Thorn/BRC 2000

[Refugee]

Perhaps I should have put the link between the two sentences.
I was just pointing out that the part is made.
I had a quick look in a drawer full of pulls from old computer screens and spotted a BU2508 in the fully insulated package.
I don't think I have seen a high gain transistor in anything else but 12V portable sets.

[ppppenguin]

I've started to run the other LTB board and it's promising. I'll give it full volts later. With a 32V external supply there was about 280V peak on the upper collector. So with full volts it will be around 500V. Hence a pair of BU102 should be fine on the faulty board if I decide to get it going.

[ppppenguin]

A friend who's not on the forums pointed me towards Cricklewood Electronics who have a stock of the later TI/Thorn R2008 line output transistors. At £1 each! I've ordered a few.

In the meantime the original LTB board with the squre transistors is looking promising. There's a problem with the regulator so I've got it on an external PSU for now. It's happy, it's locked and I took the scope probe off the collector of the top transistor when it reached 400V p-p. I don't have a high voltage probe, nor a 100:1 probe and my 2465B scope only goes down to 5V/cm.

I'm going to go for broke and hook up the EHT board. Again with external power so I can bring it up gently.

[ppppenguin]

First light!

EHT currently about 20kV with board being run from external PSU. LTB still on external PSU. All sorts of nasty intermittent effects but there's a picture. It's even fairly converged and purified.A quick degauss showed near perfect purity. It comes into focus, gives at least some brightness and the red doesn't bloom as you raise the brightness which was the classic problem with a failing CRT. So fingers crossed I've got a good tube.

[pwdrive]

Lawrence.

[ppppenguin]

I'm quitting today while I'm ahead. Friends coming for dinner this evening so much kitchen activity and I ought to be helping a bit.

I need to wean the LTB and EHT off their external PSUs. Once I've got a fair looking picture I can find out why there's no colour. Absolutely nothing when I turn up the saturation. The decoder is all discrete and pretty accessible. I don't see any problem getting it to work. Famous last words.

Funny thing is that I've designed a number of PAL coders using nothing more complex than 1496 modulators and a bit of CMOS logic. I've nver done a discrete decoder, for the one design I did that needed an analogue one I used a Mullard telly chipset. Beyond that I've used digital decoder chips such as the Philips SAA7111. The more modern of these chips do an astonishingly good job. I've not used it myself but the TVP5150 used in the Aurora SCRF is excellent. Composite video in, 8 bit digital component video out, complete with good comb filtering and minimal artefacts.

[Murphyv310]

Good stuff Jeffrey.
These are great sets and well worth the effort.
Enjoy your evening. Fish supper then tell them you have a pressing engagement.............. BRC200    

[ppppenguin]

Trevor, how did you know it was a fish supper? I poached a couple of smallish whole salmon. With salads and pink wine. Delicious. About to have meringue(sp?) which Ruth baked.

I've had enough pink wine that I'm not going to be mucking around with electrickery.

[ppppenguin]

After a long break, part of which was on holiday in France, I finally switched on the 2000 again. Glad to say that it's still working very much as before, still with external PSUs for the line scan and EHT. The message this time is that there are hints of colour when I turn up the saturation control.

The next job is to wean it off the external PSUs. not sure when I'll get to it as I'm meant to be doing some actual work for a client and the 2 things are rather fighting for space on the bench.

[Murphyv310]

Ah well you need to make money to live........ work then play Jeffrey.