power supply sag, selecting transformer

[martin manning]

A regulated power supply is one which has some active elements that work to maintain a constant output voltage regardless of changes in supply voltage or load. In that regard, the typical guitar amp power supply is unregulated. In my opinion a transformer regulation spec is oxymoronic, since it really indicates how unregulated the transformer's output voltage is with respect to the load.

[statorvane]

I think a lot of builders don't take the transformer current rating into account other than to make sure it is as high or higher than is needed.

Guilty as charged. Maybe this link will help? http://www.dreamtone.org/Calculate_Current_Form.htm

I'm pretty sure the numbers produced are a first order approximation; the voltage estimation is constant - invariant with the number or type of power tubes, but the current varies. I've been using that link to size a PT for a parallel SE amplifier - 2 x E34Ls and two 12AX7s. Seems that a Hammond 270FX would be sufficient.

[talbany]

A regulated power supply is one which has some active elements that work to maintain a constant output voltage regardless of changes in supply voltage or load. In that regard, the typical guitar amp power supply is unregulated. In my opinion a transformer regulation spec is oxymoronic, since it really indicates how unregulated the transformer's output voltage is with respect to the load.http://en.wikipedia.org/wiki/Voltage_regulation

Correct!!.. Not to get 'regulated" and "regulation" confused as regulation just refers to the ability of keeping the voltage constant, good or poor..

In electrical engineering, particularly power engineering, voltage regulation is a measure of change in the voltage magnitude between the sending and receiving end of a component, such as a transmission or distribution line. Voltage regulation describes the ability of a system to provide near constant voltage over a wide range of load conditions. The term may refer to a passive property that results in more or less voltage drop under various load conditions, or to the active intervention with devices for the specific purpose of adjusting voltage.

http://en.wikipedia.org/wiki/Voltage_regulation

Have a great weekend!!

Tony

[VacuumVoodoo]

That's why, when specifying transformers, it's called "load regulation".
It defines voltage drop from no secondary load to nominal load. It's quoted as percentage. Your general purpose OFT transformers will usually have 10% load regulation, you can specify 5% at a premium.