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Old 3rd Jul 2020, 9:05 pm   #21
McMurdo
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Default Re: Peto Scott 12" console model TV122 1948

looks a pretty tv and a well adjusted picture courtesy of the gaffer!
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Old 3rd Jul 2020, 10:45 pm   #22
FERNSEH
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Default Re: Peto Scott 12" console model TV122 1948

Circuit diagram and description of the sync separator.

From page 390 of the television servicing book, volume II:
"The double stage sync separator comprises a diode amplitude limiter followed by a pulse amplifier. The former stage clips at 30 per cent of the modulation level, thus eliminating the video content, whilst the latter stage amplifies the remaining sync pulses prior to amplification to the timebases."

The circuit is similar to the sync separators found in some pre-war sets, the RGD 391 for example, and many post war models which supplied positive going video to the CRT grid.

DFWB.
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Old 4th Jul 2020, 8:38 am   #23
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Default Re: Peto Scott 12" console model TV122 1948

Thanks for an entertaining write-up.

Having gone into the servicing business in the 70's I have suffered a few belts off the line frequency derived EHT, the worst being from a PD500, but I don't know whether I would have the nerve to tackle a set with mains derived EHT. Well done
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Old 4th Jul 2020, 9:22 am   #24
alanmoore
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Default Re: Peto Scott 12" console model TV122 1948

Hello John ,yet another brilliant restoration .I think I've said before i love the restoration of these late 1940's sets
This one looks like another cracking good job .
Again another fantastic written account of the work you have carried out and well done , another 70+ year old set gets a brand new lease of life.
Regards Alan
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Old 4th Jul 2020, 10:16 am   #25
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Default Re: Peto Scott 12" console model TV122 1948

Hello John
Lovely stuff.Were the EF50s T- cutted and finished with Auto Glym by any chance? As usual a master class from a master craftsman!
Many Thanks for sharing it with us.
Regards Steve.
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Old 4th Jul 2020, 10:55 am   #26
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Default Re: Peto Scott 12" console model TV122 1948

It may be a pre war circuit David but it works very well. The Murphy V114 series uses a double diode sync separator without the sync amplifier, one diode feeding the line and the other the frame. Thyratron generators are employed for both timebases with the tube grid modulated. I have posted both circuits.

One oddity with the P.S. exists in the signal circuits. Two R.F. amplifiers are employed followed by the mixer and a single vision I.F. stage. The sound taken off at the mixer anode has two sound I.F. stages.

I would have thought it an advantage to have swapped this arrangement over giving the vision channel a much needed higher gain especially in the low signal areas.

With such a high gain sound I.F. amplifier the signal was of sufficient amplitude to feed the EL33 direct. Maybe with only one stage a triode audio pre amplifier would have been called for requiring an extra valve. I presume this was the original arrangement in the earlier P.S. TV121 and the VIDOR CN369A of similar vintage employing the old faithful EBC33. They could have used an EBC41 and deleted the EB91. They must have had their reasons.

The design departments all had their own ideas back then and this is what makes restoring these old receivers interesting.

The Peto Scott employs what must be one of the earliest uses of the co-ax aerial input. There were one or two manufacturers that used it but then returned to other ideas. The Bush TV11/12 comes to mind with a co-ax input in 1949 but with a hard wired input for the 1950 TV22.

It may have been a bit costly. I believe Belling Lee may have held the patent for it and commanded a premium price for the chassis mounted socket the plug of which was normally supplied with the customers information packet.
Jules Thorn probably had the right idea and used the AD4 type battery connector costing only pennies with complete success in a large range of Ferguson models. It was almost made for the job with it's large pin for the screening and the smaller one for the inner of the co-ax.

A few minor improvements were carried out on completion of the TV122. The video output valve EF42 proved to be tired giving reduced drive resulting in a slightly flat picture that overloaded easily with an increase in gain. A new Mullard replacement soon cleared that up.

