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Old 18th Nov 2020, 4:43 pm   #1
Denis G4DWC
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Default What do you recognise in this?

A few weeks ago, someone on this forum said "we like pictures".

I went up in the loft recently and brought the items in the Pic down with a view to taking it all to pieces but after looking at it for an hour or so I decided to put it back again. Maybe I'll get it working one day.

Anything you recognise?

Denis
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Old 18th Nov 2020, 5:08 pm   #2
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Default Re: What do you recognise in this?

Looks like a very high quality home made tv.
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Old 18th Nov 2020, 5:11 pm   #3
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Default Re: What do you recognise in this?

A Philips/Mullard pushbutton UHF/VHF tuner and the two PCBs are from a Murphy Astra series TV’s UHF converter plinth. Plus an RBM line linearity control.
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Old 18th Nov 2020, 5:56 pm   #4
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Default Re: What do you recognise in this?

Was it from one of those huge school tv sets in a custom wooden box case with lockable doors on a tall stand? Must have cost a fortune.
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Old 18th Nov 2020, 7:41 pm   #5
Denis G4DWC
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Default Re: What do you recognise in this?

Yes it is a home made TV. I would have been about 21-22 when I made it

Dazzlevision is right. The IF PCBs are from a Murphy Astra Plinth. The Plinth originally sat under my very much modified Monster, 21" Pye Continental on legs that used to sit at the bottom of my Bed. A remote system switch was operated by a couple of car trafficator solenoids powered by a car battery that sat underneath the set and unfortunately leaked acid into the carpet. Mother wasn't at all pleased. I bet many youngsters don't know what a trafficator is these days.

The units were made in a 6' x 4' shed about 100 yards from Grim Joseph. The Timebase chassis circuit is a direct copy of a Rank Bush Murphy 171 or 181 I seem to recall. The Coax sockets between the two units is a link for the Sync. I haven't a clue what the missing valves on the receiver chassis were but I suspect I would have copied the Murphy Astra Video circuitry. I'll have to search online for a circuit. The Sync separator must be on the Timebase chassis. Over the years I've lost all the documentation on it, not that there would have been much originally. These days I document everything.

The Power supply used a large Gardners transformer I bought from an advertiser in PW and with the odd WW resistor here and there had all the voltages needed for the valve heaters in various series combinations.

There's a relay base missing as you can see from the Power supply. Adjacent to it was a VLS631 Thermal delay valve. The valve heaters would warm up via a Thermistor which was then shorted out by the relay and which also turned on the HT when the VLS631 timed out. There was a small push button to bypass the VLS631 to avoid having to wait every time the mains was applied when trying to get the whole thing to work.

The underside of the RF unit isn't very pretty at all and I remember it giving me a hard time trying to get it to work with no access to an oscilloscope. All I had was a home made multimeter, a neon screwdriver and an aerial.

The Audio amplifier used a Sinclair Module in a box I'd made with Bass and Treble controls. That connected to the 4 way Painton socket on the PSU.

My soon to be wife lived next door and together we built several items of furniture which included making the cabinet for this. It was some time later I realised what other courting couples got up to!! Never thinking we would ever be able to afford a colour TV we made the cabinet large enough to take a 26" Colour tube just in case. It was a console arrangement made from Mahogany veneered Conti Board the same height as some Loudspeaker cabinets we'd made previously. The Power supply and 10" x 6" loudspeaker in the bottom and a full width shelf which took the RF and Timebase chassis. Some Handy Angle (a bit like Dexion) provided some rigidity at the front and also gave strong fixing points for the 24" CRT and Philips tuner unit.

It was about 23:00 one night when we thought we would glue the cabinet together. Annoyingly I couldn't get the dowels to drive fully home. Fiance's parents had gone to bed so we took it out in the street put a blanket on the path and with a block of wood and a mallet finally hammered it together. The most difficult part of the cabinet was cutting the hole for the CRT in the piece of thin veneered plywood. I cut it the size of the cabinet and put a rough hole in the middle then it was file and sand it to fit the CRT. It took several evenings. I have to say the fit wasn't bad at all.

Overall it was an interesting project and one that was reliable and used for several years of our early married life. I don't recall it ever going wrong.
We did manage to to afford a 26" Colour CRT some years later and did convert things to colour in the same cabinet but that's another story.

Denis
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Old 18th Nov 2020, 7:50 pm   #6
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Default Re: What do you recognise in this?

