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I have a question about using the KT88 tube in my Tramp. What wattage is the KT88?

I read the specs which say it is a 42 watt dissipation tube. But I have read somewhere that it is only 12watts in our Tramps. I assume this has to do with the voltage applied to the tube, but I can not find a chart that shows why it is 12watts in our Tramps.

The reason I ask is that I have a amp tech that want to sell me a great vintage P12r which is a low wattage tube. This is one of the old jensens made in the USA. He is concerned that to make sure that I am using a low wattage amp. I told him that the biggest tube I would use is a KT88. The problem I see is that the specs say it is 42 watts.

[[edit: I am only interested in using this p12R low wattage inefficient tube in my home and studio, not for gigging--I know it is not efficient and would not be loud enough. However, jensen vintage alnico's sound so good in my Tramp. I have been using 2x10 from my 1960's Blackface Super Reverb. Using a pair of the vintage 10's is just beautiful. So when I found a vintage p12R and at a great price I thought I would add it to my studio for use with my Tramp, but I don't want to blow it by using a KT88 in it on rare occassions.]

So my question is: why is the KT88 only 12 watts in a Tramp circuit?

Thanks in advance for the advice and expertise

The Tramp is a single ended class A amp which by design is very inefficient. This coupled with the voltage being used on the tube and the output transformers primary impedance; you will never get anywhere close to 42W.

The OT is also a limiting factor, I believe it is only rated at 15W.

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Thank you so much for this info. I knew that you guys would have the correct info. I remember reading around here that the output would only be 15w maximum, but needed someone to confirm that.

You have been very helpful indeed!