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 Everything is now connected up. I want to get the set going, even though it still lacks the EHT transformer. The picture tube won't be connected up yet either.

Nevertheless the radio section can be got going, and aligned.

One little problem. This set dates from long before the 'Belling-Lee' coaxial aerial plugs that we know today, even though these go back more than 60 years!

Instead there are two flat slots, one above the other, to connect to the two poles of a television aerial feeder. You can see these over to the left - the round holes on the right are for the radio aerial and a gram pick-up.

Although this arrangement looks like it might be a balanced aerial input, in fact it is not. One side is grounded, just like a modern domestic TV aerial. Once I've got everything else working, I'll measure the impedance of this - it'll be interesting to see if it comes to anywhere near the modern figure of 75 ohms.

But how to connect a television aerial to this very ancient socket?


Well, I was able to adapt a pre-war American mains plug. This meant changing the spacing and profile of its pins and shortening them, but the plug now fits well and could even pass as an original HMV television aerial plug!

Coaxial cable will be connected into this plug and the other end will go to a modern coaxial plug, suitable for connection to an Aurora 405-line converter.

The radio section was then switched on and tried. After a connection to the aerial circuit was fixed it worked first time. A very good radio is included with this set! Performance on all the bands appears to be excellent.

One of the tasks of the EHT transformer is to supply the heaters of the television section's valves, so the television section cannot yet be tried. I shall now await delivery of this transformer. Until then nothing much more can be done...


 ... except to re-mount the dial and band pointer, and give the radio section a complete IF and RF alignment. This proved to be slightly out.

On this set, the dial pointer is moved by a chain drive. The chain is quite fragile, and one of the links broke, necessitating a tiny repair involving a little solder.

At this point I receive a letter from a member of the Vintage Radio Restoration Board called line sync. He tells me that In the past he restored an original 907, and this still had the original electrolytic block atop its chassis. He includes some photos. So I now can create a copy of the original Dubilier (not Hunts) unit that was fitted. Thank you !

The rebuilt mains EHT transformer, which also supplies some of the valve heaters - has arrived. Today I fit it.

Mike Barker has done a really fantastic job here. This transformer not only will perform exactly as the 1938 original - it looks exactly the same too!

The power supply chassis is now complete and ready for action.

 Everything is now connected up and run up for the first time - on the variac. After some attention to the brightness and contrast potentiometers, and replacement of the volume control (the faulty one was not original), operation - of a sort - is obtained from the television.

The picture is much brighter than reported by the last owner, probably thanks to the tube rejuvenation process, but it is still rather insipid, with an obvious ion burn (as expected).

However I haven't even started to explore all the various adjustment options possible; nor have I looked at the IF and RF alignment yet...

 A full TV section alignment followed. This had to be carried out over two sessions, since two of the coils requiring adjustment were underneath the chassis and couldn't be reached when the chassis was upright on the bench. There seemed to be lots of wires to connect and disconnect when manhandling the heavy chassis units, and of course at all times I was very careful never to go anywhere near the mains EHT !!!

There's a minor problem that appears to be originating from Valve V3, early on in the Vision IF strip, whereby this takes off (oscillates) as the set is first switched on and then 'pops' into a stable state after a few minutes. I'm hopeful that valve replacement, or even just adding a top cap to the screening can, will fix this.

I am extremely impressed with the quality of Mike Barker's work on the EHT transformer, which not only looks correct, but is providing exactly the right readings under load. This is not the first time I have used him for demanding transformer work. In my opinion, the value of his contribution to the cause of keeping vintage televisions working ranks alongside RACS, to whom the tube will now have to be sent...

Yes, I'm afraid the effect of the rejuvenation didn't last, and the tube has now returned to almost its previous dimness. However, following alignment the underlying picture is now much better and I expect the set will deliver good results once the tube has been attended to.

The two restored plinths (skirts at the bottom of the cabinet) are now re-attached.  

A final touch before this set is put to one side to await the tube rebuild... a new label has been made to replace the torn and incomplete original.

