Nuvistors are interesting!? I had two of them in a 2 meter rx preamp back in the late 60's.? The tubes are still available, the sockets not so much.? Least expensive 5 pin socket I found just now was about $9 if you buy 10 of them ($90).? I can deal with a 6C4 much easier now.
73!? Mark K9TR
Mark K9TR