Bush CTV184S

[MickMcmichael]

This set was perched at the front of the stage at Harpenden about 18 months ago. It fluttered its tube lashes at me as I walked by and I was smitten. I already had a Bush A823 but its one of the later ones with varicap tuner....too new, you may say.

I'd been looking for one of these for some time. One of our senior engineers at British Relay had one back in 1975 which he bought from a trade warehouse and he spent his lunch times (plus!) mending every panel in the set. So for me it was, from a nostalgia point of view, a good project to take on.

There was a little interest in it on the day. Several people were looking at it on the stage. Lights on mobile telephones were trying desperately to look inside it to peek an eyeful in the somewhat darkened hall.

Auction time came and there was one bidder (and I soon found out why)....me! One crisp ten pound note later and it was in the back of the van.

The reason there was no interest was because the set was missing its power supply and decoder boards. I put out an SOS on here and Dazzlevision came to my rescue with the two boards that I wanted. Many thanks indeed for that!

Life intervened shortly afterwards with things that life does so there has been a delay in me attempting this repair.

The set was interesting. It had many of its cables extended with home lash ups and had obviously been used as a workshop jig to repair individual panels. The tripler is loose but connected properly (not bodged in) and it looks as if the LOPT may have been replaced in the distant past.

I put it on the bench yesterday and gave it a full inspection before fitting the power and decoder boards. The smoothers look ok with no bulging or white stuff. I swung the timebase board out and removed the plate behind the line transistors. If there's one thing that can turn me into a jibbering twiching wretch like Chief Inspector Dreyfuss (Pink Panther) then it's a nasty bodge in this department on the A823. Changing the transistors on these is a nightmare.

All looked good and original. That's amazing for a test jig, eh!

So I fitted the panels, checked everything again and reached for the variac...

[MickMcmichael]

The sound started shushing pretty quickly and the tube heaters were evident somewhere between 60 and 80 volts on the variac.

I was amazed that by some miracle the set was working.

By the way, the pink pics are NOT colour - the pink is knackered tube!

There is no colour at the moment but I'll sort all the geometry first before looking into that.

Quite pleased so far. This set could not have been run in many years. Let's see how much needs doing...

[dazzlevision]

Watch out for those two Plessey TCC Duopack 0.0047uF 1500V green sleeved capacitors in the line output transistor compartment. They will almost certainly be leaky and are critical components for correct line output stage operation.

[MickMcmichael]

Yes I think it might be a good idea to change those caps before I go too much further. They could be a heartbreaker!

[FERNSEH]

I've still got good stock of those 0.0047uF flyback tuning capacitors which were specially rated for 15,625Hz operation. Trouble is I can't get at them because the shop is closed for the duration of the corona virus crisis.
There is a procedure to balance up the line two output transistors.

DFWB.

[dazzlevision]

Originally Posted by MickMcmichael

Yes I think it might be a good idea to change those caps before I go too much further. They could be a heartbreaker!

Definately!

I use a Vishay/Roederstein 2kV rated axial metallised Polypropylene film type MKP1845, from Farnell (a few years ago). I still have some NOS Plessey types, but they’ll be u/s.

[neil29]

The 1970 set I've got was missing several panels had scruffy trim and a butchered back cover. but luckily a wormy 1971 set came my way and all was restored so far as completeness was concerned but i've yet to actually do any repairs electrically and despite that it actually works ok at the moment. and if you need a tube I have a good one going if you want it.


Cheers
Neil.

[MickMcmichael]

Thank you kindly Neil. I'll bear that in mind.

This one will plainly need a bit of a tickle and I'll see how that goes. I wouldn't want to wreck a complete set just to improve this one. I'll get everything else sorted on the set and see if the tube improves with a long run - they often do.

[MickMcmichael]

Rightly or wrongly (time will tell) I decided to leave the existing scan caps in situ. I have a drawer full of new old stock ones which when checked were all somewhat out of spec' by more than the rated 5-10% tolerance. The originals in the set measured almost bang on. So they stayed, at least for now.

A picture with just the blue gun switched on looked like a ghost. Red and green only marginally better. A clean and balance helped a great deal. It's by no means perfect but at least watchable.

Set up EHT and frame to a degree and things are starting to look a lot better. Far left hand side of the screen is a little dark, or am I being picky? Maybe. Will look further into this tomorrow. The purity is still far from perfect and that needs to be addressed too. Some of the old convergence pots are a bit graunchy as to be expected. Will replace a few of those in good time.

