Bush Dual standard chassis.
 

Can anyone tell me if the LOPT in a Bush TV125 is the same as the LOPT in a TV135RU ?
The reason I ask is that I have a 135RU which is not too far from working with a good CRT but is showing signs of LOPT problems. The overwind gets hot after a few minutes and the picture starts to balloon. I haven't run it for long, I switched off as soon as the picture started to darken in the centre so hopefully no further damage has been caused.
The set has been stored in a warm dry place so I don't think it is damp in the overwind but I will try the drying out procedure before I give up with the LOPT.
I have an earlier set, a TV125 which has a duff tube and a few other problems. I intend to restore this set at some point but I wonder if the LOPT is the same ? I could borrow it for the time being to enable me to run the 135RU and repair the other faults.
I know Bush / Murphy produced LOPTs that looked the same but had different windings so I thought I would ask here before I look into it further.
Final questions, are these pitch coated windings rewindable? Would it be OK to just rewind the overwind or is it best to have both done (if this is possible ) .
Any info greatly appreciated!
Rich.

Re: Bush Dual standard chassis.
 

Not sure if they are the same. I think they are but the service manuals are out of reach at the moment! Pass some current through it for a couple of days and it should be OK. They can be rewound. J.

Re: Bush Dual standard chassis.
 

Was the 135 the one with two printed circuit boards mounted vertically and the lopt was on a plug? I seem to remember the 161 better.



Got my chassis mixed up, the 135 had an upside down PCL82, yes, I believe they are the same LOPT

Re: Bush Dual standard chassis.
 

Bush list the part number for the Bush TV125 as ES41262. The TV135U with a very similar chassis lists the LOPT as AS42561 OR DS45775. The line output stage looks almost identical with similar transformer connection and layout. At a guess I would say it will work ok.

The chassis has the same layout as the TV125. I had to look up the chassis layout as similar to T.T. I could not remember when they went vertical. I think it was the TV141. J.

Re: Bush Dual standard chassis.
 

Hello Tony. I think the first with the vertical panels was the TV141U with the valve IF/video/audio panel. Bush made so many differing models around this time, some not very nice that it is difficult to remember all the combinations.

The TV135 appears to be very similar to the TV125 and looking at the circuit the line output stage appears to be identical. The part numbers given in the manuals do not agree but they changed the design of the LOPTs as the reliability was very bad with the tar overwind style. The end result was the same but as the picture states that the tag connections may differ..

TV125 LOPT part no: ES41262. [ Early version 1963
TV135 LOPT part no: AS42561 OR DS45775

John.

Re: Bush Dual standard chassis.
 

Yes, it's come back. The 141 with the valved if. I remember the 125 but I couldn't remember if the 135 was the same as a 141. So long ago now. Remember them being rather heavy sets, even the 19in ones. I know they used to go through PC86/88 valves, happy days.

Re: Bush Dual standard chassis.
 

I'm confident they are the same.

Rank Bush Murphy did also use an alternative and functionally equivalent LOPT for the TV125/TV135/TV135R/TV135L models (plus the 23" sets and the Murphy equivalents), which was made by Plessey Windings.

The difference being that the Plessey LOPT didn't use the (black) pitch encapsulation. Instead, the EHT overwind had a coloured plastic outer cover (usually red or grey) and the primary windings had a translucent resin covering. There was also a coupling winding on the EHT overwind side, that was would on a fairly thin plastic bobbin.

Re: Bush Dual standard chassis.
 

Bush TV135 was a hybrid, I remember seeing them looking new and gleaming c1964.

Lawrence.

Re: Bush Dual standard chassis.
 

Yes indeed, but with virtually the same main chassis as a TV125.

The TV135R was a cheapened (i.e. for rental customers) version of the TV125, with a printed circuit receiver unit and a small, square PCB fitted in the top region of the RHS main chassis panel, with the PCL82 (sound), PCL85 (frame) and PCF80 (line Osc.) valves on it.

The TV135L was a TV125 chassis, with a "quick release" chassis mounting feature (providing quicker removal for servicing).

Re: Bush Dual standard chassis.
 

SS IF as far as I can remember.

Lawrence.

Re: Bush Dual standard chassis.
 

Yes, the TV135 (but not the R or L suffices) UHF and VHF tuners used Ge transistors, as did the IF panel. A PFL200 was used on the 405/625 IF panel as the video amp, with the other pentode (usually used as a sync separator) used as a black level correction device (as per a Mullard circuit design, IIRC), as the main chassis used the pentode section of a PCF80 as the sync separator (as per the TV125).

