[Techman]

Just to mention - I may have confused you slightly by saying 'first smoother'. I tend to call them all 'smoothers', so what I probably should have said was the 'reservoir' capacitor, as it's the ones that follow that are strictly the 'smoothers' which you have identified in post #114.

Edit: Just to add - you could probably monitor the HT anywhere along the 'smoothing' line, but I think that monitoring at the first stage 'reservoir' capacitor is the best place to clearly see what's going on.

Second edit: Watch out for any sparking about in that rectifier valve. These old directly heated rectifiers can sometimes be dodgy.