Unfortunately, all-tube amps cannot have a headphone output. The type of output transformer (the device that sends the signal from the amp to the speaker) needed for an all-tube amp must drive a speaker when the amp is on. Running an all-tube amp without a speaker connected to it (with headphones, for example) will cause the output transformer to overheat, resulting in damage to the transformer. On most tube amps, this is the most expensive single component to replace. So a headphone jack simply is not compatible with an all-tube amp.

However, hybrid amps (combination tube and solid-state amps) employ a different type of output transformer that can be used with a headphone jack. This allows you to use headphones and still get that "tube tone."