Ekco TS46 1948

[FERNSEH]

The attachment shows the video amplifier stage and the white spot interference limiter. With V6 removed the only source of the negative grid voltage has to be diode V7 rectifying AC ripple or HF from the HT supply.
Do you have access to an oscilloscope?

DFWB.

[G8KBG Tony]

Hi Matt,

Have you checked R22 and L13 to see if either are O/C?

Regards,

Tony

[Freya]

To Avoid confusion, Matt is using the genuine Ekco sheets which have different references.
I can see that David and myself were essentially saying the same capacitor but different sheets.

[G8KBG Tony]

Thanks Stephen,

In that case R19 and L11.

[matspar]

Thanks to all for your advice, plenty of things to look into. I will quote references from both circuits to avoid any confusion when I next have a look. Best regards Matt

[matspar]

A major breakthrough tonight!! after more and more head scratching I discovered that the dreaded negative voltage was appearing on the plus side of C65 (32uf)
I hung a new one in to rule this out and there were no improvements. The incoming HT is delivered via a nice big 5w 1K resistor (R77) mounted above deck on a small sub assembly, and yes you've guessed it by now....it was o/c!!
With a nice new old stock RS replacement we have a fairly happy TS46 with what looks like a very decent CRM92 and no more negative voltage readings. I am to be mocked for eternity for being so foolish and missing a simple resistor!

There's still a bit to do, the frame linearity is poor and the sound output is now horribly distorted. There's still plenty of waxies in both areas to be restuffed so I'm quietly confident of a decent result now!! thanks again to everyone for your help. More to come soon!

Matt

[Freya]

That's a good looking tube, they do get a bad press but out of all the 8 or 9 sets I have with CRM92`s, none have been bad at all......so far.

Glad you got it sorted, it had us all thinking.

[mark pirate]

That's a good looking tube, they do get a bad press but out of all the 8 or 9 sets I have with CRM92`s, none have been bad at all......so far.

It does look to be a decent CRT, I have five sets fitted with a CRM92, only one has reasonable emission, the others are only watchable in the dark

I bet that the tube in the TS46 has been replaced at some point, back in the day these were commonly going low emission after less than two years!

Mark

[matspar]

There's a good chance the tube has been replaced, possibly quite late in the sets life before it was abandoned for eternity. It's very bright and certainly hasn't clocked up many hours. Very lucky with this one.
With the exception of a pair of slightly later smoothing cans (probably middle fifties) the TS46 was totally original underneath.

Matt

[mark pirate]

Hi Matt, looks like you have a really good set there. I am pleased to see you are going to the trouble of restuffing the original caps, this set certainly deserves it!

The tube certainly looks very good, I suspect it will get even better after a few hours use.
I look forward to seeing the end results, should be a cracking little set.

Mark

[Heatercathodeshort]

That looks really great. For your sound distortion check the coupling capacitor C48 [Ekco circuit] C52 ERT.

Check also R51 4.7m in noise limiter circuit. R41 ERT. The frame problems are probably the usual caps. John.

[matspar]

Spot on John, C48 was indeed leaky and replacing this has cured the distortion. Sounds very good. The pair of 4.7m resistors were surprisingly innocent.
The linearity was a bit fussy. Hanging in temporary caps didn't make any real difference so I performed the Ekco mod and replaced the PEN45's 680k cathode resistor.
I first hung a 2k pot in place first and gave it a twiddle, noting the effects on the testcard and the final value (1.1k) when I was happy with it. The service manual says to fit a 1k so not a million miles away!
Some pics from earlier. That's about it for the chassis so attention will be now be turned to the cabinet

[matspar]

As a little post script to this thread I'll wind it up by showing a few photos of the finished set. The cabinet has the lighter front fabric, quite 'golden' when you get it in the right light. I haven't seen another online the same so presuming this is less common. Would anyone know if this would indicate an early or a late set?

She has behaved herself so far with good eht regulation. The focus requires some small adjustment during the first few minutes but then settles down and doesn't want to drift, however the focus pot reaches virtually the end of its track and only just about in range. Can any physical adjustment to the focus coil assembly be performed on the TS46 to make the correctly focused picture more central on the pot? think I may have read this somewhere but can't now find the reference.
I was overly lucky with the CRM92A which has fantastic emission. I have restuffed all the wax caps that I've replaced along with one smoothing can C65 8+32uf. The rest of the capacitors are all still the originals and haven't objected (yet!) Many o/c and out of tolerance resistors were replaced.
I've maintained the original appearance of the chassis and the cabinet came up pretty well with some various polishes and a bit of retouching in places. I still may refinish the mask which has suffered from some paint loss. Can't decide whether to let it show its age or not!
The only valve which required replacement was the P61 which was looking very tired and liked blowing the pair of 500ma fuses. A new one has completely cleared this.

[matspar]

A few more!

[HamishBoxer]

Very nice job,mine is sat here and awaiting inspiration as is the mirror lid version I have.

Hope my crt,s are as good.

[mark pirate]

I was overly lucky with the CRM92A which has fantastic emission.

I knew that there must be one out there, looks like you found it
The set has turned out very well indeed, I guess you could repaint the mask if it bothers you, but personally I think it is not too bad.

Mark