Input voltage range for tube oscilloscope

[glebert]

I'm trying to figure out what is a safe input voltage range for my old Telequipment S51b tube oscilloscope. Manual for it is here: https://www.hobbielektronika.hu/foru....php?id=118371 From a simplistic standpoint I would assume that since it has a 50/v division setting I should be able to go full screen at that setting which would be 400V.
I am more used to solid-state scopes that give a max voltage on the front plate or in a manual but I don't see one. Also, because of the age, am wondering if the DC blocking cap may fail in AC mode if I go too high in voltage even if it is within the range that the scope was designed for.

Thanks for any input,
Greg

[J M Fahey]

400V is a safe assumption, check whatb the input cap rating is, you won´t go higher than that, it´s for sure.

I suggest making an extra high voltage attenuator for higher voltges, **including** power tube plates, which rest *at idle* near 500VDC , regularly reach twice that (many ignore OT see-saw action) on resistive lods, can easily reach 1100 or 1200V peaks with speaker loads and if you forgot to plug a load, the Sky is the limit.

Ok, ok, not the Sky ... but *can* reach 2500V peaks or even higher.
After all, there must be a physical reason for OT to die, punched through and through , or sockets arc and burn when you forget your speakers and strum chords full blast.

[glebert]

Thanks Juan!