UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Television and Video

Notices

Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

Closed Thread
 
Thread Tools
Old 14th Jun 2017, 7:11 pm   #1
12jslater
Pentode
 
Join Date: Nov 2016
Location: Wolverhampton, West Midlands, UK.
Posts: 117
Default Making A Pre-War Style Television?

Down at my local charity shop there are around 4 televisions, 2 of which are the cheap 1980s type b/w 5 inch screen type. I wondered if I could take one of these, remove the internals and mount them in a wooden cabinet, and replace the controls with old radio knobs. Make it like the HMV 905.

What do you think, I mean it's not like we can easily get pre war sets.

Thanks, Jake
12jslater is offline  
Old 14th Jun 2017, 7:23 pm   #2
FERNSEH
Dekatron
 
FERNSEH's Avatar
 
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 7,444
Default Re: Making A Pre-War Style Television?

Would be a real fun project. But why not consider making a mirror lid television? Cabinet would be easier to construct.

DFWB.
FERNSEH is offline  
Old 14th Jun 2017, 7:29 pm   #3
12jslater
Pentode
 
Join Date: Nov 2016
Location: Wolverhampton, West Midlands, UK.
Posts: 117
Default Re: Making A Pre-War Style Television?

I would do a mirror lid, however I'm 15 and I don't think my parents would be too happy to have a great big television in my room. Plus I don't mind the wood work I do it in my spare time anyway and I'm fairly good.

Thanks for the suggestion.
12jslater is offline  
Old 14th Jun 2017, 7:36 pm   #4
TonyDuell
Dekatron
 
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 5,188
Default Re: Making A Pre-War Style Television?

If it's like the little 5" monochrome TVs that Maplin sold, then I can offer a few hints, as I've been inside and repaired that model.

There are 2 tuning knobs, one for the radio funtion (tuning capacitor), the other for the TV function (potentiometer, controlling a varicap tuner module). Two PCBs. One horizontal with all the TV circuitry and audio amplifier on it, the other vertical with the radio stuff on it. You could completely remove the latter if you didn't want the radio function. And you can extend the leads to the TV tuning pot to any (sensible) length.

IIRC there is a volume control on the TV PCB, you could mount this elsewhere in the cabinet and would probably have to extend the leads with screened cable. Three presets on the back, also mounted on the TV PCB -- brightness, contrast, vertical hold. No idea how they would take to being moved off the PCB on longer wires.

If you mount the CRT vertically and make a mirror lid set (what will you use for the mirror?) you would have to reverse one of the deflections (which one depends on which way round you mount the CRT). You can do this by swapping the appropriate wires on the yoke. Being monochrome there is, of course, no convergence, etc to worry about.

IIRC the ICs used in this set do have available data sheets so it wasn't hard to work out what was going on.
TonyDuell is offline  
Old 14th Jun 2017, 7:46 pm   #5
12jslater
Pentode
 
Join Date: Nov 2016
Location: Wolverhampton, West Midlands, UK.
Posts: 117
Default Re: Making A Pre-War Style Television?

Thanks Tony but i'll just make the 905 type set as I do not have room for a larger set, however your advice is still valued for the smaller set.

Thanks, Jake
12jslater is offline  
Old 14th Jun 2017, 9:54 pm   #6
julie_m
Dekatron
 
Join Date: May 2008
Location: Derby, UK.
Posts: 7,735
Default Re: Making A Pre-War Style Television?

If it's the type of TV I'm thinking of, with a little mono screen about 14 cm., a battery compartment underneath and a built-in radio, you should be able to modify it easily enough to be able to feed in baseband video and audio. Then you could add a set-top box, or use something like a Raspberry Pi to play suitable programme material through it.

PoundWorld have some rectangular wooden-framed make-up mirrors that you could cannibalise one of to make a replica mirror-lid set. Fun quiz time: What could you do to the set, that would reverse the picture on the tube so the reflection was the right way around?
__________________
If I have seen further than others, it is because I was standing on a pile of failed experiments.
julie_m is offline  
Old 14th Jun 2017, 10:33 pm   #7
Argus25
No Longer a Member
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
Default Re: Making A Pre-War Style Television?

Quote:
Originally Posted by 12jslater View Post
I mean it's not like we can easily get pre war sets.
Thanks, Jake
Jake,

You are quite right about that. In fact it has been estimated for some American pre-war sets there are only numbers left in the range of 11 to 20 sets of some types and for the HMV904 or similar perhaps about 40. This makes many pre war sets rarer than any violin made by Stradivari.