Re: Bush Dual standard chassis.
 

A TV135 was one of the first TV's I repaired in paid employment, after that one it was back to banging out Ultra 1770's....

Lawrence.

Re: Bush Dual standard chassis.
 

Photos of the Plessey version LOPT.

Re: Bush Dual standard chassis.
 

Hi Rich, it is possible that the overwind is perfectly ok and it is in fact fabric tape between the overwind and the small earthy tuning winding close to the core that has become conductive at high voltage. Here in the below link, I delt with this nasty problem by replacing the fabric tape with polythene tape.....
https://www.radios-tv.co.uk/communit...overwind-cure/

Re: Bush Dual standard chassis.
 

Many thanks for all of the replies and help. I have just read through Andrew's thread on the VRAT forum. I think I will try putting some current through the overwind first and then have a look at taking it apart to check for leakage between the windings if that doesn't cure the problem.

I was surprised to find this set is fitted with a valve UHF tuner as it is surely a later model having the PCB IF and timebase and direct vision tube. I am sure the tuner was fitted when the set was built as the model number is RU. Rental UHF? Maybe Rank had some valve tuners left over and used them on the cheaper rental model?

The set has had a few varied repairs in the past the rear controls have been changed and I don't know what that big capacitor hanging on the smoother is for? all part of its history I suppose?!

Re: Bush Dual standard chassis.
 

1973 date code on that lopt Dazz.
I must admit I didn't find those plastic overwind Plessey transformers any better than the tar one.
Plessey were a superb company that supplied transformers and component parts to the whole of the TV manufacturers. That plastic overwind turned up in many chassis including the Thorn 850, Decca and many others including of course the later 640 RBM chassis, all of which we all know was not very reliable. The good bit, they were not expensive or difficult to replace.
I was never a great enthusiast for the RBM chassis introduced between the TV125 to the 640. probably just a sign of the times with those touchy hybrid models including the TV161GU that was a wolf in sheep's clothing! It's many years since I have seen any of that series. John.

Re: Bush Dual standard chassis.
 

It was not uncommon to find valve UHF tuners fitted in "second generation" dual standard mono sets. The TV135R would have been made around 1964-5 and used the same "NSF132" (German) UHF tuner factory fitted in the TV125 series. Certainly, the Thorn 900 chassis used (factory fitted) valve UHF tuners at first.

Those rear customer accessible controls were awful - easily damaged, but much cheaper than the lovely Plessey moulded track type used in the preceding Bush TV chassis over many years. The TV135R controls are very similar to the ones used in the Murphy Astra series.

Re: Bush Dual standard chassis.
 

We had a Bush 135 on rental from a local outfit called Whites.
I took this picture of Neil and Buzz off the screen.

Attachment 233100
I purposefully used a 405 line picture, as 625 always looked a bit washed out on that chassis.

Re: Bush Dual standard chassis.
 

I'm very surprised that transistors were used on the cheaper models' tuner and IF strips - this would be one of the earliest examples of them being used on a large screen TV, wouldn't it?

Re: Bush Dual standard chassis.
 

Hello John,

I would agree that the Plessey version of the in-house made pitch covered Bush LOPTs were no better or worse than each other. However, when TVs using these were "pensioned off", I have found the Plessey versions usually still work when the TV is "woken up" again after many years of disuse. Looking at the relevant RBM service manuals, it seems that their production began fitting Plessey (or RBM made) LOPTs from the all-valve TV141 and hybrid TV145 mono chassis era.

The TV141 all-valve chassis was, in essence, just a rearranged version of the TV135R one. The TV161GU was, electrically, very similar to the RF & IF stages of the TV135 hybrid chassis - but without back level correction - big mistake!

I definitely agree that the period from the TV135R until the arrival of the RBM A640 chassis, was not one of RBM's "finest hours"! They were driven too hard by trying to keep the selling price competitive.

Re: Bush Dual standard chassis.
 

I found the hybrid TV135U a decent set and gave very little trouble often the first repair after 4 or 5 years. The TV135R however was a different matter.
I didn’t have many LOPTX failures in those models but the TV141 and later models had a bad reputation, I kept transformers on the van, at least they were easy to replace.

Re: Bush Dual standard chassis.
 

