| A transformer will increase the output by the same percentage as it's input has been increased, so a 10 volt increase on the primary to 230 will equate to a lerger voltage increase from the secondary, if the secondary is putting out 12-1400 volts allready it would increase by about 50 volts "allegedly".
Buy some better valves just in case.
Watford valves are a good source. | 
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