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Old 20th May 2018, 8:38 am   #21
Heatercathodeshort
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Default Re: Pye CTM4.

Blast! Worth checking the screened lead to the line scan coils on the tag board. I had it go S/C a few times. One LOPT, a set of scan coils and a bucket of caps to go.. Good luck with it.

Oh David. I suppose you didn't mistakenly take my Garbardine mackintosh back to the North East with you? I covered the CTM4 with it in a hope that you would not see it. I haven't seen it since! John.
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Old 20th May 2018, 12:02 pm   #22
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Default Re: Pye CTM4.

"Oh David. I suppose you didn't mistakenly take my Garbardine mackintosh back to the North East with you? I covered the CTM4 with it in a hope that you would not see it. I haven't seen it since!" John.

Hi John,
So it was yours. I dumped it a clothes recycle bin at a motorway service station en route back to Geordieland.

Took a chance and 'scoped the anode connection of the EY51. There's a pulse present which has an peak amplitude of 600volts. Should be something like 11KV!

DFWB.
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Old 20th May 2018, 5:54 pm   #23
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Default Re: Pye CTM4.

Shame, My Grandad gave me that mac back in 1960. It had been passed down to him having been worn for Queen Victoria's funeral in 1901. Oh well, all good things have to part company eventually but it was a sad way to end it's life in some desolate motorway recycling bin. Just thinking, it was a bit moth eaten and smelt a bit funny. Maybe it was time to let it go.

600v. That sounds very bad even for a duff LOPT. I think these LOPTs were just about managing in their hey day. The regulation could have been better from new.

The chassis is hardly worthy of a quality rewind and it may be difficult to transplant another LOPT due to feedback pulse windings for the flywheel sync circuit.

You can't win them all but with the aid of one of your infamous adapter plates, who knows? Bye, John.
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Old 20th May 2018, 8:46 pm   #24
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Default Re: Pye CTM4.

Quote:
The chassis is hardly worthy of a quality rewind and it may be difficult to transplant another LOPT due to feedback pulse windings for the flywheel sync circuit.

You can't win them all but with the aid of one of your infamous adapter plates, who knows? Bye, John.
Hi David,

Just to follow on from HKS's comments wasn't a certain Scottish friend of yours responsible for a rather natty LOPTectomy on a VT4 ?
https://www.youtube.com/watch?v=7nIHG0ZvyFo

Marc.
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Old 21st May 2018, 2:08 pm   #25
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Default Re: Pye CTM4.

Hi Marc,
The line output transformer Trevor fitted in the VT4 was most likely removed from a Ferguson 992T .
The attachment shows the circuit of the line output stage of the Ferguson 992T series of TVs.

DFWB.
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Old 23rd May 2018, 9:09 pm   #26
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Default Re: Pye CTM4.

Wired in the substitute transformer this evening. Using the Rank-Bush-Murphy EHT meter to monitor the results I find that just under 11KV is available at the cathode of the EY86 rectifier, just about right figure for the 14" CRT.
It's likely a higher EHT voltage will be possible when the CRT is connected.
Tomorrow the chassis will be refitted in the cabinet so then we'll find out if the French 819 line transformer will work properly in the 405 line CTM4.
At least this evenings experiment proves that the original line output transformer is faulty.

The attachment shows a similar line output transformer which was used as a substitute for the original transformer in a Pye CTL58F.

DFWB.
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Old 24th May 2018, 6:59 am   #27
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Default Re: Pye CTM4.

Oh dear. I fear the substitution of the LOPT in my Pye LV20 is catching. I sense another adapter plate is not far away. J.
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Old 24th May 2018, 10:57 am   #28
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Default Re: Pye CTM4.

This morning I tried out another line output transformer in the CTM4. This one is of unknown origin, most likely it was taken out of an early fifties set.
Can anyone identify it?

Anyway, it's of no use in the CTM4, the EHT voltage is only 7KV, so it's most likely it was once fitted in a 12 inch CRT receiver. The EHT rectifier is an EY51.

DFWB.
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Old 24th May 2018, 3:19 pm   #29
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Default Re: Pye CTM4.

I have seen that LOPT David but cannot remember what it came out of!

Oh yes I remember. It's a MouldVision 'Tar Baby' from 1955. I can't trace it in Newnes.

It looks terrible but it is often the rubbish that works.. John.
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Old 25th May 2018, 12:06 am   #30
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Default Re: Pye CTM4.

This evening the chassis was reinstalled into the cabinet.
The scan coils refitted on the tube neck, the ion trap positioned in line with CRT base pin 3, the link between CRT heater pins 1 and 12 removed.
The set is ready for testing.
The attachment shows the results. Even with only 10KV the picture is quite bright. The height control has no effect on the picture, turns out the coupling capacitor between the frame oscillator and the grid of the PL82 output valve needs rewiring so that the height control is in series with the capacitor. No frame sync will almost certainly be the miniature selenium interlace diodes having gone high forward resistance.
No line sync because the reference pulses to the flywheel discriminator are absent.

