time in the tuner. I replaced the dried out electrolytic on top of the chassis, cleaned the PCL82 valve holder as it crackled when I tapped the chassis.

I am happy with the set now. I will give it a few good runs and catch up with the antics of Miss Marple.

Your TV125 reminds me that it was the first set I remember us having when I was a toddler. Ours also didn't have a UHF tuner fitted. If I wanted to watch Play School or those short trade test films on BBC2 it would be when I was at my Nanna's. My fave trade test film was Evoluon. Sorry about going off topic.