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Old 24th Jan 2019, 10:05 pm   #1
FERNSEH
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Default Special cabinet 24" KB TV set.

Took delivery today of this unique 24 " CRT console TV set. The set is a Kolster-Brandes PV100 in which the chassis has been installed into a specially made console cabinet. The seller told me that the set was purchased in 1958 by an American Gentleman who lived in Kent.
Before any attempt is made to power up the set the line output transformer will be warmed up to drive out any moisture. The method used to do this has been discussed in this forum. A current of 20 to 30 mA will be passed through the EHT overwind and primary winding.
The chassis of the PV100 is nothing special being simply a modified version of the popular OV30 model. The CRT is a Brimar C24KM which was imported from the Continent.

The cabinet is solid and beautifully made only let down by the awful pegboard back.

Link to previous thread about big screen 405 line TVs: https://www.vintage-radio.net/forum/...d.php?t=114091

DFWB.
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Old 24th Jan 2019, 10:28 pm   #2
high_vacuum_house
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Default Re: Special cabinet 24" KB TV set.

That must be the smallest ratio of working telly bits to empty space in that cabinet!!

Must be the easiest set to remove the chassis from as well. Looks like it should be an easy one to get going. I expect it should be fairly reliable as no excuse for heat build up wearing out components.

Christopher Capener
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Old 24th Jan 2019, 10:39 pm   #3
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Default Re: Special cabinet 24" KB TV set.

Hi Christopher, I'm looking forward to seeing what a 405 line picture looks like on the big screen. Let's hope the interlace is good.

DFWB.
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Old 24th Jan 2019, 10:58 pm   #4
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Default Re: Special cabinet 24" KB TV set.

I presume it doesn't have any spot wobble circuit. The scanning lines on my 23" thorn 1400 set are fairly clear to see.

Wonder if you could get away by having the focus out slightly to make the spot larger though there is the risk of losing definition.

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Old 24th Jan 2019, 11:43 pm   #5
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Default Re: Special cabinet 24" KB TV set.

According to the information in the 1958/59 Radio and Television servicing book the EHT is 15.8KV, that's the figure quoted for the 17" model, the OV30. Perhaps it is higher in the 21" and 24" PV70 Kolstar and PV100 Regina models?
The pentode gun in the C24KM is similar to the one fitted in the MW53-20 so it will be possible to alter the shape of the spot by applying different voltages to the second anode. Described as "prefocussing" in the Mullard data books.

But really 15.8KV is too low for a 24" CRT.

DFWB.
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Old 25th Jan 2019, 10:20 am   #6
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Default Re: Special cabinet 24" KB TV set.

The chassis is dwarfed by that huge CRT, I bet that the chassis ran nice and cool in a cabinet that large.
Here's hoping the CRT is up to snuff.

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Old 25th Jan 2019, 10:27 am   #7
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Default Re: Special cabinet 24" KB TV set.

Perhaps apart from schools' televisions,a slightly later Thorn set used a Sylvania U.S. tube

https://www.thevalvepage.com/tv/hmv/hmv1918/hmv1918.htm

Look forward to seeing pictures !
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Old 25th Jan 2019, 11:06 am   #8
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Default Re: Special cabinet 24" KB TV set.

I think KB called that model 'The Old Queen special', the last of the Queen series.

I had two of these on my books David. One was identical to yours with a 50CD6G line output valve. The other was much better looking with a high finish polyurethane cabinet that sloped downwards at the back to give the allusion that it was not so deep. The LOP valve was a PL81.

It was front heavy and the customer had a hook screwed into the wall at the back with a length of string fixed to the rear cabinet rail to prevent it falling forward.

The picture was poor compared to other KB models of the time. EHT regulation was not 100% and advancing the brilliance resulted in lack of width and a drop in focus.

It will be interesting to see how yours performs. John.
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Old 25th Jan 2019, 11:18 am   #9
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Default Re: Special cabinet 24" KB TV set.

Hi John, The 1957 17" model was called the "New Queen Special" and the 24" PV100 was given the name "Regina"
Word: Regina
Dictionary result for Regina
/rɪˈdʒʌɪnə/ (IPA)
noun
noun: Regina; plural noun: Reginas
the reigning queen (used following a name or in the titles of lawsuits, e.g. Regina v. Jones, the Crown versus Jones).

