Can anyone help me with these. I've never used them before so its a bit daunting.

It says on the label 500va 42v. I'm getting around 42v AC before the rectifier, but after im getting 60v DC. That would blow my 48v amplifier that I'm trying to use it for.

I'm guessing it may end up around 48v after voltage drop but it scares me to apply it to the amp. Does this sound right ? And also, if there's no drive for a few seconds, it wouldn't be drawing much current and receive 60v. Id end up looking like doc from back to the future after it blows up in my face.

Makes no sense to me

The voltage on the output of the rectifier is supposed to be higher than the output of the transformer by about 1.4x. You’ve measured it unloaded so it will be a bit lower than 62v when it’s powering something. I think a 36V transformer would be better for ~48v.

Hi,
You said:
"It says on the label 500va 42v. I'm getting around 42v AC before the rectifier, but after im getting 60v DC. That would blow my 48v amplifier that I'm trying to use it for."

That depends on your amplifier's load. If it draws some 8 A, you'll possibly get around 47V DC.

It all depends on the amplifier power output and current.

However, if you want to be on the safe side, you can just use a LM317 regulator, driving a pass transistor and you will get our intended output voltage. This is true for both laminated and toroidal transformers .

Unfortunately, the LM317 only works up to 36V. It will go bang at 50V.

However, there are plenty of power regulator circuits on line.

My suggestion is based on my past experience. LM317 is a very important circuit for linear power supplies. I have used it for more than a decade to build 50V/12A power supplies. I used to use 650VA transformers with 45V and 15V outputs. After being rectified and smoothed 45VAC gave 63 VDC that were sent to LM317 to be regulated down to 48V and sent to a series pass darlington transistor. Those power supplies used to be very reliable.