Measure the DC resistance per Damir. Or just using the dc resistance of the secondary will be close enough to tell if the transformer could work.

As a rule a choke input filter will give you about .7 of the rated voltage cap input about 1.4

Remember if you have say a 250-0-250 transformer, in Psu2 with a full wave rectifier (normal hook up for a 5y3) you state the transformer as 250V.

If you can’t get a high enough voltage, switch to a full wave bridge (SS or tube) and try again. Only in this configuration, you state the above transformer as 500V

Have fun…John