All the excellent COLVERN wire wound pots were in good condition. After all these years you usually have to replace one or two of these due to age related deterioration but these were as new after 70 years.

The loudspeaker after cleaning was given a coat of light gray paint to brighten it up. It had a bit of rust on the frame and had become scratched during my efforts at rubber removal.

It is all too easy to look back on the TV trade with rose tinted spectacles. At a time when this receiver was produced it must have been a pleasure to service service with good access but replacing the time base, particularly the power supply chassis is a real fiddle and must have been a struggle between the customers dog and lining up the small holes with the chassis mounts.

When you think about it, servicing television receivers and radiograms must have been a great pain. Huge heavy cabinets with inaccessible components and dark living rooms lit by a single 100w bulb clothed in a very restrictive shade.
If the monster could not be repaired in the home it would have to be removed to the workshop for service requiring a two man team to shift it into the Ford Thames 5cwt van with it's side valve engine, dim lights, no heater, lack of power steering, crash gearbox, power steering [what's that?], to say nothing of the 6v electrics the battery of which may or may not have been charged up enough to actually turn the engine over and start the vehicle! If all else failed you got the starting handle out. I know, OLU 956 was my first vehicle after passing my test in 1965. It was presented to me by a retiring radio shop owner who had been in business since 1919. Pooles radio Service 4 High Street Merton. The shop had been built in 1798.

It was only when television rental became popular, that the rental companies mostly owned by the manufacturers, realized that ease of service was essential if satisfactory repairs could be carried out economically in the customers home. Difficult to service receivers were soon rejected by the local repair shop and this must have led to a lot of replacement receivers being sold especially with the coming of the I.T.A. in 1955.

I can imagine the crackling bonfires consuming the HMV 900s and COSSOR 1210s. The repair guys of the day must have been delighted and I certainly would have been one of them.

Finally the Peto Scott was a well designed and built television receiver. It would not have been produced in large numbers but I have no doubt that most of their production would have gone to the 'better off' customers in Central London and the Home Counties.
The sight of 'H' aerials on the roofs of Surrey homes would still have been a rarity.

Well I think I've covered it all and a bit more.. Regards, John.
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Old 4th Jul 2020, 11:07 am   #27
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Default Re: Peto Scott 12" console model TV122 1948

Quote:
Originally Posted by beltinge bore View Post
Were the EF50s T- cutted and finished with Auto Glym by any chance? Regards Steve.
Oh stop it Steve! I'm just an old dabbler of ancient brown boxes. If I'd been around as a child in 1890 I would have probably been employed cleaning up horse dung on Westminster Bridge. [One of my customers actually did that]

A brass wire brush, 1800 grade paper, De Oxit and a touch of MS4 clears the bad contact problem for ever. Some of the EF50s have silver plated pins so you have to be careful. They can be recognized due to the pins being tarnished completely black!
Thanks for your comments. Regards, John.
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Old 4th Jul 2020, 4:30 pm   #28
line sync
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Default Re: Peto Scott 12" console model TV122 1948

Another great restoration john.
I`ve never seen that model before and I love the the chassis lay out.
I`ve had a few sets in the past where the crt mask has melted but not that bad.
I`ve only owned one peto-scott television and this was a 1955 ish model.
Is it possible for you to show a few pictures of the cabinet in a well lit room , are the consumer controls on the side ?

Robin

Last edited by line sync; 4th Jul 2020 at 4:36 pm. Reason: Added more text
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Old 4th Jul 2020, 6:07 pm   #29
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Default Re: Peto Scott 12" console model TV122 1948

I'll have a go Robin. It weighs a ton. Yes the control panel is on the right side of the cabinet. Thanks, John.
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Old 4th Jul 2020, 8:23 pm   #30
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Default Re: Peto Scott 12" console model TV122 1948

Another interesting and enjoyable read. The new black satin sprayed mask certainly enhances the excellent picture. Thanks again for sharing.

Alan.
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