I have a number of vintage tube power transformers which specify a 115vac primary input voltage. However, the voltage at my wall outlets measures an average of 125v, with occasional drifts as high as 127v.
The transformers I'd like to use are decent quality -- Stancor, Hammond, Triad, and the like -- and some are exceptionally well-made, like the potted UTC mil-spec pulls from vintage power supplies.
I'd like to drop the secondary output voltages back to where they belong, especially the filament windings. I've read of three methods to do this, and would like to know which is the best.
The first is to insert two 12-volt zeners (of adequate current rating) in one primary leg of the transformer. This brings the input voltage back down to a reasonable value, and the secondaries back into spec.
The second method is to add a bucking transformer to the primary, and thus reduce the input voltage.
The third method is to ignore the overvoltage on the primary, and reduce the plate secondary by using a lower value first capacitor right after the rectifier, or going to a straight choke-input filter. This method also requires putting zeners on the filament windings to drop them to the proper levels.
Are vintage transformers typically safe to operate at a continuous 110% rated voltage on the primaries, or is this an unwise practice? Thanks in advance for your observations.
The transformers I'd like to use are decent quality -- Stancor, Hammond, Triad, and the like -- and some are exceptionally well-made, like the potted UTC mil-spec pulls from vintage power supplies.
I'd like to drop the secondary output voltages back to where they belong, especially the filament windings. I've read of three methods to do this, and would like to know which is the best.
The first is to insert two 12-volt zeners (of adequate current rating) in one primary leg of the transformer. This brings the input voltage back down to a reasonable value, and the secondaries back into spec.
The second method is to add a bucking transformer to the primary, and thus reduce the input voltage.
The third method is to ignore the overvoltage on the primary, and reduce the plate secondary by using a lower value first capacitor right after the rectifier, or going to a straight choke-input filter. This method also requires putting zeners on the filament windings to drop them to the proper levels.
Are vintage transformers typically safe to operate at a continuous 110% rated voltage on the primaries, or is this an unwise practice? Thanks in advance for your observations.