[slidertogrid]

That's looking a bit better mate! I wonder if the slight shading will be cured when you get the purity right? The tube still looks a bit poor. you should chuck that B&K in the bin and borrow my bulb bopper! That will get the sparks flowing!
If I remember rightly I was at the Harpenden meet with you when you bought that set and neither of us bought anything else ! Previously the set had not sold at RWB ISTR, and you were the only bidder at Harpenden no doubt you saved it's life! I doubt it would have had a third chance...
But it just goes to show some people will buy any old tut!
Only joking...

Rich

[Welsh Anorak]

Nice to see quite a rare A823 on the road to recovery. Lots of 1122s were made, but the CTV184 was unusual with its CRT surround and it dated quickly. Now I rather like it!
Of course that's why it was a mule - it wouldn't have been worth replacing the CRT to put it out for sale, and it's [probably had many boosts over the years.
The old decoder should give a better picture than the 2-chip one - when you get it working. There was a pretty good setting up procedure in Television in the late Seventies. Don't forget the first chroma stage is on the IF panel.
Nothing wrong with a BK - mine came in very useful over the years, though I admit my old 'bulb bopper' rarely came across anything it couldn't make sparkling again! For a while...

[MickMcmichael]

All this talk of bulb boppers brings back memories of engineers at British Relay desperately trying to save tubes to avoid a new tube being charged to their monthly bonus.

Set heaters? Nah, just whack it!

Set cut off? What the **** is cut off? Just whack it!

Tracking? Errr... Try whacking it!

Yeah I know, the CRT is still a bit low. As Glyn says, it's probably been boosted on all sorts of home and manufactured devices over the years and it is what it is.

The set had been on quite a while today while I did my best with the grey scale on an ageing tube and convergence with some dicky old pots - some of which I replaced.

As I swung the convergence board up and down the colour would come and go. Further investigation produced intermittent colour when applying pressure to the decoder, more noticeably around the bottom left of the board.

3RV7 is the bistable phase pot and this simply turned out to be a bit iffy. I cleaned the pot and all is well. The colour drops in straight away on channel change and if the set is switched off and on again. I'll consider that fixed.

One other slight adjustment was the delay line driver 3RV3. Just a slight Hanover effect but much better now.

I think I'll now leave well alone. The CRT will never be better than this and any major time spent on very minor issues could end in disaster.

I did have one other issue today that turned out to be silly but made me despair until I sussed the problem. The set appeared to be suffering from a very bad case of sound on vision. I then realised that the effect was still there during quiet passages, so no sound on vision!

The symptom disappeared when I turned the set round ... Huh? Surely not the workshop flourescent lights? No.

I switched off my little Pye Rambler bench telly and the effect went away on the A823. Line stage interference or something...

The CTV184S is a nice old set that was saved from the proverbial hammer if it didn't sell on that Sunday afternoon 18 months ago. Job done, I think!

[neil29]

Its looking better. But if you do want to swap the tube at a later date i'll probably still have it here and it is a good one. and I also have quite a few panels, good useable ones as well as parts only if you or anyone needs them.

Cheers
Neil.

[MickMcmichael]

Thanks Neil. Much appreciated. Tubes not easy to come by.

You never know...

[slidertogrid]

That is looking better mate, well worth saving!

It's odd that the new capacitors you have in stock have drifted in capacitance and yet the ones in the set haven't ? Does it look as if the ones in the set have been replaced ?

[MickMcmichael]

There wasn't much difference. The originals were just a bit closer to home. The only difference is a bit of usage and storage over the years, I suppose.

[Welsh Anorak]

What CRT is fitted to this? Also, has it got the 'right way up' timebase panel from early production?

[MickMcmichael]

The CRT is a Mullard A56-120X.

The frame transistors are at the top with the pots facing inside the cabinet.

[dazzlevision]

Originally Posted by MickMcmichael

The CRT is a Mullard A56-120X.

The frame transistors are at the top with the pots facing inside the cabinet.

That must be later production, as the two preset controls with spindles were originally accessible with the back cover in place.

I think there was a problem with interaction between different parts of the circuit with the original arrangement.

[slidertogrid]

Originally Posted by dazzlevision

I think there was a problem with interaction between different parts of the circuit with the original arrangement.

There was ! There is an edition of Television magazine showing the 823 chassis on the front cover with the panel propped open with a matchbox. the article on the set mentions that the matchbox was there to stop interaction between the frame panel and the line stage.
That presumably was the unofficial mod. The official mod was to turn the panel upside down..
British design and engineering at it's best!