DFWB.
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Old 25th May 2018, 6:45 am   #31
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Default Re: Pye CTM4.

Wow! So the AW36-21 was OK after all. J.
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Old 25th May 2018, 7:42 am   #32
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Default Re: Pye CTM4.

Glad to see the crt is OK. How will you work out the line sync without the pulse winding? At this rate it won't be long until your making a new back and giving it a final polish.

A testament to a bit of determination. A lot of people walked past that set.

Keep up the good work. John Joe.
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Old 25th May 2018, 9:11 am   #33
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Default Re: Pye CTM4.

Hi John Joe,
There is a spare winding on the 819 line transformer which will provide the reference pulses to the line flywheel sync discriminator.
Considering that the getters are milky it came as surprise to see a good picture on the AW36-21 CRT.
I might have a use for the 7KV transformer that was tried out in the CTM4.

There is a Sobell T121 Bakelite console TV in the shop which has the crudest looking line transformer substitution that one would ever see in a TV set.
The 7KV transformer has four proper 4BA mounting studs which will be a lot tidier than the tie wraps used to secure the bashed up LOPTx presently fitted on the chassis.
See attachment.

DFWB.
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Old 28th May 2018, 9:48 am   #34
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Default Re: Pye CTM4.

Report on yesterday travails on the Pye CTM4. The vertical amplitude control had little or no effect on the picture height. The 500Kohm control itself was found to be OK but the linearity control was found to have an open circuit track. Fortunately it was an easy fix, just a simple matter of changing the connections of the outer tags around.
A mysterious 1.2Mohm resistor was found to be wired across the linearity control, presumably an attempt to solve the excessive height fault. Tracing through the circuits revealed that C85 was missing, clipped out by a previous repairer for some reason or other. C85 is wired in series with the linearity control, it's function will be described later in this essay. A new 0.05mfd capacitor has been soldered in.
Testing the receiver: after all this work one would expect an improvement to the picture height adjustment and linearity, not so. Check those controls again, test OK. The fault was traced to the new capacitor C85 having a bad soldering joint on the cathode bias capacitor. Resoldering the tag connection has solved the problem. The height and linearity controls now work perfectly.
The linearity control works on the pre-distortion principle, the shape of the waveform supplied to the grid of the output valve is altered to correct any non linearity in the output stage.
The donor line output transformer has an isolated winding which could be employed as the source of the reference pulses for the flywheel sync circuits. However when it was connected into the circuit the low impedance primary winding of the phase splitter transformer T11 damped the performance of the line output stage. A solution to that problem will have to be found.
The second attachment shows the connections on the 819 line transformer.

DFWB.
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Old 28th May 2018, 9:57 am   #35
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Default Re: Pye CTM4.

Great fun David.
I can see the use of an old valve intervalve transformer coming into use to cure the mis match. J.
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Old 28th May 2018, 2:31 pm   #36
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Default Re: Pye CTM4.

Hi John,
I've an even better solution, now we know the set is a viable proposition I intend to have the original line output transformer rewound.

The attachment shows the results of todays work. The line flywheel sync system is working albeit not as good as it should because the shape of the reference pulse is not the correct shape.
It is also the reason why the gated vision AGC doesn't work, so for the time being the RF gain control is being used to adjust the contrast.

DFWB.
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Old 28th May 2018, 6:48 pm   #37
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Default Re: Pye CTM4.

Really impressed David. The M3 diodes are probably u/s together with the small caps in the line sync circuit.
Yes a rewind and why not. It looks good. John.
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Old 30th May 2018, 7:10 pm   #38
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Default Re: Pye CTM4.

Hi David,
Great results so far. You are lucky you didn't have a tube with the dreaded dodgy Mullard M shaped heater.
Cheers
Andy
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Old 30th May 2018, 7:25 pm   #39
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Default Re: Pye CTM4.

Hi Andy,
The excellent condition of the CRT came as a pleasant surprise, in fact the pictures look good with only 10KV so let's imagine what it will like with the correct 14KV EHT.
The heater voltage measures 6.1V so it's slightly under run. The mains dropper resistor is open circuit in two of it's three sections. Roger demonstrated that this component can be repaired with the correct type of resistance wire.

DFWB.
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Old 31st May 2018, 4:59 am   #40
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Default Re: Pye CTM4.

hello Everybody,
Nice work as usual David. I have some resistive wire at hand, the one I used for repairing the LV30 bleeder, and it look to be very good. So, I can help on this.
On my side, I suffered some time trying to restore the recent purchased Firestone 13G3. I finally go through it and waiting for the RF modulator for final testing.
Roger
Note: LV30 still superb pictures..
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