Yokogawa TY720 without gas discharge tubes

[Bobson]

I've got second hand TY720 which lacks both GDTs. Since I have dozens of other DMMs, I don't plan to use it to measure higher voltages, but would like to know, what max voltage would be safe without GDTs?
If up to 300V AC is ok, it would be ideal.

tia

[Kean]

Presumably whatever it is specified to measure - which seems to be 1000V AC & DC.  The GDTs should not normally conduct under those measurement conditions.

But be aware that it may not survive any unexpected spikes/surges, and it may not still meet its specified CAT rating.

Why are the GDT parts missing?

[Bobson]

I don't know why are they missing, the DMM is well used. All functions work ok, and measurements are still  to specs.