It is in fact possible to build a replica that is pretty darn close, it has been done here in Australia by Mr Victor Barker:

http://www.earlytelevision.org/barke...4_replica.html

(obviously we do more than drink beer down here)

But that of course does require a substantial working knowledge of vacuum tube & television technology which takes a while to acquire. However, it can initially give you an inspiration for the cabinet and dial. The dial was created from a scan of an original 904. There would certainly be plenty of room in a 904 cabinet to fit a TV set based on modern electronics.

When I was your age (back in the late 1960's) I became enamored with pre war television too, especially the articles on how to build TV's with oscilloscope tubes like the 5BP1 as the pre & post war versions of these were essentially the same. There were a number of articles published, including a very good one from Australia in Radio Television & Hobbies Sept 1957,
here is a link to a built one:

http://members.iinet.net.au/~cool386...0receiver.html

Finally after many years I got around to building Practical television's Argus:

http://worldphaco.com/uploads/ARGUS.pdf

I think it is admirable that you are interested in pre war television and the interest will take you on a great journey.
Argus25 is offline  
Old 14th Jun 2017, 11:20 pm   #8
Oliver35
Pentode
 
Oliver35's Avatar
 
Join Date: Apr 2016
Location: Halesworth, Suffolk, UK.
Posts: 188
Default Re: Making A Pre-War Style Television?

I dismembered one of those little sets, with the same end in mind- they're quite demountable, with a compact board and a separate carrier for the tuning knob etc. mine had an RCA video input, I seem to remember. Rotten little speaker, you could include a small amplifier and a larger speaker in your 'hack'.

I never got any further than extending the necessary leads on mine, although I still have the 'tube somewhere. I quickly became dissatisfied with the cosmetic approach, and marked upon building a pre-war style console set from scratch- although I'm still a long way off completing that!

I sometimes think about picking up another of these little B&W sets to make a mini working model of the Marconi 702, but that may never happen..

Oliver
Oliver35 is offline  
Old 14th Jun 2017, 11:29 pm   #9
peter_scott
Dekatron
 
peter_scott's Avatar
 
Join Date: May 2003
Location: Edinburgh, UK.
Posts: 3,273
Default Re: Making A Pre-War Style Television?

https://www.youtube.com/watch?v=GyqrXlco76M
peter_scott is offline  
Old 15th Jun 2017, 4:53 am   #10
TonyDuell
Dekatron
 
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 5,188
Default Re: Making A Pre-War Style Television?

Quote:
Originally Posted by julie_m View Post
If it's the type of TV I'm thinking of, with a little mono screen about 14 cm., a battery compartment underneath and a built-in radio, you should be able to modify it easily enough to be able to feed in baseband video and audio. Then you could add a set-top box, or use something like a Raspberry Pi to play suitable programme material through it.

PoundWorld have some rectangular wooden-framed make-up mirrors that you could cannibalise one of to make a replica mirror-lid set. Fun quiz time: What could you do to the set, that would reverse the picture on the tube so the reflection was the right way around?
I initially bought one when Maplin were selling them off with the intention of modifying it to feed in composite video, so that I could use it on my bench for testing home computers, terminals, etc that output TV-rate video. When I got it home I found there were 2 RCA phono sockets on the back to feed in audio and composite video, they had break contacts to disconnect the signals from the detector stage. So no modification needed.

I thought the mirrors in mirror-lid TVs were front-silvered to avoid multiple reflections. A 'normal' mirror might produce such reflections which would look horrible I think.

As for reversing the picture, didn't I comment on this in my earlier post? Just swap over the leads to the appropriate deflection coil.
TonyDuell is offline  
Old 15th Jun 2017, 5:48 am   #11
Karen O
Rest in Peace
 
Join Date: Jul 2011
Location: Bridgnorth, Shropshire, UK.
Posts: 787
Default Re: Making A Pre-War Style Television?

I have made such TVs myself using wooden bread bins. The effect is quite pleasing.

Many of those 5.5" TVs have A/V sockets on the back, which avoids the need for a UHF modulator.

The brilliance / contrast controls are presets on the rear. It is straightforward to replace these with proper controls.

Assuming you're modifying a monochrome TV, the HT is about 80...100V and is not too dangerous but I did get a nasty surprise when a whisker of wire pierced my skin

The EHT can give you a nasty jolt too - do be careful if you disconnect the tube from the PCB - the EHT can linger for quite a while and can get you when removing the anode cap.

I always connect a slim screwdriver to the tube earth connection (often no more than a strip of metal pressing against the flare) using a croc lead. I then slide the end of the screwdriver under the anode cap and wait for the telltale 'crack!'.

