Restoration of a 1937 first generation pre-war television (HMV 900)
 

Hi,

This thread will discuss the restoration of a first generation pre-war television dating from 1937. In writing this thread, my intention is to make it accessible and hopefully interesting to both non-experts and experts alike. Previous feedback has shown people like a certain amount of back-ground explanation, but, I don't want to get too bogged down with the basics, and so I'll try and keep a balance. Feedback has also shown people like a lot of photographs (rather than simply exposition), and so I'll try and put in as many as I can.

The start of the story/restoration is when someone called Mark Parsons back in 2014, appeared on this forum asking about his "HMV 900", which was his grandfather's. This was interesting in itself because this suggested it was a previously unknown first generation set survivor, which had been passed down the family, and would hopefully be untouched since about 1950 and completely original - which makes for the perfect restoration.

After advice on this forum about its value, he later put it up for sale on ebay, and I bought it.

If you've never seen a pre-war television, and especially a first generation pre-war television, the first thing that will strike you is they're huge and heavy, and the CRT picture is small. This HMV 900 is about the size of a sideboard. Because they're so heavy they have castors so that you can wheel them about without lifting them.

Picture 1 shows an artist's impression of a first generation television taken from a popular science book of the time (aimed as always at children). That picture conveys the basic essentials of a first generation set, they're extremely large, they're packed full of multiple chassis containing 1930s sized electronics, which makes them large and heavy, and the CRT is so long it has to be mounted vertically, and the picture viewed using a mirror. This is why first generation sets are called "mirror lid" sets.

Peter Scott has produced some web pages which discuss first generation sets, and the general background to the introduction of high definition television in 1936 here http://www.nostalgiatech.co.uk/Vintagetech.htm.

After I bought the set, I arranged for its collection from London. On arrival after paying over the money, he announced the set couldn't be wheeled on its castors as it might damage his new floor (stripped pine floor). Cue you do know how heavy this is? To no avail. In the end we had to remove as many of the chassis as possible, and then half drag (on a piece of old carpet) and half carry the television out of the house.

On getting it back home to Wales and into the house (with the help of a neighbour as it needed three people to get it up the rise from the road), I put it back together, took some "as found" pictures and then left it where it was for the next year. This is because I was busy at the time on my first pre-war television restoration (a HMV 904, the restoration thread of that is here https://www.vintage-radio.net/forum/...d.php?t=115533).

The next four photos are some of those taken at that time.

The first thing you should see is the television is very original, and has probably been untouched electronically since the re-introduction of television in 1946, which is when it would have been serviced.

The second thing you should see is it has some signs of being stored in a damp environment (i.e. rust and damage to the cabinet). Some parts are worse affected than others. Whether coincidence or not, anything at the bottom of the cabinet is more corroded than chassis which where mounted away from the bottom of the cabinet. So this means the PSU (power supply unit) was considerably more corroded than the "television" chassis (sync and trf video) which apart from a small visible patch of rust looked in very good condition.

Which meant although it was not in wonderful condition, it looked in considerably better condition than my other two pre-war televisions (the HMV 904 I was working on at the time, and a Murphy A56V).

I was tempted to switch work from the HMV 904 onto this, but, resisted the temptation, and only after the completion of the HMV 904 restoration in late 2015, did I start to do any work on this television.

Re: Restoration of a 1937 first generation pre-war television (HMV 900)
 

I love the artist's impression, a real period piece, with the couple both smoking in their big armchairs, and the "laboratory" on the left! But the artist clearly didn't understand how the mirror-lid worked - it looks as if he thought the "screen" was something that hung down from the lid. The picture should, of course, be a reflection positioned "behind" the lid. That sort of thing really annoyed me as a child - how could I understand it if he didn't?

Anyway, can you tell us the source of the illustration, please?

Les.

Re: Restoration of a 1937 first generation pre-war television (HMV 900)
 

The "Condenser" is pointed out as a major part like the tube or timebase.
Maybe the artist thought it was like one in a fridge or a still!
One thing that I find strange is why the mirror was full length of the lid reflecting not just the tube face but the controls as well ? Why didn't they fit a smaller mirror to reflect just the tube face? I have never watched anything on a mirror lid set but wouldn't it have been less distracting?
Good luck with your restoration!
Rich.

Re: Restoration of a 1937 first generation pre-war television (HMV 900)
 

Unlike the picture frame that "condenser" really is there and quite a major component.

Peter

Re: Restoration of a 1937 first generation pre-war television (HMV 900)
 

There's an HMV 900 here in the shop which is said to be a very early production model. The cabinet is slightly narrower than most other 900 models and there is only one strut to hold up the mirror lid.

DFWB.

Re: Restoration of a 1937 first generation pre-war television (HMV 900)
 

I'd love to get the chassis and cabinet serial numbers from your 900 David and also your 902 if possible.

Peter

Re: Restoration of a 1937 first generation pre-war television (HMV 900)
 

Hi Catkins,
As always, I'm very keen to read your restoration write ups.
I must admit, I'll be a bit jealous of this one as an EMI mirror lid is very much on my wanted list. I missed the chance to but a 702 a few years ago as the timing was all wrong, I was between jobs and had nowhere to store such a thing.
I hope to get hold of one someday, though I'm not too bothered it if has already been restored.
I got a spare Bulgin standards switch kicking about somewhere, if you are interested in putting the facility back, but I figure it must require a 'U' shaped bracket to be fabricated to hold the switch below the escution rather than simply be fitted to the escution on its own (as I have seen in one so-called 'original' set). Such a bracket would probably be attached to the timebase chassis using those lovely EMI self tapping screws, so there should be some witness marks one would think.
For my HMV905 restoration I had missing brackets made from 2mm Zintec and the look compares quite well with the age darkened cadmium plating of the chassis.

