"Serge Auckland"
This will do it.
http://cpc.farnell.com/_/bt936/louds...all/dp/AV01580
It's a transformer-based design (presumably a variable auto-transformer,
like a Variac). A bit more expensive than a couple of 5-10 watt resistors,
but the extra flexibility is worth-while.
** Do NOT under any circumstances use this device.
It is a 100%, guaranteed amplifier DESTROYER !
Attenuators used with solid state hi-fi amplifiers must not be of the
auto-transformer type.
Seen the damage using them does, many times.
Think low frequency core saturation, very low DC resistance.
Bad news !!!
...... Phil