Bush A774

[linescan87]

Hi,

Started on this a few weeks ago, first fault was no raster. The screen grid resistor(3R56)was found sprung open, that was caused by the screen grid decoupling cap(3C37) being leaky. The set then started up but a lot of tracking from the eht rectifier heater winding and from the DY to it's holder. I decided the best thing to do was replace it with an eht stick.

With that done I powered up, OK for the first minute and then what sounded like eht tracking with disturbance on the raster. With the lights off in the workshop I could not see any tracking. I did see a blue flash in the PY when it occurred, tried a new PY but still the same. I then tried swapping the PL and that cured it, it must have been breaking down inside.

The frame linearity wanted a tweak the tuner needed a good clean. The tube is a little weak, but may improve with use. I read here a while ago in a thread were a number of people were giving out about the performance of these compared to the A640, I have to agree. My A640's knock spots off this yoke!

Cheers, John Joe.

[neil29]

I must be mad as I have 10 A774 chassis sets which when tested a while back all worked. although I doubt they all still do now..


Cheers
Neil.

[linescan87]

Hi Neil,

10 A774's! It's not the worst set in the world, but it's not the best either.

Cheers, John Joe.

[Heatercathodeshort]

Probably the only 10 left working in the World.

Seriously they were very unreliable when new requiring frequent LOPT replacement and other problems. The few that survived were probably the good ones. J.

[linescan87]

Yes John, we'll see how long it lasts. That was half my thinking in fitting the stick rectifier, reduce the load on the lopt a bit.

John Joe.

[FERNSEH]

In the late seventies the Rank Radio service department supplied a replacement A774 line output transformer equipped with an EHT tripler. That solved the transformer reliability problems but still didn't make it a better set.

I disposed of the last rental A774 set in 1980. Just glad to see the things gone for good.

DFWB.

[linescan87]

Hi Fernseh, the tube in this one was very flat. I decided to give it a tickle and it has responded well, we'll see how long that lasts.

John Joe.

[Heatercathodeshort]

It's a shame really. LOPT problems should have been sorted out by the early 70's especially from such a high grade and respected company as Plessey.

There were other stock faults on the A774 and I suffered them all selling the TV181SS from the start.

To be fair other leading manufacturers suffered similar problems with their all transistor chassis but RBM certainly put a top hat on LOPT failure. All history now but it did cause me problems when this chassis was new. J.

[jayceebee]

Working for an RBM dealer at the time we knew we were in trouble as soon as we lifted the first one out of the box to have a look. Straight off without a signal even the "snow" didn't look right, with a signal the picture just looked flat. A tweak of the video bias improved matters, I'm not sure if RBM approved of this but it helped.

Just weeks later they became known as the bouncing Bush due premature failure of the LOPT EHT rectifier heater winding, problems with the oscillator stage capacitors and poor soldering of the chassis metal bracing strips.

Does anyone remember an A774 being shot at on the feature "Heap of the week" on That's Life?

John.

[Philips210]

Originally Posted by jayceebee

even the "snow" didn't look right, with a signal the picture just looked flat.

John.

Hi.

I do remember the pictures displayed by these sets had that plastic look about them. It was a shame really as I generally found the A774 easy to work on. That LOPT was a problem in most sets, though the replacement version with stick EHT rectifier helped a little towards improved reliability. With a BRC/Thorn Jellypot LOPT they wouldn't have been too bad.
I remember a lot of problems with those plastic bushes cracking on the 4-Button tuner. I seem to remember the replacements were blue and supposedly an improved type. I've still got a few in the spares somewhere in the depths of my garage.

Regards
Symon.

[Nuvistor]

We sold few large screen BW sets in the 1970’s, I remember the TV181 but not much about its reliability. The plastic bushes in the tuner I do remember failing and RBM LOPTX’s were not that reliable in previous models.
Anyone have a photo of the chassis, it may jog my memory?

[jayceebee]

Here you go Frank. This is a late and much improved version, the PCBs on the earliest models were red. Spot the replacement LOPT with EHT tray.

https://vintage-radio.net/forum/show...0&postcount=18

John.

[Nuvistor]

John , Thank you. Doesn’t bring back many memories like the earlier two PCB models so I wouldn’t have fixed many.

[jayceebee]

I've a lot of time for the A816 chassis that followed, a huge improvement but it wasn't liked by a lot of people in the trade at the time.

[Nuvistor]

I left the trade around 1980 so when these sets were getting ready for repairs I would have moved on.

[Heatercathodeshort]

I had 6 carefully delivered by the Bush distribution company 'Lenham Storage'. On the side of the boxes were written in large black letters, 'GET A BUSH AND YOUR SET FOR LIFE'. Ha! Ha!

To cut a long story short, all had failed within the week, some within hours. The early faults were caused by CRT flash over, normal with new CRTs. This damaged the line sync diodes causing lack of line hold. The cure was to include a 1k resistor in series with each diode. The LOPTs failed in others and one had a distinct hum bar. [chassis soldering]

My experiences were identical to John's. I used to increase the video drive till sync crushing became evident, then back it off a little. The technical dept at RBM did not like this action but it gave a just about acceptable picture.

We were of course expecting it to be a similar picture to the A640/793 chassis. Some hope!

The 20" and 24" tubes lost emission rather sooner than the earlier Mullard types reproducing a milky picture and that was just after 24 months use.

I only had one A816 brought in for repair. They were a rare site down South. At my first view of the chassis I thought it was a colour receiver!

It was an expensive model and by this time most new buyers were looking towards colour.

I must admit I never really liked all Bush/Murphy models from the end of the TV125U to the introduction of the A640. The public wanted quality but were rarely willing to pay for it! Regards, John.

[Nuvistor]

The hybrid TV135U I found very reliable and gave a good picture, we sold them and perhaps saw them 4 or 5 years later for the odd valve.
The rental version TV135RU was a completely different set and not that reliable but I think about £10 cheaper.

[linescan87]

It seems I indeed have a very rare and valuable set in this A774, possibly one of only a handful left in working order. I shall treasure it dearly! Haha!! (According to that Bush slogan "I'm set for life!")

John Joe.

[FERNSEH]

The other reason why I haven't any good memories about the A774 was because it wasn't just the unreliability but also I was guy who bought the things to rent out. Paid good money for these awful sets when in the early 1970s there was much better black and white TVs available, the Thorn 1500 for example. In fact I did have many 1500 series sets out on rental in the guise of Alba and Marconi models. The A774 sets were bought direct from Rank-Bush-Murphy as the company was known was then.
All those who worked in the TV rental trade will remember that discipline of having to do every service call within a matter of a few hours from receiving the request for service from the customer. I do remember always having a large stock of replacement line output transformers for the A774. Also the plastic tuner slugs. Worked out a quick method of removing and refitting those.

The A816 series of receivers were much better. Later versions of the popular Murphy Acoustic Deluxe models were fitted with the A816 chassis in lieu of the A774 chassis.

DFWB.

[Welsh Anorak]

The confusing numbering didn't help much. The TV183D was the excellent A640, the TV183S was the even better A793 and one slip of the pen and you had the TV183SS with the A774.
I bought a good few A640s with supposed poor tubes from a local dealer ex-rental. One BC108 later (video circuit) and we had sparkling pictures! Luckily (?) we were one of the later areas to get full UHF coverage so single-standard mono sets were thin on the ground.