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Old 5th Oct 2019, 1:34 pm   #1
thermionic
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Default Marconiphone VT55A - any info?

Hello all.

After looking through my volumes of Ďthe red bookí, I canít find any circuit that matches my set. Itís a single channel Ally Pally set, but states ĎAC Onlyí which I guess is due to the CRT heater transformer you can see mounted top right.

The Mazda CRT appears to be original, but I could be wrong.


Any leads, please?

Many thanks.

Simon.
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Old 5th Oct 2019, 2:22 pm   #2
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Default Re: Marconiphone VT55A - any info?

That appears to be a CRT booster transformer, so wouldn't be original.
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Old 5th Oct 2019, 2:36 pm   #3
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Default Re: Marconiphone VT55A - any info?

There is a large transformer on the bottom right of the middle photo, presume a mains transformer.
Agree the small transformer feeding the CRT will have been fitted later in the sets life, either to boost the tube or isolate it for a heater/cathode short.
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Old 5th Oct 2019, 5:56 pm   #4
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Default Re: Marconiphone VT55A - any info?

Hi Simon
That is a Plessey chassis and you will find it in the red book pre 1953 models volume 111.
That chassis was used in lots of sets , look for regentone T15L ,philco BT1410.
There is also a trader sheet for the Plessey chassis number 984/T10.

Robin
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Old 5th Oct 2019, 7:50 pm   #5
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Default Re: Marconiphone VT55A - any info?

Ahh...Many thanks, Robin.

I would never have looked at Plessey, a mixed bag of valves in this chassis.

Any idea why Marconiphone went to Plessey for this model?


Cheers. SimonT.
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Old 5th Oct 2019, 8:38 pm   #6
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Default Re: Marconiphone VT55A - any info?

The Plessey chassis is very reliable and they must have wanted something that worked for more than a week after the 1807 saga!
Unfortunately the Mazda CRM121B fitted in these chassis had a very poor life. The good news is that the large mains transformer has heater taps for all the reliable tubes. You can fit virtually any 12" tube in this chassis. John.
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Old 5th Oct 2019, 9:43 pm   #7
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Default Re: Marconiphone VT55A - any info?

Surprise to see Mazda valves in a Marconi TV set. Apart from the 6SN7GT and 6D2 which have the Marconi equivalent types B65 and D77 all the others have no Marconi equivalents.
Plessey did later on supply Marconi with TV chassis which employed rebranded Mullard valves either as Emitron or Marconi.
On an historical note, in the 1920s Plessey made radios for Marconi and did so up to the formation of Electrical and Musical Instruments, EMI.

DFWB.
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Old 5th Oct 2019, 9:49 pm   #8
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Default Re: Marconiphone VT55A - any info?

Hi John.

Well,itís good news that it can accommodate other tubes without too much fuss. Iím in the process of sorting out my sets collected over many years to a new store, so Iím unearthing items Iíve forgotten about!

I have a few different Marconiphone / HMV sets to sort out...😬

Thanks for the information.


SimonT.
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Old 5th Oct 2019, 9:53 pm   #9
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Default Re: Marconiphone VT55A - any info?

The screen looks quite small. Is it twelve inch CRT?

DFWB.
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Old 5th Oct 2019, 9:53 pm   #10
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Default Re: Marconiphone VT55A - any info?

Hi David.

I must admit, I was surprised to learn that this is a Plessey chassis. But the valve types used on this chassis, as you say, are not what you would expect to encounter in a Marconiphone/ HMV set.
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Old 5th Oct 2019, 9:54 pm   #11
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Default Re: Marconiphone VT55A - any info?

Quote:
Originally Posted by FERNSEH View Post
The screen looks quite small. Is it twelve inch CRT?

DFWB.
It is 12íí David.
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Old 5th Oct 2019, 10:08 pm   #12
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Default Re: Marconiphone VT55A - any info?

It's the later version of the Plessey Mark 1 chassis which has the electric picture shift controls. A small amount of DC is introduced into the scanning coils and adjustment is done by the multi-turn controls positioned above the pre-set slider controls.

I have a Philco console TV set which has a very American look about it. Like the Marconi VT55 it also has the Plessey Mark 1 chassis. However, in this set the valves are with the exception of the EL38 are all Brimar and instead of those Mazda 6F1 pentodes the chassis has 8D3 or 6AM6 B7G base valves.

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