One of my old ham buddies [W0boy] put me on to an interesting new development. Seems that he works on maintaining Lithotripsy and other medical equipment and they have two pairs of 4-400 type tubes in their acoustic mass driver “finals”. Using focused HIGH POWER audio shock waves in a water tank evidently breaks up kidney type of stones internally without the patient needing surgery. Please see:
https://en.wikipedia.org/wiki/Extracorporeal_shockwave_therapyWhats cool about this is that as a ham he wanted to pass along the info that Fujitsu has produced and is releasing a solid state drop to do away with the tubes. He kids me about the boat anchors that I have been restoring / using these tubes: my Thunderbolt, 500, and Invader so he thought of me. This SIT* upgrade eliminates the filament and its heat and improves efficiency overall. I was able to order one thru him for my Johnson 500 for only $401, to try it out on the ham bands.
* See:
https://en.wikipedia.org/wiki/Static_induction_transistorIts more of a pulse device and not for AM operation but seems at home on SSB with my Johnson 500 & SSB adapter. My Johnson 500 only applies 2300 volts on the 'plate', well below the 3300 volt rating of the AF1-2023. In the AM mode 'plate' voltage would have exceeded that rating on voice peaks and the resting current would likely have also caused thermal over dissipation.
An 1.3 cu meters/minute flow (35.1 CFM) is needed to ensure proper forced air cooling, Iam just re-using the existing emiac glass chimney and so far have not seen any operational issues. The physical dimensions are very similar to the old 4-400, so the “plate lead” connects without issue, see photos. An added benefit is that the old screen voltage supply is not needed, so pulling the old OD3 voltage regulator tubes is recommended. Thought you might want to know about this **Static Induction Transistor (SIT) develop. I feel that having a HYBRID 1950 era transmitter is kinda cool and Ill be considering adding a pair of the SIT devices to my lnvader 2000 when I can save up the ca$h.
Enjoy Woody N4MQ



