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Old 25th Oct 2021, 6:45 pm   #1
Niechcial,Steve
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Default Bush Dual Standard Colour Restoration

I have just started out on restoring this 25 inch ctv. This one is the later version of the CTV25 with an EHT quadrupler instead of the original horrendous 25KV overwind. Not for nothing was this particular model dubbed 'The Burning Bush'!
As anticipated, the LOPT was u/s as shown on a handy little transformer ringer. I thought it worth a go to rewind it myself. I stripped it down winding by winding, testing as I went. Once I had taken off the top 3 windings it rang probably again so I decided not to push my inexperienced luck further, and just replaced those 3 windings rather than strip the whole thing. That was successful in that connecting an eht meter via a diode produced a healthy 7Kv output. If the other windings fail, I think I now have the confidence to rewind the whole thing.
The quadrupler was u/s too. I could have built one but there was a nice American silicon jobbie that I got hold of and works well.
Afer replacing a few Cs and Rs on the timebase unit I now have reasonable pictures on both systems- even a bit of colour which is remarkable as I haven't touched the signal stages. Tube is good, convergence is way out. I have been running without the PD500 connected, so next job will be to connect that, put the screening back, then set up the EHT by the book before moving on to the signal stages.
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Old 26th Oct 2021, 8:14 am   #2
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Default Re: Bush Dual Standard Colour Restoration

My first colour receiver was a Murphy CTV2210D, the 22" model with the first colour I/C the SL901. It also had the MK3 timebase.
It gave a bit of trouble during the first month, mostly mono type faults such as boost cap, 3rd harmonic tuning that was modified and just one colour fault when the bistable stopped due to a faulty BF115. It then settled down for 11 years and yes we watched the moon landing in colour. Seems only yesterday.. Agh yes, the PD500 in the jam jar. John.
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Old 26th Oct 2021, 8:42 am   #3
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Default Re: Bush Dual Standard Colour Restoration

That sounds like quite a task! Slightly before my time, but I did get a few in the workshop when they were past their best with, yes, LOPT failure which was usually enough to write them off. Can we see a few pictures? ISTR colour faults were often due to the pre-amp on the IF panel which could have you spending hours on the decoder looking for low colour.
I never understood why the PD500 AND a quadrupler - GEC managed very well without the shunt as did ITT.

Ah - the 2210/CTV174D with the original finned SL901 on the wrong side of the PCB. The solid state RGB stage gave a much better picture than the CTV25. "IC Colour Lock" it said proudly on the front.
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Old 26th Oct 2021, 1:01 pm   #4
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Default Re: Bush Dual Standard Colour Restoration

Yes it was a bit over the top but as far as I can remember it was the only chassis to be fitted with a quadrupler. Maybe if they had put a few more turns on the overwind they could have fitted a conventional tripler.

I think the quadrupler unit was the only open type, colour that is. I think it was made by Plessey. John.
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Old 26th Oct 2021, 7:29 pm   #5
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Default Re: Bush Dual Standard Colour Restoration

Yes, it was my family's first CTV too. The original CTV 25 with the 25 KV overwind. I paid £80 for it. It got through two LOPTs in 4 years! You mention the BF115 John. The design had that curious quirk whereby both the ident and bistable had to be working for the colour killer to switch on. I remember it well, because our set had a re-built crt, and a couple of times when it flashed over it took out one of those BF115s in the bistable resulting in no colour.
I will do a bit more work and post some pictures Glyn.
I am going to keep the PD500 because even with a silicon quadrupler (as opposed to the original selenium) the regulation without PD500 is not great , and the pic size varies quite a bit with scene content.
I've actually got two of these sets now. I paid just over £200 for one which had been stored in awful conditions with duff LOPT but good CRT, and then before I even had a chance to collect it, a much nicer one came up. The crappy one has the same LOPT/quadrupler arrangement so inspired by my re-winding success I will probably give that a go when I have finished this one. It is a complete set apart from someone has robbed the systems change solenoid and the Bowden cable link to the switch on the IF panel. If anyone has these kicking around, I would be grateful.
I have never seen the version with video jungle IC. There can't have been many of them made I guess before the A823 appeared. One of the troubles working on the set is that they had about three major re-jigs of all the panels, then variations within each panel, then loads of modifications/ For instance is the A821 Mk. 3. There were at least two other major variations, and heaven knows how many 'MKs' within them. It's often very hard to know exactly what circuit diagram matches what.
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Old 27th Oct 2021, 8:25 am   #6
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Default Re: Bush Dual Standard Colour Restoration

