Bush TV12B Restoration

[line sync]

Hi Mark
Great write up and nice to see it working.
Did you find the cause of the picture size increasing when the brightness control was advanced ?
I noticed from the picture showing the chassis fitted back into the cabinet that the silver foil is a bit ripped.
I`ve used aluminium kitchen foil to replace this and it looks good but care is needed when fitting it because it rips easily.

Robin

[mark pirate]

Hi Robin,

Did you find the cause of the picture size increasing when the brightness control was advanced ?

I suspect that the EY51 is to blame, I did swap out both the PZ30 and PL38 but they were proved blameless.

I do have some new EY51's but can't remember where they are at the moment
The problem is not severe, but I will change it when I find them.

Mark

[Tazman1966]

What a nice little set and a super write up. Well done Mark!

[mark pirate]

Thanks Tas, I must admit I am very happy it has turned out so well, it is not hard to see why people love these little sets, the cabinet is so pleasing to look at.
I just need to find a TV12AM to have the full set

I managed to find my NOS valves, so wasted no time in fitting a new EY51.
Once the PL38 was removed, access to the valve was easy with no need to remove the cabinet.

On close inspection, the old one does look very tired and darkened when compared with the new one.
Once soldered in place, the set was fired up and is much better for the new EY51. The EHT has increased by nearly 1kv, the picture is both brighter and sharper.
The picture still increases in size when the brightness is turned right up, but much less than it did before.

Mark

[Heatercathodeshort]

A cracking write up and restoration Mark. I have always preferred the TV12 to the 22. The RF unit is a work of art and must have been expensive to produce.

I put this TV12A aside in the late 1960's. It is the second receiver of my collection, the first being a Pye B18T.
It has not been touched in the last 45 odd years and with the help of a friend, managed to recover it from a top shelf in my collection.
To cut the story short, just a handful of capacitors and a pot clean has produced this picture. There is no trace of an ion burn on the original MW22-14C tube so I guess it had an easy life through the 50's.
If we switch them on at the same time it will probably be the only moment in the World that two TV12s are switched on and working together in 2016! Regards, John.

[mark pirate]

The RF unit is a work of art and must have been expensive to produce.

Hi John, I must agree with you there, it also used decent quality mica capacitors rather than the nasty little TCC caps that are such a fiddly job to change on the TV22.

Great picture on your TV12A, and no ion burn!
Looks like it has seen little use in it's life, my set looked to have been well used and then badly neglected. But has turned out better than I expected, although I did need to replace a few more components than you

Mark

[TV_Madness]

What an amazing restoration! Excellent, and thorough write up too. Well done! And that EY51 has yellow print, so the picture must look better than it did!

[Heatercathodeshort]

You 12B was a much more difficult job than mine but imagine if my example had been in a damp shed or loft all those years! It might have been a completely different story. Of course there are more capacitors to replace to bring it up to spec but it proves how well built these TRF receivers are. I did forget to mention that the 'VISCONOL' was leaking badly reducing the EHT to 2KV and soon disconnected.
The arrival of the EF91 and EF80 RF pentodes must have been well greeted by engineers of the day.
The EF50 was manufactured by many companies both at home and abroad. I don't think two were alike requiring realignment of the RF strip if any were replaced. Bush do state this in the service manual.
I have a RF unit in the workshop at the moment that suffers from sound on vision after a overhaul and clean. I will use this TV12A chassis as a rig to align it up correctly with the E2 and the frequency counter. Should be a nice job on a quiet afternoon.

[mark pirate]

I did forget to mention that the 'VISCONOL' was leaking badly reducing the EHT to 2KV and soon disconnected.

This is par for the course when restoring 60 year old TV's, like mains filter caps, these are the first thing to disconnect from the circuit. to be fair, all the capacitors are many decades past their expected service life, particularly when the set has spent many years stored in less than ideal conditions.

One thing that always amazes me is that the main smoothing/reservoir caps seem to survive. There are three large cans in the TV12, all of which have reformed perfectly.

The EF50 was manufactured by many companies both at home and abroad. I don't think two were alike requiring realignment of the RF strip if any were replaced. Bush do state this in the service manual.

