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1953 (Coronation year!) HMV 1824 television set..

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mark pirate
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I just use a pair of standard wander plugs to connect my Aurora, works fine on sets with this type of aerial socket.

 
Posted : 09/06/2013 12:16 pm
IJK2008
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Marion

I have a few wander plugs that will do the job. You are welcome to 2 if you would like them. I used these in my Pye LV20 - there may be a photo on that thread showing the aerial lead. What I did was strip back the cable end and soldered PVC insulated wires on to the conductor and screen hiding the soldered connections with a bit of sleeving or heat shrink. It works fine.

I got the wander plugs from Birkett's - they may have some left. Farnell also have new ones - but they are not cheap.

PS My post has crossed with Mark's.

Cheers

Ian

 
Posted : 09/06/2013 12:21 pm
Katie Bush
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Marion

I have a few wander plugs that will do the job. You are welcome to 2 if you would like them. I used these in my Pye LV20 - there may be a photo on that thread showing the aerial lead. What I did was strip back the cable end and soldered PVC insulated wires on to the conductor and screen hiding the soldered connections with a bit of sleeving or heat shrink. It works fine.

Cheers

Ian

Hi Ian,

That's very good of you to offer, and I've just got to say 'yes please'.. I'll PM you shortly.

I always though it was necessary to insert a 'balun' or similar type of circuit to adapt from 75Ω coax to twin feeder? Though I guess that given the Aurora's output power, and the shortness of lead length being used, these "technically correct" methods can be waived?

Now.... How about the EHT cap and the burning paxolin?

Well, I've found a short piece of 'blue polythene' underground waterpipe which is perhaps a shade over the top, but it's the nearest thing I can find that will accommodate the diameter of the new cap.. I have already cut it down to the same length as the old waxy, and have it in mind to try plugging the ends, once the new cap is hidden inside, then wrapping the whole thing in insulating tape, in an effort to disguise it as a 'black beastie' or something.

I will need to extend the leadouts from the new cap, and also have in mind to pinch some sleeving from the EHT wiring out of an old microwave oven, to insulate the new leadouts.. I'm taking pictures as I go, so lets set what kind of a mess I can make by tea-time?

Marion

 
Posted : 09/06/2013 4:00 pm
Anonymous
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I always though it was necessary to insert a 'balun' or similar type of circuit to adapt from 75Ω coax to twin feeder? Though I guess that given the Aurora's output power, and the shortness of lead length being used, these "technically correct" methods can be waived?

Yes.
I have a few 300 TV baluns that alleged to work 40MHz to 900MHz if anyone needs one ever. They are not complicated to make either, especially if you only need VHF.

With a mismatch you get Ghosts (distance on screen related to distance x2 as 1st ghost is 2nd reflection, the next ghost will be fainter as it's 4th reflection). Also the cable radiates and picks up local interference as the outer becomes an "aerial".

If you have lots of signal you can make an attenuator that is 75 Ohms for coax and the impedance at 300 Ohm socket irrelevant as the wire so short, only a few resistors.

I've stuffed the end of coax in holes held with match sticks for test ...

The resistive attenuator pad is good if it's a long 75 Ohm cable and the "wander plug" socket on equipment is a semi-random impedance as then the mis-match is reduced by twice the attenuator value. The "typical" balun is useless unless the socket really is 300 Ohms balanced about earth. There is a second type balun circuit which is not really a balun, and that is a 2:1 transformer. That makes 75 Ohms be 300 Ohms, it's narrower band than a true balun but it is "floating" so the 300 Ohms can any amount of unbalance.

 
Posted : 09/06/2013 4:23 pm
sideband
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and have it in mind to try plugging the ends, once the new cap is hidden inside, then wrapping the whole thing in insulating tape, in an effort to disguise it as a 'black beastie' or something.

I will need to extend the leadouts from the new cap, and also have in mind to pinch some sleeving from the EHT wiring out of an old microwave oven, to insulate the new leadouts.. I'm taking pictures as I go, so lets set what kind of a mess I can make by tea-time?

The idea is sound but I'm not sure about 'wrapping it in insulation tape'. Not sure what insulation tape is like at EHT voltages. Heatshrink might be better. Alternatively you could encapsulate or 'pot' the assembly in araldite and then the EHT leads from the old microwave can protrude through the 'potting' at each end. It's up to you of course and whatever is easiest.

Rich

 
Posted : 09/06/2013 4:30 pm
Anonymous
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625 a line is a bit less than 64us visible, so 1/400th delay ( a ghost that softens image) is 6400/400 ns = 16 ns
That is coax distance x 2. Speed in coax is closer to 200M m/s than 300M (vacuum or air) so 1us delay is 100m, 1ns is thus 10 cm, 16ns is 160cm

450 line visible is about 1.54 slower, resolution a bit lower so maybe regard 32ns approx as minimum, that's 320cm.

