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.