There was an era of some UK manufacturers offering either a traditional all-valve (apart maybe, from the UHF tuner) d/std mono TV concurrently with a Germanium hybrid model:

RBM with the TV135 hybrid and the TV135L (restyled cabinet version of the TV125).

GEC Sobell with the 2012 and 1012 hybrid and the 2010 and 1010 all-valve.

Thorn had a version of the 950 all-valve chassis with a transistor integrated UHF/VHF pushbutton tuner - the 970 chassis.

Pye/Ekco were the bravest, with their 31F/40F hybrid chassis (following on from their all-valve 11U chassis), which was let down by the "rocket propelled, flying pushbuttons" of the integrated UHF/VHF pushbutton tuner!

Decca stayed with valves throughout the d/std era (IIRC) and ITT/STC/KB did the same.

Philips were a bit later in the hybrid market with their 210 hybrid d/std chassis sets.

Re: Bush Dual standard chassis.
 

Just to add to my confusion with these chassis' I decided to look at a Murphy version I have. This has the same chassis as the Bush but this set has a Fenbridge guard which I would expect to predate the direct vision tube in the Bush This set however has a Transistorised UHF tuner so presumably a later model to the Bush...
This set needs a few broken controls replacing it has no EHT and when switched to 625 promptly burnt out its Brightness control! Happy days!
Bad news is that it has a Mazda " Gold star" Tube- Good news it seems to have a replacement LOPT..
I will come back to this one!
I had lots of the earlier sets with the plate glass screen back when I was I lad but I didn't see many of these later PCB ones, I went on to the A640 which I really liked, they seemed to go on for ever if the LOPT held on!
Rich

Re: Bush Dual standard chassis.
 

Pictures of the Murphy.

Re: Bush Dual standard chassis.
 

Your set is the Murphy version of the TV135R. Murphy sets seemed to use the Fenridge guard rather than a direct vision CRT for a few years after Bush sets went direct view. The last ones were used in the Murphy V153 and V159 (which used the same chassis as the Bush TV141 & TV148. The transistor UHF tuner in your Murphy may have been added after it was bought....

Out of interest, what is the model number of your Murphy, which looks like the earlier model V849, which was designed for rental (and had a simpler/cheaper cabinet).

Re: Bush Dual standard chassis.
 

I worked on loads of those TV125s and their variants back in the mid 70s. I really liked them, but I remember that the line transformers didn't like damp old houses, other than that, I seem to remember that most of the faults were a thermistor or various valves.

Re: Bush Dual standard chassis.
 

The attached photo of an RBM fitting instructions sheet might be of interest. It reinforces my view that the Bush TV125 and TV135 models (and the Murphy V800 & V900 series) all used the same LOPT.

Re: Bush Dual standard chassis.
 

That is a very useful sheet especially as the connections were changed with modified transformers. The Mazda Gold Star tubes held up well on emission compared with the earlier CME1901 etc but they did suffer from O/C cathode connections. You will probably find it is OK as most of the problems were encountered within the first three years. J.

Re: Bush Dual standard chassis.
 

Yes very useful ! Many thanks.:thumbsup:
I am going to get the Bush back on the bench first and put some power through the overwind. Then I will see if I can find out what is wrong with the Murphy .
What is the best method to warm up the overwind?
I have got a mains transformer that I think is around 20/24 Volts secondary will that do ? Should I use AC or rectify it or doesn't it matter?
Rich.

Re: Bush Dual standard chassis.
 

I should add that the colour of the LOPT connecting wires can vary (according to the relevant Bush service manuals).

Re: Bush Dual standard chassis.
 

AC or DC it won't matter, but I found about 35v was needed to get it hot enough to aid seperation of the overwind in my case. Obviously you want it to slide off without undue force, but not so hot that you can't hold it.
Oh, and it will be messy. Be prepared to peel off all the soft tar to reveal just the overwind doughnut. You won't harm the windings as they will be covered in a fabric tape.

Re: Bush Dual standard chassis.
 

Seperating the overwind from the bobbin and the inner 625 tuning winding may seem quite drastic and would never have been done back in the day when replacement LOPT's were readily available. Different story now of course.

A supply of 2inch Kapton tape could be used to re-insulate the tuning winding. It may withstand the heat better than polythene tape, although my effort is still working well almost six years after doing it.

One thing to watch is that you maintain correct position and connection of the tuning winding upon re-assembly otherwise there will be no 625 line EHT.