Restoration of an Ekco TS46

[line sync]

Thanks guys for all your suggestions .
Danger man , I`ve tried rotating the crt but it makes no difference.
The single screw you see is for rotating the scan coils.
John , I suspected the crt so tried another which I had labelled as good but got the same effect.
The 32uf cans have new caps inside.
Stephen , Interesting idea for checking the crt beam current.
The TS46 has the brightness control on the crt cathode , so can this check still be done ?
The 2K focus pot is good and works as it should.
Victor , The 2.4kv eht reading was taken with the brightness pot fully advanced and no picture can be seen just a very bright screen.
I`m looking to buy a new P61 valve for the eht unit which might improve the eht a little but I am tempted to leave it as it is and put it back in its cabinet.
PJL , The vertical lines are more effected than the horizontal.
The frame output transformer is very near the crt so I`ll move it and see what happens .
It`s interesting what you say about modulation but I don't know what to do about it or how to check for it , you`ve lost me im afraid .

Robin

[PJL]

The theory may be wrong but:
1. The 'out of focus' area at the bottom of the screen in picture 1 may not be a focus problem as there appear to be distinct lines in the picture indicating the scan is in focus but is being deflected.
2. It is worst at the bottom of the picture and this is where the frame drive current and therefore the HT current is at a maximum.
3. As the brightness increases the EHT current increases along with the HT current when the modulated deflection appears more widespread but still worst at the bottom.
4. The deflection appears to be in both the vertical and horizontal directions (there is a distinct diagonal shift).

One possible explanation is the current in the focus coil has an AC component which is introducing the deflection. A simple but not conclusive test would be to set the picture to look as in your picture 1. Adjust the focus control and see if this changes the amount of distortion/deflection you are seeing at the bottom of the screen.

An AC component in the scan coil could be caused by a number of faults including failure or poor connections to either of the 32uF caps, shorted turns in the scan coil or choke, a faulty or inappropriate rectifier.

The ultimate test would be to take the scan coil out of circuit and replace with a suitable power resistor and use an external DC supply to power the focus coil.

As the distortion is not confined to a specific area it is unlikely to be induced by a transformer unless it was near to the neck of the tube.

[PJL]

I mean take the focus coil out of circuit.

[line sync]

I`ve tried moving the frame o/p transformer and screening it but neither had any effect.
I completely disconnected the first 32uf cap (reservoir) and fitted a 220uf instead but no improvement was noticed .
Then while waiting for the picture to appear I realised that it always came up out of focus and as the picture brightens up the focus pulls in , so I checked the filament volts on the crt and found them a bit low at 1.96 v.
I then disconnected the sets filament supply to the tube and hooked up a variable bench power supply starting at 1.9v and increasing slowly until I reached 2.5v.
At 2.5v the picture had brightened up quite a bit and what`s better is the focus had improved so much that it was acceptable with only a little de focusing at the bottom.
Perhaps my crt is not as good as I thought ?
PJL , thanks for your replys and I will try powering the focus coil externally and see what happens.
John , in your ekco ts46 manual does it show any other crt tappings on the mains transformer ?

Robin

[Heatercathodeshort]

Just checked. The Ekco manual just shows the standard 2V winding. [1.96v is about as close as you can get] The Mazda triodes other than the CRM122 are all 2v. I suspect the tube is a little tired but not actually expired! The Mazda triodes do tend to display some odd characteristics when they age particularly the focus. Your pictures look good to me and I must admit after all your tests I think it's about time you stopped prodding the poor old girl.
It's probably performing better than it's done in years with the rewound EHT coil. Time to slide the chassis back in and enjoy watching it. I would strongly recommend that you do not overrun the heater. It can die without warning or go very low emission as most of these will have done by now. Chassis back in, Back on, soak test, write the bill out and return to customer... John.

[Freya]

Hi John,
Would you be able to post a scan of the circuit details description from the Ekco data please.

Thanks

[Heatercathodeshort]

Sure. Do you want the whole circuit? Maybe better if I email it to you due to limitations with file size/quality. J.

