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

Hi disconnect the eht smoothing cap and see if the eht comes up ! the set will work without it. the valve could be faulty as i would have thought a short would damp the line output stage. danny

Alternatively, is it possible that the EHT smoothing capacitor is "dead short" and drawing all of the U151's output (giving the impression of a dud valve)?

It was short in the ekco t161, disconnecting bought it all back.

stephen

Okay then..

Circumstances permitting, I'll bring it into the "workshop" tomorrow, and try snipping the EHT smoother 

I somehow got the idea that a shorted smoother would have loaded the rectifier enough to maybe cause something weird inside the valve, or to pull down the EHT input to a noticeable degree.

Trouble is of course, the set was put away in a hurry, and more or less forgotten..

Marion

Well, here it is.... Lurking in the vintage Mustang Stallion caravan.

I had a mad half hour and went to my storage department (my 1974 vintage, Mustang Stallion) and brought the set back to the Workshop.. Sadly, it was about as much as I was ble to manage for today (health issues get in the way).

Once I'd got the set indoors, I took off the back cover and took a few piccies of the interior.. I forgot just how clean this set was inside, and just how good a condition it appears to be in.. All the valves would seem to be original "Marconi" branded with little oval paper stickers on them, although some came off in the past.. I stored them away somewhere, but can't just put my hands on them at the moment.

What a lovely, clean, and rust free chassis..

The chassis had a good layer of clean dry dust on it when I bought the set, and it was duly "dismissed" with compressed air to reveal a lovely clean chassis underneath the dust.. Just take a look at that mains dropper.. Looks like new, don't you think, yet looks like it has never been replaced.. I have wondered at just how much, or how little, this set has been used.

Could this Emiscope be the orignal CRT from 1953?

Likewise, I wonder about this Emiscope '4'/14' CRT.. It looks to be the original tube from the factory.. 4/14 referring to tetrtode, 14 inches diagonal measurement.

I forgot about this broken thermistor.. I does actually function, but will not last long.. It is only by the grace of God that the two parts press against each other and make a good enough contact to complete the circuit.

That thermistor could be a problem.. I have no spares, and can't find any markings to even give the slightest clue as to a type number - any advice or guidance on replacing this would be most welcome.. As it stands, the thermistor was still working/conducting despite being broken, although it was purely the force applied by the leads that kept the two parts pressed together to make a good enough contact to work at all.. If I remember correctly, there was a little glowing hot-spot at the point of contact.. I doubt it would live long like that

Luckily, I have some service data.. It is the manufacturer's original (albiet provisional) service information.

As luck would have it, I was able to find this service information, only a matter of weeks after buying the set.. To me, the circuit diagram looks like a minimalist design.

The Marconi Z152 (sensibly, EF80?) is used almost universally throughout the chassis.. That has to be a masterpiece of design, but I'm not sure if the humble EF80 type valve was ever cut out for some of the jobs it's being used for in this set (sound output and line 'generator' for example).. Interesting uses for an RF/IF valve!

Marion

Hi Marion,

Wow that chassis looks great, amazing what a good layer of dust can protect os long as its dry.
I shall be watching and learning with keen interest as this HMV comes back to life 

Cheers
Marc.

... That thermistor could be a problem.. I have no spares, and can't find any markings to even give the slightest clue as to a type number - any advice or guidance on replacing this would be most welcome ...

Marion, simply work out the total voltage drop across the heater chain and calculate the voltage across the dropper.

If you add then together and subtract from the nominal mains voltage you will know the drop across the thermistor at its operating temperature.

You should then be able to identify suitable replacements from component data tables ...

On the other hand, the Brimar CZ1 was virtually a universal component when that set was built so, if you can find one, fit it and see how the voltage drop compares with the calculations. I doubt it will be far out.

On the other hand, the Brimar CZ1 was virtually a universal component when that set was built so, if you can find one, fit it and see how the voltage drop compares with the calculations. I doubt it will be far out.

Now that's the sort of "belt n' braces" approach I need.. I'm totally useless at mathematics (courtesy of childhood head injury) Dyscalculia is my problem there (just to reveal a personal secret).. I have a seriously hard time working with numbers.

I'll have a look at applying some power tomorrow.. Just now, the set is bathing in the flow of air from the dehumidifier.

Marion

I'll be following this restoration with interest. I have no experience of the 1824 series, never repaired one.
I notice that the set has an EHT smoothing capacitor, it's C55 in the 1824 service manual. Clip it out and see what happens.

Confirm that the CRT first anode has at least 250 volts. If it is at HT volts then C54 SC or leaky. The boost capacitor C53 should be also be checked. The Emiscope 4/14 CRT is unique to HMV and Marconi TV sets. The Mullard MW36/24 will work in this set, has a different base.