The American pots, well you will have seen them in your 904 I expect. I did get a very poor example of an incomplete 907 chassis to help with the restoration of my 905. It did yield some of those American pots, but alas they were too corroded to be of any use, so I had to fit Colvern pots in the end. At least the scrap chassis provided me with the Morganite dual Brightness and Contrast control.

Anyway, I need to stop writing waffle.

I look forward to your next instalment.

Cheers
Andy

Re: Restoration of a 1937 first generation pre-war television (HMV 900)
 

Good to see another ‘pre-war’ thread. I doubt I’ll ever be able to find or afford one, but I love the early sets.

Oliver

Re: Restoration of a 1937 first generation pre-war television (HMV 900)
 

Yes, it was an inverted U with feet _|-|_ if that makes sense.

Peter

Re: Restoration of a 1937 first generation pre-war television (HMV 900)
 

Hi Peter,
here is the model I.D. plate on the HMV 902. No indication to model type. It's the same with the 900. Both sets are described as machines!

The 900 has all the original chassis assemblies. When I get a chance to examine it I'll supply you with the chassis numbers.

DFWB.

Re: Restoration of a 1937 first generation pre-war television (HMV 900)
 

Thanks David the chassis numbers would be great. Sorry, I forgot that you had already sent me a photo of the 902 cabinet serial plate. Did you get the 900 from the same source?

Thanks,

.Peter

Re: Restoration of a 1937 first generation pre-war television (HMV 900)
 

Hi Peter,
The 902 was bought in the autumn of 1988 from the late Gerry Welles.
The set had been rescued from a house in North-West London. Bits of it were found in the garden. Gerry made a new power supply chassis because the original was too far gone with rust.

Bought the 900 sometime in the 1990s.

DFWB.

Re: Restoration of a 1937 first generation pre-war television (HMV 900)
 

Yes, stuff like that annoyed me too. There was another picture of a real mirror lid television (a Marconi 702) and so it was clear as to what it should look like. That would have been the first picture of a mirror-lid television I would have seen.

The previous picture was an excerpt from a larger picture.

I've attached both photos.

It's from a book called "Miracles of Invention and Discovery" published by Odhams Press Ltd.

I would have got the book about 10 years old from a jumble sale, about the time I started to get interested in electronics and old radios.

Re: Restoration of a 1937 first generation pre-war television (HMV 900)
 

I'm assuming it's to give some leeway over the horizontal viewing angle, otherwise only a 'straight-on' viewer could get a full view of the screen.

Re: Restoration of a 1937 first generation pre-war television (HMV 900)
 

Book ordered!
Thanks.

Re: Restoration of a 1937 first generation pre-war television (HMV 900)
 

Hi Beery,

The bane of moving between jobs, when you often have to relocate, especially when you're young you seem to end up following the jobs. During that period of my life I found it difficult to do any collecting. I didn't join the BVWS or seriously start collecting again until my late 30s, as I was wary about getting saddled down with too much stuff.

I think I mentioned this in the previous post. The major stumbling block with putting everything back is the riveted top mount blanking plate. I'm not comfortable with removing it, especially if it was fitted before leaving the factory.

It would be nice to have some of the missing circuitry, but if I don't think I'm going to use it .....

But I'll be interested in seeing a photo of it.

American pots, yes, there's some in the 904 and quite a few in the 900, and I've had problems with insulation breakdown. But a lot seem to be used in high voltage places. They're certainly not the worst I've seen. The Murphy A56V had open backed wirewounds, and they all were completely open-circuit on the chassis, and many of the carbon track ones were way of spec too.

None of the 30's vintage pots I've acquired had the right resistance (how come however many you have, they're never the value you need :) ), and I used Colvern pots from about 1950. They work and do look better than modern replacements.

Re: Restoration of a 1937 first generation pre-war television (HMV 900)
 

There's no need to remove the blanking plate. I did consider building the V8 circuitry on a separate panel that made no permanent change to the chassis but then I realised that if you include inverted line pulses in your 240 line signal then you don't need the V8 circuit at all and you can watch 240 line complete with 25 Hz frame flicker just as nature intended!

Peter

Re: Restoration of a 1937 first generation pre-war television (HMV 900)
 

I was hoping you would say that.

Does it rely on generating the 240 line signal via a video graphics card, and/or is it circuitry interposed between the standards converter and the television?

Re: Restoration of a 1937 first generation pre-war television (HMV 900)
 

Hi Catkins,
Here is the correct switch, a Bulgin S301.
It is not a change over switch as such, but has two N/C and two N/O contacts that are connected as four separate switches, ie there is no common contact between them.
These are quite rare. A 1950's Goblin Teasmade has a slightly lager bodied switch with the same function, but the actuator lacks the pre-war style bobble top.

Cheers
Andy

Re: Restoration of a 1937 first generation pre-war television (HMV 900)
 

I imagine the Aurora World converter will generate the original Baird frame syncs. Clearly the 405 line Aurora doesn't generate 240 line signals.

It might be that Frank could arrange to have the inverted line pulses in his plan for a multi-standard Hedghog converter.

The video graphics gives you the pulses by default.

Peter