I finally got around to winding a set of 40 meter coils for the TNT. I didn’t have any more bakelite tube for the grid coil, but I found some 1″ diameter phenolic tube at U.S. Plastic Corp. Cheap! It is light brown so it doesn’t look authentic for the 1920s period, but I decided to use it. The TNT has a bit more of a growl to it on 40 but otherwise works fine. I did notice things behaving strangely if I tuned it just above the 40 meter band. The power supply starts producing a loud mechanical buzz, as though severely overloaded, yet I am only drawing 40 milliamperes from it. The note also becomes very growly. My suspicion is that there is a series resonance in the TNT RF choke at around 7.5 Mc.
Wanting to see if it would go higher, I wound set of 30 meter coils. No problem! it works quite nicely at 10 Mc. as well. At this frequency I started to notice metal objects in the room starting to have a very pronounced affect on the rig’s frequency. If I touched any large metal object or if I moved any such object around (even one that was completely isolated from all wiring and other objects) the TNT frequency shifts! Fascinating.
Ever the more curious, I next wound coils for 20 meters. At this frequency the affect of metal objects and positioning of my body produce a profound affect on the rig’s frequency. This is at once aggravating and useful. It is nearly impossible to get the rig on a desired frequency due to the extremely fast tuning rate even with the 5 to 1 vernier. Also, it moves a few Kc. when my hand is removed from it’s immediate vicinity! However, by rolling my office chair back and forth several inches and/or leaning my body over somewhat, I can affect a frequency change of at least 2 or 3 Kc., which I found could be used for fine tuning! However: it is imperative that one not move or change position during a QSO!Antenna coupling for a good note is very critical at this frequency, bu it sounds surprisingly good when all is right. Listen to it on 20 meters.
Still curious, I spent several hours experimenting with even higher bands. I found, however, that it would not work. At any amateur band above 14 Mc. it goes spurious and puts out multiple extremely dirty emissions spread over a 2 to 3 Mc. portion of the radio spectrum.
Remembering I had an old, beat up piece of B&W coil stock, some 2-1/2″ in diameter and 10 turns per inch, I cobbled up some very quick and dirty plate tank and antenna coils for 160 meters. The grid coil for this band was problematic until Larry, NE1S, helped me out with some very small cotton covered wire which was able to fit enough turns on the form. Although there is a tendency toward frequency shifts with the somewhat floppy plate and antenna coils simply hanging by their leads, the rig works splendidly on topband. The slower tuning rate is a pure joy! I am very anxious to make proper coils for this band when I find suitable old wire.