The suffix A models have a 14 position incremental tuner. I notice although that most of the circuits are similar to the 5 channel models the component numbers differ. For example, the EHT smoothing capacitor in the 1824 it is C55, in the 1824A it is C66.

Best of luck with the resto.

Till Eulenspiegel.

I'm looking forward to a blow by blow account (not the compressed air variety which you have already done) and seeing first light!

As an OT aside, why has the farmer round here sprayed the circumference of his arable fields with herbicide? Right the way round including down between a nature strip and the crop!

... I'm totally useless at mathematics (courtesy of childhood head injury) Dyscalculia is my problem there (just to reveal a personal secret).. I have a seriously hard time working with numbers ...

In the absence of the service data, I can't do the sums for you but I note that the earlier 1807 model uses a CZ1 Thermistor, so I was probably right on that score ...

This may help..

Thermistor_about214.html

Or whip one out of an old radio. Very common part.

Cheers,

Steve P.

Hi Marion, I'm sure that I've got the Mullard thermistor VA1026 if you'd like one. Send me a PM if you are interested.
The VA1026 is the one for television 0.3amp heater chains.

Till Eulenspiegel.

Two television heater chain thermistors.

Till Eulenspiegel.

Hi Marion, I'm sure that I've got the Mullard thermistor VA1026 if you'd like one. Send me a PM if you are interested.
The VA1026 is the one for television 0.3amp heater chains.

Till Eulenspiegel.

Hi Till,

Or can I say David? - Yes please, I'd be interested.. Though yours look different, I'd trust to it that that is a design, rather than functional, difference?

PM on its way.

Marion

... I'm totally useless at mathematics (courtesy of childhood head injury) Dyscalculia is my problem there (just to reveal a personal secret).. I have a seriously hard time working with numbers ...

In the absence of the service data, I can't do the sums for you but I note that the earlier 1807 model uses a CZ1 Thermistor, so I was probably right on that score ...

Hi Terry,

That's also an offer I'd appreciate I can scan the service information, that's no real problem, but making it available could be more difficult.

I wonder if Chris would put my service data into the library 

Also helpful, would be an "Idiot's Guide" to some of these calculations, as or when necessary?

Marion

I wonder if Chris would put my service data into the library 

I have the exact same manual Marion, also trader sheet 1144, I will scan and upload them.

I will scan and upload 

Hi Chris,

That's brilliant - thank you..

I ought to point out that this is likely to be a slow and somewhat painful 'restoration'.. I'm most definitely not in full fixing fettle, but it's getting me down, just sitting around.

Marion

Hi Marion It may be of interest.

I've got a lot of HMV data, I think most of it must have come from a main dealer. Anyway I've dug out the actual dealer 1954 service manual for the 1824. It covers circuit description, alignment, dismantling, waveforms, valve voltage analysis and parts.

I've also uncovered the 1955 Dealer Conversion service manual for the Band I and Band III tuner unit for the 1824 series.

Both manuals contain schematics also the main service manual has some typed up notes glued in from the service department. It details information about occasional 1824 sets being returned due to EHT Brushing. Just thought it all might be of interest to scan.

There's a fair bit so ( 40+ pages) I will start it tomorrow.

Hi Marion It may be of interest.

I've got a lot of HMV data, I think most of it must have come from a main dealer. Anyway I've dug out the actual dealer 1954 service manual for the 1824. It covers circuit description, alignment, dismantling, waveforms, valve voltage analysis and parts.

I've also uncovered the 1955 Dealer Conversion service manual for the Band I and Band III tuner unit for the 1824 series.

Both manuals contain schematics also the main service manual has some typed up notes glued in from the service department. It details information about occasional 1824 sets being returned due to EHT Brushing. Just thought it all might be of interest to scan.

There's a fair bit so ( 40+ pages) I will start it tomorrow.

HI Chris,

Yes please If you don't mind dedicating the time to the task..

I've just had the set on power, and though I have line whistle, it seems rather weaker than it did when I first bought the set, and was way to high in frequency (almost ultrasonic).

Anyway, me being me, I made my first mistake in the proceedings.. Since I didn't have my side cutters to hand, I thought I'd be clever and just unsolder the the EHT feed to the smoother, and see if I got a spark at the U151's output.. I was dismayed to see the valve was not even lit up.. I lost time tinkering with the line hold to get the Hz down to a sensible level, thinking it may be the cause of the lack of heater volts, only to discover that In disconnecting the feed to the cap, I had also disconnected the U151's heater supply 

Muddle headed thinking needs to be eliminated 

Confirm that the CRT first anode has at least 250 volts. If it is at HT volts then C54 SC or leaky. The boost capacitor C53 should be also be checked.

Best of luck with the resto.

Till Eulenspiegel.

Hi david,

I've found 255VDC 

Marion