Isolation Transformers--Richard Gray or Torus?

Ever measured your output voltage ? The Plitron 2kVA isolation transformer they sell to DIYers (SKU # 8575-X0-02), has a 115V primary (I don't know why, with North American standard voltage being 120V?). I tried one many years ago. With my household voltage ranging betwen 122V-123V, I was getting up to 130V output from the Plitron, even when moderately loaded.

Hello Chart.

116 VAC in, 121-2 VAC out, both transformers, no load. Same model number.

Seems similar to what I experienced Terry. You're getting a no-load increase of +5-6V over nominal input. You have 116V in, so the secondary voltage is not an issue for you. Anyone with 120 VAC line will see 125V-126V on the secondary with a Plitron tranny -- more if they have high line like I do. I have tried other brands of balanced toroids with a 120V primary instead of 115V, and not experienced such an increase in no-load voltage.

Gbart makes an excellent point that rarely gets brought up. 115V primaries have given me headaches, especially in tube amps. Just about every tube amp I have had had to be tweaked to accommodate for this since my wall voltage is consistently around 124V (sometimes 126!). Otherwise the anodes and heaters are overdriven. This issue is WAY underestimated because I think most people's wall voltage is just as high these days and creeping up higher each year. Correcting for it makes a big difference when you're talking 400V anodes! Not to mention most tube filaments I've seen run at 7V instead of 6.3 when the feed is taken right off AC secondaries. I just modified a pair of monos the other day that had 15V instead of 12.6V. This will adversely affect the sound and shorten the life of the tubes by about 60%. I think a lot of people haven't really 'heard' their tube amps because of this. I just don't understand why 115V primaries are still so common. It's an old legacy design that really needs to move on. Ironically, the only amp I've had that can select between 117 and 125 Volt input is my 50 year old McIntosh MC240.

Arthur