The CTV174D is indeed quite rare now, as is the Philips G22K503, as they were for people who needed a dual standard colour TV. Unlike the CTV25 and '500 they both looked modern with 'push through' 22" tubes.
The CTV174 used the Mk3 timebase like yours and a similar power supply and IF/audio unit. However unlike the 19" CTV162D with its folded up panels it used a completely redesigned decoder and had a solid-state RGB stage. This gave much improved reds over the earlier design.
In fact I would say the CTV174 gave far superior pictures to the A823 which was muddy by comparison.
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Old 27th Oct 2021, 8:51 am   #7
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Default Re: Bush Dual Standard Colour Restoration

Quote:
Originally Posted by Heatercathodeshort View Post
My first colour receiver was a Murphy CTV2210D, the 22" model with the first colour I/C the SL901. It also had the MK3 timebase.
It gave a bit of trouble during the first month, mostly mono type faults such as boost cap, 3rd harmonic tuning that was modified.
John.
Hello John,

Could you provide details of the mod(s) to the third harmonic tuning, please?

I also have a Murphy CV2210D and can get only just enough width with everything set up as per the service manual.

I have the two part RBM service manual and all “Service Skill” publications, but don’t recall any reference to this.

Thanks
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Old 27th Oct 2021, 2:23 pm   #8
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Default Re: Bush Dual Standard Colour Restoration

Hello Daz, The original high voltage ceramic failed when the 2210 was almost new. The mod involved using a much high value cap around 350pf and connecting it across two lower potential points on the LOPT tag strip. It's a long shot but I will dig out my original 2210 manual and see if I tucked the mod sheet in it. The other possibility is that it was published in the Murphy Service News. I will have a go! John.
Found it! The original capacitor 3C34 180pf is removed from tags 3 & 10 of the LOPT. The replacement 340pf is connected between pins 8 & 10. Information taken from Murphy service manuals TP1723 and TP1729-1 1-10-70. Hope this helps.
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Old 27th Oct 2021, 2:25 pm   #9
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Default Re: Bush Dual Standard Colour Restoration

Quote:
Originally Posted by Heatercathodeshort View Post
Hello Daz, The original high voltage ceramic failed when the 2210 was almost new. The mod involved using a much high value cap around 350pf and connecting it across two lower potential points on the LOPT tag strip. It's a long shot but I will dig out my original 2210 manual and see if I tucked the mod sheet in it. The other possibility is that it was published in the Murphy Service News. I will have a go! John.
Found it! The original capacitor 3C34 180pf is removed from tags 3 & 10 of the LOPT. The replacement 340pf is connected between pins 8 & 10. Information taken from Murphy service manuals TP1723 and TP1729-1 1-10-70. Hope this helps.
Thank you John. I will check whether my set has already been modified.
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Old 27th Oct 2021, 6:27 pm   #10
Niechcial,Steve
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Default Re: Bush Dual Standard Colour Restoration

Dave I'm a couple of hours ahead of you on this one! I ordered some 330 pf 30 kv caps this morning. If you need one let me know, and I'll stick one in the post
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Old 27th Oct 2021, 6:44 pm   #11
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Default Re: Bush Dual Standard Colour Restoration

Quote:
Originally Posted by Niechcial,Steve View Post
Dave I'm a couple of hours ahead of you on this one! I ordered some 330 pf 30 kv caps this morning. If you need one let me know, and I'll stick one in the post
Thanks for the offer Steve.

I'll check my pulse ceramic disc capacitors drawer and if I don't have any, I'll get back to you.
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Old 27th Oct 2021, 8:07 pm   #12
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Default Re: Bush Dual Standard Colour Restoration

By employing an EHT quadrupler the regulation will be no way as efficient as the earlier versions with the 25KV winding on the LOPTx. That being so, the PD500 shunt regulator should remain in the circuit.

