Hi from RR. Which LOPT do you think was the most reliable? For me it was definitely the old Rank A823 series, closely followed by the Thorn TX9. Both of them British, although having said that my spare TX9 one has Hitachi printed on the side. I had loads of A823s and while I had all manner of failures with these I never had to replace a LOPT in any of them, or those belonging to friends and neighbours which I used to fix either, I had to replace plenty of triplers on these sets but I never had one take out the LOPT with it as so many others did. Another brilliant piece of British engineering. What a pity Rank didn't manage the same brilliant reliability with the dreadful T20. RR.
The only problem CTV LOPTX I had was the original dual standard RBM, the one we fitted the Davy lamp mod to, I cannot recall changing any others.
Apart from the RBM TV161 and later B/W range and the earlier pre Pye Ekco LOPTX which I carried on the van, I found other B/W ones reliable, this of course was in their service life.
Frank
Thinking about the Rank T20, i only serviced these for a couple of years from new, two faults that come to mind, tripler arcing over and the resistor in the base of the line output transistor going high and damaging the line output transistor, cannot remember if it was 1 ohm or 10 ohm, it went high keeping the transistor longer in themiddle of its bias instead of cut off or fully on increasing its dissipation.
Frank
Hi, from RR. I've never had any contact with a Rank that old. I know they had a "quadrupler" instead of a tripler like the others. I found the T20 to be dreadfully unreliable. Especially the power supply which as I remember the positive + o/p from the mains bridge was connected to the chassis and HT which if I remember was about 200 volts was sat on top of the 320 volts or so from the bridge so between the negative - o/p and the HT+ you had over 500 volts! and all live! And the scancoil connector on these chassis was underrated too and used to burn out and make a right mess of the board it was fitted to. The Rank TV161 LOPT used to fail and so did the de-sat coil that was with it. I found the old Thorn 900/950 "jellypot" to be reliable too, and somewhere I have an article showing how to fit one on an old Bush TV125. RR.
The original RBM CTV had a 25Kv winding with PD500 and GY501 valves for shunt stabiliser and rectifier, think I have the numbers correct.
The LOPTX caused a few fires in the set, no idea if it caused damage to the room etc. Rank brought out the Davy lamp mod kit, I.e. a wire mesh to fit inside the Line can so flames could not escape the confines on the can and cause other damage. I fitted the mods to a few sets but never had one go up in flames.
The quadrupler was I think I marketing tactic to say" look our new sets have a much lower voltage on the LOPTX to make it safer, others only use a tripler" At least that was the story the rep tried to sell us.
Frank
Frank
G11. Saw 1000's of them, never changed a lopt. May have swapped the odd panel for burn ups, but never changed a lopt.
TX9 too, also TX10's EHT (chopper) transformer and Lopt (two different TX's.) Never changed one of those either.
All those early Japanese sets, Sony, Sanyo, National, Hitachi. Never had the back off those really.
Something I noticed with the Japanese built sets was the much better insulation on the EHT sections, even the anode cap on the CRT was much better than many UK sets. I presumed at the time, rightly or wrongly that they had much more experience with their sets in humid climates and not worth down grading for European climates.
Frank
Frank
For me the Thorn jellypot range of loptx were by far the most reliable, Malc.
There is one unused Bush A823 line output transformer in the shop. Perhaps it might work in the G8? The line output stages are very similar as is the frame output stage.
Ekco line output transformers were among the best, it was the Perspex housing that gave all the problems.
How about the line output transformer employed in the GEC colour single standard hybrid chassis? Models 2040 etc. I can't remember having any problems with that one. Same goes for the C2110 single standard solid state chassis.
The worst? It's got to be the Decca CTV25. Horrible unreliable line output transformer in a horrible set.
The single standard CS2500 receiver was a lot better.
Malc is right about the Thorn jellypot. Very reliable tranny.
Till Eulenspiegel.
I did quite a bit of servicing on VDA screens when they were still worth it and the worst LOPTs were grey Phillips ones. They were potted and just went to shorted turns and failed the ring test.
