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Old 1st Dec 2019, 4:35 pm   #1
sabaman
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Default Marconiphone VT155 television.

Hi,

Curiosity got the better of me and I purchased the model shown above. It had been in the family from new, was in good cosmetic condition & came with its instructions and tube guarantee.

I'm reasonably proficient with valve radio repair and have been in the consumer electronics repair trade for most of my life (until recently - change of career - the usual reasons), so I'm familiar (or used to be familiar anyway) with CRT tv repair.

However, I'm new to valve tv repair. I'm aware of valve radio pre-checks before applying power and I assume that a lot of these checks also apply to valve tv.
Could anyone give me some pointers before I apply power to my tv? Is it ok to apply power via a variac?

I removed the back and discovered an EY86 covered in dust on the floor of the set. It appears to have been removed from the EHT section. What I presume to be the LOPT has a large crack in it. Would this mean the LOPT has had it?
Any advice would be much appreciated.

Thanks very much.

Seth
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Old 1st Dec 2019, 8:29 pm   #2
slidertogrid
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Default Re: Marconiphone VT155 television.

Hi I have a HMV version which is similar in appearance but embellished with some brass trim.
Once restored your set should give excellent pictures. the cracked pitch on the LOPT doesn't necessary mean it has failed, some TV22 LOPTs look terrible but work OK.
If the set has been stored in anything other than a heated room it may be best to dry the LOPT out well before running the set.
Some people repair faults as they occur preferring to keep the set as original as possible others prefer to block change capacitors before applying power.
the first thing I would do would be to check and reform or replace the main smoother. then disconnect or replace any capacitor(s) wired across the mains. there is usually only one...
My set works well with excellent definition but I cannot make any claims here I bought it years ago from another collector he had done all the work I have never had the back off!
If you can find a diagram that will make life easier...
A nice set good luck with it!
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Old 1st Dec 2019, 9:18 pm   #3
Colourstar
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Default Re: Marconiphone VT155 television.

Very nice and quite rare these days to find a one-owner-from new set.

Presumably this Marconiphone dates from after Thorn's acquisition of the brand. The chassis looks closely related to the Ferguson 306T, which has a side mounted tuner where the space is, bottom left. This is the first time I've seen the chassis used in anything other than a 306

Best of luck with the restoration. It looks to be in decent shape.

Steve
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Old 1st Dec 2019, 9:51 pm   #4
slidertogrid
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Default Re: Marconiphone VT155 television.

Here are some pictures of my HMV version. The picture width is a bit low due to a slow warming valve I think as it does fill the screen eventually...
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Old 2nd Dec 2019, 8:17 pm   #5
sabaman
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Default Re: Marconiphone VT155 television.

Thank you both very much for your advice and comments. I'm most grateful. It's so nice to be able to chat with fellow enthusiasts on a forum such as this. Slidertogrid, your HMV version looks lovely - what a fantastic picture! Mine has a 'mahogany' effect cabinet, not as attractive as yours but it's in good condition fortunately. Steve, thanks for the heads up regarding the Ferguson 306T similarity. I shall bear that in mind when obtaining service info. This will be a winter project that I plan to start over Christmas. If things go well I will probably purchase an Aurora - I had one previously but sold it as it only got limited use. Too busy with radios.
Thanks again,
Seth
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Old 3rd Dec 2019, 12:18 pm   #6
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Default Re: Marconiphone VT155 television.

A very straightforward repair/restoration or at least it should be. Plenty of wax capacitors that will require replacement.Watch out for the line coupling capacitor to pin 2 of the PL81 line output valve.
If original it will be a type that looks like a resistor. It's .001uf. Replace it with a .01uf to ensure adequate line drive. The original slowly went O/C often damaging the LOPT.
Speaking of the LOPT, they did fail on the overwind but considering the massive number of these chassis produced it was probably a small percentage. Radiospares used to stock a replacement [LOPT 108. 1960's catalogue]
Few stock faults but an alarming fault that can surprise you is an O/C sound cathode bias capacitor. As the sound stage warms up it bursts into incredibly loud motor boating and oscillation! Turning the volume down does nothing and you panic for the on/off switch! The symptom is unlikely to damage your cat..
A final note. Take care when replacing the tuner valves. They are the reverse of the normal. The 'knob end' of the tuner is the PCC84 and the rear end is the PCF80.
Good luck with it and I hope it's a winner. Regards, John.
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Old 5th Dec 2019, 11:05 pm   #7
sabaman
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Default Re: Marconiphone VT155 television.

Hi John,

Very kind of you to add such specific advice. It's really appreciated. I gather capacitor replacement is going to constitute much of the work, but it's really helpful to know which caps should be replaced as a matter of course before even applying power. I'm going to be nervous enough anyway on powering up the set & certainly wouldn't relish being greeted by incredibly loud motor-boating from the audio stage. I shall also perform the line coupling capacitor value modification as you suggest.
The Aurora has been ordered from Gerry at Crowthorne Tubes and should be here soon. Just got to get the set going now. I will also check/replace the main smoothing cap as suggested by slidertogrid before applying power. Still not sure if I should power up gently by variac or just feed it straight from 230 volts?

Many thanks,

Seth
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Old 6th Dec 2019, 2:16 am   #8
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Default Re: Marconiphone VT155 television.

As mentioned earlier in this topic the chassis is a modified Ferguson 306T. In 1956 EMI licensed the Marconi and HMV brands to Thorn Electrical Industries. The license to use the two brands ended in 1977. Marketing policy continued as before, Marconi distributed through wholesalers and HMV only to accredited dealers.
The last EMI manufactured TV sets were the Marconi VT153 and HMV 1854. These are very rare sets, I've never seen either set. The 1957/58 Radio & Television servicing book informs us that both sets employ printed circuit techniques but the PCB is in fact a tiny thing and has only the PL81 and PY81 valveholders on it.
Getting back to the VT155 there should be no issues with the EY86 EHT rectifier. Certain Ferguson 306T models needed a special EHT rectifier valve, the Mullard TY86F. The valve has 7.4volt heater.
A 21" CRT model was also made which like the VT155 employed the Ferguson 306T chassis. The CR tube was the 70* MW53-20.

DFWB.
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Old 6th Dec 2019, 11:48 am   #9
mark pirate
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Default Re: Marconiphone VT155 television.

Quote:
Still not sure if I should power up gently by variac or just feed it straight from 230 volts?
I usually bring a set up on a variac or dim bulb (100w), as it gives the main smoothers a chance to reform.

I would advise just replacing the bare minimum of caps before applying power, it is not a good idea to blanket replace caps beforehand, ask me how I know

I am sure you will get first light quite easily, the chassis was reliable for it's time.

Mark
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Old 6th Dec 2019, 12:36 pm   #10
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Default Re: Marconiphone VT155 television.

Generally the main smoothing block holds up well. The one to watch is the mains filter [.1uf 300V AC]connected across the set side of the on/off switch. Just snip it out. It does not effect the operation of the chassis in any way but will fail with a loud pop if it is left in circuit causing alarm.. Ensure the mains selector is set for 250/250V. J.
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