Information was kindly provided by Brian Cuff about the label on his Marconiphone variant of this set (a 709). From this, an HMV equivalent label was worked up in Paint Shop Pro and then printed onto yellowed paper. An attempt at ageing the label was then made by lightly spraying it with clear lacquer.

Finally, the new label was lightly attached to the cabinet using spray-on Scotch paper adhesive. The original damaged label remains accessible beneath, for the benefit of future researchers.

The old label was slightly crooked - as is this one!

Well, it's been approaching two years... but the story now continues. The Emiscope 3/3 picture tube was duly despatched to RACS in France. I later followed up with a personal visit. They had encountered a problem when taking the vacuum down to air: cracks appeared in the pyrex around the EHT connector. The original tube was in separate parts and it's now impractible (and pointless) for it to be reassembled and returned.

The only solution now is to use a different tube. What can be done?

It just so happens I have an even earlier 9-inch pre-war tube in stock! This is an Emiscope 6/5, as used in the first generation of pre-war EMI television sets. This tube was used in some of their 1936-7 models whereas the 3/3 was used in the 1938-9 range. This 6/5 is in its original crate and believed to be new and unused. Its good condition has now been confirmed on the tube tester.

The 6/5 is a few inches longer than the 3/3 and has the earlier base but I've found it fits the HMV 907's rubber screen mask very well. Since the original tube now won't be coming back from RACS, this would appear to be a very acceptable substitute for a 9-inch EMI pre-war set.

This 'sympathetic' tube substitution will actually be easier than putting in a post-war 9-inch tube, since a later tube would have a wider deflection angle and there could be problems with providing enough scan power. Also, there could be complications regarding the area on the replacement tube over which the scanning effort (and focus field) should be applied. This might not be matched by the existing scanning & focussing coils.

The 6/5 uses electrostatic focus rather than electromagnetic, so there will be no need now for the focus coil. Fortunately, this 'new' 6/5 comes with its own set of scan coils, which I shall be using instead of those from the 907. I believe the 907's timebases should electrically match reasonably well into these, though there may need to be some minor mods. As it happens, I would have had to do this anyway, since the 907's original focus/scan assembly wouldn't have gone over the side-pin base on the 6/5 !

So the set will remain "all-EMI" and "all-pre-war". I also believe that doing it this way will ensure the set's market value will be maintained.


Time to trial-fit the replacement tube. The original mounting spars prove fine for the job. The only change required is the omission of a 'crinkle' type spacer around the neck within the rear bracket, and its replacement with a thick ring of felt. A long sponge pad is also added to the forward bracket where it passes under the tube.

The rear end of this tube is now 4½ inches proud of the back. A larger protection box will have to be fitted to the 907's back to cover this. It will have to be done so it looks original. I may have such a box amongst the other old television backs in stock...

The screen looks fine at the front and suitably 'vintage' in appearance... a post-war tube would not have looked as correct.

I've also tried irradiating the screen phosphor with an ultra-violet torch. This confirms it is white, and there appear to be no central burns either...

 I now have to make some minor changes to the set, to adapt it to use electrostatic focus. This replaces the former electromagnetic focus, which involved a focus coil.

First the original 3Kohm focus potentiometer must be replaced by one of a much higher value. The 'new' pot is here seen in the centre, before wiring up. It's a high voltage shrouded type of around 250K and is of a vintage design.

There now needs to be a lead run between the main and power chassis units so that the focus control can reach the tube bleeder resistor network. This entails fitting connectors at the junction. I've used a pair of Bulgins, which should be up to the job.

A high voltage decoupling capacitor is now also added to the focus feedpoint on the bleeder chain.

Apart from the focus connection, which goes to the 1st anode, this older tube also requires a voltage for an 'accelerator anode' (shown as 'acc' here). To start things off, I'll connect this to the HT rail via a 100K resistor. This is what was done in the set from which it came.

In the HMV 907, vision is fed to the tube cathode and 'brightness' bias to the grid. This is the other way round to the set from which it came.

Since the tube heater winding is locked to deck via a centre-tap potentiometer, there will be some voltage stress between heater and cathode. The only difference to before is that this stress will vary with the vision signal rather than be static and determined by the brightness control setting. I believe this will be OK...

The story continues... click here...

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