Designing around PT tolerances

[number11]

Wondering how people deal with PT secondary tolerances when designing from scratch?

I recently rebuilt my 5F1 champ clone I bought off a local builder a few years ago. Lower voltage PT, replaced the cc resistors with cf, larger filter caps, cathode caps, better ground wiring scheme, etc. Overall it made the amp sound better, less noise, but I redesigned it around a 5AR4 with a hammond PT of 500CTVac and when I hooked it up under load it's supplying 533Vac/333Vdc B+ so I went back to using a 5Y3 to get the rails closer to what I wanted, not such a big deal.
However, in the future I'd like to be able to anticipate and plan around it. I've built a few clones (bfpr, 5e4, yba2a...) and they sounded pretty good and the voltage differences on the rails was low enough not to be a big deal, but this is the first time I re/designed a circuit. I have other designs I want to prototype.

[loudthud]

The tolerances are not as wide as you assume, you just don't understand the specifications and how transformers are rated. The first thing you need to do is look at an actual spec sheet for a transformer. Hammond has them. I think this is the one for the 5F1 link: http://www.hammondmfg.com/pdf/EDB290AX.pdf

If you want to predict the output voltage under certain conditions, you need a modeling program. Things like rectifier type, winding resistance, open circuit voltage, filter capacitance and ESR, and current draw all need to be taken into account.

If you are running a Windows PC, Download a copy of PSU2 link: PSUD2

Learn how to use it, especially the part where measure the resistance of a transformer's windings and the open circuit voltages. If you put all the data into the program, the results are fairly accurate.

If you are running a Mac, you will have to find some other program.