Hi Hugo,
It doesn't help that this set has such a low valve count. There is only 11 including the CRT. Had there been more valves, especially an HT rectifier, the total heater plus dropper dissipation would have been the same, but the heat would have been spread out round the chassis rather than concentrated in the dropper.
We also have high mains voltage in the UK, typically 245 but sometimes even 250V!!
When the chassis is in the cabinet, there is only about 1/2 inch between the top of the chassis and the woodwork. The heat at the top would be intense especially with the back on
I imagine the back would have ended up a big charred mess!!
Still, one of the interesting things with restoring a TV, is seeing what it's shortcomings were and how it would have performed at the time. I'm not sure yet what my ultimate solution will be, but I might investigate the series diode idea- thanks for the suggestion.
Andy, I wasn't sure how much glow you got from a U26- I'm much more familiar with DY87's and the like which glow like a normal valve.
I'd already tried a NOS U191 but that made no difference, so I dug out the only spare 30P4 I could find- a really dreadful looking thing!! That made quite a bit of difference and brought the EHT up to 12KV and a tiny glow from the U26.
Suspecting that this 30P4 might also not be 'top notch', I hooked up a brand new PL504 using terminal block to connect to the pins!!
That worked fine but no better than the 30P4- still 12KV eht.
Obviously I would like to try another U26 but the only spare I have seems to be full of air!! I must order some next week.
The boost voltage is now about right at 525V so things are getting better!
Many thanks for your input,
All the best
Nick