Nice AMP. I have the AL 572 . 4 tube 1.3KW 572/B tube version. 572/B tubes are drop in for 811A . gives longer life not more power. That is the power supply and tank circuit limits. Some of them 3 tube ones had a swamping resistor off one of the tubes threw a cap. It kind of looks like a transistor buy has 2 leads . It is non inductive . Some have MOV on board or GDT . depending on age. They go bad if a tube flashover. The china 811A known for that. I tune up under low power drive and bring up to where I want and re tune and dip grid current. If way out of tune on full power the air variable caps can arc and damage them. For digital modes drop drive way down like for or AM or FM. The duty cycle is what to watch for. I keep my 572 down to 800 watts or less. Much less digital unless a short burst. I got Russian 572/B tubes and JAN Cetron ones . Penta labs have heavy duty 811A and 572/B now .If you ever need tubs check out penta labs . Or use like RF parts . The new 3-500ZG have wight base and are better . 73
Nice AMP. I have the AL 572 . 4 tube 1.3KW 572/B tube version. 572/B tubes are drop in for 811A . gives longer life not more power. That is the power supply and tank circuit limits. Some of them 3 tube ones had a swamping resistor off one of the tubes threw a cap. It kind of looks like a transistor buy has 2 leads . It is non inductive . Some have MOV on board or GDT . depending on age. They go bad if a tube flashover. The china 811A known for that. I tune up under low power drive and bring up to where I want and re tune and dip grid current. If way out of tune on full power the air variable caps can arc and damage them. For digital modes drop drive way down like for or AM or FM. The duty cycle is what to watch for. I keep my 572 down to 800 watts or less. Much less digital unless a short burst. I got Russian 572/B tubes and JAN Cetron ones . Penta labs have heavy duty 811A and 572/B now .If you ever need tubs check out penta labs . Or use like RF parts . The new 3-500ZG have wight base and are better . 73