Much impressed, as much by the statement that the wife to be helped, as to the build.

I tend to believe that the approach to build ones own gear/furniture that was around then has just disappeared from the UK in general now, probably find the attitude is in India/Pakistan and budding countries where you can not just nip down to the supermarket.

Why not get it back into action?

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Old 18th Nov 2020, 8:00 pm   #7
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Default Re: What do you recognise in this?

Yes, a very understanding and supportive girlfriend - definitely a keeper!
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Old 18th Nov 2020, 9:04 pm   #8
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Default Re: What do you recognise in this?

A very impressive bit of home construction!

The smaller of the two Murphy panels had a Mazda 6F28, which was the (dc coupled) video amplifier (at least, in the Astra TV sets with VHF/FM radio built in). The other valve on it was a 6F23 6MHz sound IF amp.

The larger panel had a three stage vision IF amp, using 6F23s - so plenty of gain - which was definitely needed, given the original Philips valve UHF tuner in the Murphy 625 converter plinth.
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Old 19th Nov 2020, 3:10 am   #9
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Default Re: What do you recognise in this?

It looks much nicer than what I remember of the inside of old black and white TVs back in the early seventies. They were usually 5 to 10 years old before we got them, maybe lasted a couple of years before they stopped working, and then sometimes able to get them going again by swapping tubes from the last one that was still in the outhouse, or resoldering a couple of bad joints. They were normally replaced only if we were given a better replacement or completely dead, then stripped of anything that might be kept to keep the next one going.

I never knew or learned much about how they worked or how to fault find properly. Just what my uncle would call a bottle changer, at least for TVs. I was much more interested in computers and the box of old ttl and other bits that he gave me.

I’m impressed you built your own TV and it sounds like you should keep it just for the memories even if it never works again.
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Old 19th Nov 2020, 9:52 am   #10
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Default Re: What do you recognise in this?

What a wonderful story and also, a very tidy and impressive bit of construction.

Thanks for sharing that, Denis. I sense something of the magic of using a home-built set as an integral part of life.
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Old 19th Nov 2020, 11:35 am   #11
Denis G4DWC
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Default Re: What do you recognise in this?

Thanks for all the comments it's sort of rekindled my interest in it. I'm grateful to Dazzlevision for the Valve assignment on the Astra Plinth PCBs. That's making some sense but what of the other three valves mounted directly on the chassis?

For anyone who's interested and looks at the picture of the underside of the RF unit, at the middle left must be the the Video Amplifier/Sound IF PCB Dazzlevision mentioned. Was this just a video preamplifier on the PCB and the main Video Amplifier supposed to be in the Astra set proper or was this normally routed via a system switch direct to the CRT Cathode?

At the Top left is a yellow wire that splits two ways. One way though a tubular Ceramic to what I assume is the Video Amplifier proper as the Blue wire above goes to the Black 4mm socket that I know went to the CRT cathode.

To the right of this valve is a B7G valve holder and I can't remember any sets of that mid 60s era having a B7G base apart from maybe an EB91.

Further to the right, on the right of the Chassis capacitor is another unknown valve but the Yellow wire going to that Belling Lee Coax socket is the Sync output to the Timebase.

There must be some AGC arrangements in those three valves stages.

Any ideas would be appreciated. I haven't managed to find a circuit on line of that Astra Plinth so far.

Oh, nearly forgot. Yes Paul, she has definitely been a keeper especially on late night Cumulative Amateur 432MHz contests on hilltops in the snow, restoring Motorbikes and helping with the building of two new cars.

Thanks.

Denis
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Old 19th Nov 2020, 12:39 pm   #12
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Default Re: What do you recognise in this?

The 6F28 was the video output stage and directly fed the CRT’s cathode via the system switch.

I have the circuit for the Murphy UHF converter. There were two versions. One for non-FM sets and one for sets with FM radio built in.

The vision AGC circuit is the main difference between the two (gated or mean level).
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Old 19th Nov 2020, 1:01 pm   #13
Denis G4DWC
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Default Re: What do you recognise in this?

Thanks for that additional Info. I hadn't realised there were two versions of the plinth. I'm pretty sure that the problems I had when getting it all to work were AGC related. Interesting that Mr Murphy intended the Video Amplifier in the Plinth to directly drive the CRT via the system switch. That's given me a clue that one of those valves is probably a cathode follower I'd added.

Small steps....

Denis
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