ok so i just recently got a speaker cab of 60 watt max output. but my head is 100watt. the guy from the avatar factory told me to keep the volume no more then half and you'll be fine. but i heard tube amps will sound best at high volume. this is where the attenuator comes in. with the attenuator. will i be able to put the head master volume on desired level without blowing the cab since the cab can only handle 60 watt while the head is capable of 100watt?
That'll work fine. The attenuator goes in between the amp and speaker cab, so it will lower the overall output of the amp before it even touches a speaker.

*edit* btw, make sure you match the ohms on the attenuator as well.
yeah since the hughe and kettner have all the ohm(4,8,16) and the hotplate and the speaker is 8ohm.

btw my question is. can i put the volume pass more then half on the head and do some adjustment on the hotplate so my speakers wont blow?
Yeah. Like I said, the attenuator is what will be controlling your actual audible volume. The controls on the head will be there just to shape the tone.