What happens to a 110v stereo amplifier when connected to a 220v supply?

Answer 1

Perhaps nothing, assuming the amplifier converts the AC to a DC signal. If this is done, the power supply may not filter the AC signal to as clean of DC as it did at 60Hz, which could cause a little bit of power supply hum.

To be 100% sure, a schematic would need to be looked at.

If it's any help, I was looking at a Vox Night Train. I don't have access to schematics.

Here's a link for schematics (might be useful in the future for you):

http://www.prowessamplifiers.com/schematics/Vox/

The bottom right has the power input; The "inrush device" I believe is a power capacitor, if it is an SL22, it is rated for 20A at 60 Hz. the amp is fused at 1.25A; scaling to max for 50 Hz brings it to ~16 amps, which is more than enough, so this is not at risk of burning up.

The secondary of the transformer splits off into two parts - the main and a lower voltage circuit for powering the input. BR1, Q1, and Q2 are rectifiers used to convert AC to DC - rectifiers "chop" the wave off so it is unidirectional voltage from the output of these, but it is not true "DC", since it will have substantial ripple. The capacitors and resistors to the left of these are used to reduce the ripple. So everything beyond this point doesn't really care what frequency you use. The impedance of the capacitors will be more at 50Hz, which will cause less ripple smoothing, which could result in some hum.

The real issue here will be the transformer - at 60Hz, less turns and/or a smaller iron core can be used vs. 50Hz (FYI, this is one reason marine power is ~400Hz - it allows equipment to be sized down). I'd find a serial number or data for this transformer, and look up whether it is made to run at 50Hz. If it is not, it will likely overheat. It may be necessary to replace with a beefier transformer to run at 50Hz.

Answer 2

It explodes