Hello: I have been looking for a schematic diagram for this old Roland spirit 25a amp, with no luck so far. One net advert says they will send me one for 23 dollars, almost what the amp was worth.
I believe the 10a, 25a, 40a, are prety much simillar so any one will be great for me. If anyone has one or a link to one could you please post it here. Thank's very much

Regards: Andy. 8|

Hi' I have a yamaha 20w ss amp, yes the old wedge shaped one
with the strange planar type speaker.It's in excellent external condition,and sounds great,but dose have a bit of hum.It also has tremolo and reverb that work.The trouble is,after about 1hour from turn on, it suddenly gennerates loud horrific sounds similar to thunder and lightning strikes.This happens every time,even with nothing connected and all pots at zero.I must have spent 20hrs searching for a schematic for one of these but have only found promos.I recapped it,but problem remains.The only parts that get hot is a 120ohm 5w resistor,the transformer only warm.There are no IC's and the only diodes are 2, for the rectifier.I changed them as well to no avail.The 2 power transistors are the same NPN,(is this a linear design) I changed these with plastic substitutes,again everything sounds sweet until that 60min mark.this is definately a heat related problem. I've used a can of freezer on it, perhaps replace 120 ohm  resistor with a 10watt.?    :loco