1. Unless you are upgrading and altering the circuit designs within your amp, the new transformers must have the same turns ratio for voltage in and out. In other words, whatever the original input and output voltages are in your current transformer, that is what it must be for your new transformers. With Higer VA rating, that means for the example I stated above, that the current output will be different.
2. Current in-rush must be considered. you would need a slow start circuit.
I have found more benefit by upgrading my power supplies, larger capacitors, separate power supplies, etc. and upgrading the output transistors and pre-drivers to newer, more linear powerful transistors. I have also added Threshold style heat sinks to my amps and altered the bias accordingly to more class A operation. Amps such as Bedini, Threshold, etc. really benefit from this.
By-the-way, you can bias for various levels of Class A. What most people feel is class A is bias whereby the output drivers are producing rated current with no signal. you can bias to lower amounts also. Say, for example the amp is a 100 WPC amp. Nelson Pass on his web site gives several examples of heat sinking, transformer characteristics, amp design, etc. so take a look at his web site, but, for full class A, this means that the output drivers are biased for current output that equates to 100 WPC for the amp. you can bias for 5 WPC, 10 WPC, 50 WPC, etc. This totally depends on the transformer capacity, other circuit considerations and mostly proper heatsinking. To have true full output class A, you need rediculous heat sinks and they cost a ton of money. This is why most amps are not true full output class A, but are biased to class A for lower wattage.
So, if you really like your amp and want to upgrade it. Try upgrading the power supplies first. Then look into new more linear output transistors and pre-drivers. for tube amps, that is a totally different story.
enjoy
2. Current in-rush must be considered. you would need a slow start circuit.
I have found more benefit by upgrading my power supplies, larger capacitors, separate power supplies, etc. and upgrading the output transistors and pre-drivers to newer, more linear powerful transistors. I have also added Threshold style heat sinks to my amps and altered the bias accordingly to more class A operation. Amps such as Bedini, Threshold, etc. really benefit from this.
By-the-way, you can bias for various levels of Class A. What most people feel is class A is bias whereby the output drivers are producing rated current with no signal. you can bias to lower amounts also. Say, for example the amp is a 100 WPC amp. Nelson Pass on his web site gives several examples of heat sinking, transformer characteristics, amp design, etc. so take a look at his web site, but, for full class A, this means that the output drivers are biased for current output that equates to 100 WPC for the amp. you can bias for 5 WPC, 10 WPC, 50 WPC, etc. This totally depends on the transformer capacity, other circuit considerations and mostly proper heatsinking. To have true full output class A, you need rediculous heat sinks and they cost a ton of money. This is why most amps are not true full output class A, but are biased to class A for lower wattage.
So, if you really like your amp and want to upgrade it. Try upgrading the power supplies first. Then look into new more linear output transistors and pre-drivers. for tube amps, that is a totally different story.
enjoy