I would certainly agree with that, it seems many Mullard EF50's were just rebranded American made 'Tubes'. In many Bush and Pye sets from the late 40's there seem to be a real mixture of both British and American made types in each set. There were also some 'special' types with two black stripes across the top.

The valves in the first two photos show the different types, one of these states 'British made', only to have 'made in USA' on the rear!
In my experience it seems the american types are a darker, more glossy red than the British type.

I have stripped the aluminium jacket from the zero emission valve removed from the Bush. As can be seen in the last three photos, it has a healthy getter and heater and no sign of any physical damage. Why there is absolutely no emission will remain a mystery.

Mark

[brianc]

Maybe there is an opec circuit between the pin and anode! I suggest the anode as there is more than one pin for the cathode!

[Sideband]

What a fantastic result Mark and an equally excellent write-up!

[Heatercathodeshort]

Hello again Mark,
I hope you don't mind me adding my TV12A to your thread but as the work was a lot less than yours I thought it pointless to open a new thread.

This afternoon I decided to tackle the second RF assembly from the TUG12A at the museum at Dulwich. It had gone mad, buzzing, sound on vision the lot after having worked quite well for a number of years! All the decouplers as you stated are silver mica so I set these aside and checked the alignment against the makers data. Most of the problems were located around the final vision RF amplifier and a replacement EF50 cleared most of this up.
All the valve pins had been very carefully cleaned when the receiver was overhauled originally but just to make sure they were cleaned again.
The alignment had drifted a small amount but enough to degrade performance. The sound RF's were about a turn out and peaking these at 41.5mc/s gave a marked improvement in sound output. It was still only 50% of my original RF unit and it was noticed that the sound reaction trimmer [gain] did absolutely nothing!
The cathode volts were zero on the Ist sound RF amplifier due to a short to earth on the trimmer. After much haad scratching I discovered that the insulating washer from the spindle was missing shorting the body of the trimmer down to chassis....
The sound rejector trimmer was correctly set and a final check made on the vision RF's.
A long soak test has proved stability. Time will tell. Regards, John.

[vidjoman]

Back to front test card, first time I've seen that in a while. Remember doing TV repairs in the 60s and using the mirror on the bench to set up the picture size etc.

[mark pirate]

I hope you don't mind me adding my TV12A to your thread but as the work was a lot less than yours I thought it pointless to open a new thread.

Not at all John, although I am rather jealous of that corrosion free RF unit, not to mention the mask

It seems that these EF50's are more troublesome than the later EF91 and EF80.
Or maybe it is just age,
Glad to hear you sorted it out though, as for my TV12, it ran perfectly for five hours last night. I contacted the former owner, who was amazed that I have got it working so well.

Mark

[Heatercathodeshort]

Thanks Mark. The corrosion free unit is the one from the TUG12A at the museum. Mine is very clean, just a bit dusty but after all these years I think I will leave the dust sleeping.
Cleaning it up might break the spell..
The 12 series are incredibly stable. I was so confident that I left it switched on all day while I was away doing non TV related work. It was still glowing away on test card C nine hours later. Regards, John.

[mark pirate]

There is one thing that puzzles me, why did Bush change the standard Belling Lee aerial socket fitted to the TV12 to the awkward terminals on the TV22?
This seems to be a strange thing to do, I have never seen this arrangement on any other TV. Pye used two wander plugs, Alba used a car aerial plug while most other sets had adopted the Belling Lee plug by the early fifties.

Mark

[Heatercathodeshort]

I suspect it was something to do with the cost of the Belling Lee co-ax plug and socket and possibly slightly poor connections leading to a loss of signal.
The saddle clamp used in the TV22 is completely secure allowing the transfer of every microvolt, an important point in fringe areas.
I think the TV11/12 was the first model to employ the traditional co-ax plug and socket.
J.

[mark pirate]

I think the only problem with the Belling Lee co-ax plug, is how it is connected to the coaxial cable. As we know, the centre core should be soldered to the pin!

Even today, I still see many plugs that have been poorly crimped or just have the centre core stuffed down the centre pin with no effort made to ensure a good connection.

Although the method of connection is undoubtedly secure on the TV22, there is an area of the centre core that is unscreened, so could still pick up local interference. I have had this when the set was too close to a switching PSU causing noise on the picture.

Mark