Hehkus are tube amplifiers. Since the tubes wear in use they should be changed regularly. Hehkus are equipped with JJ-tubes unless agreed otherwise due to their great price-quality ratio. Your Hehku has a 2-year guarantee, during which time it can be modified according to your wishes without additional cost. After the two years, it can still be maintained and modified for an affordable price. The guarantee does not apply to the tubes due to their wearing nature despite the manufacturer.