I tried to make a miniature Predicta using one of those TVs. Disappointing. It rather less resembled a Philco Predicta than it resembled a cheap 5.5" telly tube on a box. The tube is simply too deep to retain proportions.
Karen O is offline  
Old 15th Jun 2017, 2:07 pm   #12
beery
Heptode
 
beery's Avatar
 
Join Date: Jun 2006
Location: Ware, Hertfordshire, UK.
Posts: 988
Default Re: Making A Pre-War Style Television?

Hi Jake,
I actually converted one of those 5" Maplin sets to be dual standard, ie 625 and 405.
I didn't invert the video detector to make use of its VHF capable tuner, mearly used it with with the AV inputs. The linearity on 405 was not great, but is was used for basic picture comparisons between 625 and 405 line signal sources.

Cheers
Andy
beery is offline  
Old 15th Jun 2017, 3:52 pm   #13
Guest
Guest
 
Posts: n/a
Default Re: Making A Pre-War Style Television?

I very much like the idea of a mirror lid 5" scale replica. It's almost perfect for the relatively long CRT used in those portables. Enough room for a DTV converter and batteries too.

Oh no, I have started another project in my head.
 
Old 15th Jun 2017, 4:46 pm   #14
Philips210
Nonode
 
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,562
Default Re: Making A Pre-War Style Television?

Hi.

What a great idea for a project.

I have several 5" monochrome sets. I picked up two for £3 at the local car boot sale last year. One is a Deccavision made around 2000 and could be a good candidate to convert as the plastic cabinet is cracked and not worth fixing. The set had a frame fault due to duff dried out electrolytics which is now working fine. One of many projects to undertake, the problem is finding the time what with pressures of modern day life.

Regards
Symon.
Philips210 is offline  
Old 15th Jun 2017, 4:49 pm   #15
Philips210
Nonode
 
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,562
Default Re: Making A Pre-War Style Television?

Quote:
Originally Posted by beery View Post
I actually converted one of those 5" Maplin sets to be dual standard, ie 625 and 405.
Hi Andy.

Did you have to alter the tuning of the line output transformer for 10.125kHz operation?

Regards
Symon.
Philips210 is offline  
Old 15th Jun 2017, 5:37 pm   #16
Karen O
Rest in Peace
 
Join Date: Jul 2011
Location: Bridgnorth, Shropshire, UK.
Posts: 787
Default Re: Making A Pre-War Style Television?

I made one of those TVs work on 405. I first attacked the time constant of the line oscillator so that it could lock to 10.125kHz. This would lead to overscan and excessive EHT so I disconnected the line output supply before starting. I then powered the line output from a bench supply and brought that up until the line width was right. This worked but the EHT ended up on the low side resulting in a dimmish picture. But then it's an old, tired tube, isn't it?

Another issue is self resonance of the LOPT which should be three times the line frequency. When it's not, there may not be full energy recovery and consequent low efficiency. In practise, I didn't find this to be a problem.

The final step was to add a regulator to supply the new, lower power rail for the line output section.
Karen O is offline  
Old 16th Jun 2017, 12:30 am   #17
beery
Heptode
 
beery's Avatar
 
Join Date: Jun 2006
Location: Ware, Hertfordshire, UK.
Posts: 988
Default Re: Making A Pre-War Style Television?

Hi Symon,

I didn't bother with correcting the third harmonic tuning, though that might have solved the linearity problem.
I basically did exactly what Karen has just described, using an LM317 to drop the supply to the line output stage to about 7.5 volts IIRC (it was maybe 20 years ago now). The EHT seemed ok on my set though.
I then fitted a double pole relay activated by a latching push switch. The relay changed the time constant of the line timebase and of course switch in the LM317 for 405 line mode.

Cheers
Andy
beery is offline  
Old 16th Jun 2017, 10:58 pm   #18
Philips210
Nonode
 
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,562
Default Re: Making A Pre-War Style Television?

Hi Andy.

Very interesting, so it shouldn't be too difficult to get the line output stage to work at 10.125kHz. Thanks for the info, when I find the time I'll do some experiments on my little Decca set.

Regards
Symon.
Philips210 is offline  
Old 17th Jun 2017, 11:37 pm   #19
Graham G3ZVT
Dekatron
 
Graham G3ZVT's Avatar
 
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,675
Default Re: Making A Pre-War Style Television?

Hi Jake,

if you are going to make a prewar TV, I would advice you to make a caricature of a historic set rather than trying to make a replica.

Now that's a bit of an ask with a wooden box or console, or even the styling of an HMV905, but here's my suggestion, not pre war though and not even British. Reassemble a modern CRT mono (or even colour) set into a a caricature of a Philco Predicta.
Graham G3ZVT is online now  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 11:53 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.