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Old 25th Jan 2019, 2:02 pm   #10
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Default Re: Special cabinet 24" KB TV set.

if this is to be restored, and being a bit Nerdish about high quality mono TV sound, that bottom area looks as if it could very easily be adapted to a vented speaker enclosure!
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Old 25th Jan 2019, 5:48 pm   #11
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Default Re: Special cabinet 24" KB TV set.

Hi Edward, a vented loudspeaker enclosure is a good idea. The set employs a PCL82 as the audio output valve. A few OV30 models used a 6AT6 and 9BW6 in the audio amplifier.

DFWB.
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Old 25th Jan 2019, 6:24 pm   #12
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Default Re: Special cabinet 24" KB TV set.

From my online dabbling into American TV's, it seems alot of their designs were huge half-empty cabinets with invariably a flat pegboard back. May be something to do with ventilation in a hot country? Perhaps the client wanted something to remind him of home.
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Old 25th Jan 2019, 6:55 pm   #13
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Default Re: Special cabinet 24" KB TV set.

Hi Kevin,
here's a picture of the peg board back. I'll make something better for the set. Millboard is ideal for making cabinet backs.

DFWB.
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Old 25th Jan 2019, 10:02 pm   #14
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Default Re: Special cabinet 24" KB TV set.

As a precaution to the line output transformer failing when the mains full supply voltage is supplied to the set, the windings are presently being warmed up by passing a small current between the R19 top cap connector and the anode connection of the 50CD6G. Winding resistance is about 220 ohms. The power supplier is set to 20 volts, this will give just under 2watts, sufficient to drive out any moisture.

DFWB.
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Old 29th Jan 2019, 12:28 pm   #15
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Default Re: Special cabinet 24" KB TV set.

The line output transformer has been receiving the warm up treatment for more than four days. I reckon it should be dried out now.
The set has a big CRT and line output valve but look at that puny little transformer.

DFWB.
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Old 7th Feb 2019, 12:00 pm   #16
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Default Re: Special cabinet 24" KB TV set.

The console cabinet KB PV100 has a big CRT but the same can't be said about the loudspeaker, it's a tiny 6 X 4" elliptical unit.
The line output transformer should be dried out so it's about time to power up the set. For the initial tests the variac must be used to supply power before any attempt to connect the set direct to the mains supply.

DFWB.
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Old 7th Feb 2019, 12:23 pm   #17
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Default Re: Special cabinet 24" KB TV set.

Plenty of scope to do something good with the audio, I think Edward's idea of a vented speaker enclosure could be interesting. Looking forward to seeing a picture on this one.

Regards, John Joe.
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Old 7th Feb 2019, 5:00 pm   #18
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Default Re: Special cabinet 24" KB TV set.

Hi John Joe,
I've found a 10" X 6" loudspeaker for the set. The audio output stage employs a single PCL82 so there's not going to be a lot of power. A vented loudspeaker enclosure will be necessary.
Or, better still, an audio amplifier similar to the one fitted in the Baird 638 schools TV receiver.

DFWB.
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Old 7th Feb 2019, 5:04 pm   #19
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Default Re: Special cabinet 24" KB TV set.

Does the Baird circuit use a pair of PCL82’s, I can see they are series heaters? It appears a plug in unit to replace the normal sound output valve.
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Old 7th Feb 2019, 5:24 pm   #20
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Default Re: Special cabinet 24" KB TV set.

Hi Frank,
The Baird 638 push-pull amplifier uses a pair of PCL82s. Very easy to fit. Plugs into the V16 valveholder. HT supply is a separate connection to the smoothing choke.

Before any work can start on the TV chassis the 6BW7 common IF amplifer valve V3 must be refitted. Not an easy job and it looks like the CRT will have to be removed to gain access to the valveholder. Another big scary tube!

This is a early production model (1958) later sets used a Brimar 9D7 vari-mu pentode for the common IF amplifier. Improves AGC performance.

DFWB.
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