LM3875 gainclone help!!!

[MJL21193]

It is possible to use two transformers to get a split power supply, but they should be identical. Voltage is not the only consideration either. The transformer must be capable of suppling enough current( amps) otherwise your amp will try to use more power then is available. If you are serious about building your own amp, then you should get the correct transformer. No, they are not cheap, but they do have a resale value if you decide you are not interested anymore.
In the meantime, do what I did for my first amp - build a cheap lower voltage split power supply to test fire your amp. At Radio Shack or where ever buy a cheap center tap transformer(2 wires on the primary side, three wires on the secondary) 12-0-12 at 1amp is enough. Unless you have one of these laying around of course.
Have fun

 

[DavidWardlaw]

I have 2 or 3 transformers with 2 wires for input (these connect to 120Volt) and 3 output wires. Here's how I found out the output wires work work:

Voltage between 1st and 2nd is 6 volts
Voltage between 2nd and 3rd is 12 volts
Voltage between 1st and 3rd is 18 volts

Is this what you're talking about?

 

[MJL21193]

Not quite. Center tap means the coil was connected to in the middle, spliting the voltage. You would have 12v on 1 and 2, 12v on 2 and 3, 24 v on 1 and 3. The last thing you want for an amp is unequal supply voltage.

 

[DavidWardlaw]

I found 2 transformers that were close in voltage (26 & 28 Volts) and I unwound some of the coils on the 28 Volt transformer to make it 26.05 Volts. So I hooked up the 26.00 Volt and 26.05 Volt transformers to the amp and it worked. (yay!)

I have a heatsink that is solid aluminum. Dimensions are 4.3" wide, 1.7" high and 1" thick. Is this enough?

About the Voltage...is 26 VAC in the proper working range, or is it too high? I'm using an 8 ohm speaker.