So as approximation perhaps for 625 if cable is less than 1m or 3' approx and 405 if cable is less than 2m or 6' approx any mismatch might not be noticeable?

All figures very approximate just to have an idea of magnitude.

 
Posted : 09/06/2013 4:42 pm
Katie Bush
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Hi Rich,

Well, I'm yet to get a proper start on it... Other little things keep cropping up to stop me, so I can still vary the plan.

I have to say though, the insulating tape would only be on the cylinder wall, not the ends.. I couldn't imagine faffing about with little bits of tape, trying to make it look tidy.

I still have yet to "harvest" the insulation from the microwave oven, so not progressing at all well.

Marion

 
Posted : 09/06/2013 4:44 pm
Anonymous
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You don't have a suitable old Bingo / giant felt pen marker case?

PVC tape is naff. Even some Laminator wallet split and wrapped into a tube and then heated to Glue it, then sprayed suitable colour, then the cap held in place with a little glue gun at each end?

 
Posted : 09/06/2013 4:45 pm
Terrykc
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... Another thing that comes to mind.. This set would have originally had a 'twin feeder' lead to the aerial, as apposed to the more conventional coax.. What's going to be the best way to match up my Aurora (coax) output to the set's twin feeder input?

Are you sure about this, Marion? You have the service data - what does it say?

Don't forget that the common or garden Belling & Lee connector wasn't the de facto standard when these sets were built - Bush were still using terminals and saddle clamps for 75Ω coax at the same time.

I doubt that the 300Ω/75Ω imbalance would cause you any problems but it might be intuitive to examine the input circuitry if the manual doesn't give you the answer. If the input coil is centre tapped with the 'earth' terminal going to the centre tap, then the centre tap to one end is 75Ω input, with 300Ω across the ends (don't overlook that a 2:1 turns ratio is a 4:1 impedance ratio ...)

When all else fails, read the instructions

 
Posted : 09/06/2013 4:57 pm
Katie Bush
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... Another thing that comes to mind.. This set would have originally had a 'twin feeder' lead to the aerial, as apposed to the more conventional coax.. What's going to be the best way to match up my Aurora (coax) output to the set's twin feeder input?

Are you sure about this, Marion? You have the service data - what does it say?

Don't forget that the common or garden Belling & Lee connector wasn't the de facto standard when these sets were built - Bush were still using terminals and saddle clamps for 75Ω coax at the same time.

Hi Terry,

Not sure at all, really.

I've had a look at the circuit diagram, and it shows a coil across the RF input, and no centre tap.. The Earth connection is via a low value capacitor to the cabinet foil.. So, you're probably right about it being 75Ω, though where I can see the logic of the AE connector used for coax in early Bush sets TV24 etc. for coax, this one just looks more likely to have been a twin feeder.

Now.... Back to this blessed capacitor.. I'm hanged if I can find anything I'd be happy to use to 'bung' the ends of my polythene tube.. I'm thinking seriously in terms of just using the tube as shielding, and placing the capacitor inside it, with the ends open.. It's quite a big chunk of plastic, and I have reservations as to the potential fire risk it may present.

Right now, I'm trying not to let myself get too bogged down in sorting out this single issue, which has taken up too much time as it is.

I have a busy week, this week, with two hospital trips to contend with, plus my normal shopping trip, and it's looking like Friday before I can really get into making any headway again.. I'm just a bit keen to get on with replacing those caps, and general fault finding.

Marion

 
Posted : 11/06/2013 12:16 am
Marc
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Now.... Back to this blessed capacitor.. I'm hanged if I can find anything I'd be happy to use to 'bung' the ends of my polythene tube.. I'm thinking seriously in terms of just using the tube as shielding, and placing the capacitor inside it, with the ends open.. It's quite a big chunk of plastic, and I have reservations as to the potential fire risk it may present.

Hi Marion,

Not sure if this idea would be any good, but what about using an old 35mm film container to pot the cap in

Marc.

Marc
BVWS member
RSGB call sign 2E0VTN

 
Posted : 11/06/2013 12:35 am
Terrykc
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... I've had a look at the circuit diagram, and it shows a coil across the RF input, and no centre tap ... though where I can see the logic of the AE connector used for coax in early Bush sets TV24 etc. for coax, this one just looks more likely to have been a twin feeder ...

Hi Marion, I've looked at the circuit of the earlier 1807 which I would expect to be similar and that is definitely has an unbalanced input, although it is shown as 50Ω.

The multiple aerial sockets on the 1824 as seen in the photograph suggests that a simpler method of including the optional attenuator has been used (or that the plug operates the switching when the A2 socket is used) ...

I would treat it as 75Ω unbalanced ...

When all else fails, read the instructions

 
Posted : 11/06/2013 12:31 pm
Katie Bush
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And at last,

We will be moving ahead on this project, shortly.

