Interchangeable power transformers

[stevenball]

I was wondering if anyone could answer this question: would a PT with 340v – CT – 340v @ 70ma be compatible for a project that needed a 290v – CT – 290v @ 100ma power transformer? Using Ohm’s law would these PT’s be kind of electrical synonym? Using Ohm’s law they are only at a 10 watt output difference (48 watts vs 58 watts) and approximate 4000Ω difference in resistance. I am building home brew tube guitar amps and have a few old Stancor PT’s I would like to use. This may seem like a dumb question but I am full of them as a beginner.

[52 Bill]

I was wondering if anyone could answer this question: would a PT with 340v – CT – 340v @ 70ma be compatible for a project that needed a 290v – CT – 290v @ 100ma power transformer?

Welcome to the place. As for your question, in a word no.

I think you are confusing the concept of power here. While the two above mentioned transformers may be only 10 watts apart in power ratings, the differences in the voltages is enough to make them unsuitable substitutions in circuit applications.

If the circuit is spec'd for a 290-0-290 volt secondary, then depending upon what sort of rectifier is used, the circuit is expecting to see a specific dc voltage, let's say 405vdc. If you build it with a 340 volt transformer the dc output would increase to 476vdc. While some tubes and circuits may handle this sort of increase, the majority will not.