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B&W TV Another Philips line output transformer substitution, model 19TG108U.

 
Till Eulenspiegel
(@till)
Famed V-Ratter Registered

Like my previous line transformer substitution in a Philips TG100U type of TV receiver the replacement transformer will be a BRC 1500 jellypot. 

The line oscillator has already been rewired as multi-vibrator so at least that job is out of the way.

The set.

Philips 19TG108U

 The faulty line output transformer.

Philips 19TG108U LOPTx 1

 Till Eulenspiegel.

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Topic starter Posted : 30/10/2021 10:49 am
colourmaster
(@colourmaster)
Reputable V-Ratter Registered

Hi David,

I'm looking forward to seeing the finished results , especially on a rare 19" version. Hopefully one day my Aunty Elsie's old Stella will live again . 

Regards Gary.

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Posted : 30/10/2021 3:12 pm
Till Eulenspiegel
(@till)
Famed V-Ratter Registered

The replacement line transformer was fitted this afternoon. Also all the wiring done as well. The line linearity coil is retained as it was in the 21" Stella.  Provision for an alternative line output valve, PL36 or PL504.  The adaptor plate will accept an octal of magnoval valveholder.

Philips 19TG108U LOPTx 2

Till Eulenspiegel.

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Topic starter Posted : 30/10/2021 8:34 pm
ntscuser and PYE625 liked
Katie Bush
(@katie-bush)
Illustrious V-Ratter Moderator

That little LOPTy looks like it was always destined to mounted in there!

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Posted : 30/10/2021 8:40 pm
PYE625
(@pye625)
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Yes, it just sort of looks natural there.

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Posted : 30/10/2021 8:46 pm
Till Eulenspiegel
(@till)
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Results from yesterdays work on the set, a picture with excessive width.
Today, the EHT voltage will be measured and if it isn't too high the value of the flyback tuning capacitor will be reduced. That action will increase the EHT and reduce the picture width.
At 182V the HT voltage is slightly low, that's about 10volts lower than the figure in the 1961/62 R & T servicing book.
The Plessey scanning coils are of unknown origin. The Philips AT1030 coils can be tried again but it's likely insufficient width will be the result of using this coil set.
EHT is supplied from a BRC doubler unit. Boost HT is 470volts.

Like the line output transformer substitution carried out in the 21" Stella ST1011U the line oscillator in this 19" set was rewired to become a multivibrator by using the circuit from the Alba T655 and T909.   The Alba circuit was chosen because like the Philips an ECL80 triode-pentode is employed. It does mean however, the line sync clipper circuit is deleted which is the triode connected pentode section, V611B. See original circuit.

Philips 19TG108U Line TB cct
Philips 19TG108U Chassis
Philips 19TG108U TCC

 

Till Eulenspiegel.

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Topic starter Posted : 02/11/2021 12:03 pm
Nuvistor liked
Till Eulenspiegel
(@till)
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Earlier today the EHT was measured and found to be 13KV. Easily get away raising it to 15KV. Guess that is highest safe figure for the AW47-90 CRT final anode. 

Till Eulenspiegel.

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Topic starter Posted : 02/11/2021 4:02 pm
Till Eulenspiegel
(@till)
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The flyback tuning capacitor changed to the original value of 180pF. EHT is now 15.5KV but still too much picture width even with the width control on the minimum setting. The three 75 ohm resistors in series with the HT supply to the boost diode anode are in the circuit.
Also, the horizontal linearity is not good. This might be caused by the BRC 1500 line output transformer designed for 625 lines being used for the 405 line frequency of 10,125 c.p.s.

Philips 19TG108U TCC 2

Till Eulenspiegel.

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Topic starter Posted : 02/11/2021 6:33 pm
PYE625, Nuvistor, Lloyd and 1 people liked
colourmaster
(@colourmaster)
Reputable V-Ratter Registered

Hi David, another fantastic result . The picture looks nice and bright , the line linearity looks ok.

Regards Gary.

 

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Posted : 03/11/2021 9:09 pm
PYE625
(@pye625)
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I wonder if a shorted turn line-linearity sleeve would be suitable to fit with this application of the 1500 Lopt?

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Posted : 03/11/2021 9:31 pm
Till Eulenspiegel
(@till)
Famed V-Ratter Registered

The scanning coils in presently in use can be fitted with a linearity sleeve. To check the activity in the PL81 a 1 ohm resistor will be inserted between the cathode and ground. This will allow oscilloscope assessment of the valve's conduction activity during the 98.8uS scanning line period.

The modified line oscillator.

Stella ST1011 Line Sync

 Till Eulenspiegel.

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Topic starter Posted : 04/11/2021 12:03 pm
PYE625 liked