I now have some interesting parts to assemble into a fake cylindrical capacitor.. It will consist of the ceramic cap, to replace the original waxy, a short polythene tube (waterpipe) and a couple of black plastic discs from a kids game (pogs).. I have also 'harvested' some EHT insulating sleeve (if it will strip cleanly away from its original wiring).

So, over the weekend, I will be taking some pics of the bits and pieces, and attempting to shape and fit these parts together, ultimately, fitting them into the set.. Once done, I can get back to changing some caps, and checking/changing some resistors.

Aches and pains aside, of course. 

Marion

 
Posted : 14/06/2013 11:13 pm
Till Eulenspiegel
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While looking thought the June 1960 Practical Television I noticed that Les Lawry-Johns did a write up about the HMV 1824 series. The article is a continuation from the previous month. L L-J wrote excellent articles about servicing TV receivers and along with the first class diagrams produced by the PT team one could in those days do fault finding in TV sets much easier.
The May and June 1960 PT magazines might exist in the VRAT library.

Till Eulenspiegel.

 
Posted : 06/08/2013 7:04 pm
Katie Bush
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Hi Till,

I'll take a look and see.. I do want to get things moving on this set, but I seem to be dogged by little health problems of my own that keep getting in the way. 

I had some bit put aside, ready to build up the EHT capacitor, but I think Lucy (one of my cats) has had other ideas for them.. I'll need to round them up again.

As you might know, I had a bit of an unscheduled pit-stop yesterday, and that just goes to add to the problems at the moment.

I'll have to give the HMV a little warm-up again, and re-familiarise myself with what lies within.

Marion

 
Posted : 07/08/2013 10:36 pm
Katie Bush
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I had some bits put aside, ready to build up the EHT capacitor, but I think Lucy (one of my cats) has had other ideas for them.. I'll need to round them up again.

Marion

Guess what?

Lucy has yielded up the capacitor building parts.. Hidden away with a few other things - the little darling!

So, notwithstanding the shrub project, I aim also to give the HMV some bench time, over the coming weeks. :aad

Marion

 
Posted : 21/10/2013 11:05 pm
Till Eulenspiegel
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The very last real HMV TV set to be made by EMI was the model 1854. A two band 17" table model which according to the 1957/58 Radio & Television servicing book was a set that employed a printed circuit board.
This 1956 or 1957 set employs many circuits which are similar to Marion's 1824 of 1953. The cabinet presentation of the 1854 is also similar to the 1824. It's got that EMI look about it
So when a service manual for the 1854 turned up on ebay I had to have it. Well, it would appear that the 1854 is really a hand wired set and the printed circuit board is a tiny thing that carries the PL81 and PY81.
Nevertheless, it would be an interesting set to acquire. I doubt if EMI made many 1854 sets or the Marconi version the VT153. The next HMV model, the 1864 was made by Ferguson. The first TV set to made under the twenty-one year contract between Thorn and EMI. The deal was signed in 1956. In 1977 Thorn consumer Electronics (TCE) declined to continue marketing HMV and Marconi branded products and the HMV name was sold or licenced to Fidelity Radio Ltd.

Till Eulenspiegel.

 
Posted : 30/04/2014 1:29 am
Till Eulenspiegel
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Picture of the HMV 1854.

Till Eulenspiegel.

 
Posted : 30/04/2014 12:05 pm
Katie Bush
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Hi, yes...

If I can only get on top of things again, I want to advance this set a little further.

As it stands, it has first light, and we can see a clear and well focussed raster, albeit a bit dim and geometrically challenged.

The trouble now is, I've acquired more sets with stronger life-force and you might say, the moment has passed, with regard to the Coronation broadcasts.. That's not to say the set can be neglected, far from it, but with my back problem dictating terms right now, I am sorely tempted (bad choice of words) to look at the less demanding sets - ie. the ones that can be considered as working, but in need of work doing.

Now then,

The set in Till's picture looks interesting, and does have a certain HMV character about it.. I can honestly say I've never seen one, or at least not that I can recall.

I wouldn't mind one of those - or on the other hand, maybe I have enough to be going on with?

Marion

 
Posted : 30/04/2014 10:18 pm
Till Eulenspiegel
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Hi Marion,
Yes indeed it would be an interesting project to restore one of the last true EMI TV sets.
I'm often reminded that the 1824A, 1842 and the 1854 series were very unreliable sets. The CRTs would go low emission after only a year, it was said that there were design problems, although looking at the circuit diagrams I would say these sets appear to be pretty competent enough. The construction quality is good. Excellent service manuals were issued to dealers. I think the only thing to do is find an example and put it through a thorough examination to find it's good points and the bad ones.

Till Eulenspiegel.

 
Posted : 01/05/2014 2:15 am
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