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  RESTORATION OF A 1951 BUSH TV22
                                                                                                    Page 6

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The labels are added. Next, to switch it on !

 

Well, a raster of sorts... My guess for the position of the ion trap magnet has proved almost spot on. Without this, I'd have got no raster at all.

At this stage, basic checks are done on the tube heater voltage, the HT, the tube's 1st anode voltage and the sound output valve's cathode voltage.

The Aurora converter is plugged in and the set tuned in. After first setting the channel knob adjuster for maximum sound, I am now adjusting the two coils on the RF input stage for maximum vision.

I'm not a believer in doing a full IF re-alignment on televisions unless it is clearly necessary. This is because damage to the little cores can so easily occur. With experience, it's possible to judge the state of alignment quite accurately from close inspection of the test card; also by looking at sensitivity, and checking for absence of interference between the vision and sound signals.

C25 (on the trader sheet) is set up for maximum width and general picture health. A large mirror the other side of the bench is useful during operations like these...

When a set is being run up for the first time, it's a good idea to gently waggle the valves to check the contacts are reliable. Despite having been cleaned and lubricated beforehand, sometimes they're not ! 

But after a few gentle circular motions (don't bend the pins!) any disturbances tend to disappear.

One thing worth checking is that the focus magnet is nicely centered about the the tube neck. You can adjust the position of this bracket to ensure this. I should have done this before, but it's only a five-minute job to whip this off and do it now.

 

The EHT checks in at 7Kv and since the U25 rectifier was a non-standard part, its heater glow colour is now checked - it looks very comfortable.

A picture and sound is obtained. The ripple toward the bottom of the picture is a camera artifact.

Now the set will be run for four hours continuously to 'wake up' the tube and generally settle everything down.

 

Next to tackle the inevitable 'niggling' faults. The line hold control cuts off altogether at one end of its travel. It proves too difficult to repair internally, so is replaced by another vintage pot - first stuffed with Waxoyl of course.

There's also an unpleasant jitter on the line timebase which causes ragged edges on the Test Card. It seems to improve as the set warms up. This is improved by replacing the 2M2 grid leak/load across the sync separator input with 470K and then abolished by fitting another PL38 line output valve.

 

A habit of mine with these sets is to to check the operating temperature of the line output transformer after it's been running a while.

The set is switched OFF and a finger pressed firmly on the top of the laminations.

This tells me whether the laminations are in good condition. These are - the transformer is only gently warm.

Another little touch I always do is to paint the top of the laminations matt black for better heat radiation.

 

Let's now look at the cabinet...

The picture mask and armour-plate screen glass are cleaned. The mask has some light crazing but once cleaned looks almost perfect. It is being left as it is.

The rubber insulation on the wire connecting the chassis to the internal cabinet screening foil is cracked and perished - as it usually is.

It suffers from the heat of the dropper nearby.

It is replaced with new black rubber-covered wire.

 

Fortunately this cabinet is already in quite fair condition. It is now polished with soft wood wax, applied sparingly - important this - and with some preparation beforehand using P.O. Polishing Paste No. 5.

The knobs are also cleaned. It's possible to improve the appearance of their markings by lightly scraping off the top layer of the gilt with a small screwdriver blade, under a magnifier.

When the cabinet is offered up to the chassis and slid back to its final position, it's important to ensure that the tube front face exactly abuts the back of the mask.

Almost invariably the earlier tube position set up on the bench will have to be changed.

The mounting bracket and rim band is loosened - and the tube pushed as far forward as possible. Then the cabinet is withdrawn and everything tightened up again.

Here the fastenings are loosened before the cabinet is slid back.

 

Another necessary job at this point is to ensure the line and frame hold knobs are adjusted on their shafts so that their faces are flush in their holes with the cabinet tightened up on the chassis.

But unfortunately this one thing I have forgotten to check..

The on/off volume pot shaft is sitting too high for the knob to be inserted and tightened.

This means I'll have to take everything out of the cabinet again. But it's all bolted together now so I think I'll leave this for tomorrow...

But after dinner I am filled with more energy and enthusiasm !  The pot position is soon put right and the back goes on.

However I have had to take both securing screws out to get the front knobs in through their holes. Then I had to insert the screws back into the knobs through the bottom of the set. This was a bit of a fiddle...

 

Purists may hold up their hands in horror but I am using new 2BA screws and large, shaped washers to secure the back. The washers are ground to produce flats on one side so they will correctly match up to the inner edge of the cabinet.

In my opinion it is far more important that the back is held properly on the cabinet, than to re-use the old fasteners in homage to originality.

When putting on the back of a TV22, don't forget there are also two screws (with washers) underneath...

Anyway, let's switch it on and have a look. Here's Test Card 'C' plus some reflections from the fluorescent lights !

This was taken after I had loosened off the centering magnet and bodily shifted it about - before re-tightening.

Note the rather wasteful 'Double-D' shaped picture mask. The earlier TV12 had a more rectangular mask.

 

There was one other thing to attend to though... something I've noticed this in other TV22s... the picture height expands by an inch or so over the first half hour or so from switch-on.

After a lot of head scratching and component substitutions, this was improved by replacing all the high value resistors in the frame timebase, despite their values originally measuring OK.

Some believe there may also be a LOPT dimension to this, with changes occuring in internal insulation leakage in the overwind as it heats up.

Scoping the output of the frame timebase revealed that the expansion was mirrored by the increase in voltage across the frame scan coils but not across the primary winding of the frame output transformer. Cooling the coils with a fan seemed to help, even though they are not running warm to the touch. Weird! (I'd already confirmed the frame output transformer primary winding resistance remains steady, and is the correct value, so shorted turns are unlikely there.)

So a small fan was installed, powered from a rectified dropper section, and this was arranged to blow across the scan coils, thence into the LOPT housing via a new hole punched in its inner side.

At this time the U25 fitted as EHT rectifier was returned back to the original EY51, now that I have them back in stock.

A re-gunned aluminised 9-inch cathode ray tube was also tried now, obtained from a French supplier. This turned out to have a faint shadow in the centre of the screen and is being returned to France for evaluation.

Anyway, this is one of the best TV22s I have ever come across. The cabinet is virtually pristine. I hope that in restoring it I have now made it better still.

And here's the owner and very valuable customer David White come to collect.

But has Cinderella's coach turned into a pumpkin? No, this is a fine G.E.C. BT 302 which is to be the next project.

 


Please note I am unable to enter into any correspondence if you are servicing your own TV22, nor can I supply spares. Thank you.

The story concludes.
   
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