DFWB.
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Old 30th Oct 2021, 1:46 pm   #13
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Default Re: Bush Dual Standard Colour Restoration

Yes indeed. Presumably the glass tube around it has a high lead content a X-ray reduction. I don't think I will impair this just by washing it will I?
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Old 30th Oct 2021, 4:33 pm   #14
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Default Re: Bush Dual Standard Colour Restoration

I understand the lead is in the glass, as it is in shadowmask CRTs.
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Old 2nd Nov 2021, 10:20 pm   #15
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Default Re: Bush Dual Standard Colour Restoration

Good progress on this. I now have the shunt stabiliser in circuit with good width, focus and EHT stabilisation on both systems. I've been through all the pots, Cs and high value resistors on the timebase unit replacing where necessary (I completely rebuilt the focus chain). As far as I can see there is actually no beam limiter on this Mk 3 timebase unit. Can someone tell me if I'm wrong on that? I've cleaned up the tuner which needed very little work, and restored the operation of the system switch solenoid. I need to organise the mechanical switching linkage between tuner and IF which someone has just chopped.
I attach pictures of 405 and 625 operation. As you can see, there is the same very bad Dynamic Convergence on both systems. I haven't explored yet, but it looks too bad just to be mis-adjustment- must be a fault somewhere. I also have almost non-existent Frame sync
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Old 3rd Nov 2021, 10:54 am   #16
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Default Re: Bush Dual Standard Colour Restoration

The static convergence is miles out too - maybe a wire off the coils or they've been messed with? Luckily it's a very basic circuit. The verticals look a bit wonky too, so perhaps a waveform isn't right.
Nearly there though - and the colour looks good!
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Old 4th Nov 2021, 2:04 pm   #17
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Default Re: Bush Dual Standard Colour Restoration

The convergence problem was an o/c 50 mfd electrolytic which couples the frame output pulses to the convergence board. Scoping the sync input to the timebase board shows that it is of the right amplitude but has a lot of video content on it. This no doubt accounts Glyn for the wavy verticals and poor frame sync.
Now that the picture is decently converged, poor low frequency response with smearing is apparent, some of it coloured (see attached). The definition is otherwise excellent so I don't suspect a tricky IF problem, but rather couplers/decouplers throughout the signal stages. Rather than fault find I will now just go through the signal panels replacing all the horrible red TCC electrolytics and take it from there. I haven't finished on the convergence set -up as yet but it's more than good enough at present
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Old 4th Nov 2021, 4:32 pm   #18
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Default Re: Bush Dual Standard Colour Restoration

Isn't that a CTV167 - the one without the doors? Early versions of this used the CTV25 back with a 167 sticker over the model number!
Nice to see steady progress.
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Old 4th Nov 2021, 5:25 pm   #19
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Default Re: Bush Dual Standard Colour Restoration

Yes Glyn- the 167 and no doors.
The other one I've got has got doors and is badged as a Granada. It is in a terrible state having been kept with several other sets in a leaky wet shed for years. The back is missing and closer inspection reveals that not only is the systems change solenoid missing, so is the band switch mechanism on top of the tuner. Where those tuners the same type as fitted in the contemporary Bush monos?
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Old 7th Nov 2021, 2:52 pm   #20
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Default Re: Bush Dual Standard Colour Restoration

I have now got the IF and decoder/cda panels out for work (photos attached). They all just unplug quite easily. Although the Thorn 2000 gets all the credit for being serviceable simply by panel replacement, this Bush would not have been too hard to service in that way either. Does anyone know if anyone adopted that panel changing approach, maybe with rentals? Admittedly not all variants were compatible with each other so that might have influenced things.
I went straight to the sync separator (on the IF panel), where I found 3 out of the 4 resistors in the circuit way out of value. I also replaced the tantalum coupling capacitor for good measure, and tested ESR on all other electrolytics on the panel, replacing another two of them. I cleaned up the contrast pots. and now consider this unit ready to go back.
This set has no user contrast control, only pre-set internals, one for each system. With 405 mean level AGC on the original panels this must have led to some mediocre results on that system, so later IFs were modified with a gated 405 agc system on a little sub panel. My IF is one of the earlier ones.
On now to the decoder/cda panel.
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