Peto Scott TV169 Restoration.

[Murphyv310]

Hi.
My friend in Poland (Leningrad T2) has sent me a very rare projection set to restore a Peto Scott TV169.
Fortunately without the cabinet 
As yet the B16T has not been collected so I have had relocate some of my own stuff elsewhere, plus I am getting a few audio amps to repair next week.

The set is untouched and all is present, the optics though are in a bit of a state, with the corrector lens corroded and the mirrors pitted. The corrector lens is model specific and matched to the distance from screen and the angle of the beam from the optics to screen, it also is only fitted one way on its housing even though it can be rotated, there are paint marks that are done on assembly in the factory. There is a setting up procedure od the Schmitt unit but if the corrector is not correctly fitted you'll never get this set up right, its a precision item.
I'm not envisaging any real issues with the electronics bar possibly the EHT generator TX.

I'll update here regularly.

[ppppenguin]

It looks like a good solid chassis. How was it shipped?

The optics certainly look horrible. Presumably they are all the standard Mullard unit apart from the special Schmidt plate.
https://en.wikipedia.org/wiki/Schmidt_corrector_plate

[Panrock]

Gosh your workshop looks neat and tidy and well organised!

Steve

[Murphyv310]

It looks like a good solid chassis. How was it shipped?

Came here by TNT, it was a Polish company initially. The boxes were opened by the Border force here in the UK, they put all the packing back perfectly though and re taped the boxes very well indeed.

[Murphyv310]

Hi.
Today I decided to test the EHT unit just in case the output transformer or the internal EY51's were faulty.
Using my little DC to DC converter I set it to 6.3v for the heaters, the DC to DC converter is fed from my 12v solar supply. The HT was derived from my Radford via the variac.
The unit worked first time once the HT reached 100v, I gradually raised the HT to 250v which gives 18kv on my rather low reading Eagle EHT meter (will need to look for a better one) there was a good old fizz going on so I am confident it was around 24Kv in real terms.
I decided to recap the unit and check the resistors, all the Philips black caps were leaky but all the close tolerance resistors were just about bang on.
After replacing the caps the oscillator would start at 55v HT. There is also a little increase in EHT so I'm assuming it is now to spec.

[Geordie McBoyne]

Hi Trevor,
            most of the circuits in the your projection set are similar to the 12" CRT model TV127.
I have the service information for that model and will be pleased to send it to you.  The EHT generator unit will be the standard Philips unit which was fitted in the Decca 121. It appears that the TV169 is equipped with the "World Series" valves, EF80, ECL80 etc.  Evidently, Peto-Scott made an earlier model which employed B8A base valves, TV166?

Attachment shows a rather rusty Peto-Scott TV127 chassis.

Geordie McBoyne.

[Murphyv310]

Today I'll give the main chassis some gradually increasing HT, also that way I'll be able to check what caps need to be replaced before the first full test. This process takes a good few hours.

[Murphyv310]

Hi.
After really good progress today, a few caps in positions that could increase anode current in following stages were replaced. The RF gain pot was replaced as it was open circuit, literally as the wiper was long gone. I was rewarded with good sound and a weak unlocked picture for about a minute then it faded away.
I had a bad feeling and my gut was right the EHT transformer has failed.
This is a known issue and these transformers are sealed and definitely contain a PCB oil.
I dont have a spare one so will need to try and find one or come up with another answer.

[Jac Janssen]

Hi Trevor,

In the 1980's I had some transformer oil from a Philips 25 kV can analyzed at the chemical laboratory of my employer, and the analyst assured me that it contained no PCBs.
No guarantee for the oil in your 25 kV can of course, but personally I wouldn't worry too much.

Hope this helps (a tiny bit).

Jac

[Murphyv310]

Thanks Jac.
That is reassuring. I read this many moons ago on the UKVRRR that it was. The thing is how to open it up. If it was possible I'd fit BY8210 diodes and new caps.