I could have bought a perfectly respectable example of this set at Harpenden 5 years ago - I think the fact that it said 'good working order' was the reason I didn't: after all, where's the fun in that!?
Instead, I bid on a tatty one in the auction, hoping to get it for a fiver or so, but ended up in a bidding war and had to pay £23 quid!
I got it back home and gave it a quick look over. It had obviously sat somewhere very damp as the plywood bottom had rotted and was very soft. The metal trim on the front was covered in corrosion spots and the VHF tuner knob was broken. The cabinet was tatty and there were a few scratches on the screen. All in all, it looked rather sorry for itself.
Removing the back at least confirmed that there was actually a chassis present! Both tuners were also in residence and apart from the 6F28 video amp valve having a white top, the rest of the chassis looked fairly unmolested from what I could see of it under the grime and damp cobwebs!
I hooked up the tube tester and was pleasantly surprised that the Mazda Goldstar had plenty of emission. Actually, people knock Mazda tubes, but I've never found them to be any worse than Mullard ones - I guess by the mid '60's they had become much more reliable.
I replaced the back, made a mental note to get a 6F28 and poked the set away in a corner and forgot all about it for five years....
....Until last night! I suddenly had an urge to drag it out and do something with it. So I did!
Removing the back showed that three more valves had leaked all their vacuum away and now had white tops. I rifled through my meagre stock of second hand valves and found a PCL85 frame valve, a 30PL1 Audio O/P valve and an EF184 IF valve. The ones I removed all had green pins due to corrosion.
I stripped back the very hard mains lead to reveal completely black conductors - another sure sign that it's been very damp, and connected it up to some mains.
Turning the on/off switch produced a bright flash from the 1.5A fuse and that was the end of that! A quick check with the meter showed that the HT rectifier diode, W11, was short, so a BY133 was fitted in its place. A new fuse and a second power up and the results were less dramatic. The valve heaters started to glow and shortly a loud buzz came from the speaker.
So far so good, Ah, where's that smoke coming from? Looks like R97, 470R feed to the audio stage. Check the circuit and find it's decoupled by a 12mfd capacitor - check the board and oh look: it's a Callins! This was hot to the touch confirming its guilt and was quickly replaced with a 22mfd temporarily.
At least with Thorn sets that use the 'jellypot' LOPT's, you know the line stage is always going to work. Powering up again proved the point and a raster appeared. Applying some UHF signals and giving it a quick tune, produced a quite decent, contrasty picture although with a very distorted frame scan.
Changing the system switch manually to 405 and applying some test card 'C', proved that the signal side was working on 405 as well.
So I am happy with initial progress and so far the tube looks to be pretty good. The next step is to sort out the frame stage. There are plenty of capacitors there which will inevitably be leaky, but none of them are of the notorious 'change on sight' types, so we shall see who the culprits are later on this evening!
I shall add some pictures later on as well once I've had a further play.
All the best
Nick