[Freya]

OK, PM sent

[Heatercathodeshort]

I've sent the scans. It is a very large file! J.

[Heatercathodeshort]

Hello Robin,
The CRM92 in my TS88 is a bit weird but still gives a reasonable picture. I have uploaded two pictures taken a few moments ago, one with the brightness turned well up causing whiteout and the other very close up. You should be able to see the thick make up of the screen phosphor, more like a paste than a micro fine coating!
The other picture is from the TS46. 1/15th second, hand held, not good but it gives you some idea compared with yours. The focus is perfect in the flesh. I think yours is very good example considering it's age etc. Regards, John.

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Haha yes john I`m also getting fed up of prodding the old girl but I must try a new P61 as the only spare I have is not as good as the one in the set and I want to try PJL`s advice of powering the focus coil externally as this will prove a few things.
I`ll take your advice john to leave the crt filament volts as it is.
Thank you for checking your ekco service sheet for me.
The picture on the ekco ts88 is a soft focus but very acceptable.
My ts46 picture whites out just like yours , I`m surprized what a huge brightness range my chassis has .

Robin

[Leon Crampin]

Remember if you are testing the ability of a focus coil to produce a constant flux, you must supply it with a constant current. Flux is a function of current and the number of turns on the coil.

Mind the back-emf from such a coil when you remove the supply. Fitting a parallel inverse connected diode might be a wise precaution, as you wouldn't want to stress the old dear's insulation - or yours for that matter.

Leon.

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Hi guys , I`ve been busy with other things but am now back on the TS46.
Right , I got a new P61 and that made no difference so next I tried running the focus coil from an external supply.
After disconnecting the coil I fitted a 112ohm dropper resistor to complete the TS46`s circuit and then connected the focus coil to a variac via a bridge rectifier and smoothing cap.
This worked very well and only took 25v to focus the picture.
The focus problem was still there along with the hum so that proved that nothink was affecting the focus coil although I did notice that if I reversed the focus coil wires the focusing was worse.
After fitting every thing back to normal I fitted a new MU14 rectifier in place of the cossor 451U which gave me another 18v of HT , so now the HT1 line is spot on 360v.
R81 on the eht transformer ( R35 on johns diagram ) which should be 68k was 73k and I had accepted that as close enough but on fitting a 68k I got a small increase in eht , approx 300v.
I`m tempted to wrap it up now and put it back in its cabinet but still cant help thinking about that hum that either goes up or comes down the picture and pulls the focus out as it goes , any more ideas ?

Robin

[line sync]

Hi Guys
Its been a while since I added something to this thread.
Right , I had access to another valve tester so I re tested all the valves and found some of the r.f valves had some heater/cathode leakage so these were replaced.
These replacement valves seemed to make no improvement at all.
On reading threw some valve data books I found out that the MU14 rectifier I had fitted was only capable of passing 150ma and a check on the chassis revelled it was drawing 225ma which is also stated in the service data so I fitted the correct UU8 and mazda octal base.
If you remember my chassis came fitted with a cossor 451U which uses a british 4 pin base and the 451U was a bit tired .
After this I fitted the chassis back into its cabinet and have watched the set for a few evenings .
The picture can only be viewed under low lighting levels so that the brightness level can be kept low but the focus varies a lot between dark and bright sceens.
The eht regulation on this set is disappointingly poor but I do know things could be better if my crt was more healthy .
Please see pictures below showing off screen shots and the completed set.

[Heatercathodeshort]

The R.F. EHT system was never a great success. It was only incorporated in receiver designs for about a year and most manufacturers did not use it at all.
It was the first attempt to get rid of the bulky and dangerous mains derived EHT transformer that the manufacturers had jitters over since its introduction.
Your Ekco looks good to me. My TS46 struggles after a couple of hours use but the TS48 I restored at the BVWTV museum at Dulwich holds up quite well. All the same they are all on the tip of technology as it was in 1948.
You may discover your CRM121B is slightly, very slightly gassy and this will have some odd effects with the beam current.
It's as old as me..Nothing is perfect.
Regards, John.