[Amps] Attenuator needed

[Vic K2VCO]

I made a 6 db attenuator for the input of my grid-driven amplifier in order to bring the 
drive requirement up a bit and to provide a better SWR for the exciter during tuning. I 
used some film resistors from Mouser. I suspect that these have a low voltage rating, 
because one of them shorted after a few minutes of 10-meter operation. They didn't show 
any sign of heating, so I think it was a voltage/frequency issue and not simply overheating.

Anyway, I need a 50-ohm attenuator that can dissipate about 40 watts and can be used at 
HF. Anything from 3 to 6 db will work. I had a Henry solid-state amp that had a couple of 
these, which bolted to the heat sink. Does anyone know where I can buy such a thing, or 
how to make one from reasonably priced parts?
-- 
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/