Re: My first telly TV22
 

Thanks Andy
I will check those points

Re: My first telly TV22
 

That's fantastic! Very bright and wide raster too!

Re: My first telly TV22
 

Just checking my notes , and R37 the brightness pot measured 1.5 Meg and should be 50k so looks like I may have a duff pot

Re: My first telly TV22
 

It's easy to open the top cap on those pots (with a small suction cup or a piece of blu tak) so you can check whether you have a broken track or a bad/dirty contact between the winding and the top/down contacts). I had this problem in my pot and fixed it by cleaning and retightening one of the contact holders, which was isolated from the winding.

Re: My first telly TV22
 

Hi Helder
When I got the set the width control was set to max so I was expecting to find some issue here, in fact it is working somewhere in the middle of its range. There was an O/C resistor in the line output stage so maybe this is what caused the sets decline.

Re: My first telly TV22
 

Sounds very good. Was that the 820k anode load on the ECL80? If it goes high, as it usually does, or O/C as in your case, then you get reduced width.

Re: My first telly TV22
 

It was an 8k in the feed to the screen of the line output valve PL81 , listed as a mod on later sets

Re: My first telly TV22
 

The resistor you mentioned measured 890k v 820k on the trader sheet

Re: My first telly TV22
 

Ok, I had forgotten you have the later Mk2 set with the PL81 and associated mods.
The 890k is fine and well within tolerance.

Re: My first telly TV22
 

So measured A1 voltage , that’s the one from the metrosil right?
Getting about 205 v , so a bit low.

I checked the brightness pot and the track was OC right at one end. Managed to fix it for now by wedging a bit of foil under the end contact

Now the brightness is working I can get a better focus by twiddling with the Ion trap magnet but ends up being rather a dim picture. Not sure how sharp/bright it should be

Maybe the tube needs to run in a bit

Any way low A1 voltage may be the culprit?

Re: My first telly TV22
 

Latest screen taken in the dark
Gently glowing valves

Re: My first telly TV22
 

Well done, looks good

Re: My first telly TV22
 

Just reading on the forum and note that ion trap should be adjusted for max brightness right? - in which case my last adjustment may not have been the best thing to do.

Re: My first telly TV22
 

Its easy to reset, best to work with a low brightness to start with so you can see it increase easily as you adjust.

Re: My first telly TV22
 

Are you measuring A1 with respect to HT or chassis? The quoted value is 210V with respect to HT.

Re: My first telly TV22
 

to chassis

Re: My first telly TV22
 

With a DMM you should get at least around 250V, as even the DMM loads the circuit a bit. Low A1 could cause poor focus. The ion trap magnet should indeed be adjusted for maximum brightness.

Re: My first telly TV22
 

Im using a DMM

Any suggestion why I would be getting a low voltage - where should I be measuring from Chassis or HT?

Cheers

Re: My first telly TV22
 

From chassis is fine. The value should be stable, an according to several posts on the forum it should be between 200-300V when measured with a DMM. I get 250V on mine, and it's fine (tried a replacement metrosil, and got the exact same value). I guess it will depend on the exact impedance of your DMM/scale. The value quoted in the service sheet (300V with respect to chassis) is for an electrostatic voltmeter. The Bush fault sheet quotes 210V with respect to HT, so basically the same thing.

Re: My first telly TV22
 

Hi Travellingwave,
the clue as to whether you are loading the A1 supply significantly when you measure it is to see if the raster dims a lot when you take the measurement.

Have you replaced the A1 decoupling capacitor? It is 0.1uF 500V and is hard to spot as it is underneath the tag board that is below the chassis.
If you have replaced it then metrosil if probably faulty, which is quite a common problem with these sets.

The circuit I have attached will replace the metrosil.

Cheers
Andy