Used pair of 3-500Z based HF amplifier are the best bargain out there and the tubes are available new for a reasonable cost. But, the 'budget' priced pair of 3-500Z HF amplifiers are not equal in performance. Some amps struggle to achieve 1200 watts PEP out and some hams may believe two 3-500Z tubes always produces the legal limit power out. The following are what I consider to have a weak power transformer listed in weight. (Note- a 23 lb Peter Dahl C core is equal to about a 32lb standard IE lamination transformer that most amps use). The list below are commonly available amplifiers for sale. The B&W PT-2500 is somewhat rare. These are common amplifiers that should not be operated above 1000 watts PEP out, CW about 700 watts and RTTY at 450 watts out. The light weight transformers are the reason of the limited output from a pair of 3-500Z tubes. Ten Tec Centurion- 23lbs Swan MKII- 21lbs Heathkit SB-220- 23lbs Note- the single 3-500Z Ameritron AL-80B has a 26lb transformer and produces 1000 watts PEP out. The amplifiers below using a pair of 3-500Z tubes will deliver 1500 watts PEP out. The Drake L4 & L7 just make 1500 watts PEP out and require over 100 watts drive to achieve it. Amp Supply LK-500- 23lb Peter Dahl C core (equal to 32lb standard transformer) B&W PT-2500- 40 lbs Drake L4 & L7- 29lbs Henry 2K Classic- 42lbs Henry 2K Ultra- 38lbs Henry 2K Desk- 29lbs Note- some Henry amps had 3-400z tubes from the factory, but most for sale have 3-500z installed.