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Old 13th Oct 2020, 12:01 pm   #1
FERNSEH
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Default Stella ST1007 replace on-off switch.

The on-off switch has never worked in this set. I've found a modern push-button switch and fitted it into the bank of front panel push-buttons.
Bits used are a switch of unknown origin, a piece of tinplate from a tobacco tin and the button from a 1990s TV.
The switch has been wired into the circuit and works.

Anyone recognise the switch?

DFWB.
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Old 13th Oct 2020, 12:15 pm   #2
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Default Re: Stella ST1007 replace on-off switch.

You'd normally use an adapter plate David. Is this a new approach?
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Old 13th Oct 2020, 1:07 pm   #3
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Default Re: Stella ST1007 replace on-off switch.

Hi Trevor,
guess you could call the piece of tinplate an adaptor plate.
The on-off switch now works but the brightness control has given up.

DFWB.
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Old 13th Oct 2020, 4:01 pm   #4
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Default Re: Stella ST1007 replace on-off switch.

Quote:
The on-off switch now works but the brightness control has given up.
The joys of vintage TV's! Neat fix on the power switch, I have a stash of similar switches, my last replacement switch repair involved bits of Meccano!
That set does look a bit odd with controls on the left....


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Old 13th Oct 2020, 5:05 pm   #5
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Default Re: Stella ST1007 replace on-off switch.

Yes, It look odd as we are so used to seeing the controls on the right...hopefully now corrected,
Regards, Alan.
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Old 13th Oct 2020, 5:19 pm   #6
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Default Re: Stella ST1007 replace on-off switch.

Mark Pirate wrote: "That set does look a bit odd with controls on the left...."
It is an odd arrangement but the cabinet is slimmer than the previous model, the ST8617U. Because the large control unit is situated on the left side, the cabinet had to be extended so the control unit is well away from the CRT. Much better if they had opted for a symmetrical design and added a matching panel to the right of the cabinet.
Couldn't do anything with the brightness control so the vision interference limiter on the rear of the chassis has been replaced by a 500Kohm pot which now serves as the brightness control. The vision limiter control is now under the chassis and anchored into position with a tag strip.

DFWB.
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Old 13th Oct 2020, 5:29 pm   #7
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Default Re: Stella ST1007 replace on-off switch.

Quote:
Originally Posted by stacman View Post
Yes, It look odd as we are so used to seeing the controls on the right...hopefully now corrected,
Regards, Alan.
And yet I remember the sets were well liked by the owners although I'm told some dealers had difficulties selling this model.

DFWB.
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Old 13th Oct 2020, 5:50 pm   #8
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Default Re: Stella ST1007 replace on-off switch.

I hope you used the right brand of tobacco tin David.
Switches and cosmetic bits are a real pain with vintage TVs. You can always repair the innards but the cabinet and specific bits are not so easy.

I would have drilled a hole in the side of the cabinet to allow the flex to connect to one of those old c1900 era light switches. You know the type with a fluted brass cover.

Those fancy push button switch banks, bass/treble/on/off always were a problem as they became obsolete rather quickly. Nothing could be done other than short the contacts out and unplug it from the mains as most people did anyway.

That was a smart tv but it did look a bit odd. John.
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Old 14th Oct 2020, 6:30 pm   #9
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Default Re: Stella ST1007 replace on-off switch.

Hi David,
As I'm not familiar with these sets, can you tell me what it is about the original brightness control that makes it difficult to replace?
Maybe some pictures of the side control panel from the outside and the inside of the set will make it clearer.

Cheers
Andy
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Old 14th Oct 2020, 8:29 pm   #10
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Default Re: Stella ST1007 replace on-off switch.

Hi Andy,
The brightness control is part of a dual concentric potentiometer unit with the volume control. Inner volume and outer brightness. The reason why the brightness control was relocated to the rear of the chassis was because it proved impossible to dismantle the side controls unit because all the screws and fasteners are rusted up.

the preset controls at the rear of the chassis are of a type that used in the late fifties through to the early sixties. See attachment. These controls are not very robust and are prone to go high ohmic value, in fact the 2Mohm pots used as the frame hold and interference limiter were found to be totally useless. The plan was to swap the controls around because the frame hold was erratic in operation. It's since been replaced with a much better component and the interference limiter is now not in the circuit.

I'll take picture of side controls assembly when I return to the workshop.

DFWB.
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Old 15th Oct 2020, 12:46 am   #11
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Default Re: Stella ST1007 replace on-off switch.

The control panel is situated on the left side of the cabinet. The unit was first fitted in the 1957 Philips and Stella models 1768U and ST8617U.
The original tuner was equipped with PCC84 and PCF80 valves. Later sets including the Stella ST1007U employ a PCC89 in lieu of the PCC84.

DFWB.
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Old 15th Oct 2020, 9:29 am   #12
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Default Re: Stella ST1007 replace on-off switch.

