Depending on your amplifier, it is often possible to change the output tubes for a different type to adjust the output power and/or change the tone.
For example, with the new 500V rated 6V6 tubes, it is usually possible to cut the power of your 6L6/EL34 amp in half with minimal change in overall tone. Some amps sounds great with 6L6s, some better with EL34s. Then there are the higher-power tubes like the 6550/KT77/KT88 etc. KT66s are great-sounding tubes as well.
There are MANY possibilities. Some conversions are more complex that others, some are not possible at all, some would just sound terrible. It depends on the amp. If you are interested in trying a different output tube type in your amp, or are curious about what conversions are possible, please contact me about options.