As I get older, I find nostalgia plays a bigger part in choosing the sets I want to play with. I seem to be on a mission to re-discover sets that I first encountered when I was a kid in the early '80's.
The Thorn 1500 was something that came my way fairly often. I was given several, repaired others for use with ZX81's at school, and often found the remnants of them dumped in ditches and farm gateways near our house.
TV's then were free. People, knowing I had an interest, just gave them to me, much to the annoyance of my mother. Even now, I can't accept that they are worth the price that Ebay would have us believe! So the sets that I am now re-acquiring have to be attractively priced- i.e. free, or very near it!
I had been on the lookout for a 1500 which met these criteria for a while, when Neil29 offered one which I was lucky enough to secure.
Thanks to the generosity of Neil and Colourstar, it found it's way from Wales via Sollihull, to the NVCF where I collected it on Sunday.
Back at base, on the workbench with the back off, I gave it a quick check over. I was surprised to see a green pcb:- I remembered them as red but maybe that was the 1400?
There were a couple of tired looking caps with crusty bottoms and the spring off resistor feeding the line stage had sprung off! As I like to do, I hooked the tube up to the tube tester just to see what to expect picture wise. Considering the B&K tends to read low, the emission showed well over into the green, so that was encouraging.
So I plugged it in and switched on. Valve heaters lit and eventually the frame timebase could be heard purring away. Nothing much else though, no line whistle. I'd forgotten this was 625 and that I'm not 20 any more!
I really must remember that I can't hear 625 line whistle these days!!
Looking round the front, showed a bright raster. Connecting a signal showed a very bright picture. The brightness control didn't do anything.
Amazingly, I still have the very tatty photocopy of the circuit that I last used in about 1985! Referring to this showed that the wiper of the brightness control (hence the cathode of the CRT) was at 2V, hence the very bright screen. Further investigation revealed that instead of the 470K control, someone had fitted a 3k9 instead!
The same had happened to the volume control as well.
Fitting a temporary rotary control of the correct value cured the fault.
As we are now back in the 1980's, my test card of choice is the channel 4 one. This has always been my favourite and I still maintain that it's the best one for setting picture geometry and linearity. I much prefer it to test card 'F'. I have a VHS tape recorded in the mid '80's on my 3V16, which I have used many, many times for this purpose.
After a few tweaks and a new width pot which was open circuit, the picture was excellent. The tube is fantastic and displays a sharp contrasty picture- even the focus at the edges is good!! Thankfully, it's a Mullard tube.
Unsurprisingly, as it uses full AC coupling to the cathode, the black level performance is awful. The background brightness is all over the place! This will definitely be a candidate for a black level clamp mod.
Also, it still has all it's Lockfit transistors present! I know people seem to condemn these on sight but I must confess, I've always found them to be very reliable;- I really can't remember ever having a failure!
So all in all, this is going to be a cracking set, especially once the black level clamp has been sorted. Cheers neil
All the best
Nick