Thank you to those who have contributed so far.
Well, I managed to get the two caps on the LOPT replaced. The trouble was the only suitable capacitors I had in stock were physically larger than the ones that needed replacing, so whilst I could have taken the LOPT out from the bottom, I decided not to in case I ran the risk of replacing them and then not being able to fit the LOPT assembly back into the set. So I elected it would be more practical, although more difficult, to take the tube out. First I unsoldered the LOPT connections from the set as it would have been much easier to do if (of course) the LOPT was totally free.
I think the tube mounting is different on the V300 than it is on Jon (and possibly Mark's?) example or chassis, as the CRT on this is anything but easy to get out. As you would expect, the top panel needs unscrewing first, then the four CRT mounting screws, two bottom, two top. The bottom ones are fixed through sections that are bent upwards at 90degrees so the screws can tighten up to them. Easy? So far it is.
The next stage, i.e. actually removing the tube is difficult because those two bottom screw mounts being bent upwards are precisely the things that stop the tube from sliding out. You can't simply "pull it up", because just behind these mounting holes the rimband slots into holes on the chassis. You can't remove the tube by sliding forward out of the slots (because of the screw mounts) and you can't pull it upwards because of the slots. I searched all around the front part of the chassis for the best part of half an hour trying to work out how to remove it. I thought about sliding the CRT about an inch or two to one side and then pulling forward, as the rimband "arms" that slot into the chassis came into the slot from a side, but on each slot the arms slot in opposite sides, so as you slide the tube one way, one of the slots meets the rimband end of the arm. Slide it the other way and the same happens on the other rimband slot. The "arms" that slot into the slots are so long that it meets the rimband end of an arm before it meets the clear end of the other rimband "arm".
Short version is: The tube wouldn't come out.
(Why didn't they just design this with the arms that slot in both facing the same direction? That way you could just unscrew, then slide to one side by a few inches to release the rimband from the slots and then the tube assembly would be free!)
I hope that's a detailed enough description of how awkward I found it to get the CRT out of this.
In the end I came to the conclusion that the only way to get the tube out is to slide forward *but* first to bend the bottom screw mounts downward using pliers or somesuch. This frees the CRT and rimband to come out of the rimband slots. Overkill maybe, but in the face of what I was confronted with, it looked like the only option, so I'd welcome anyone explaining or showing me an easier way to get the CRT out as I tried for a good length of time and found no answer.
I then unscrewed the LOPT, did the capacitors, slotted and screwed the LOPT back in, put the CRT back in, bent the screw mounts back as best I could, screwed the tube back in, screwed the top panel back on, then resoldered the LOPT assembly.
All that hassle just to replace two capacitors on a s&£!$ng LOPT! I get the feeling that if the whole thing had been designed from the servicing point of view, then a lot of time and anger could have been saved! But no, they had to design the most awkward chassis I have restored so far! *rantover*.
I also replaced a wax capacitor, C91, directly below the LOPT assembly. I only had an old used TCC yellow plastic capacitor as a suitable replacement, so until I got some new ones I had ordered, I thought I might as well use this one to prove that the circuit works. When I got some of these capacitors as part of an eBay auction for some valves, I tested each one and they all seemed to work OK, so possibly one slipped through the net and got fitted to the set. I mention this because there is now no line whistle at all. So on to the next stage, measuring the valve voltages in that part of the set, but first, yet another deviation, except this one was much more fun than replacing the caps on the LOPT!
To measure the LOP stage valve voltages you obviously have to turn the set on to its front. The strange thing was that when the set was upright, there was sound of the test tone from the Aurora through the speaker. on its front and switched on, there was no such thing as sound. Before I even went to check the speaker and audio stages, I noticed something I have never seen before.
When switching the set on with it upright, all valve heaters lit normally and, apart from the LOPT stage, it all worked fine.
However, with the set switched on but on its front, I noticed something strange as it was warming up. The heater in valve 6 would come on first, be brightest for a few seconds, then flicker back to about normal brightness as the remaining valves all warmed up. Then, after about 5-100 seconds, the heaters in valves 1, 2, (both tuner valves) 3 and 4 (both vision I.F.) would extinguish but they were still passing current (the valves before and after valves 1-4 were brighter than usual) as the valve chain as a whole didn't go out. Of course it couldn't be a dry joint in the heater circuit as all valves would go out if there was, so it had to be a defective valve (far more likely) or heater decoupler (far less likely).
Using the clue that it worked OK when upright, I powered on with it upright, waited for all valves to be fully heated then began slowly tilting the set forward. Did the valves go out? Did they hell as like! So it seems whatever it was was only affecting the valves when they were in the first few seconds of warm-up.
And lo and behold, replacing V9 (EF80, first sound I.F.) solved this. The valve heaters now work fine whether upright or screen facing downwards. Of course sorting this was essential as the power supply and heater chain need to be working properly in order to take voltage readings to diagnose another fault.
So a real mixed bag of a day, from the depths of pure hatred, spitting blood and screaming blue murder and a whole shedload of other blue words at the thing when going through the labour intensive task of replacing two capacitors on the LOPT to the much more fun task of diagnosing an electrical fault.
Even just recounting yesterday's events has soured my mood! I think I'd better calm down before tackling the lack of EHT! Even though my typing/prose style is that of someone who is permanently grumpy, I am actually quite a docile person so something really has to push me hard to come to the point of swearing and cursing out of anger. Yesterday, this set pushed all the right buttons!
One thing's for sure though, this chassis is not service-friendly! If the lack of EHT is down to a simple mistake on the LOPT - I didn't want to go through this again as it was so labour intensive so I made sure I wasn't making any - I am not going to go through the rigmarole of stripping this set down again!