The tuner knob seems to have the letters as well as numbers. This is a Radio Rentals thing, is it not?
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Old 15th Oct 2020, 9:58 am   #13
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Default Re: Stella ST1007 replace on-off switch.

It was indeed, certainly the RR sets marketed as MRG were.
That channel selector knob in the Stella might be of continental origin, as might well be the tuner unit.

DFWB.
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Old 15th Oct 2020, 5:20 pm   #14
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Default Re: Stella ST1007 replace on-off switch.

That TV looks so alien, but it's just convention, of course. I think the bow-fronted GEC with its symmetrical front looks much more elegant.
That switch you've used was a common one in many Nineties TVs. Possibly Sanyo - I've got a few left in the drawer. The black switch cap is from a Sony, I think.
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Old 15th Oct 2020, 10:46 pm   #15
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Default Re: Stella ST1007 replace on-off switch.

Hi David,
Thanks for the photos.
Yuk and yuk. Even the speaker is moldy!
Yes those clip together presets are nasty.

Still it's nice to see a set that looks a little different.

Glad you came up with a way to replace the switch. I once replaced the on-off volume control (which is concentric to the brightness control) on a Bush TV56 by using a spindle adapter. I replaced the original switched rear cover of the volume control with a plain one and drilled a 10mm hole in it to bolt a new switched volume control on the back of it. It looked a bit odd from the inside, but it worked perfectly.

However, I do like John's idea. I reckon you could go one step further and replace the mains switch with a safeblock screwed to the top of the cabinet. I think a nice bright red one would look nice. What do you think?

Cheers
Andy
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Old 15th Oct 2020, 11:12 pm   #16
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Default Re: Stella ST1007 replace on-off switch.

"However, I do like John's idea. I reckon you could go one step further and replace the mains switch with a safeblock screwed to the top of the cabinet. I think a nice bright red one would look nice. What do you think?"

Hi Andy,
I'm not sure if the owner of the would be too keen on having a SafeBloc attached to the set. There's a few safeblocs in the shop somewhere.
I'll hunt one out tomorrow. Are those things still allowed to be used in workplaces?

DFWB.
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Old 16th Oct 2020, 8:40 am   #17
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Default Re: Stella ST1007 replace on-off switch.

Maybe one of those old red metal clad fireman's switches, the type you used to see on the front of commercial buildings that had high voltage Neon advertising signs. They had a ring switch that could be operated by a long pole with a hook on the end.

One advantage of course would be the added feature of remote control switching. Just a long pole with a hook on the end and no batteries required!

Thinking about the odd cabinet configuration, the chassis used is the Philips 1768 first released in late 1957. It had the detachable panel complete with loudspeaker, tuner and the volume/brightness controls.

It would have a lot of modification to transfer this unit to the right hand side. The Stella was a last hurrah for the very reliable and popular 1768U chassis that was superseded by the TG100U series the same year.

The Stella is a very smart receiver and I feel it would have sold in very large numbers if presented in a conventional style. Regards, John.

[David, If you feel like fitting a fireman's switch I know where there is a redundant one. It just needs detaching from a garage wall so a ladder will be required.]
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Old 16th Oct 2020, 10:47 am   #18
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Default Re: Stella ST1007 replace on-off switch.

No funny switches, yet. However, the Stella TV receives another modification to the original circuit specification. The recently replaced AW43-80 CRT is exceptionally bright so in order to provide some protection to the tube itself and the line output transformer a simple beam current limiter has been fitted.
The circuit consists of a 0.39uF capacitor and a 1N4007 diode connected in parallel and inserted between the anode of the video amplifier and the CRT cathode. A 390Kohm resistor is connected between the CRT cathode and chassis, this is the beam current sensing device.
At normal brightness and contrast settings the diode is conducting so there is no loss of the DC component. When the beam current is increased the voltage across the resistor rises to the point when the diode ceases to conduct and the video signal passes through the capacitor.
The circuit is very effective in use. The Rank-Bush-Murphy A816 employs a similar circuit.

DFWB.
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Old 16th Oct 2020, 8:42 pm   #19
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Default Re: Stella ST1007 replace on-off switch.

When the set is switched off a brilliant spot appears on the screen and takes a long time to disappear. Something is needed to rapidly discharge the EHT capacitor.
About the time the Stella ST1007U was made a simple circuit modification was employed to do this, the earthy end of the brightness control was returned to the un-switched end of the mains neutral.
It is desirable that the mains neutral is connected to the chassis which nowadays is no problem because we use non-reversible main plugs.

The spot suppression is discussed on page 28 in the 1960/61 Radio and Television book.

DFWB.
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Old 17th Oct 2020, 10:35 am   #20
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Default Re: Stella ST1007 replace on-off switch.

Yesterday evening I carried out the spot suppression modification. It works perfectly, now when the set is switched off the collapsing raster brightens up and the increased beam current discharges the EHT capacitor.

DFWB.
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